CA1232938A - High frequency oscillator-inverter ballast circuit for discharge lamps - Google Patents
High frequency oscillator-inverter ballast circuit for discharge lampsInfo
- Publication number
- CA1232938A CA1232938A CA000428909A CA428909A CA1232938A CA 1232938 A CA1232938 A CA 1232938A CA 000428909 A CA000428909 A CA 000428909A CA 428909 A CA428909 A CA 428909A CA 1232938 A CA1232938 A CA 1232938A
- Authority
- CA
- Canada
- Prior art keywords
- circuit
- oscillator
- inverter
- lamp
- transformer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/295—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
- H05B41/298—Arrangements for protecting lamps or circuits against abnormal operating conditions
- H05B41/2988—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the lamp against abnormal operating conditions
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S315/00—Electric lamp and discharge devices: systems
- Y10S315/07—Starting and control circuits for gas discharge lamp using transistors
Abstract
PHA.21116 26 22-04-83 ABSTRACT:
"High frequency oscillator-inverter ballast circuit for discharge lamps", A current fed high frequency oscillator-inverter ballast circuit includes a parallel resonant tank circuit for driving a pair of series connected discharge lamps via a series ballast capacitor. A regenerative power supply switches on when a fluctuating main DC supply voltage drops below a given level thereby providing a constant level auxiliary DC supply voltage to the oscillator inver-ter to maintain oscillation and lamp operation. When the main DC supply voltage exceeds said given level, the re-generative power supply switches out. The oscillation fre-quency is f2 during operation of the main supply and auto-matically switches to a frequency f1 when the regenerative power supply takes over. The frequency shift is automatic during each hal cycle of 50 to 60 Hz AC supply and is in a direction so as to maintain lamp current relatively con-stant. A novel high frequency leakage transformer is pro-vided to couple the high frequency inverter to the dis-charge lamp load to provide both a current limiting (bal-last) action and automatic control of the lamp heater cur-rent to maintain high efficiency operation.
"High frequency oscillator-inverter ballast circuit for discharge lamps", A current fed high frequency oscillator-inverter ballast circuit includes a parallel resonant tank circuit for driving a pair of series connected discharge lamps via a series ballast capacitor. A regenerative power supply switches on when a fluctuating main DC supply voltage drops below a given level thereby providing a constant level auxiliary DC supply voltage to the oscillator inver-ter to maintain oscillation and lamp operation. When the main DC supply voltage exceeds said given level, the re-generative power supply switches out. The oscillation fre-quency is f2 during operation of the main supply and auto-matically switches to a frequency f1 when the regenerative power supply takes over. The frequency shift is automatic during each hal cycle of 50 to 60 Hz AC supply and is in a direction so as to maintain lamp current relatively con-stant. A novel high frequency leakage transformer is pro-vided to couple the high frequency inverter to the dis-charge lamp load to provide both a current limiting (bal-last) action and automatic control of the lamp heater cur-rent to maintain high efficiency operation.
Description
~L~3293~
PHA Z1116 1 22~04-83 HIGH FREQUENCY OSCILLATOR-INVERTER
BALLAST CIRCUIT FOR DIS~HARGE_LAMPS
BACKCTROUND OF THE INVENTION
This invention relhtes to a high frequency circuit for starting and ballasting gas di~charge lamps.
More particularly, the invention relates to a ~igh effi-ciency, high frequency electronic inverter circuit forope~ating one or more electric disharge lamps.
One significant feature or aspect of the present invention is the provision of a unique oscillator-inverter ballast circuit that produces multiple high frequency modes of operating frequency in which the inverter frequency of operation automatically changes during each period of the 50 to 60 Hz AC ~upply voltage in a manner so a~ to regu-late the lamp disharge current.
The prior art has employed a variety of tech-niques for energizing and ballasting electric dischargelamps. The early balla~t circuit~ were energized by means of a DC voltage or a 60Hz AC voltage and, i~ the ca~e of the ac supply voltage, nece~itated the use of a rather large magnetic ballast transformer. These early b~llast circuit were characterized by a relatively poor effic-iency caused in part by the relatively large power losses in the ballast system itself. More recently it has beeen proposed to i~prove the efficacy of a system for ener-gizing discharge lamps by op~rating the lamps at a high frequency, generally in a range of 15 KHz to 50 KXz.
: ~ One such high frequency balla~t system is des-cribed in U.S. Patent 4,220,896 by D.A. Paice. This patent ; discloses a high frequency resonant feedback inverter energized from a DC power source for operating a discharge lamp via a ballast circuit including an inductor and capacitor connected in series~ The discharge lamp is ` connected across the capacitor and the inverter frequency : ~
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PHA. 21116 2 22-04-~3 is adjusted to regulate the inverter AC output voltage level and to maintain almost unity power factor at the input to the ballast filter.
U.S. Patent ~,259,614 by T.P. Kohler employs a push-pull transi~tor oscillating inverter for energizing a pair of discharge lamps via a ballast circuit comprising a serie~ resonant LC circuit that determines the inverter oscillation frequency. The peak lamp current is sensed and used to control the inverter frequency so tha-t the fre-quency is reduced as the lamp current is increased, there`y by limiting the power dissipation of the circuit.
Another high frequency inverter oscillator is illustrated in U.S. Patent 4,017,785 by L.J. Perper which pro~ides a supplemental DC power supply connected so as to supplement a fluctuating main DC supply to maintain contin-UOU9 oscillator operation and to substantially reduce thepeak AC l:ine curr~nt.
A second unique aspect oP the present invention is the provision of a novel magnetic impedance transformer for coupling the inverter oscillator to the discharge lamp or lamps. A high frequency leakage reactance transformer is used to provide an automatic reduction in the heater power or current supplied to the discharge lamp filament electrodes once the lamp ignites thereby producing a so-called auto-heat mode o~ operation. At the same time, the leakage reactance of the transformer also produces a bal-last function to protect the discharge lamp.
The use of a small high frequency leakage in-ductance transformer for coupling a high frequency in-verter-oscillator to a discharge lamp is shown in U.S.
Patent 3,579,o26 in the name of F.W. Paget. This patent discloses a fuIl wave rectifier which supplies an unfil-; tered rectified direct current to a high-frequency oscil-lator inverter that is coupled to a pair of discharge lamps via the high frequency leakage transformer. The in-verter oscillation frequency is dependent on the applied voltage. The lamps have preheatable electrodes energized ; by secondary windings of the leakage transformer which .~
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PJ-IA.21116 3 22-04-83 are tightly coupled to the transformer primary winding.
A low frequency ballast utilizing a manually adjusted var-iable reactance to control the lamp discharge current is described in U.S. Patent 2,458,277 by G.T.K. Lark et al.
In the Lark et al ballast the heating current for the lamp filaments is reduced as the lamp discharge current is in-creased. And Canadian Patent 670,797 discloses a discharge lamp ballast circuit including a novel arrangement of transformer windings by means of which the heating voltage for the lamp electrodes is higher before lamp ignition than it is after ignition.
S~-M~IARY OF THE INVENTION.
... ..
Accordingly, it is a prime object of the pre-sent invention to provide an improved static inverter for operation of one or more gas discharge lamps.
Another object of the invention is to provide a novel lightweight and physically small ballas-t-inverter which is simple and economical in construction and reli-able in operation.
A further object of the invention is to provide a ballast-inverter which exhibits a high efficiency and a sys-tem power factor approaching unity.
Still ano-ther object of the invention is to provide a ballast-inverter in which the third harmonic distortion is reduced to a very low level and radio Pre-quency interference (RFI) is substantially eliminated.
Ano-ther object of the inven-tion is to provide a ballast-inverter which supplies an essentially sinusoid~
output voltage to the discharge lamps with the concomitant benefits derived therefrom.
In accordance with the second aspect of the invention, another principle ob,ject of the invention is to provide the high frequency ballast-inverter with a novel leakage reactance transformer which provides not only in-- 35 ductive ballasting of the discharge lamps, but also auto-matic control of the lamp filament currents to provide optimum cathode temperature before and after lamp ignition thereby providing extended lamp life and higher system ~ .' : : , .
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P~IA~21116 1~ ~2329~8 22-04-83 efficacy due to reduction in system power losses.
A further object of the lnvention i9 to provide an improved high frequency ballast transformer that will simultaneously provide automatic control of tbe lamp heater power and high efficiency ballasting of the lamp operating current.
Another object of the invention is to provide an improved high frequency ballast transformer with sub-stantially reduced levels of conducted and radia-ted inter-ference.
These and other objeets are achieved in aeeor-dance with the present invention by providing a high fre-quency ballast-inverter for one or more gas discharge lamp comprising a current-fed class D high frequency oscillator-inverter suppliad with an un~iltered rectified direct cur-rent from an AC-~C converter. A demodulator circuit in the form of a switched regenerative power supply is coupled to the class D oscillator and supplies power to the inverter-oscillator whenever the varying unfiltered DC input vol-tage drops below a given level. The inverter-oscillator is coupled to the lamp load by means of a high frequency im-pedance matching transformer and an additional series connected capacitor or inductor for current limiting bal-last purposes. The provision of a new and improved leakage transformer as the matching transforme:r makas it possible to el:iminate the series connected reactive ballast element.
The oscillation frequency of the inverter is dependent on the level of the inverter supply voltage and automatically vzries so as to vary the impedance of the series connected reac-tive ballast element in a sense to maintain the lamp current approximately constant even in the presence of a 120 ~Iz ripple component of the supply voltage.
The provision of the regenerative po~er supply makes it possible to substantially reduce the size of the large filter capacitor normally utilized in the AC/DC
converter thereby providing a high power factor and a ]-w inrush current. A tuned network is included in the regener-ative power supply in order to reduce the third harmonic ' ., ~
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PHA.21116 5 22-04-83 level in the power supply lines and to reduce the inter-ference fed back into said power lines. The demodulator circuit also reduces the line frequency ripple to a level so as to insure that the minimum pea~ lamp voltage is al-ways greater than the lamp arc voltage so that the lampdoes not deionize. ~n addJtional benefit is that the in-verter/oscillator frequency is modulated so as to reduce lamp current variations due to any 120 H~ residual ripple from the rectified line voltage.
The high frequency transformer for coupling the oscillator to the lamps may consist of a new leakage reactance transformer arrangement which provides not only the current limiting ballast function but also automatic control of the heater power for the discharge lamps. The transformer produces a heater power (current) that has an inverse relationship to the lamp current. In particular, the heater power is automatically reduced after ignition of the discharge lamp in order -to provide the optimum ca-thode temperature for extended lamp life due to minimum daterioration of the cathode.
The high frequency leakage transformer consists of a ferromagnetic core (e.g. a ferrite material) includ-ing a primary section, a secondary section and a shunt section that contains a gapped core, i.e. an air gap or the like. The primary winding is designed to have an in-ductance value that will form a parallel resonant circuit with a parallel capacitor to determine the fundamental operating frequency of the oscillator-inverter. The prim-ary winding will consist of N turns of wire which, in con-junction with an adequate cro:;s-secl-ion of the ferrite core, will insure that the transformer primary core sec-tion does no~ saturate. Freferably, the transformer is dimensioned so that no portion of the entire transformer core will be allowed to saturate, thereby producing low power dissipation in the transformer, optimum power coup-ling and low distortion.
The transformer secondary winding, consisting of M turns of wire, is mounted on the transformer secondary ~, :, . ,, ~ ,. :
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PI~A.21116 6 22-0~-83 section and is physically separated from the primary win-ding and functions as a leakage reactance (inductance) which is coupled to the primary only via the magnetic fie~l The transformer secondary section also in-cludes the filament heating windings for the discharge lamp (or lamps) which normally will have a low turns ratio relative to the secondary winding turns, M. The heater windings are preferably tigh-tly coupled to the secondary winding, although this is not an essential requirement of the leakage transformer. A portion of the heater winding may also be wound around the magnetic shunt portion of the transformer magnetic circuit in order to develop a non-linear response function, which may be desirable in special applications.
Before ignition of the discharge lamp, essen-tially all of the magnetic flux generated by the primary winding links the secondary to provide the maximum heater power for the lamp filament as well as the requisite high pen circuit voltage for ignition of the lamp. After ig-nition, some of the magnetic flux is coupled through the gapped leg of the transformer core so that the secondary flux linkage decreases, resulting in a reduced cathode heater power. The change in flux coupling to the secondary section is influenced by the secondary winding turns (M) and the current flowing in the secondary winding. A de-crease in lamp current results in an increase of heater current and vice versa so that -the heater power bears an inverse relationship to the lamp current. This mode of operation is termed the auto-heat mode and results in higher efficiency due to the reduction in heater power during lamp operation. The reduced coupling to the secon-dary after lamp ignition provides a leakage reactance for limiting the lamp current. The ballast function for the lamp is now provided by the transformer leakage reactance making it posslble to eliminate or reduce in size the usual ballast capacitor or inductor.
The secondary impedance is frequency sensitive and is coupled to the discharge lamp load and sets the : ~ :.
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PHA.21116 7 ~Z3~93B 22-04-83 operating levels of` this load. As the oscillator-inverter operating frequency, which is determined by the primary resonant tank circuit and the magnetically reflected reac-tance from the secondary, varies, the secondary impedc-~lce will also vary. The variation in secondary impedance mo-difies the resonant frequency of the oscillator-inverter such that the power delivered by the secondary to the lamp load tends to remain constant during lamp operation.
It is a further object of` the invention to pro vide an improved non-saturating leakage transformer ex-hibiting low power dissipation and optimum power coupling.
BRIEF DESCRIPTION OF THE DRAWINGS
__ _._ _. . ....... . . _ The novel and distinctive features of the in-vention are set f`orth in the appended Claims. The present invention, both as to its organization and manner of oper-ation, together with further objects and advantages there-of, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Fig. 1 is an electric schematic diagram of a preferred embodiment of` the oscillator-inverter f`or the ignition and operation of one or more gas discharge lamps;
Figs. 2A and 2B illustrate waveformc useful in describing the operation of the apparatus of Fig. 1;
Fig. 3 shows an impro~red leakage reactance transformer adapted for use in the apparatus of Fig. 1 for coupling the oscillator-inverter stage to the dis-charge lamps; and Fig. 4 is an electric schematic diagram showing a portion of` the electrical connections of the transf`ormer of Fig. 3 for use as a coupling transformer for a pair of discharge lamps.
DESC~IPTION OF THE PREFERRED EMBODIMENTS
Referring now to Fig. 1 of the drawings, a 120 Volt 60 Hz, AC supply voltage is coupled across a bridge rectifier 10 via an RFI filter 1 1 . The passive RFI filter - 11 will minimize the interaction between the power lines and the oscillator-inverter and consists of a pair of bi-~.
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P~A.2l116 8 ~3~ 22-04-83 filar coils 12 and 13 wound on -the same core (e.~. two E
cores, a toroid core, etc,) and each is connected between a respective AC supply terminal and a bridge input terminal 14 and 15. The coils are connected and wound so that the mutual coupling will attenuate the high frequencies while passing the 60 Hæ line current. The fiLter also includes a capacitor 16 connected across the 60 Hz AC input termin-als and a capacitor 17 connected across the bridge input terminals 14 and 15. The capacitors provide normal (dif-ferential) mode rejection of high frequency conducted ra-diation.
Capacitors 18 and 19 are connected in series across terminals 1LI and 15 with a junction point there-between connected to ground. These capacitos are chosen so as to provide a maximum amount of common mode filtering while limiting leakage currents to a value less than 5 ma peak. The RFI filter is a basic ~r section low pass filter that provides 60 db/decade attenuation above the cutoff frequency (2 ~V~C).
A varistor element 20 is coupled across the terminals 14 and 15 to provide transient voltage suppres-sion and protection of the ballast circuit from the AC
power lines by virtue of its voltage dependent nonlinear resistance function (I = ~V~ where ~ represents the non-linearity of conduction which will normally be greater than 25 for a varistor device to be used in a ballast cir-cuit. Upon the occurrence of a high voltage transient across VDR 20, its impedance changes from a very high va-lue (approximately open circuit~ to a relatively low value so as to effectively clamp the transient voltage to a safe leve]. The inherent capacitance of varistor 20 will pro-vide an added filter function.
The bridge rectifier 10 rectifiex the 60 Hz line voltage applied to its input terminals 14, 15 to derive at the output terminals 21, 22 a pulsating DC out-put voltage with a 120 Hz modulation envelop3. Smoothing of this pulsating DC voltage is provided by a unique tuned regenerative power supply, to be described below. With ~' ' ` ,.
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PHA.21116 9 22-04-83 this supply, the maximum vol-tage (Vmax~ will correspond to the peak voltage of the 60 Hz AC input voltage, whereas the minimwm voltage (Vmin) will correspond to a minimum value selected to minimize the period during which the voltage does not change, while insuring that the discharge lamps do not extinguish at any time within each 50 ~Iz p9-riod of operation~ The smoothed pulsating DC supply vol-tage at the bridge OUtpllt terminals 21, 22 will then have a general wave shape as illustrated in Fig. 2A.
A low value smoothing capacitor 23 (e.~. appox-imately 0.5/u~) is coupled across the bridge output ter-minals to provide RFI suppression, additional transient suppression, and a minimal filtering action. Because of its low value, the circuit exhibits a high power factor.
A high frequency oscillator-inverter stage 24 is supplied with the pulsating DC voltage via an inductor coil 25 which is wound on a high frequency coupling trans-former 26 and is gapped to handle a DC current. The in-ductor 25 is connected to a center tap of the transfotmet primary winding 27, 28. A capacitor 29 is connected in parallel with the primary winding 27, 28 and has a capa-citance value chosen to resonate with the primary induc-tance at the selected frequency of the oscillator-inverter circuit (fO = 1/2 ~r ~C).
A pair of NPN switching transistors 30, 31 have their collector elec-trodes respectively connected to oppo-site ends of the primary winding 27, 28 and their emitter electrodes connected to output terminal 22 of the bridge rectifier. This circuit may be termed a current fed (via series inductor 25) parallel resonant (27-29) switched mode power oscillator/amplifier. The circuit is extremely efficient in generating a high frequency output and, if all components were ideal (no losses), it would have an efficiency of l00%. A prsctical circuit will have an ef-ficiency exceeding 95%.
A transformer secondary winding 32 has end ter-minals connected to the base electrodes of switching tran-sistors 30 and 31 and a center tap connected to bridge ~ ' :' :, P~IA. 21116 10 ~3~938 22-04-83 output terminal 22 via a series circuit consisting of inductor 33, re3itor 31~ and diode 35. The winding 32 and the series circuit 33-35 demonstrate one Ineans for pro-viding the switching drive ~ignals for transistors 30 and 31. Oti-1er appropriate base drive circuits for bipolar transistors may also be used.
Although transistor~ 30 and 31 are bipolar transistors in the preferred emhodiment, other semicon-ductor switches may be use~d, such as JFET3, MOSEETs, TXIACs etc. A starting re~i3tor 36 couples a source of voltage Vc (terminal 21) to the junction point betweenresistor 34 and diode 35 90 as to apply the voltage V
to the base electrodes of -the ~itching tra~l3i~tors in 1 order to start the circuit oscillating. The basc drive circuit provides essentially a square wave of current to the transistors so that the tranqistor switches are driven into a saturation state in the on condition.
The inverter circuit for convertitlg t;1r-~ DC
~upply voltage into a high frequency AC voltage is thus seen to consi~t of a pair of active switches, transistors - 30, 31 and a tuned parallel resonant circuit 27-29. The tran~istor s~itches are driven by the base drive circuit 32~35 ~o th3t tney act like a two pole ~witch which defines a rectangular current wa-veform. A3 the resonant circuit is tuned t~ the switching frequency, harmonics are removed by it 90 that the resultant output voltage is essentially sinusoidal. The choke coil 25 forces essen-tially a constant DC current (IdC) into the center tap of primary winding 27, 28. Each switching transistor carries the full DC current when it is on 90 that the current through each transistor varies from zero to I
dc The switching tran3istors conduct in mutually exclusive time intervals.
A pair of series connected discharge lamps 37 and 38 are coupled to transformer secondary winding 39 via a series ballast capacitor 40. The discharge lamps may consist, for example, of conventional raped start 40W
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~23Z~3~3 P~IA.21116 11 22-04-83 fluorescent lampsO The lamp cathodes are heated by means ~ transformer 8econdary winding~ 41, 42 and 43. In this ca~e, the output voltage of each of these windings will be chosen to conform to the requirements for igniting rap-id start lamp~. A capacitor 44 is connected in parallelwith discharge lamp 37 in order to provide sequential starting of the lamps after proper cathode heating there of.
In order to insure that one lamp starts before the other and that neither lamp will "in~tant start", the open circuit voltage across the windings 41, 42 is ad-justed, by mean~ o~ the transformer winding turns ratio, to be lower than the value required to instant start a discharge lamp. In some cases the capacitor 44 will not be required, espectially where the inherent lamp to lamp and lamp to ground plane capacitance is sufficient to produce lamp ignition.
'~leicapacitor ~O operatesjes a frequency depen-dent ~ariable impéndance conneoted in series with the dis-charge lamps 90 as to ballast the lamps by limiting andcontrolling the lamp current. As will be explained in greater detail below, a change in the operating frequency of the oscillator-inverter circuit will re3ult in a change in the impendance of ~erie~ capacitor 40 in a direction that tends to maintain the lamp current constant. Al-though a capacitor is used as the ballast element in the circuit shown, it could be replaced by another frequency dependent impedance element,;such~as an inductor ~
The demodulator or switched regenerative power supply in combination with the low capacitance value of capacitor 23 provides a high power factor for the system, harmonic suppre~sion, i.e. a reduction in the harmonic content of the AS line current, and automatic frequency variation of the oscillator-inverter. The regenerative power supply consists of another pair of transformer windings 45, 46 coupled to a full wave riectifier circuit including diodes 47, 48. The windings 45, 46 are bifilar .-J-~
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, ~2~93~3 PHA. 21116 12 ~2-04-83 wound and tightly coupled to the primary windings 27, 28 of the trans~ormerO The cathodes of diodes 47, 48 are connected together to a common junction point between a series circuit consisting of capacitor 49and diode ~witch 50. Thiis series circuit is connected across the output terminal~ 21, 22 of the bridge rectifier 10. A center tap on the winding~ 45, 46 i~ connected to terminal 22 via Q
resonant "smoothing" filter consisting of a capacitor 51 and an inductor 52 connected in parallel.
The LC network 51, 52 forms a parallel resonant tank circuit which effectively integrates the peak charging currents that would otherwise flow into capacitor ~9 during the conductance of diodes 47 and 48. In 90 doing, it provides a smooth and continuou~ energy transfer out of the tank circuit 51, 52 and into the storage capacitor 49. ~y adjusting the LC network 51, 52 it is possible to control and vary the harmonic content of the input 60 Hz AC ~upply current. Aproper choice of the inductance and capacitance values will result in acceptable levels of the third, fifth , etc. Harmonics without adver~ely affecting the operation of the rest of the circuit.
A similar circuit constructed with and equi-valent regenerative power supply but without this tuned LC
network will have an unacceptable level of line current harmonic cont3nts, e.g. above 40% for tho third harmonic.
Although the "~moothing" network is shown as a single parallel LC network, other circuits may be designed to perform the same function. The regenerative power ~upply may be implemented using active circuits to control and regulate a regenerative power source. ~or example, the di-ode switch 50 may be replaced by an active switch, e.g. a MOSFET, JFET, etc 3hich is triggered in accordance with t:e requirements of the inverter circuit, the load and the input 60 Hz AC line.
The elements 45-52 together compri~e a regene-rative power ~upply which effectively demodulates the rec-tified 60 Hz AC supply voltage and powers the oscillator-:
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~LZ3~38 PHA, 21116 13 22-04-83 inverter during the period when diode 50 eonducts. The turns ratio of bifilar winding~ 45, 46 are ehosen 9e as to provide a feedbaek voltage at the output of diode 50 (terminal Vcc~ sufficient to keep the lamp voltage above the deionization potential while at the same time minimi-zing the time period during which the demodulation func-tion occurs. The diodes 47, 48 are preferably fast reco-very rectifier devices characterized by a low reverse recovery time (trr) along with a ~oft reverse recovery characteristic to minimize RFI problems.
A high frequency AC ~ignal is developed in the windings 45, 46 of the transformer and is reetified by the diodes 47, 48 and stored as a DC voltage level on capacitor 49, This eapacitor should be chosen so that it can store suffieien-t charge to provide enough power to operate the oscillator-inverter while the demodulation function is occurring.
Diode 50 functions a~ a switeh which turns on whenever the rectified pulsating 120Hz DC voltage at ter-minal 21 is at a level below the voltage across capacitor 49. During this time the diode bridge 10 is back biassd thereby effectively isolating the AC power lines from the frequeney eonver~ion stage. Thus, the energy to drive the oscillator-i~verter is supplied by capaeitor 49 via diode switch 50. When the recitified pulsating DC supply voltage(-again rises above the voltage on capacitor 49 (al~o capa-citor 23), the diode 50 is back biased 90 that the regene-rative power supply is effectively switehed offO
During the time that diode 50 conduct~, the voltage acros~ capacitor 23 follows the voltage aeross capacitor 49, Therefore, with diode 50 on, the voltage Vcc at terminal 21 is nominally the voltage on capacitor 49.
30 that the peak voltage at the~at the co].lectors of tran-sistor~ 30 or 31 is~/time~ the voltage of capacitor 49.
During this time, the cathode3 of diodes 47 and 48 are at the voltage level of the capacitor, whereas their anodes reeeive a voltage /! times this capaeitor voltage reduced `;: ~ :
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PHA. 21116 14 22-0~-83 by the turns ratio of the windings 45, 46 to the windings 27, 28. This ratio may be selected so that the diodes are non-conductive and thus the network including capacitor 51, inductor 52 and capacitor 49 will be isolated from the tank circuit. The "off" time of the diodes is chosen as a balance between the amount of demodulation and the power losses in the regenerative feedback circuit.
With the diode 50 biased off and with the vol-tage Vcc at terminal 21 increasing toward the peak voltageof the 60 Hæ AC supply voltage, a point will be reached where diodes ~7 and'~8 begin to conduct, thus effectively shunting the parallel resonant circuit 27-29 with the regenerative power supply. The reflected impendance, tightly coupled to the primary of transformer 26, will lS effectively modify the resonance frequency of the parallel resonant circuit 27-29 to produce a shift in frequency of the oscillator-inverter.
The solid state power supply of this invention features a high frequency oscillator-inverter that produce~q multiple-modes of cperating frequency, i.e. the frequency of operation varies over a given 60Hz period. In particular, the circuit described above will operate at all times at the frequency required to provide a continous lamp current ovar a full 60Hz cycle. This is achieved by operating the oscillator-inverter at two di~qtinct high frequency limits, fl and f2, with a smooth transition between the twe frequencies. The oscillation output frequency of the oscillator-inverter is automatically modified without changing the~esonant components or the lamp circuitry, and with essentially a sine wave output voltage for driving the discharge lamps at all timss.
The regenerative power supply circuit makes it possible to use a simple bridge rectifier system (10) without the need for a large value filter capacitor, as is required in most conventional AC-DC bridge circuits. The use of a regenerative power supply provides a system power supply provides a system power factor above 90~ and at .
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~:3~3~3 PH~. 21116 15 22-04-83 the same time reduces the harmonic content of the line current and the level of conducted radiation. This same circuit is also the cont-rol element which makes possible the frequency shift of the 3eries fed parallel rosonant tank circuit 27-29.
The power supply output stage consists of an impedance matching transformer and a series reactance to limit lamp current. The transformer also provides continuos filament power for operation of the lamps. The reactive element (either capacitive or inductive) in series with the lamp has its impedance varied by varying the oscillator inverter operating frequency in a sense so as to maintain the lamp current within selected limits, thus insuring , that the plasma never deionizes .
The modulation envelope of the high frequency signal generated by the oscillator-inverter circuit without a load is shown in Fig. 2b. The frequencies fl and f2 will be found within the modulation envelope. The sinusodial high frequency fl will occur in the region of maxium supply ~oltage and the sinusoidal high frequency f2 will occur during the period when the r egenerative power supply is coupled to the oscillator-inverter via diode switch ~0.
The voltage supplied to the oscillator-~invertor during the latter period is substantially constant, as is evident from the horizon-tal flat portions of the waveforms in Figs.
2a and 2b. During the period when the regene~ative power supply is decoupled from the oscillator-inverter, the frequency f1is generated with the amplitude of the sine waves varying with the amplitude variations of the rectified pulsating DC voltage supplied by bridge recit-- fier 10 at its output teminals 21, 22.
The frequencies ~1 and f2 within the modulation envelope will vary dependent on whether the series reactan-ce element for the discharge lamps is inductive or capactive, and also on the choice of circuit elements. For the case where the series reactance is capactive, i.e.
capacitor 40 in Fig. 1, tlle circuit will be adjusted so that the frequency f1 is less than the frequency f29 e.g.
~3;~3~3 PH~o 21116 16 22-04-83 a 25-30~ differential in tank frequency. Thus, when the oscillator supply voltage is at its low value, represented by the ~lat portion of the supply voltage waveform (Fig.2A) a voltage of frequency f is generated to produce a lamp current of a given amplitude. When the supply voltage increases, i.e. after the regenerative power supply is cut-out by diode switch 50~ then the oscillator-inverter generates a higher amplitude voltage. This higher voltage would tend to increase the lamp current. However, when the regenerative power supply was effectively switched out of the circuit, there occurred a change in the reflected impedance of the secondary circuit of transformer 26 that produces a change in the frequency of oscillation of the oscillator-inverter circuit to the lower frequency f1 .
This lower frequency voltage f1 is coupled via the trans-former 26 an-l ~eries capacitor 40 to the lamps. The lower frequency f1 causes an increase of the capactive reacta~ce 90 as -to maintain the lamp current fairly constant despite the substantial variation in supply voltage over a full period of the 60Hz ~C supply.
~ t is therefore seen that the change in reflec-ted impedance into the parallel r~sonant tan~ circuit as the regenerative power supply is switched in and out of the circuit at a predetermined level of the pulsating DC vol-tage produces an automatic change in the oscillation freq-uency in a direction so as to maintain the lamp currentconstant by an automatic variation of the impedance of the series reactance leement.
For the case where the series capaci-tor 40 is replaced by an inductor, the frequency f generated will be greater than the frequency f2. Thus, for an inductive ballast the higher operating frequency will occur at the peak values of the supply voltage while the lower freq-uency will be produced during the period of lower supply voltage, which occurs when the circuit is operated by the fi~ed DC voltage of the regenerative power supply circuit The inductive reactance thus will be higher for the higher .
PH~. 21116 17 ~ 938 22-04~83 values of the supply voltage so as to maintain a constant lamp current. It should be noted that the frequency trnsition between the frequencies f1 and f2 and vice versa is essentially smooth and occurs durillg the pel~io~ at the regenerative power supply is coupled to the oscillator-inverter via the conductive diode switch 50. By maintaining a given minimum DC supply voltage when the bridge supply voltage is low, the regenerative power supply thus prevents the deioni~ation of the lamps during normal operation.
The frequencies f1and f2 are chosen so that the lamp current will be held within prescribed limits to ob, tain an optimum lamp current crest factor, related to ex-tended lamp life, and optimum generation of 254 nm radia-tion within the arc for a maximum conversion of energy bythe phosphor into useful light.
Fig 3 ill1lstrates an impedance transformation device in the form of a new leakage transformer configu-ration that provides both a current limiting (ballast) function and an automatic control of the lamp heater power ~-so as to improve the efficiency of the overall power supply-ballast system. The leakage trabsformer will couple the oscillator-inverter circuit to the discharge lamps and may therefore be substituted for~ the transformer 26 and bal-last capacitor 40 of Fig. 1, thus saving on a ballast ca-pacitor. Inductive ballasting of the discharge lamps is now achie-ved by means of the leakage reactance of the transformer itself. The l~mps thus may be connected di-rectly across the transformer secondary winding 55 so that the varying reactance of the secondary will limit and control the lamp volt-ampere requirements. This leakage transformer arrangement provides a significant reduction in radiated and conducted ~FI. The connections between the transformer secondary windings and the discharge lamps are illustrated in Fig. 4. The windings 32, 45, 46 of the transformer are connected in an identical manner to that shown for the transformer in Fig. 1 and will therefore not be further illustrated.
PHA.21116 18 ~232g3~ 22-04-83 The high frequency leakage transformer includes a magnetic core 56, preferably of ferrite material, with an air gap 57 formed in the middle leg. The secondary win~
ding 55 along with the lamp heater windings 58, 59 and 60 are wound on the right leg of the transformer core and a primary winding 61 is wound on the left leg. The heater windings are thus tightly coupled to the secondary winding 55. The capacitor 29 of Fig. 1 will be connected in paral-lel with the primary winding 61 to form therwith a tuned parallel resonant tank circuit for the oscillator-inverter stage. The ends of the primary winding are connected to the collector electrodes o~ switching transistors 30, 31 (Fig. 1).
The secondary portion of the transformer is not lS electrically connected to the primary winding and will provide both the transfer of energy to the load and the control and regulatiGn of the load, especially where the load is a negative impedance device such as a discharge lamp.
In order to ignite the discharge lamps coupled to secondary winding 55, the open circuit voltage across the secondary must exceed the voltage required to initiate a discharge in the lamp. For the case of a fluorescent lamp load, the transformer also provides the power to produce electron emission of the lamp cathodes, which assists in the initiation of the discharge. The heater windings 58-60 for the discharge lamps are tightly coupled to the secon-dary of the transformer such that, when there is no load current flowing, and thus nu current in the secondary, the heater windings provide a maximum power transfer to -the lamp cathodes.
The transformer consists of primary and secon-dary sections plus a shunt section comprising a gapped core and with the primary winding inductance resonated with a paralLel capacitor to set the fundamental operating frequency of the oscillator-inverter. The primary winding is composed of N turns of wire and the ferrite core has an adequate cross-section to insure that the transformer pri-.
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' , :, 1~3293~, PHA.21116 19 22-0~-83 mary section does no-t saturate. In fact, it is preferable to arrange the -transformer so that no portion o~ the entire transformer will be allowed to saturate at any time, -thus providing low power dissipation in the transformer, mini-mum distortion and optimum power coupling.
The transformer secondary is physically separ-ated ~rom the pri1nary. It is a leakage reactance ~induc-tance) which is coupled to the primary only by means of the magnetic field. With no secondary load, the secondary open circuit voltage will be determined by the primary -to socondary turns ratio. Before ignition of the lamps, es-entially all of the magnetic flux generated by the pri-mary winding links the secondary winding to provide maxi-mum heater power and open circuit voltage. After lamp ig-nition, a current flows in the secondary winding so thatsome of the primary flux flows through the gapped center leg of the core 56, thus providlng a leakage reactance for limiting the lamp current. The flux linkage or coupli~g to the secondary is reduced after lamp ignition which also results in an automatic reduction of the cathode heater power.
The impedance of the secondary winding, which is in parallel with the load (lamps) and sets the load ;operating level, is frequency sensitive. As the oscilla-tor-inverter operating frequency, determined by the reso-nated primary and magnetically reflected reac-tance from the secondary, varies the secondary impedance will vary so as to modify the resonant frequency (oscillation fre~
quency) of the apparatus in a manner such that the power delivered by the secondary to the lamps tends to remain constant. The magnetic circui-t will vary as required to control the load power, and the volt-ampere characteris-tics of the load will be governed by the variations in the impedance of the seconidary winding.
The operation of the transformer after lamp ignition may also be explained in the following manner.
As current flows in the secondary, conservation of primary magnetic flux coupled with the magnetic flux generated by .,. ' . .1 ~ . ~ . ' ' `
, :~ : .:., ~3293~3 PHA.21116 20 22-04-83 the secondary results in flux leakage across the relative-ly high magnetic reductance of the gapped shunt portion.
This effectively results in a v~riation in magnetic coupl-ing to the secondary. ~s the magnetic coupling varies, the resultant reactance of the secondary winding will also va-ry as it is a function of both the number of turns and the generated magne-tic flux carried by the ferrite core on which the winding is mounted. This effect is equivalent to a secondary leakage reactance.
Another way of looking at the transformer oper-ation is that a constant primary flux flows before ignition and the ferrite core provides a low reluct~nce path. After lamp ignition, the current flow in the secondary winding causes a reverse flux to flow so that less of the primary flux is coupled to the secondary winding and the heater windings.
This mode of operation has been termed the auto-heat mode in which the heater power bears an inverse relationship to the lamp current. In contrast, the appar-atus of Fig. 1 provides a relatively constant cathodeheater power. After ignition in the apparatus of Figs. 3 and 4, the flux linkage decreases resulting in reduced heater power. A subsequent decrease in lamp current re-sults in an automatic increase of heater current. For ex-ample, if the lamps are dimmed, resulting in a reducedlamp current, the filamen-t heat ~current) will automatical-ly be increased to maintain the filament temperature. After ignition, the heater current is significantly reduced which provides optimum cathode temperature and extended lamp life due to a slower deterioration of the lamp cathodes. If a power interruption occurs and the lamps current stops, or is appreciably reduced, the filament heat will automatical-ly return to the required level to provide the optimum filament temperature.
The cathode heater windings of -the leakage trans-former will normally have a low turns ratio in relation-ship to the turns of the secondary winding 55. It is alter-natively possible to wind a portion of -the heater windings : -- :, : .' ,', ' :
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~32931!3 PI~A.21116 21 22-0LL-83 around the magnetic shunt portion of the transf`ormer core in order to develop a non-linear response function. The amount of the reduced heated current after ignition is related to the turns ratio of the heater windings to that of the secondary winding and to the current flowing in the secondary. Minimum power losses are insured by designing the rnagnetic structure o~ the trans~ormer so -tha-t it never saturates. The operation of the oscillator-inverter ballast using the leakage transformer of Fig. 3 for coupling the lamps through the oscillator-inverter stage will be ths same as that described in connection with Fig. 1 for a circuit which is inductively ballasted.
~ hile we have described our invention in connec-tion with certain specific embodiments and applications, other modifications and alterations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
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PHA Z1116 1 22~04-83 HIGH FREQUENCY OSCILLATOR-INVERTER
BALLAST CIRCUIT FOR DIS~HARGE_LAMPS
BACKCTROUND OF THE INVENTION
This invention relhtes to a high frequency circuit for starting and ballasting gas di~charge lamps.
More particularly, the invention relates to a ~igh effi-ciency, high frequency electronic inverter circuit forope~ating one or more electric disharge lamps.
One significant feature or aspect of the present invention is the provision of a unique oscillator-inverter ballast circuit that produces multiple high frequency modes of operating frequency in which the inverter frequency of operation automatically changes during each period of the 50 to 60 Hz AC ~upply voltage in a manner so a~ to regu-late the lamp disharge current.
The prior art has employed a variety of tech-niques for energizing and ballasting electric dischargelamps. The early balla~t circuit~ were energized by means of a DC voltage or a 60Hz AC voltage and, i~ the ca~e of the ac supply voltage, nece~itated the use of a rather large magnetic ballast transformer. These early b~llast circuit were characterized by a relatively poor effic-iency caused in part by the relatively large power losses in the ballast system itself. More recently it has beeen proposed to i~prove the efficacy of a system for ener-gizing discharge lamps by op~rating the lamps at a high frequency, generally in a range of 15 KHz to 50 KXz.
: ~ One such high frequency balla~t system is des-cribed in U.S. Patent 4,220,896 by D.A. Paice. This patent ; discloses a high frequency resonant feedback inverter energized from a DC power source for operating a discharge lamp via a ballast circuit including an inductor and capacitor connected in series~ The discharge lamp is ` connected across the capacitor and the inverter frequency : ~
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PHA. 21116 2 22-04-~3 is adjusted to regulate the inverter AC output voltage level and to maintain almost unity power factor at the input to the ballast filter.
U.S. Patent ~,259,614 by T.P. Kohler employs a push-pull transi~tor oscillating inverter for energizing a pair of discharge lamps via a ballast circuit comprising a serie~ resonant LC circuit that determines the inverter oscillation frequency. The peak lamp current is sensed and used to control the inverter frequency so tha-t the fre-quency is reduced as the lamp current is increased, there`y by limiting the power dissipation of the circuit.
Another high frequency inverter oscillator is illustrated in U.S. Patent 4,017,785 by L.J. Perper which pro~ides a supplemental DC power supply connected so as to supplement a fluctuating main DC supply to maintain contin-UOU9 oscillator operation and to substantially reduce thepeak AC l:ine curr~nt.
A second unique aspect oP the present invention is the provision of a novel magnetic impedance transformer for coupling the inverter oscillator to the discharge lamp or lamps. A high frequency leakage reactance transformer is used to provide an automatic reduction in the heater power or current supplied to the discharge lamp filament electrodes once the lamp ignites thereby producing a so-called auto-heat mode o~ operation. At the same time, the leakage reactance of the transformer also produces a bal-last function to protect the discharge lamp.
The use of a small high frequency leakage in-ductance transformer for coupling a high frequency in-verter-oscillator to a discharge lamp is shown in U.S.
Patent 3,579,o26 in the name of F.W. Paget. This patent discloses a fuIl wave rectifier which supplies an unfil-; tered rectified direct current to a high-frequency oscil-lator inverter that is coupled to a pair of discharge lamps via the high frequency leakage transformer. The in-verter oscillation frequency is dependent on the applied voltage. The lamps have preheatable electrodes energized ; by secondary windings of the leakage transformer which .~
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PJ-IA.21116 3 22-04-83 are tightly coupled to the transformer primary winding.
A low frequency ballast utilizing a manually adjusted var-iable reactance to control the lamp discharge current is described in U.S. Patent 2,458,277 by G.T.K. Lark et al.
In the Lark et al ballast the heating current for the lamp filaments is reduced as the lamp discharge current is in-creased. And Canadian Patent 670,797 discloses a discharge lamp ballast circuit including a novel arrangement of transformer windings by means of which the heating voltage for the lamp electrodes is higher before lamp ignition than it is after ignition.
S~-M~IARY OF THE INVENTION.
... ..
Accordingly, it is a prime object of the pre-sent invention to provide an improved static inverter for operation of one or more gas discharge lamps.
Another object of the invention is to provide a novel lightweight and physically small ballas-t-inverter which is simple and economical in construction and reli-able in operation.
A further object of the invention is to provide a ballast-inverter which exhibits a high efficiency and a sys-tem power factor approaching unity.
Still ano-ther object of the invention is to provide a ballast-inverter in which the third harmonic distortion is reduced to a very low level and radio Pre-quency interference (RFI) is substantially eliminated.
Ano-ther object of the inven-tion is to provide a ballast-inverter which supplies an essentially sinusoid~
output voltage to the discharge lamps with the concomitant benefits derived therefrom.
In accordance with the second aspect of the invention, another principle ob,ject of the invention is to provide the high frequency ballast-inverter with a novel leakage reactance transformer which provides not only in-- 35 ductive ballasting of the discharge lamps, but also auto-matic control of the lamp filament currents to provide optimum cathode temperature before and after lamp ignition thereby providing extended lamp life and higher system ~ .' : : , .
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P~IA~21116 1~ ~2329~8 22-04-83 efficacy due to reduction in system power losses.
A further object of the lnvention i9 to provide an improved high frequency ballast transformer that will simultaneously provide automatic control of tbe lamp heater power and high efficiency ballasting of the lamp operating current.
Another object of the invention is to provide an improved high frequency ballast transformer with sub-stantially reduced levels of conducted and radia-ted inter-ference.
These and other objeets are achieved in aeeor-dance with the present invention by providing a high fre-quency ballast-inverter for one or more gas discharge lamp comprising a current-fed class D high frequency oscillator-inverter suppliad with an un~iltered rectified direct cur-rent from an AC-~C converter. A demodulator circuit in the form of a switched regenerative power supply is coupled to the class D oscillator and supplies power to the inverter-oscillator whenever the varying unfiltered DC input vol-tage drops below a given level. The inverter-oscillator is coupled to the lamp load by means of a high frequency im-pedance matching transformer and an additional series connected capacitor or inductor for current limiting bal-last purposes. The provision of a new and improved leakage transformer as the matching transforme:r makas it possible to el:iminate the series connected reactive ballast element.
The oscillation frequency of the inverter is dependent on the level of the inverter supply voltage and automatically vzries so as to vary the impedance of the series connected reac-tive ballast element in a sense to maintain the lamp current approximately constant even in the presence of a 120 ~Iz ripple component of the supply voltage.
The provision of the regenerative po~er supply makes it possible to substantially reduce the size of the large filter capacitor normally utilized in the AC/DC
converter thereby providing a high power factor and a ]-w inrush current. A tuned network is included in the regener-ative power supply in order to reduce the third harmonic ' ., ~
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PHA.21116 5 22-04-83 level in the power supply lines and to reduce the inter-ference fed back into said power lines. The demodulator circuit also reduces the line frequency ripple to a level so as to insure that the minimum pea~ lamp voltage is al-ways greater than the lamp arc voltage so that the lampdoes not deionize. ~n addJtional benefit is that the in-verter/oscillator frequency is modulated so as to reduce lamp current variations due to any 120 H~ residual ripple from the rectified line voltage.
The high frequency transformer for coupling the oscillator to the lamps may consist of a new leakage reactance transformer arrangement which provides not only the current limiting ballast function but also automatic control of the heater power for the discharge lamps. The transformer produces a heater power (current) that has an inverse relationship to the lamp current. In particular, the heater power is automatically reduced after ignition of the discharge lamp in order -to provide the optimum ca-thode temperature for extended lamp life due to minimum daterioration of the cathode.
The high frequency leakage transformer consists of a ferromagnetic core (e.g. a ferrite material) includ-ing a primary section, a secondary section and a shunt section that contains a gapped core, i.e. an air gap or the like. The primary winding is designed to have an in-ductance value that will form a parallel resonant circuit with a parallel capacitor to determine the fundamental operating frequency of the oscillator-inverter. The prim-ary winding will consist of N turns of wire which, in con-junction with an adequate cro:;s-secl-ion of the ferrite core, will insure that the transformer primary core sec-tion does no~ saturate. Freferably, the transformer is dimensioned so that no portion of the entire transformer core will be allowed to saturate, thereby producing low power dissipation in the transformer, optimum power coup-ling and low distortion.
The transformer secondary winding, consisting of M turns of wire, is mounted on the transformer secondary ~, :, . ,, ~ ,. :
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PI~A.21116 6 22-0~-83 section and is physically separated from the primary win-ding and functions as a leakage reactance (inductance) which is coupled to the primary only via the magnetic fie~l The transformer secondary section also in-cludes the filament heating windings for the discharge lamp (or lamps) which normally will have a low turns ratio relative to the secondary winding turns, M. The heater windings are preferably tigh-tly coupled to the secondary winding, although this is not an essential requirement of the leakage transformer. A portion of the heater winding may also be wound around the magnetic shunt portion of the transformer magnetic circuit in order to develop a non-linear response function, which may be desirable in special applications.
Before ignition of the discharge lamp, essen-tially all of the magnetic flux generated by the primary winding links the secondary to provide the maximum heater power for the lamp filament as well as the requisite high pen circuit voltage for ignition of the lamp. After ig-nition, some of the magnetic flux is coupled through the gapped leg of the transformer core so that the secondary flux linkage decreases, resulting in a reduced cathode heater power. The change in flux coupling to the secondary section is influenced by the secondary winding turns (M) and the current flowing in the secondary winding. A de-crease in lamp current results in an increase of heater current and vice versa so that -the heater power bears an inverse relationship to the lamp current. This mode of operation is termed the auto-heat mode and results in higher efficiency due to the reduction in heater power during lamp operation. The reduced coupling to the secon-dary after lamp ignition provides a leakage reactance for limiting the lamp current. The ballast function for the lamp is now provided by the transformer leakage reactance making it posslble to eliminate or reduce in size the usual ballast capacitor or inductor.
The secondary impedance is frequency sensitive and is coupled to the discharge lamp load and sets the : ~ :.
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PHA.21116 7 ~Z3~93B 22-04-83 operating levels of` this load. As the oscillator-inverter operating frequency, which is determined by the primary resonant tank circuit and the magnetically reflected reac-tance from the secondary, varies, the secondary impedc-~lce will also vary. The variation in secondary impedance mo-difies the resonant frequency of the oscillator-inverter such that the power delivered by the secondary to the lamp load tends to remain constant during lamp operation.
It is a further object of` the invention to pro vide an improved non-saturating leakage transformer ex-hibiting low power dissipation and optimum power coupling.
BRIEF DESCRIPTION OF THE DRAWINGS
__ _._ _. . ....... . . _ The novel and distinctive features of the in-vention are set f`orth in the appended Claims. The present invention, both as to its organization and manner of oper-ation, together with further objects and advantages there-of, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Fig. 1 is an electric schematic diagram of a preferred embodiment of` the oscillator-inverter f`or the ignition and operation of one or more gas discharge lamps;
Figs. 2A and 2B illustrate waveformc useful in describing the operation of the apparatus of Fig. 1;
Fig. 3 shows an impro~red leakage reactance transformer adapted for use in the apparatus of Fig. 1 for coupling the oscillator-inverter stage to the dis-charge lamps; and Fig. 4 is an electric schematic diagram showing a portion of` the electrical connections of the transf`ormer of Fig. 3 for use as a coupling transformer for a pair of discharge lamps.
DESC~IPTION OF THE PREFERRED EMBODIMENTS
Referring now to Fig. 1 of the drawings, a 120 Volt 60 Hz, AC supply voltage is coupled across a bridge rectifier 10 via an RFI filter 1 1 . The passive RFI filter - 11 will minimize the interaction between the power lines and the oscillator-inverter and consists of a pair of bi-~.
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P~A.2l116 8 ~3~ 22-04-83 filar coils 12 and 13 wound on -the same core (e.~. two E
cores, a toroid core, etc,) and each is connected between a respective AC supply terminal and a bridge input terminal 14 and 15. The coils are connected and wound so that the mutual coupling will attenuate the high frequencies while passing the 60 Hæ line current. The fiLter also includes a capacitor 16 connected across the 60 Hz AC input termin-als and a capacitor 17 connected across the bridge input terminals 14 and 15. The capacitors provide normal (dif-ferential) mode rejection of high frequency conducted ra-diation.
Capacitors 18 and 19 are connected in series across terminals 1LI and 15 with a junction point there-between connected to ground. These capacitos are chosen so as to provide a maximum amount of common mode filtering while limiting leakage currents to a value less than 5 ma peak. The RFI filter is a basic ~r section low pass filter that provides 60 db/decade attenuation above the cutoff frequency (2 ~V~C).
A varistor element 20 is coupled across the terminals 14 and 15 to provide transient voltage suppres-sion and protection of the ballast circuit from the AC
power lines by virtue of its voltage dependent nonlinear resistance function (I = ~V~ where ~ represents the non-linearity of conduction which will normally be greater than 25 for a varistor device to be used in a ballast cir-cuit. Upon the occurrence of a high voltage transient across VDR 20, its impedance changes from a very high va-lue (approximately open circuit~ to a relatively low value so as to effectively clamp the transient voltage to a safe leve]. The inherent capacitance of varistor 20 will pro-vide an added filter function.
The bridge rectifier 10 rectifiex the 60 Hz line voltage applied to its input terminals 14, 15 to derive at the output terminals 21, 22 a pulsating DC out-put voltage with a 120 Hz modulation envelop3. Smoothing of this pulsating DC voltage is provided by a unique tuned regenerative power supply, to be described below. With ~' ' ` ,.
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PHA.21116 9 22-04-83 this supply, the maximum vol-tage (Vmax~ will correspond to the peak voltage of the 60 Hz AC input voltage, whereas the minimwm voltage (Vmin) will correspond to a minimum value selected to minimize the period during which the voltage does not change, while insuring that the discharge lamps do not extinguish at any time within each 50 ~Iz p9-riod of operation~ The smoothed pulsating DC supply vol-tage at the bridge OUtpllt terminals 21, 22 will then have a general wave shape as illustrated in Fig. 2A.
A low value smoothing capacitor 23 (e.~. appox-imately 0.5/u~) is coupled across the bridge output ter-minals to provide RFI suppression, additional transient suppression, and a minimal filtering action. Because of its low value, the circuit exhibits a high power factor.
A high frequency oscillator-inverter stage 24 is supplied with the pulsating DC voltage via an inductor coil 25 which is wound on a high frequency coupling trans-former 26 and is gapped to handle a DC current. The in-ductor 25 is connected to a center tap of the transfotmet primary winding 27, 28. A capacitor 29 is connected in parallel with the primary winding 27, 28 and has a capa-citance value chosen to resonate with the primary induc-tance at the selected frequency of the oscillator-inverter circuit (fO = 1/2 ~r ~C).
A pair of NPN switching transistors 30, 31 have their collector elec-trodes respectively connected to oppo-site ends of the primary winding 27, 28 and their emitter electrodes connected to output terminal 22 of the bridge rectifier. This circuit may be termed a current fed (via series inductor 25) parallel resonant (27-29) switched mode power oscillator/amplifier. The circuit is extremely efficient in generating a high frequency output and, if all components were ideal (no losses), it would have an efficiency of l00%. A prsctical circuit will have an ef-ficiency exceeding 95%.
A transformer secondary winding 32 has end ter-minals connected to the base electrodes of switching tran-sistors 30 and 31 and a center tap connected to bridge ~ ' :' :, P~IA. 21116 10 ~3~938 22-04-83 output terminal 22 via a series circuit consisting of inductor 33, re3itor 31~ and diode 35. The winding 32 and the series circuit 33-35 demonstrate one Ineans for pro-viding the switching drive ~ignals for transistors 30 and 31. Oti-1er appropriate base drive circuits for bipolar transistors may also be used.
Although transistor~ 30 and 31 are bipolar transistors in the preferred emhodiment, other semicon-ductor switches may be use~d, such as JFET3, MOSEETs, TXIACs etc. A starting re~i3tor 36 couples a source of voltage Vc (terminal 21) to the junction point betweenresistor 34 and diode 35 90 as to apply the voltage V
to the base electrodes of -the ~itching tra~l3i~tors in 1 order to start the circuit oscillating. The basc drive circuit provides essentially a square wave of current to the transistors so that the tranqistor switches are driven into a saturation state in the on condition.
The inverter circuit for convertitlg t;1r-~ DC
~upply voltage into a high frequency AC voltage is thus seen to consi~t of a pair of active switches, transistors - 30, 31 and a tuned parallel resonant circuit 27-29. The tran~istor s~itches are driven by the base drive circuit 32~35 ~o th3t tney act like a two pole ~witch which defines a rectangular current wa-veform. A3 the resonant circuit is tuned t~ the switching frequency, harmonics are removed by it 90 that the resultant output voltage is essentially sinusoidal. The choke coil 25 forces essen-tially a constant DC current (IdC) into the center tap of primary winding 27, 28. Each switching transistor carries the full DC current when it is on 90 that the current through each transistor varies from zero to I
dc The switching tran3istors conduct in mutually exclusive time intervals.
A pair of series connected discharge lamps 37 and 38 are coupled to transformer secondary winding 39 via a series ballast capacitor 40. The discharge lamps may consist, for example, of conventional raped start 40W
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~23Z~3~3 P~IA.21116 11 22-04-83 fluorescent lampsO The lamp cathodes are heated by means ~ transformer 8econdary winding~ 41, 42 and 43. In this ca~e, the output voltage of each of these windings will be chosen to conform to the requirements for igniting rap-id start lamp~. A capacitor 44 is connected in parallelwith discharge lamp 37 in order to provide sequential starting of the lamps after proper cathode heating there of.
In order to insure that one lamp starts before the other and that neither lamp will "in~tant start", the open circuit voltage across the windings 41, 42 is ad-justed, by mean~ o~ the transformer winding turns ratio, to be lower than the value required to instant start a discharge lamp. In some cases the capacitor 44 will not be required, espectially where the inherent lamp to lamp and lamp to ground plane capacitance is sufficient to produce lamp ignition.
'~leicapacitor ~O operatesjes a frequency depen-dent ~ariable impéndance conneoted in series with the dis-charge lamps 90 as to ballast the lamps by limiting andcontrolling the lamp current. As will be explained in greater detail below, a change in the operating frequency of the oscillator-inverter circuit will re3ult in a change in the impendance of ~erie~ capacitor 40 in a direction that tends to maintain the lamp current constant. Al-though a capacitor is used as the ballast element in the circuit shown, it could be replaced by another frequency dependent impedance element,;such~as an inductor ~
The demodulator or switched regenerative power supply in combination with the low capacitance value of capacitor 23 provides a high power factor for the system, harmonic suppre~sion, i.e. a reduction in the harmonic content of the AS line current, and automatic frequency variation of the oscillator-inverter. The regenerative power supply consists of another pair of transformer windings 45, 46 coupled to a full wave riectifier circuit including diodes 47, 48. The windings 45, 46 are bifilar .-J-~
. . , . ~ .
' ., ~' ' -. ~
, ~2~93~3 PHA. 21116 12 ~2-04-83 wound and tightly coupled to the primary windings 27, 28 of the trans~ormerO The cathodes of diodes 47, 48 are connected together to a common junction point between a series circuit consisting of capacitor 49and diode ~witch 50. Thiis series circuit is connected across the output terminal~ 21, 22 of the bridge rectifier 10. A center tap on the winding~ 45, 46 i~ connected to terminal 22 via Q
resonant "smoothing" filter consisting of a capacitor 51 and an inductor 52 connected in parallel.
The LC network 51, 52 forms a parallel resonant tank circuit which effectively integrates the peak charging currents that would otherwise flow into capacitor ~9 during the conductance of diodes 47 and 48. In 90 doing, it provides a smooth and continuou~ energy transfer out of the tank circuit 51, 52 and into the storage capacitor 49. ~y adjusting the LC network 51, 52 it is possible to control and vary the harmonic content of the input 60 Hz AC ~upply current. Aproper choice of the inductance and capacitance values will result in acceptable levels of the third, fifth , etc. Harmonics without adver~ely affecting the operation of the rest of the circuit.
A similar circuit constructed with and equi-valent regenerative power supply but without this tuned LC
network will have an unacceptable level of line current harmonic cont3nts, e.g. above 40% for tho third harmonic.
Although the "~moothing" network is shown as a single parallel LC network, other circuits may be designed to perform the same function. The regenerative power ~upply may be implemented using active circuits to control and regulate a regenerative power source. ~or example, the di-ode switch 50 may be replaced by an active switch, e.g. a MOSFET, JFET, etc 3hich is triggered in accordance with t:e requirements of the inverter circuit, the load and the input 60 Hz AC line.
The elements 45-52 together compri~e a regene-rative power ~upply which effectively demodulates the rec-tified 60 Hz AC supply voltage and powers the oscillator-:
~ ~ :
::
.
' , `.:
~LZ3~38 PHA, 21116 13 22-04-83 inverter during the period when diode 50 eonducts. The turns ratio of bifilar winding~ 45, 46 are ehosen 9e as to provide a feedbaek voltage at the output of diode 50 (terminal Vcc~ sufficient to keep the lamp voltage above the deionization potential while at the same time minimi-zing the time period during which the demodulation func-tion occurs. The diodes 47, 48 are preferably fast reco-very rectifier devices characterized by a low reverse recovery time (trr) along with a ~oft reverse recovery characteristic to minimize RFI problems.
A high frequency AC ~ignal is developed in the windings 45, 46 of the transformer and is reetified by the diodes 47, 48 and stored as a DC voltage level on capacitor 49, This eapacitor should be chosen so that it can store suffieien-t charge to provide enough power to operate the oscillator-inverter while the demodulation function is occurring.
Diode 50 functions a~ a switeh which turns on whenever the rectified pulsating 120Hz DC voltage at ter-minal 21 is at a level below the voltage across capacitor 49. During this time the diode bridge 10 is back biassd thereby effectively isolating the AC power lines from the frequeney eonver~ion stage. Thus, the energy to drive the oscillator-i~verter is supplied by capaeitor 49 via diode switch 50. When the recitified pulsating DC supply voltage(-again rises above the voltage on capacitor 49 (al~o capa-citor 23), the diode 50 is back biased 90 that the regene-rative power supply is effectively switehed offO
During the time that diode 50 conduct~, the voltage acros~ capacitor 23 follows the voltage aeross capacitor 49, Therefore, with diode 50 on, the voltage Vcc at terminal 21 is nominally the voltage on capacitor 49.
30 that the peak voltage at the~at the co].lectors of tran-sistor~ 30 or 31 is~/time~ the voltage of capacitor 49.
During this time, the cathode3 of diodes 47 and 48 are at the voltage level of the capacitor, whereas their anodes reeeive a voltage /! times this capaeitor voltage reduced `;: ~ :
' .
. - ' : ~
PHA. 21116 14 22-0~-83 by the turns ratio of the windings 45, 46 to the windings 27, 28. This ratio may be selected so that the diodes are non-conductive and thus the network including capacitor 51, inductor 52 and capacitor 49 will be isolated from the tank circuit. The "off" time of the diodes is chosen as a balance between the amount of demodulation and the power losses in the regenerative feedback circuit.
With the diode 50 biased off and with the vol-tage Vcc at terminal 21 increasing toward the peak voltageof the 60 Hæ AC supply voltage, a point will be reached where diodes ~7 and'~8 begin to conduct, thus effectively shunting the parallel resonant circuit 27-29 with the regenerative power supply. The reflected impendance, tightly coupled to the primary of transformer 26, will lS effectively modify the resonance frequency of the parallel resonant circuit 27-29 to produce a shift in frequency of the oscillator-inverter.
The solid state power supply of this invention features a high frequency oscillator-inverter that produce~q multiple-modes of cperating frequency, i.e. the frequency of operation varies over a given 60Hz period. In particular, the circuit described above will operate at all times at the frequency required to provide a continous lamp current ovar a full 60Hz cycle. This is achieved by operating the oscillator-inverter at two di~qtinct high frequency limits, fl and f2, with a smooth transition between the twe frequencies. The oscillation output frequency of the oscillator-inverter is automatically modified without changing the~esonant components or the lamp circuitry, and with essentially a sine wave output voltage for driving the discharge lamps at all timss.
The regenerative power supply circuit makes it possible to use a simple bridge rectifier system (10) without the need for a large value filter capacitor, as is required in most conventional AC-DC bridge circuits. The use of a regenerative power supply provides a system power supply provides a system power factor above 90~ and at .
: ' ~' .
~:3~3~3 PH~. 21116 15 22-04-83 the same time reduces the harmonic content of the line current and the level of conducted radiation. This same circuit is also the cont-rol element which makes possible the frequency shift of the 3eries fed parallel rosonant tank circuit 27-29.
The power supply output stage consists of an impedance matching transformer and a series reactance to limit lamp current. The transformer also provides continuos filament power for operation of the lamps. The reactive element (either capacitive or inductive) in series with the lamp has its impedance varied by varying the oscillator inverter operating frequency in a sense so as to maintain the lamp current within selected limits, thus insuring , that the plasma never deionizes .
The modulation envelope of the high frequency signal generated by the oscillator-inverter circuit without a load is shown in Fig. 2b. The frequencies fl and f2 will be found within the modulation envelope. The sinusodial high frequency fl will occur in the region of maxium supply ~oltage and the sinusoidal high frequency f2 will occur during the period when the r egenerative power supply is coupled to the oscillator-inverter via diode switch ~0.
The voltage supplied to the oscillator-~invertor during the latter period is substantially constant, as is evident from the horizon-tal flat portions of the waveforms in Figs.
2a and 2b. During the period when the regene~ative power supply is decoupled from the oscillator-inverter, the frequency f1is generated with the amplitude of the sine waves varying with the amplitude variations of the rectified pulsating DC voltage supplied by bridge recit-- fier 10 at its output teminals 21, 22.
The frequencies ~1 and f2 within the modulation envelope will vary dependent on whether the series reactan-ce element for the discharge lamps is inductive or capactive, and also on the choice of circuit elements. For the case where the series reactance is capactive, i.e.
capacitor 40 in Fig. 1, tlle circuit will be adjusted so that the frequency f1 is less than the frequency f29 e.g.
~3;~3~3 PH~o 21116 16 22-04-83 a 25-30~ differential in tank frequency. Thus, when the oscillator supply voltage is at its low value, represented by the ~lat portion of the supply voltage waveform (Fig.2A) a voltage of frequency f is generated to produce a lamp current of a given amplitude. When the supply voltage increases, i.e. after the regenerative power supply is cut-out by diode switch 50~ then the oscillator-inverter generates a higher amplitude voltage. This higher voltage would tend to increase the lamp current. However, when the regenerative power supply was effectively switched out of the circuit, there occurred a change in the reflected impedance of the secondary circuit of transformer 26 that produces a change in the frequency of oscillation of the oscillator-inverter circuit to the lower frequency f1 .
This lower frequency voltage f1 is coupled via the trans-former 26 an-l ~eries capacitor 40 to the lamps. The lower frequency f1 causes an increase of the capactive reacta~ce 90 as -to maintain the lamp current fairly constant despite the substantial variation in supply voltage over a full period of the 60Hz ~C supply.
~ t is therefore seen that the change in reflec-ted impedance into the parallel r~sonant tan~ circuit as the regenerative power supply is switched in and out of the circuit at a predetermined level of the pulsating DC vol-tage produces an automatic change in the oscillation freq-uency in a direction so as to maintain the lamp currentconstant by an automatic variation of the impedance of the series reactance leement.
For the case where the series capaci-tor 40 is replaced by an inductor, the frequency f generated will be greater than the frequency f2. Thus, for an inductive ballast the higher operating frequency will occur at the peak values of the supply voltage while the lower freq-uency will be produced during the period of lower supply voltage, which occurs when the circuit is operated by the fi~ed DC voltage of the regenerative power supply circuit The inductive reactance thus will be higher for the higher .
PH~. 21116 17 ~ 938 22-04~83 values of the supply voltage so as to maintain a constant lamp current. It should be noted that the frequency trnsition between the frequencies f1 and f2 and vice versa is essentially smooth and occurs durillg the pel~io~ at the regenerative power supply is coupled to the oscillator-inverter via the conductive diode switch 50. By maintaining a given minimum DC supply voltage when the bridge supply voltage is low, the regenerative power supply thus prevents the deioni~ation of the lamps during normal operation.
The frequencies f1and f2 are chosen so that the lamp current will be held within prescribed limits to ob, tain an optimum lamp current crest factor, related to ex-tended lamp life, and optimum generation of 254 nm radia-tion within the arc for a maximum conversion of energy bythe phosphor into useful light.
Fig 3 ill1lstrates an impedance transformation device in the form of a new leakage transformer configu-ration that provides both a current limiting (ballast) function and an automatic control of the lamp heater power ~-so as to improve the efficiency of the overall power supply-ballast system. The leakage trabsformer will couple the oscillator-inverter circuit to the discharge lamps and may therefore be substituted for~ the transformer 26 and bal-last capacitor 40 of Fig. 1, thus saving on a ballast ca-pacitor. Inductive ballasting of the discharge lamps is now achie-ved by means of the leakage reactance of the transformer itself. The l~mps thus may be connected di-rectly across the transformer secondary winding 55 so that the varying reactance of the secondary will limit and control the lamp volt-ampere requirements. This leakage transformer arrangement provides a significant reduction in radiated and conducted ~FI. The connections between the transformer secondary windings and the discharge lamps are illustrated in Fig. 4. The windings 32, 45, 46 of the transformer are connected in an identical manner to that shown for the transformer in Fig. 1 and will therefore not be further illustrated.
PHA.21116 18 ~232g3~ 22-04-83 The high frequency leakage transformer includes a magnetic core 56, preferably of ferrite material, with an air gap 57 formed in the middle leg. The secondary win~
ding 55 along with the lamp heater windings 58, 59 and 60 are wound on the right leg of the transformer core and a primary winding 61 is wound on the left leg. The heater windings are thus tightly coupled to the secondary winding 55. The capacitor 29 of Fig. 1 will be connected in paral-lel with the primary winding 61 to form therwith a tuned parallel resonant tank circuit for the oscillator-inverter stage. The ends of the primary winding are connected to the collector electrodes o~ switching transistors 30, 31 (Fig. 1).
The secondary portion of the transformer is not lS electrically connected to the primary winding and will provide both the transfer of energy to the load and the control and regulatiGn of the load, especially where the load is a negative impedance device such as a discharge lamp.
In order to ignite the discharge lamps coupled to secondary winding 55, the open circuit voltage across the secondary must exceed the voltage required to initiate a discharge in the lamp. For the case of a fluorescent lamp load, the transformer also provides the power to produce electron emission of the lamp cathodes, which assists in the initiation of the discharge. The heater windings 58-60 for the discharge lamps are tightly coupled to the secon-dary of the transformer such that, when there is no load current flowing, and thus nu current in the secondary, the heater windings provide a maximum power transfer to -the lamp cathodes.
The transformer consists of primary and secon-dary sections plus a shunt section comprising a gapped core and with the primary winding inductance resonated with a paralLel capacitor to set the fundamental operating frequency of the oscillator-inverter. The primary winding is composed of N turns of wire and the ferrite core has an adequate cross-section to insure that the transformer pri-.
. ,, .. ; - ~ ~ .
'.. ': :
' , :, 1~3293~, PHA.21116 19 22-0~-83 mary section does no-t saturate. In fact, it is preferable to arrange the -transformer so that no portion o~ the entire transformer will be allowed to saturate at any time, -thus providing low power dissipation in the transformer, mini-mum distortion and optimum power coupling.
The transformer secondary is physically separ-ated ~rom the pri1nary. It is a leakage reactance ~induc-tance) which is coupled to the primary only by means of the magnetic field. With no secondary load, the secondary open circuit voltage will be determined by the primary -to socondary turns ratio. Before ignition of the lamps, es-entially all of the magnetic flux generated by the pri-mary winding links the secondary winding to provide maxi-mum heater power and open circuit voltage. After lamp ig-nition, a current flows in the secondary winding so thatsome of the primary flux flows through the gapped center leg of the core 56, thus providlng a leakage reactance for limiting the lamp current. The flux linkage or coupli~g to the secondary is reduced after lamp ignition which also results in an automatic reduction of the cathode heater power.
The impedance of the secondary winding, which is in parallel with the load (lamps) and sets the load ;operating level, is frequency sensitive. As the oscilla-tor-inverter operating frequency, determined by the reso-nated primary and magnetically reflected reac-tance from the secondary, varies the secondary impedance will vary so as to modify the resonant frequency (oscillation fre~
quency) of the apparatus in a manner such that the power delivered by the secondary to the lamps tends to remain constant. The magnetic circui-t will vary as required to control the load power, and the volt-ampere characteris-tics of the load will be governed by the variations in the impedance of the seconidary winding.
The operation of the transformer after lamp ignition may also be explained in the following manner.
As current flows in the secondary, conservation of primary magnetic flux coupled with the magnetic flux generated by .,. ' . .1 ~ . ~ . ' ' `
, :~ : .:., ~3293~3 PHA.21116 20 22-04-83 the secondary results in flux leakage across the relative-ly high magnetic reductance of the gapped shunt portion.
This effectively results in a v~riation in magnetic coupl-ing to the secondary. ~s the magnetic coupling varies, the resultant reactance of the secondary winding will also va-ry as it is a function of both the number of turns and the generated magne-tic flux carried by the ferrite core on which the winding is mounted. This effect is equivalent to a secondary leakage reactance.
Another way of looking at the transformer oper-ation is that a constant primary flux flows before ignition and the ferrite core provides a low reluct~nce path. After lamp ignition, the current flow in the secondary winding causes a reverse flux to flow so that less of the primary flux is coupled to the secondary winding and the heater windings.
This mode of operation has been termed the auto-heat mode in which the heater power bears an inverse relationship to the lamp current. In contrast, the appar-atus of Fig. 1 provides a relatively constant cathodeheater power. After ignition in the apparatus of Figs. 3 and 4, the flux linkage decreases resulting in reduced heater power. A subsequent decrease in lamp current re-sults in an automatic increase of heater current. For ex-ample, if the lamps are dimmed, resulting in a reducedlamp current, the filamen-t heat ~current) will automatical-ly be increased to maintain the filament temperature. After ignition, the heater current is significantly reduced which provides optimum cathode temperature and extended lamp life due to a slower deterioration of the lamp cathodes. If a power interruption occurs and the lamps current stops, or is appreciably reduced, the filament heat will automatical-ly return to the required level to provide the optimum filament temperature.
The cathode heater windings of -the leakage trans-former will normally have a low turns ratio in relation-ship to the turns of the secondary winding 55. It is alter-natively possible to wind a portion of -the heater windings : -- :, : .' ,', ' :
, ~ .
. ;
~32931!3 PI~A.21116 21 22-0LL-83 around the magnetic shunt portion of the transf`ormer core in order to develop a non-linear response function. The amount of the reduced heated current after ignition is related to the turns ratio of the heater windings to that of the secondary winding and to the current flowing in the secondary. Minimum power losses are insured by designing the rnagnetic structure o~ the trans~ormer so -tha-t it never saturates. The operation of the oscillator-inverter ballast using the leakage transformer of Fig. 3 for coupling the lamps through the oscillator-inverter stage will be ths same as that described in connection with Fig. 1 for a circuit which is inductively ballasted.
~ hile we have described our invention in connec-tion with certain specific embodiments and applications, other modifications and alterations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
~ . ,, i :, :` : , .. ~ , . ..
Claims (9)
1. A high frequency oscillator-inverter for start-ing and operating at least one electric discharge lamp from a 50 to 60 Hz AC power source comprising, a pair of input terminals for connection to the 50 to 60 Hz AC power source, a rectifier circuit having an input coupled to the input terminals and an output for supplying a substantial ly unfiltered rectified DC current, an oscillator-inverter circuit including at least one transistor, a ballast coup-ling circuit for eoupling the output voltage of the oscil-lator-inverter circuit to at least one said discharge lamp, said ballast circuit including a transformer having a pri-mary winding coupled to said one transistor and a seconda-ry winding coupled to said one discharge lamp, a capacitor coupled to the transformer primary winding to form a paral-lel resonant circuit for the oscillator-inverter circuit which exhibits a high oscillation operating frequency rela-tive to said 50 to 60 Hz AC power source, means coupling the output of the rectifier circuit to said oscillator-inverter circuit to produce oscillation at said operating frequency, a regenerative power supply including means for switching said regenerative power supply into and out of circuit with the oseillator-inverter circuit as a function of a given voltage threshold level determined by the 50 to 60 Hz AC power source, thereby to produce a substantial change in the oscillation frequency of the oscillator-inverter circuit and in a sense that tends to maintain the lamp current constant in the operating condition thereof.
2. An oscillator-inverter as claimed in Claim 1 further comprising a frequency dependent impedance element whose electric impedance varies as a function of frequency and connected in series with said one discharge lamp across said transformer secondary winding and with its impedance being variable with said change in oscillation frequency PHA.21116 23 in a sense to maintain the flow of lamp current within given limits.
3. An oscillator-inverter as claimed in Claim 2 wherein said frequency dependent impedance element com-prises either a capacitor or an inductor.
4. An oscillator-inverter as claimed in Claim 1 wherein said regenerative power supply comprises, a third winding of said transformer for detecting the amplitude level of the oscillations in the oscillator-inverter cir-cuit, and said regenerative power supply switching means includes a second capacitor and a diode coupled to said third winding and to the output of the rectifier circuit so that the diode is biased into conduction or cut-off dependent on the output voltage of the rectifier circuit and a voltage stored on the second capacitor by means of said third winding.
5. An oscillator-inverter as claimed in Claim 4 wherein said regenerative power supply includes an LC
circuit coupling said third winding to said diode and said second capacitor and arranged to function as an integration network to provide a smooth and continuous transfer of electric energy from the third winding to the second capacitor thereby to reduce the harmonic level of the 50 to 60 Hz AC current at said pair of input terminals.
circuit coupling said third winding to said diode and said second capacitor and arranged to function as an integration network to provide a smooth and continuous transfer of electric energy from the third winding to the second capacitor thereby to reduce the harmonic level of the 50 to 60 Hz AC current at said pair of input terminals.
6. An oscillator-inverter as claimed in Claim 1 further comprising a radio frequency interference filter coupled between said pair of input terminals and the input of the rectifier circuit.
7. An oscillator-inverter as claimed in Claim 1 or 2 wherein the oscillator-inverter circuit comprises, first and second transistors connected in a push-pull cir-cuit to said parallel resonant circuit, means coupled to control electrodes of the first and second transistors for alternately triggering said transistors into conduction and cut-off in mutually exclusive time periods, and a fur-ther winding of said transformer for serially coupling the output of the rectifier circuit to a center tap on the transformer primary winding, and wherein the regenerative PHA.21116 24 power supply comprises, a third winding of said transformer for detecting the amplitude level of the oscillations in the oscillator-inverter circuit, a second capacitor and a diode connected in series circuit across the output of the rectifier circuit, a second rectifier circuit, a parallel LC circuit, and means coupling said third winding to a junction between the second capacitor and diode via the second rectifier circuit and the parallel LC circuit.
8. An oscillator-inverter circuit as claimed in Claim 1 wherein said transformer comprises a closed ferro-magnetic core having two windows therein defining first and second ferromagnetic core legs and a third ferromagnetic core leg including a nonmagnetic-gap for imparting a sig-nificant leakage inductance characteristic to the trans-former, said primary winding being coupled to the first core leg and the secondary winding being coupled to the second core leg so as to provide a significant equivalent ballast inductance for limiting the flow of lamp current in the secondary winding, and filament heater winding means coupled to the second core leg and to at least one heater electrode of the discharge lamp, said transformer being operative to supply a lower filament heater current sub-sequent to ignition of the lamp than it supplies prior to lamp ignition.
9. An oscillator-inverter circuit as claimed in Claim 8 wherein said transformer further comprises first and second windings coupled to said first core leg and to said regenerative power supply and a control electrode of the one transistor, respectively.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/382,734 US4560908A (en) | 1982-05-27 | 1982-05-27 | High-frequency oscillator-inverter ballast circuit for discharge lamps |
| US382,734 | 1982-05-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1232938A true CA1232938A (en) | 1988-02-16 |
Family
ID=23510188
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000428909A Expired CA1232938A (en) | 1982-05-27 | 1983-05-26 | High frequency oscillator-inverter ballast circuit for discharge lamps |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4560908A (en) |
| JP (1) | JPH0667214B2 (en) |
| CA (1) | CA1232938A (en) |
| GB (1) | GB2120873A (en) |
| MX (1) | MX155252A (en) |
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| US10045406B2 (en) * | 2013-01-24 | 2018-08-07 | Cree, Inc. | Solid-state lighting apparatus for use with fluorescent ballasts |
| US10104723B2 (en) | 2013-01-24 | 2018-10-16 | Cree, Inc. | Solid-state lighting apparatus with filament imitation for use with florescent ballasts |
| US9439249B2 (en) | 2013-01-24 | 2016-09-06 | Cree, Inc. | LED lighting apparatus for use with AC-output lighting ballasts |
| CA3136809C (en) | 2019-04-15 | 2024-03-12 | Atmospheric Plasma Solutions, Inc. | Asymmetrical ballast transformer |
| AU2020257386A1 (en) * | 2019-04-16 | 2021-11-11 | Atmospheric Plasma Solutions, Inc. | Frequency chirp resonant optimal ignition method |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1176360A (en) * | 1967-08-11 | 1970-01-01 | Thorn Electronics Ltd | Improvements in Inverter Circuits |
| US3579026A (en) * | 1969-01-02 | 1971-05-18 | Sylvania Electric Prod | Lamp ballast |
| GB1326392A (en) * | 1970-11-14 | 1973-08-08 | Dobson Park Ind | Fluorescent lamp and other circuits |
| US3769545A (en) * | 1972-05-25 | 1973-10-30 | Kodan Inc | Circuit arrangement for operating electric arc discharge devices |
| US4017785A (en) * | 1975-09-10 | 1977-04-12 | Iota Engineering Inc. | Power source for fluorescent lamps and the like |
| US4259614A (en) * | 1979-07-20 | 1981-03-31 | Kohler Thomas P | Electronic ballast-inverter for multiple fluorescent lamps |
| JPS6036710B2 (en) * | 1980-03-10 | 1985-08-22 | 東芝ライテック株式会社 | power supply |
| US4346332A (en) * | 1980-08-14 | 1982-08-24 | General Electric Company | Frequency shift inverter for variable power control |
-
1982
- 1982-05-27 US US06/382,734 patent/US4560908A/en not_active Expired - Lifetime
-
1983
- 1983-05-23 GB GB08314229A patent/GB2120873A/en not_active Withdrawn
- 1983-05-26 CA CA000428909A patent/CA1232938A/en not_active Expired
- 1983-05-26 MX MX197438A patent/MX155252A/en unknown
- 1983-05-27 JP JP58092584A patent/JPH0667214B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| GB8314229D0 (en) | 1983-06-29 |
| US4560908A (en) | 1985-12-24 |
| JPS5921286A (en) | 1984-02-03 |
| GB2120873A (en) | 1983-12-07 |
| MX155252A (en) | 1988-02-08 |
| JPH0667214B2 (en) | 1994-08-24 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |