CA1295013C - Power supply operable on varying inputs - Google Patents
Power supply operable on varying inputsInfo
- Publication number
- CA1295013C CA1295013C CA000548435A CA548435A CA1295013C CA 1295013 C CA1295013 C CA 1295013C CA 000548435 A CA000548435 A CA 000548435A CA 548435 A CA548435 A CA 548435A CA 1295013 C CA1295013 C CA 1295013C
- Authority
- CA
- Canada
- Prior art keywords
- transformer
- voltage
- power supply
- primary winding
- line
- 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 - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/36—Means for starting or stopping converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
- H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
Abstract
Abstract A power supply provides the stable DC voltages needed for a computer terminal from a wide range of line voltages and frequencies. The line is rectified and fed to a flyback transformer wherein primary current is controlled in duration for providing the desired energy transfer to the secondary winding. The ouputs from the flyback transformer are rectified and filtered. A separate start-up circuit uses a transformer across the line voltage, and a positive coefficient resistor provides a time limit to allow the use of a small transformer even though the line voltage may be high. The start-up circuit must produce a minimum voltage for the switching transistor in the flyback arrangement to allow operation of the power supply, and the start-up transformer is disconnected from the circuit after operation to prevent electromagnetic interference within the terminal.
The output from the power supply is used in the control of the switching transistor so that, once the start-up circuit has achieved the needed voltage level, the power supply can assist in maintaining the operation.
The output from the power supply is used in the control of the switching transistor so that, once the start-up circuit has achieved the needed voltage level, the power supply can assist in maintaining the operation.
Description
3~
POWFR SUPP~Y OPERABL~ O~ VARYI~G I~PUTS
Information Disclosure Statement It is well known in the art to provide a power supply wherein a given voltage~ or range of voltages, acts as the input, and a stabilized DC output is provided. Furthermore, it is known in the art to utilize a transormer wherein current flow through the primary winding of the transEormer is controlled by a transistor or other switching means in order to vary the energy output of the transformer. With this arrangement, a pulse can be provided, and the width of the pulse determines the length of time the switching means is on to allow current to ~Elow through the primary winding oE the transformer. ~s a result, the energy output is determined by -the width oE the pulse to the switching means.
These pulse width controls normally utilize a generally conventional transformer wherein the change in magnetic flux in the primary winding is directly reflected in an induced voltage in the secondary winding.
! With the prevalence of computer terminals, and -the need to operate these terminals from the various standard ~0 power sources available around the world, it would be desirable to utilize a single power supply for any power available. The two primary problems in utilizing the available power are the extremely low voltages that sometimes occur, either through design, or through temporary overload, or "brown-out"; and, some areas of the world utilize a relatively high voltage, or example about 250 volts, while other areas of the world utilize a relatively low voltage, for example 108 volts. Furthermore, -the requency of the power i5 not always the same~ While 50 to $~J~3 70 Hz is common, there are situations in which the ~requency is lower than intended, because of errors or the likeO
In utilizing prior art arrangements, it should be understood that the availablity of an extremely low voltage will not provide sufficient power to allow the power supply to begin to produce the desired voltages. Furthermore, if the line voltage is very close to the voltage required, but slightly low, the components receiving the line voltage may burn out because there is insufficient power to operate the controlsO When voltages are extremely high, the prior art clrcuiks are such that they would be unable to absorb or control the energ~, so components oE a circuit may be damaged, and the voltage produced by the power supply may be higher than desired.
Summary of the Invention This invention relates to power supplies for computer terminals, and is more particularly concerned with a power supply operable over a wide range of voltage and frequency inputs.
The present invention provides a power supply utilizing a flyback transformer arrangement wherein switching means determines the current flow in the primary winding of the transformer. Current limiting means is provided to protect the circuitry, and pulse width control means determines the duration of curxent flow through the primary winding. The primary winding of the flyback transformer is designed to withstand very high voltage, so a ; wide range of voltage inputs can be utilized. Because of the control for the switching means, the flyback transformer will not operate iE the voltage is too low.
1~95i~
70~56-10 A separate start-up circuit is provided, the start-up circuit yielding a reference voltage. When the reference voltage reaches a minimum level~ the power ~upply begins to operate; and, after a predetermined length of time, the start-up circuit is de-energized to prevent the production of electromagnetic interference.
At all times during the operation of the power supply, the output vol~age is sensed, and the on and off cycles of the switching means of the flyback transformer are varied to adjust the voltage as needed. When the voltage drops below a predetermined level, the power supply wlll not operate, and the start-up circuit is energized. When the voltage drops below the predetermlned level, there will always be a suff.icient time delay for the computer circuitry to reset before the power supply is reactivated.
According to a broad aspect of the invention there is provided a power supply for producing at least one stable DC
voltage from an AC line voltage, said power supply including rectifying means connected to said line voltage for produciny a DC voltage proportional to sald line voltage, a first transformer, switching means for selectively connectlng said first transformer across said DC voltage, said first transformer having a prlmary winding and at least one secondary winding, said secondary winding lncluding rectifying ~eans for preventing current flow in said secondary winding while sald primary winding is connected to said DC voltage by said switching means, characterised by control means for controlling said æwitching means for varying the length of time said primary winding of said first transformer is connected across said DC voltage, and a start-up means for said power supply, said start-up means including a second transformer havlng a ~5~3 70856-10 primary winding connected across said line volkage and a secondary winding for producing a voltage proportional to said line voltage, circult means for providing said voltage proportional to said line voltage to said control means for controlling said switching means, and means for disconnecting said second transformer from said line voltage after said power supply is producing said stable ~C voltage.
Brie~ De~cription of the Drawinas These and other Eeatures and advantages of the present invention will become apparent from consideration of the Eollowing speciEication, when taken in con~unction wlth the accompanyi.ng drawing~ :Ln which, Fig. 1 is a block diagram illustrating a power supply made in accordance with the present invention; and Flgs.2 and 3 are schematic diagrams illustrating a power supply made in accordance with the present invention.
D~tailed Description of the Fmbodi~ent Referring now more particularly to the drawings, and to that embodiment oi`. the invention here presented by way oi.
illustration, Fig. 1 is a block diagram showing operation o~ a power supply made in accordance with the present invention.
The power source is from the conventional AC line 3a ~Z~ 3l3 indicated at 10, and the line voltage may be as low as 40 VAC or as high as 440 VAC. Also, the frequency of the power source 10 may be as low as 30 ~z, or as high as several kHz.
In any event, the incoming line is fed ~o a rectifier and filter 11 to produce a DC voltage and to remove a significan-t portion oE the noise on the l.ine. It will be noted that the AC supply is also connected directly to the start-up circuitry 12, and this will be discussed in urther detail later.
The output from the rectifier and filter 11 is fed to a 1yback transformer 14. This ~lyback arrangement produces a plurality of DC outputs, and the outputs are rectified and filtered at 15. Loads may then be connected to the output lines 16, 18 and 19.
The incoming line 10 may sometimes have a voltage so low that the circuitry of -the power supply cannot produce the desired outputs. In this event, there must be some means for preventing outputs that are too low for proper operation but high enough to cause some damage to the circuitry of the load. When the power supply of the present invention is initially energized, the arrangement is such that there wil].
be no output from the 1yback transformer 14 until the start-up circuit 12 can produce a minimum voltage. Thus, the start-up circuitry 12 receives the incoming line voltage, and di.rec-ts an output to the pulse width modulator 20. If the signal from the start-up circuitry 12 is below the minimum threshold, the control 21 holds the modulator 20 : off, which holds the switching means for the flyback transformer off. There will thus be no current flowing through the primary of the flyback transformer 14.
Once the start-up circui-try 12 achieves the minimum voltage, the signal will be fed to the pulse width modulator 20, which will in turn signal the flyback transEormer 14 and cause a current to flow in the primary of the flyback transformer 14. This will result in an output to the output rectifier and filter 15, and yield a voltage on the output lines 16, 18 and 19. It will then be noticed that the output is ed to the pulse width modulator 20, and also to the timing and control 21. The timing and control 21, in turn, is connected to the start-up ci.rcuitry 12 and to the pulse width modulator.
In yene.ral, lt should be understood that the output voltage on the lines 18 and l9 i9 constantly monltored to change the width of the pulse fed to the switchinq means and the flyback transformer 14. The variation in the time that current 10ws in the primary winding is the means for control to achieve the desired output voltages at 16, 18 and 19 .
The output voltage is furthe.r monitored by the timing control 21 so that, i the output voltage drops below a predetermined voltage, the pulse width modulator 20 will prevent further operation of the flyback transformer 14, and the start-up circuitry 12 will be reconnected into the circuit. The start-up sequence will be attempted, and will not be successful until the start-up circuitry 1~ is able to produce the minimum voltage.
The timing and control 21 urther includes timing means so that, once the output voltage from the output rectifier and filter 15 drops below a predetermined minimum voltage, the circuitry is held off for a minimum length o ~5--~2~ 3 time. This is important for computer circuitry so that the computer circuitry will reset rather than become locked in a given state.
As will be discussed further hereinafter, the specific design of the flyback transformer 14 is important to the present invention since this allows a very low voltage to produce the desired voltage. When the voltage at line 10 is extremely low, the output voltage Erom the output rectifier and filter 15 is fed through the pulse-width modulator 20 to provide a longer pulse, to give the desired energy input to the primary oE -the flyback transEormer 14.
On the other hand, if the incoming line 10 is an e~tremely high voltage, the switching means on the primary remains on for a very short time to provide the same desired energy input.
For a further understanding of the power supply of the present invention, attention is directed to Figs. 2 and 3 of the drawings.
In Fig. 2, it will be seen that the available line power will be applied to the lines 30 and 31. There~ are capacitors Cl, C2 and C3 placed across the lines 3a and 31 to filter the line and remove the majority of the noise on the line. The lines 30 and 31 then con~inue to a full-wave ;~ rectiEier designated at 32~ The negative side of the rectiEied voltage i8 indicated at 34, and the positive side i5 indicated as the line 35.
Beyond the recti-Eier 32, there are capacitors C4 and ; C5 connected to the line 35, and also connected to line 34 through the bus 36. Further/ resistors R2 and R3 are connected between the bus 36 and the line 35. The bus 36 is ~L2~95~3 grounded through capacitor C6. The arrangement including capacitors C4, C5 and C6 and resis-tors R2 and R3 will therefore fil-ter the rectified voltage so that most of the noise on the line is removed. After the filtering network just described, there is a fuse designated at Fl.
Referring back to the incoming lines 30 and 31, there ~re branch lines 38 and 39 connected to -the lines 30 and 31 respectively. There is a line synchronization circuit connected to the branch lines 38 and 39 by the lines 40 and 41. A light emitting diode (LED) 42 allows current to flow in one direction, and diode CRll allows current to Elow in the opposite direction. In both directions, current is limited by the resistor ~47. It will thereEore be seen khat light will be emitted from the diode 42 at each halE cycle of the alternating curren-t from -the line, and light from the diode 42 will trigger the phototransistor 44. With ~5 VDC
applied at 45, current can flow from 45, through the resistor R46, through phototransistor 44, and to ground.
Each time current flows in this path, a signal will be transmitted along the line 46 which will yield a synchronization pulse~ Thus, if the power supply, or other related equipment, is to be synchronized with the line fre~uency, the pulse on line 46 will provide the appropriate timing signal.
Looking again at the lines 38 and 39, the line 39 includes a positive coefficient resistor designated at RT2 in series with the pri~ary winding of the transformer Tl.
When the lines 30 and 31 are connected to a power source, power will be available on the lines 38 and 39 so that current can Elow through the line 38, through the connecting ~Z~5~
line 48, through the normally closed relay contact 49, then through -the line 50 and to the primary winding o the transformer Tl~ From the transEormer Tl, current can flow through the resistor RT2 and to the line 39 9 then to the line 31. As a result, the transformer Tl will be energized -to produce a voltage on its secondary winding. The transformer Tl and its associated circuitry comprise the start-up circuit for the power supply.
The transformer Tl has connected thereto a full wave rectifier designa-ted at 51, with the negative side grounded at 52, and the positive side connected to the line 54.
One of the salient features oE the present invention is the ability to provide the entire power supply in a very small and relatively light-weight circuit to be incorporated directly within computer terminals. Considering the wide voltage range over which the transformer Tl must operate, conventional engineering would require an extremely large transformer, to the extent that -the transformer Tl could not be mounted on a printed circuit board. The use of a very small transformer is not indicated because of the hea~
generated at high voltages, so the transformer Tl would burn out after a very short operating time.
In the present invention, it is contemplated that the transformer Tl will be operated only long enough for the principal power supply to become operative, and the transformer ~1 needs to be de-energized in ordar to prevent magnetic interference from the transformer. With this in mind, a small and light-weight transformer was designed, and the resistor RT2 was installed as an additional safety feature. The operating parameters of RT~ are such -that, if :~L%~ 3 Tl is operative for a length of time that may cause damage to the transformer Tl, the resistance of RT2 will increase to the point that current flow through the transformer Tl will be effectively terminated. Since the resistor RT2 is a positive coefficient resistor, it will be understood that the temperature of RT2 is directly reLated to the cu~rent through the transformer Tl, and high current through transformer Tl will cause the resistance of RT2 to increase sufficiently that current will be negligible.
In normal operation, once the power supply is fully operational, the relay Kl will be energized to open -the contact ~9 to de-energize the transEormer Tl. T~e operation of rela~ Kl wlll be descrlbed urther hereinater, but it should be understood that, in nor~al operation, the relay contacts 49 will open before the temperature oE RT2 becomes high enough to shut down the transformer Tl.
Returning now to the start-up circuitry, and looking at the line 54 connected to the rectifier 51, the line 54 is connected to the collector of transistor Q3, and the emitter of Q3 is connected to the line 5S. The base of the transistor Q3 is connected through zener diode CR14 to ground; and, between the base oE Q3 and the diode CR14, a resistor R26 is connected to -the line 54. With this arrangement; the output at 56 will be a DC voltage that directly follows the incoming line voltage. Because the diode CR14 is a zener, in the beginning the voltage at 56 will follow the voltage at 54. Once the voltage exceeds the zener voltage, the voltage on the line S5 will be pulled down, resulting in a voltage on the line 5S at no more than one diode drop above the zener voltage. In the present _9_ ~2~
embodiment oE the invention, the zener voltage of CR14 is 30 volts, so tne voltage at 55 wi.ll be no more than approximately 30 volts.
The voltage at 56 is labeled VRAW2, and uses for this voltage will be discussed later. Since VRAW2 will never exceed about 30 volts regardless of the line voltage, another voltage labeled VRAW1 is pulled off the line 54 before Q3. It will be seen -that VR~Wl will always be proportional to the line voltage.
After the transistor Q3, there is a diode CR15 in the line 55. The diode CR15 is arranged to prevent a higher voltage on the line 55 rom damaging the transistor Q3.
Capacitors C30 and C26 are connected between the l.ine 55 and ground to smooth out the pulsed voltage :Erom -the AC
line, and to increase the signal to noise rejection of voltage regulator circuit VR1. VR1, in conjunction with the capacitor C27, provides a regulated voltage designated as VREFl. In khe present embodiment of the invention VREF1 is +12 VDC.
It will be seen that there are additional voltage regulator circuits designa-ted at VR2, VR3 and VR4. VR2 is connected to a branch 58 through a diode CR8 to prevent the start-up voltage on line 55 from attempting to power voltage regulator VR2. Again, capacitors following the regulator VR2 smooth the voltage to produce a -~12VDC, while the parallel circuit VR3 regulates the incoming -~16VDC to produce VREF2.
Returning again to the lines 38 and 39, the line 38 is connected to one side of the relay contact 59. Since contact 59 is normally closed, current will flow through the line 60, and through the positive coeEficient resistor RTl~
through coil J4~ and to the line 39. The coil J4 is a degaussing coil, so it will be understood that the cat'node ray tube will be degaussed at each start-up cycle. As was previously mentioned, the relay Rl will be energized after the power supply is in operation, and the operation of relay Kl will open contacts 49 and 59, so the coil J4 will also be de-energized. The positive coefficient resistor RTl will be heated by the degaussing current, and the heat will increase the resistance to the point that the coil is effectively de-energized. This provides the necessary decaying current re~uired to cause proper degaussing.
Returning now to the line 35 discussed above, this same line extend~ into Fig. 3, and i8 connected through the primary winding of trans:~ormer T3 to the primary winding of transformer T2. As will be recognized from the following discussion, transformer T2 is not operated as a true transformer, but the transformer T2 is utilized in a ~lyback ; arrangement that is well known to those skilled in the art.
Typical of the flyback arrangement, there is a switching means for controlling current through -the primary winding of the -transformer T2, and this switching means in the present embodiment of the invention is transistor Ql which has its collector connected to the line 61, and its emitter conne~ted through the line 62 to a bus 64 which is connecked to the line 34 from the recti~ier 32.
~In general, it will be understood that current will ;~flow through ~he line 35, and through the primary winding of the transformer T2, ~hen through the transistor Ql, line 62, to the line 34 and to the rectiEier 32, but only so long as the transistor Ql is conducting. When -the transistor Ql is ~Z~ 3 biased off, curren-t will no longer flow. It will also be noticed that the three secondary windings designated at 65, 66 and 68 include diodes arranged so that, while curren-t is flowing in the primary winding of the transformer T2, no current can flow in the secondary windings. Only when current ceases to -Elow in the primary winding oE the transformer T2, and the magnetic field begins to collapse, will current be allowed to flow in the secondary windings.
Because of this arrangement it will be understood that energy is provided to the transEormer T2 through the flow of current through the primary winding; then, the discrete amount o energy stored in the transformer is transfe~red to the secondary windings.
In operation of the power supply of the present invention, it will be unders-tood that the transistor Ql will be controlled to turn off very quickly in order to limit the energy passed by the transformer T2. Such sudden turn-offs induce great stress on the transistor. To prevent damage to the transistor, a snubber circuit is provided through the line 61, through the capacitor C7 and diode CR5. Resistors R4 and R16 are connected in parallel to the diode CR5. When the transistor Ql is turned off, current can flow through the capacitor C7 and through the diode CR5, taking the stress off the transistor ~1. The current will of course charge the capacitor C7, and the resistors R4 and R15 will discharge the capacitor C7 at the end of the inductive current. When the capacitor C7 is discharged, the circuitry is ready to act as a snubber for the next -turn-of cycle.
It is conventional in power supplies to utilize a soft start, but the conventional power supply does not have S~3 to contend with -the wide voltage ranges contemplated in the present inventlon. Thus, the present invention includes a somewhat usual soft start arrangement wherein the voltage VRAW2 is applied to the base of the transistor Q10 through the zener diode CRl9, so Q10 is not t:urned on until the voltage VRAW2 reaches a minimum voltage of 12 vol~s. As long as Ql0 is off, VREFl is supplied through resistors R53 and R52 to the line 71, thence to pin 10 of Ul, so Ul is held off. Thus, if the start-up circuit cannot produce over 12 volts at VR~W2, the power supply is unable to operate. On the other hand, once V~AW2 exceeds 12 volts, transistor Q10 will be turned on.
VREFl is applied to the stark-up circult and the modulator chip. When VREFl reaches about +5V, U2 starts to operate. As a result, even though Q10 turns on and no longer holds Ul off, U2 is high on pin 5, which holds Ul o-ff V~EFl is also applied to Ul; and, when VREFl exceeds the undervoltage lockout value, the outputs are enabled, though still held off by U2.
20Operation o U2 also makes pin 9 go high, and this turns on transistor Q9, which holds Q5 off. With Q5 off, relay Kl cannot operate even though VREF2 i5 produced. This assures that the start-up circuit will remain connected into the circuit until U2 times out.
After the predetermined length of time, pin 5 of U2 will go low, releasing pins 9 and 10 of Ul~ Pin ll will ; begin driving transistor Q2 which is part of the base drive circuit or Ql. Also, transistor Qll is turned of, so the soft start capacitor C16 will begin charging. ~s the capacitor C16 charges, the duty cycle increases to produce the soft start.
If the line voltage i5 quite high, the use of t'ne one soft start capacitor does not provide an effective soft staxt action. To resolve this difficulty, the voltage VR~Wl, which is always proportional to the line voltage, is fed through a zener diode CR21 to ~he base of transistor Ql3.
The zener voltage is selected so that Ql3 is turned on when the line voltage exceeds 180V. When Q13 is on, the capacitor C49 is connected into the timing circuit provided by resistor R23 and capacitor C16, adding capacitance to the circuit to assure a soEt start with the higher voltage.
A current limlting circuit 72 is utilized ~or constantly monitoring the current :Elowing through the transformer T2. The current limiting circuit includes a transformer T3 which has its primary winding in series with the primary winding of transformer T2. The secondary winding of transformer T3 is connected in parallel with the circuit including a diode CRl to rectify the current, and a resistor R6 is connected across the secondary winding of transformer T3 to determine the voltage output on the lines 74 and 75.
Resistors R32, R8 and R7 form a voltage divider, and ~ the capacitor C8 filters out the switc'ning noises. The : output, then, on lines 76 and 78 is fed to the IC designated :~ at Ul to pins 4 and 5. Pins 4 and 5 of IC Vl constitute an amplifier that amplifies the signal produced on lines 76 and 78.
~ It will be noted that resistor R7 is a potentiometer - 30 arranged to vary the voltage output on lines 76 and 78. This feature is to allow the arrangement to be adjusted to SC1:~3 operate at a desired curren-t level and to be adjusted for the particulax chip used as Ul.
The error signal provided to Ul on pins 4 and 5 cuts off the output of Ul; and, the higher t:he voltage on lines 76 and 78, the earlier a cycle is cut off. The result is that, as the current in transformer T2 reaches higher levels, the current limiting circuit 72 reduces the length of the cycles. When the cycle becomes short enough, the +5V
produced by T2 will be reduced to the point that zener diode CR13 will turn off transistor Q8, triggering U2, which causes pin 5 to go high and turn off Ul.
Looklng Eurther at the IC Ul, it will be understood that the power supply of the present inventLon can be synchronized with the line as has been previously discussed, or the device can be Eree running, or the device can be synchronized with an external signal. In Fig. 3 of the drawings, it will be seen that an external signal can be provided on the line 79, through resistor Rl5, through jumper Wl, and to the base of transistor Q4. Simply by removing the jumper Wl, the frequency will be free running.
Also, jumpers W4 connec-ted to pin 6 of Ul allow the selection of one of three resis-tors, which allows one of three different switching frequencies.
With the foregoing in mind, the ~eans -for operating transistor Ql should be understandable. Pin 11 of IC Ul is connected to the base of transistor Q2. Thus, an output from Ul will cause Q2 to turn on. When Q2 is on, the primary winding o transformer T4 will be connected be~ween the 3~ voltage VRA~2 or Vl and ground. Since the secondary of T4 is connected to the base of Ql, Ql will turn on to allow ~z~
current flow through transformer T2, through Ql, to the bus 64 and to the line 34.
When the power supply is first started, it will be understood that the transformer T4 is powered by the start-up circuit, VRAW2 being connected through a diode CR16. After the transformer T2 is operating, the voltage Vl becomes the power source for trans:Eormer T4, Vl being connected through resistor R49 and diode CR2. This arrangement allows the power supply to begin operation even at very low line voltage; and, once there is a significant output, that output is used to control the operation.
As Ql turns of.E, the inductor current begins flowing through C7 and CR5 to charge C7. ~fter the inducto:r current subsides, R4 and R16 discharge C7 so the snubbing circuit will be ready for the next turn-off cycle.
When transistor Q2 turns on, current flows into the primary of T4 at 85, and a positive voltage is generated on the secondary at 88. There is therefore a positive current flowing into the base of Ql and back to the secondary oE T4 at 89. The current turns on Ql and charges capacitor C10 to a value determined by R61.
When Q2 turns off, point 88 becomes negative because of the reverse current flow in the primary winding of T4, through diode CR17 and resistor Rll. The point 89 on the secondary wiIl now be positive so that Q12 is turned on, ~: connecting capacitor C10 to the emitter-base circuit of Ql ~; The emitter-base is thus reverse-biased, resulting in rapid removal of eIectrons from the base.
Reali~ing that an important part of the present invention is the fact that the condition of the circuit is ~5~
monitored, attention is directed to the IC designated at U2.
Wbile this is indicated as a 556 IC, U2 is a dual 555 timer chip, and is arranged as two monostable oscillators.
Resistor R33 and capacitor C33 control t:he delay timing, and resistor R31 and capacitor C32 control the delay timing for the relay Kl. Also, from pin 5 of U2, there is a resistor R35 in the line 71 which is connected to pin 10 of IC Ul.
Resistor R35 in conjunction with resistor R52 forms an "OR"
func-tion for controlling pin 10 of Ul and -the base of transistor Qll.
Looking briefly at the relay ~1, it should be realized that, once the power supply is operat~onal, pin 9 of IC U2 will be low 80 the transistor Q9 will be on, pulling the base of transistor Q5 down. Transistor Q5 will then turn on, allowing current to Elow from VREF2, to the relay Kll through transistor Q5 and to ground. Since relay Kl will be energized, the normally closed contacts 49 and 59 will be opened, and transformer Tl will be de-energized.
From the foregoing discussion, it will be realized that the present invention provides a power supply that is usable over a wide range of voltages and frequencies. The start-up circuit produces a voltage that is directly proportional to the line voltage, and the arrangement is such that the main transformer T2 is not operational until there is a minimum vol~age produced by the start-up circuit.
Once the start-up circuit causes the main transformer T2 to begin operation, the output ~rom the transformer is utilized in the control for the switching means so the power supply can continue operation even on very low line voltages. When the line voltage is very high, it will of course be quite ~2~ 3 easy to achieve -the minimum voltage in the start-up circuit, but the higher energy must be controlled to prevent damage to the components. This energy is controlled by the current limiting circuit, and also by the snubber circuits -to prevent damage to the switching transistor.
Once the power supply is operational, achieving the desired voltages, the start-up transformer is completely disconnected from the circuit to prevent electroma~netic interference; however, if `the voltage again drops below a predetermined voltage, the power supply is shut down, and the relay Kl is de-energized causing the start-up circuit to be reconnected. The timer circuit built into the IC
designated at U2 will require that the power supply be de-energized for a predetermined period of time, but the power supply will attempt to restart after this predetermined time. If the voltage remainæ low, the power supply will remain off without causing damage; or, iE the voltage has increased to a usable level, the power supply will restart in accordance with the beginning procedure.
It will of course be understood by those skilled in the art that the particular embodiment oE the invention here presented is by way of illustration only, and is meant to be in no way restrictive; therefore, numerous changes and modifications may be made, and the full use of equivalents resorted to, without departing from the spirit or scope of the invention as outlined in the appended claims.
POWFR SUPP~Y OPERABL~ O~ VARYI~G I~PUTS
Information Disclosure Statement It is well known in the art to provide a power supply wherein a given voltage~ or range of voltages, acts as the input, and a stabilized DC output is provided. Furthermore, it is known in the art to utilize a transormer wherein current flow through the primary winding of the transEormer is controlled by a transistor or other switching means in order to vary the energy output of the transformer. With this arrangement, a pulse can be provided, and the width of the pulse determines the length of time the switching means is on to allow current to ~Elow through the primary winding oE the transformer. ~s a result, the energy output is determined by -the width oE the pulse to the switching means.
These pulse width controls normally utilize a generally conventional transformer wherein the change in magnetic flux in the primary winding is directly reflected in an induced voltage in the secondary winding.
! With the prevalence of computer terminals, and -the need to operate these terminals from the various standard ~0 power sources available around the world, it would be desirable to utilize a single power supply for any power available. The two primary problems in utilizing the available power are the extremely low voltages that sometimes occur, either through design, or through temporary overload, or "brown-out"; and, some areas of the world utilize a relatively high voltage, or example about 250 volts, while other areas of the world utilize a relatively low voltage, for example 108 volts. Furthermore, -the requency of the power i5 not always the same~ While 50 to $~J~3 70 Hz is common, there are situations in which the ~requency is lower than intended, because of errors or the likeO
In utilizing prior art arrangements, it should be understood that the availablity of an extremely low voltage will not provide sufficient power to allow the power supply to begin to produce the desired voltages. Furthermore, if the line voltage is very close to the voltage required, but slightly low, the components receiving the line voltage may burn out because there is insufficient power to operate the controlsO When voltages are extremely high, the prior art clrcuiks are such that they would be unable to absorb or control the energ~, so components oE a circuit may be damaged, and the voltage produced by the power supply may be higher than desired.
Summary of the Invention This invention relates to power supplies for computer terminals, and is more particularly concerned with a power supply operable over a wide range of voltage and frequency inputs.
The present invention provides a power supply utilizing a flyback transformer arrangement wherein switching means determines the current flow in the primary winding of the transformer. Current limiting means is provided to protect the circuitry, and pulse width control means determines the duration of curxent flow through the primary winding. The primary winding of the flyback transformer is designed to withstand very high voltage, so a ; wide range of voltage inputs can be utilized. Because of the control for the switching means, the flyback transformer will not operate iE the voltage is too low.
1~95i~
70~56-10 A separate start-up circuit is provided, the start-up circuit yielding a reference voltage. When the reference voltage reaches a minimum level~ the power ~upply begins to operate; and, after a predetermined length of time, the start-up circuit is de-energized to prevent the production of electromagnetic interference.
At all times during the operation of the power supply, the output vol~age is sensed, and the on and off cycles of the switching means of the flyback transformer are varied to adjust the voltage as needed. When the voltage drops below a predetermined level, the power supply wlll not operate, and the start-up circuit is energized. When the voltage drops below the predetermlned level, there will always be a suff.icient time delay for the computer circuitry to reset before the power supply is reactivated.
According to a broad aspect of the invention there is provided a power supply for producing at least one stable DC
voltage from an AC line voltage, said power supply including rectifying means connected to said line voltage for produciny a DC voltage proportional to sald line voltage, a first transformer, switching means for selectively connectlng said first transformer across said DC voltage, said first transformer having a prlmary winding and at least one secondary winding, said secondary winding lncluding rectifying ~eans for preventing current flow in said secondary winding while sald primary winding is connected to said DC voltage by said switching means, characterised by control means for controlling said æwitching means for varying the length of time said primary winding of said first transformer is connected across said DC voltage, and a start-up means for said power supply, said start-up means including a second transformer havlng a ~5~3 70856-10 primary winding connected across said line volkage and a secondary winding for producing a voltage proportional to said line voltage, circult means for providing said voltage proportional to said line voltage to said control means for controlling said switching means, and means for disconnecting said second transformer from said line voltage after said power supply is producing said stable ~C voltage.
Brie~ De~cription of the Drawinas These and other Eeatures and advantages of the present invention will become apparent from consideration of the Eollowing speciEication, when taken in con~unction wlth the accompanyi.ng drawing~ :Ln which, Fig. 1 is a block diagram illustrating a power supply made in accordance with the present invention; and Flgs.2 and 3 are schematic diagrams illustrating a power supply made in accordance with the present invention.
D~tailed Description of the Fmbodi~ent Referring now more particularly to the drawings, and to that embodiment oi`. the invention here presented by way oi.
illustration, Fig. 1 is a block diagram showing operation o~ a power supply made in accordance with the present invention.
The power source is from the conventional AC line 3a ~Z~ 3l3 indicated at 10, and the line voltage may be as low as 40 VAC or as high as 440 VAC. Also, the frequency of the power source 10 may be as low as 30 ~z, or as high as several kHz.
In any event, the incoming line is fed ~o a rectifier and filter 11 to produce a DC voltage and to remove a significan-t portion oE the noise on the l.ine. It will be noted that the AC supply is also connected directly to the start-up circuitry 12, and this will be discussed in urther detail later.
The output from the rectifier and filter 11 is fed to a 1yback transformer 14. This ~lyback arrangement produces a plurality of DC outputs, and the outputs are rectified and filtered at 15. Loads may then be connected to the output lines 16, 18 and 19.
The incoming line 10 may sometimes have a voltage so low that the circuitry of -the power supply cannot produce the desired outputs. In this event, there must be some means for preventing outputs that are too low for proper operation but high enough to cause some damage to the circuitry of the load. When the power supply of the present invention is initially energized, the arrangement is such that there wil].
be no output from the 1yback transformer 14 until the start-up circuit 12 can produce a minimum voltage. Thus, the start-up circuitry 12 receives the incoming line voltage, and di.rec-ts an output to the pulse width modulator 20. If the signal from the start-up circuitry 12 is below the minimum threshold, the control 21 holds the modulator 20 : off, which holds the switching means for the flyback transformer off. There will thus be no current flowing through the primary of the flyback transformer 14.
Once the start-up circui-try 12 achieves the minimum voltage, the signal will be fed to the pulse width modulator 20, which will in turn signal the flyback transEormer 14 and cause a current to flow in the primary of the flyback transformer 14. This will result in an output to the output rectifier and filter 15, and yield a voltage on the output lines 16, 18 and 19. It will then be noticed that the output is ed to the pulse width modulator 20, and also to the timing and control 21. The timing and control 21, in turn, is connected to the start-up ci.rcuitry 12 and to the pulse width modulator.
In yene.ral, lt should be understood that the output voltage on the lines 18 and l9 i9 constantly monltored to change the width of the pulse fed to the switchinq means and the flyback transformer 14. The variation in the time that current 10ws in the primary winding is the means for control to achieve the desired output voltages at 16, 18 and 19 .
The output voltage is furthe.r monitored by the timing control 21 so that, i the output voltage drops below a predetermined voltage, the pulse width modulator 20 will prevent further operation of the flyback transformer 14, and the start-up circuitry 12 will be reconnected into the circuit. The start-up sequence will be attempted, and will not be successful until the start-up circuitry 1~ is able to produce the minimum voltage.
The timing and control 21 urther includes timing means so that, once the output voltage from the output rectifier and filter 15 drops below a predetermined minimum voltage, the circuitry is held off for a minimum length o ~5--~2~ 3 time. This is important for computer circuitry so that the computer circuitry will reset rather than become locked in a given state.
As will be discussed further hereinafter, the specific design of the flyback transformer 14 is important to the present invention since this allows a very low voltage to produce the desired voltage. When the voltage at line 10 is extremely low, the output voltage Erom the output rectifier and filter 15 is fed through the pulse-width modulator 20 to provide a longer pulse, to give the desired energy input to the primary oE -the flyback transEormer 14.
On the other hand, if the incoming line 10 is an e~tremely high voltage, the switching means on the primary remains on for a very short time to provide the same desired energy input.
For a further understanding of the power supply of the present invention, attention is directed to Figs. 2 and 3 of the drawings.
In Fig. 2, it will be seen that the available line power will be applied to the lines 30 and 31. There~ are capacitors Cl, C2 and C3 placed across the lines 3a and 31 to filter the line and remove the majority of the noise on the line. The lines 30 and 31 then con~inue to a full-wave ;~ rectiEier designated at 32~ The negative side of the rectiEied voltage i8 indicated at 34, and the positive side i5 indicated as the line 35.
Beyond the recti-Eier 32, there are capacitors C4 and ; C5 connected to the line 35, and also connected to line 34 through the bus 36. Further/ resistors R2 and R3 are connected between the bus 36 and the line 35. The bus 36 is ~L2~95~3 grounded through capacitor C6. The arrangement including capacitors C4, C5 and C6 and resis-tors R2 and R3 will therefore fil-ter the rectified voltage so that most of the noise on the line is removed. After the filtering network just described, there is a fuse designated at Fl.
Referring back to the incoming lines 30 and 31, there ~re branch lines 38 and 39 connected to -the lines 30 and 31 respectively. There is a line synchronization circuit connected to the branch lines 38 and 39 by the lines 40 and 41. A light emitting diode (LED) 42 allows current to flow in one direction, and diode CRll allows current to Elow in the opposite direction. In both directions, current is limited by the resistor ~47. It will thereEore be seen khat light will be emitted from the diode 42 at each halE cycle of the alternating curren-t from -the line, and light from the diode 42 will trigger the phototransistor 44. With ~5 VDC
applied at 45, current can flow from 45, through the resistor R46, through phototransistor 44, and to ground.
Each time current flows in this path, a signal will be transmitted along the line 46 which will yield a synchronization pulse~ Thus, if the power supply, or other related equipment, is to be synchronized with the line fre~uency, the pulse on line 46 will provide the appropriate timing signal.
Looking again at the lines 38 and 39, the line 39 includes a positive coefficient resistor designated at RT2 in series with the pri~ary winding of the transformer Tl.
When the lines 30 and 31 are connected to a power source, power will be available on the lines 38 and 39 so that current can Elow through the line 38, through the connecting ~Z~5~
line 48, through the normally closed relay contact 49, then through -the line 50 and to the primary winding o the transformer Tl~ From the transEormer Tl, current can flow through the resistor RT2 and to the line 39 9 then to the line 31. As a result, the transformer Tl will be energized -to produce a voltage on its secondary winding. The transformer Tl and its associated circuitry comprise the start-up circuit for the power supply.
The transformer Tl has connected thereto a full wave rectifier designa-ted at 51, with the negative side grounded at 52, and the positive side connected to the line 54.
One of the salient features oE the present invention is the ability to provide the entire power supply in a very small and relatively light-weight circuit to be incorporated directly within computer terminals. Considering the wide voltage range over which the transformer Tl must operate, conventional engineering would require an extremely large transformer, to the extent that -the transformer Tl could not be mounted on a printed circuit board. The use of a very small transformer is not indicated because of the hea~
generated at high voltages, so the transformer Tl would burn out after a very short operating time.
In the present invention, it is contemplated that the transformer Tl will be operated only long enough for the principal power supply to become operative, and the transformer ~1 needs to be de-energized in ordar to prevent magnetic interference from the transformer. With this in mind, a small and light-weight transformer was designed, and the resistor RT2 was installed as an additional safety feature. The operating parameters of RT~ are such -that, if :~L%~ 3 Tl is operative for a length of time that may cause damage to the transformer Tl, the resistance of RT2 will increase to the point that current flow through the transformer Tl will be effectively terminated. Since the resistor RT2 is a positive coefficient resistor, it will be understood that the temperature of RT2 is directly reLated to the cu~rent through the transformer Tl, and high current through transformer Tl will cause the resistance of RT2 to increase sufficiently that current will be negligible.
In normal operation, once the power supply is fully operational, the relay Kl will be energized to open -the contact ~9 to de-energize the transEormer Tl. T~e operation of rela~ Kl wlll be descrlbed urther hereinater, but it should be understood that, in nor~al operation, the relay contacts 49 will open before the temperature oE RT2 becomes high enough to shut down the transformer Tl.
Returning now to the start-up circuitry, and looking at the line 54 connected to the rectifier 51, the line 54 is connected to the collector of transistor Q3, and the emitter of Q3 is connected to the line 5S. The base of the transistor Q3 is connected through zener diode CR14 to ground; and, between the base oE Q3 and the diode CR14, a resistor R26 is connected to -the line 54. With this arrangement; the output at 56 will be a DC voltage that directly follows the incoming line voltage. Because the diode CR14 is a zener, in the beginning the voltage at 56 will follow the voltage at 54. Once the voltage exceeds the zener voltage, the voltage on the line S5 will be pulled down, resulting in a voltage on the line 5S at no more than one diode drop above the zener voltage. In the present _9_ ~2~
embodiment oE the invention, the zener voltage of CR14 is 30 volts, so tne voltage at 55 wi.ll be no more than approximately 30 volts.
The voltage at 56 is labeled VRAW2, and uses for this voltage will be discussed later. Since VRAW2 will never exceed about 30 volts regardless of the line voltage, another voltage labeled VRAW1 is pulled off the line 54 before Q3. It will be seen -that VR~Wl will always be proportional to the line voltage.
After the transistor Q3, there is a diode CR15 in the line 55. The diode CR15 is arranged to prevent a higher voltage on the line 55 rom damaging the transistor Q3.
Capacitors C30 and C26 are connected between the l.ine 55 and ground to smooth out the pulsed voltage :Erom -the AC
line, and to increase the signal to noise rejection of voltage regulator circuit VR1. VR1, in conjunction with the capacitor C27, provides a regulated voltage designated as VREFl. In khe present embodiment of the invention VREF1 is +12 VDC.
It will be seen that there are additional voltage regulator circuits designa-ted at VR2, VR3 and VR4. VR2 is connected to a branch 58 through a diode CR8 to prevent the start-up voltage on line 55 from attempting to power voltage regulator VR2. Again, capacitors following the regulator VR2 smooth the voltage to produce a -~12VDC, while the parallel circuit VR3 regulates the incoming -~16VDC to produce VREF2.
Returning again to the lines 38 and 39, the line 38 is connected to one side of the relay contact 59. Since contact 59 is normally closed, current will flow through the line 60, and through the positive coeEficient resistor RTl~
through coil J4~ and to the line 39. The coil J4 is a degaussing coil, so it will be understood that the cat'node ray tube will be degaussed at each start-up cycle. As was previously mentioned, the relay Rl will be energized after the power supply is in operation, and the operation of relay Kl will open contacts 49 and 59, so the coil J4 will also be de-energized. The positive coefficient resistor RTl will be heated by the degaussing current, and the heat will increase the resistance to the point that the coil is effectively de-energized. This provides the necessary decaying current re~uired to cause proper degaussing.
Returning now to the line 35 discussed above, this same line extend~ into Fig. 3, and i8 connected through the primary winding of trans:~ormer T3 to the primary winding of transformer T2. As will be recognized from the following discussion, transformer T2 is not operated as a true transformer, but the transformer T2 is utilized in a ~lyback ; arrangement that is well known to those skilled in the art.
Typical of the flyback arrangement, there is a switching means for controlling current through -the primary winding of the -transformer T2, and this switching means in the present embodiment of the invention is transistor Ql which has its collector connected to the line 61, and its emitter conne~ted through the line 62 to a bus 64 which is connecked to the line 34 from the recti~ier 32.
~In general, it will be understood that current will ;~flow through ~he line 35, and through the primary winding of the transformer T2, ~hen through the transistor Ql, line 62, to the line 34 and to the rectiEier 32, but only so long as the transistor Ql is conducting. When -the transistor Ql is ~Z~ 3 biased off, curren-t will no longer flow. It will also be noticed that the three secondary windings designated at 65, 66 and 68 include diodes arranged so that, while curren-t is flowing in the primary winding of the transformer T2, no current can flow in the secondary windings. Only when current ceases to -Elow in the primary winding oE the transformer T2, and the magnetic field begins to collapse, will current be allowed to flow in the secondary windings.
Because of this arrangement it will be understood that energy is provided to the transEormer T2 through the flow of current through the primary winding; then, the discrete amount o energy stored in the transformer is transfe~red to the secondary windings.
In operation of the power supply of the present invention, it will be unders-tood that the transistor Ql will be controlled to turn off very quickly in order to limit the energy passed by the transformer T2. Such sudden turn-offs induce great stress on the transistor. To prevent damage to the transistor, a snubber circuit is provided through the line 61, through the capacitor C7 and diode CR5. Resistors R4 and R16 are connected in parallel to the diode CR5. When the transistor Ql is turned off, current can flow through the capacitor C7 and through the diode CR5, taking the stress off the transistor ~1. The current will of course charge the capacitor C7, and the resistors R4 and R15 will discharge the capacitor C7 at the end of the inductive current. When the capacitor C7 is discharged, the circuitry is ready to act as a snubber for the next -turn-of cycle.
It is conventional in power supplies to utilize a soft start, but the conventional power supply does not have S~3 to contend with -the wide voltage ranges contemplated in the present inventlon. Thus, the present invention includes a somewhat usual soft start arrangement wherein the voltage VRAW2 is applied to the base of the transistor Q10 through the zener diode CRl9, so Q10 is not t:urned on until the voltage VRAW2 reaches a minimum voltage of 12 vol~s. As long as Ql0 is off, VREFl is supplied through resistors R53 and R52 to the line 71, thence to pin 10 of Ul, so Ul is held off. Thus, if the start-up circuit cannot produce over 12 volts at VR~W2, the power supply is unable to operate. On the other hand, once V~AW2 exceeds 12 volts, transistor Q10 will be turned on.
VREFl is applied to the stark-up circult and the modulator chip. When VREFl reaches about +5V, U2 starts to operate. As a result, even though Q10 turns on and no longer holds Ul off, U2 is high on pin 5, which holds Ul o-ff V~EFl is also applied to Ul; and, when VREFl exceeds the undervoltage lockout value, the outputs are enabled, though still held off by U2.
20Operation o U2 also makes pin 9 go high, and this turns on transistor Q9, which holds Q5 off. With Q5 off, relay Kl cannot operate even though VREF2 i5 produced. This assures that the start-up circuit will remain connected into the circuit until U2 times out.
After the predetermined length of time, pin 5 of U2 will go low, releasing pins 9 and 10 of Ul~ Pin ll will ; begin driving transistor Q2 which is part of the base drive circuit or Ql. Also, transistor Qll is turned of, so the soft start capacitor C16 will begin charging. ~s the capacitor C16 charges, the duty cycle increases to produce the soft start.
If the line voltage i5 quite high, the use of t'ne one soft start capacitor does not provide an effective soft staxt action. To resolve this difficulty, the voltage VR~Wl, which is always proportional to the line voltage, is fed through a zener diode CR21 to ~he base of transistor Ql3.
The zener voltage is selected so that Ql3 is turned on when the line voltage exceeds 180V. When Q13 is on, the capacitor C49 is connected into the timing circuit provided by resistor R23 and capacitor C16, adding capacitance to the circuit to assure a soEt start with the higher voltage.
A current limlting circuit 72 is utilized ~or constantly monitoring the current :Elowing through the transformer T2. The current limiting circuit includes a transformer T3 which has its primary winding in series with the primary winding of transformer T2. The secondary winding of transformer T3 is connected in parallel with the circuit including a diode CRl to rectify the current, and a resistor R6 is connected across the secondary winding of transformer T3 to determine the voltage output on the lines 74 and 75.
Resistors R32, R8 and R7 form a voltage divider, and ~ the capacitor C8 filters out the switc'ning noises. The : output, then, on lines 76 and 78 is fed to the IC designated :~ at Ul to pins 4 and 5. Pins 4 and 5 of IC Vl constitute an amplifier that amplifies the signal produced on lines 76 and 78.
~ It will be noted that resistor R7 is a potentiometer - 30 arranged to vary the voltage output on lines 76 and 78. This feature is to allow the arrangement to be adjusted to SC1:~3 operate at a desired curren-t level and to be adjusted for the particulax chip used as Ul.
The error signal provided to Ul on pins 4 and 5 cuts off the output of Ul; and, the higher t:he voltage on lines 76 and 78, the earlier a cycle is cut off. The result is that, as the current in transformer T2 reaches higher levels, the current limiting circuit 72 reduces the length of the cycles. When the cycle becomes short enough, the +5V
produced by T2 will be reduced to the point that zener diode CR13 will turn off transistor Q8, triggering U2, which causes pin 5 to go high and turn off Ul.
Looklng Eurther at the IC Ul, it will be understood that the power supply of the present inventLon can be synchronized with the line as has been previously discussed, or the device can be Eree running, or the device can be synchronized with an external signal. In Fig. 3 of the drawings, it will be seen that an external signal can be provided on the line 79, through resistor Rl5, through jumper Wl, and to the base of transistor Q4. Simply by removing the jumper Wl, the frequency will be free running.
Also, jumpers W4 connec-ted to pin 6 of Ul allow the selection of one of three resis-tors, which allows one of three different switching frequencies.
With the foregoing in mind, the ~eans -for operating transistor Ql should be understandable. Pin 11 of IC Ul is connected to the base of transistor Q2. Thus, an output from Ul will cause Q2 to turn on. When Q2 is on, the primary winding o transformer T4 will be connected be~ween the 3~ voltage VRA~2 or Vl and ground. Since the secondary of T4 is connected to the base of Ql, Ql will turn on to allow ~z~
current flow through transformer T2, through Ql, to the bus 64 and to the line 34.
When the power supply is first started, it will be understood that the transformer T4 is powered by the start-up circuit, VRAW2 being connected through a diode CR16. After the transformer T2 is operating, the voltage Vl becomes the power source for trans:Eormer T4, Vl being connected through resistor R49 and diode CR2. This arrangement allows the power supply to begin operation even at very low line voltage; and, once there is a significant output, that output is used to control the operation.
As Ql turns of.E, the inductor current begins flowing through C7 and CR5 to charge C7. ~fter the inducto:r current subsides, R4 and R16 discharge C7 so the snubbing circuit will be ready for the next turn-off cycle.
When transistor Q2 turns on, current flows into the primary of T4 at 85, and a positive voltage is generated on the secondary at 88. There is therefore a positive current flowing into the base of Ql and back to the secondary oE T4 at 89. The current turns on Ql and charges capacitor C10 to a value determined by R61.
When Q2 turns off, point 88 becomes negative because of the reverse current flow in the primary winding of T4, through diode CR17 and resistor Rll. The point 89 on the secondary wiIl now be positive so that Q12 is turned on, ~: connecting capacitor C10 to the emitter-base circuit of Ql ~; The emitter-base is thus reverse-biased, resulting in rapid removal of eIectrons from the base.
Reali~ing that an important part of the present invention is the fact that the condition of the circuit is ~5~
monitored, attention is directed to the IC designated at U2.
Wbile this is indicated as a 556 IC, U2 is a dual 555 timer chip, and is arranged as two monostable oscillators.
Resistor R33 and capacitor C33 control t:he delay timing, and resistor R31 and capacitor C32 control the delay timing for the relay Kl. Also, from pin 5 of U2, there is a resistor R35 in the line 71 which is connected to pin 10 of IC Ul.
Resistor R35 in conjunction with resistor R52 forms an "OR"
func-tion for controlling pin 10 of Ul and -the base of transistor Qll.
Looking briefly at the relay ~1, it should be realized that, once the power supply is operat~onal, pin 9 of IC U2 will be low 80 the transistor Q9 will be on, pulling the base of transistor Q5 down. Transistor Q5 will then turn on, allowing current to Elow from VREF2, to the relay Kll through transistor Q5 and to ground. Since relay Kl will be energized, the normally closed contacts 49 and 59 will be opened, and transformer Tl will be de-energized.
From the foregoing discussion, it will be realized that the present invention provides a power supply that is usable over a wide range of voltages and frequencies. The start-up circuit produces a voltage that is directly proportional to the line voltage, and the arrangement is such that the main transformer T2 is not operational until there is a minimum vol~age produced by the start-up circuit.
Once the start-up circuit causes the main transformer T2 to begin operation, the output ~rom the transformer is utilized in the control for the switching means so the power supply can continue operation even on very low line voltages. When the line voltage is very high, it will of course be quite ~2~ 3 easy to achieve -the minimum voltage in the start-up circuit, but the higher energy must be controlled to prevent damage to the components. This energy is controlled by the current limiting circuit, and also by the snubber circuits -to prevent damage to the switching transistor.
Once the power supply is operational, achieving the desired voltages, the start-up transformer is completely disconnected from the circuit to prevent electroma~netic interference; however, if `the voltage again drops below a predetermined voltage, the power supply is shut down, and the relay Kl is de-energized causing the start-up circuit to be reconnected. The timer circuit built into the IC
designated at U2 will require that the power supply be de-energized for a predetermined period of time, but the power supply will attempt to restart after this predetermined time. If the voltage remainæ low, the power supply will remain off without causing damage; or, iE the voltage has increased to a usable level, the power supply will restart in accordance with the beginning procedure.
It will of course be understood by those skilled in the art that the particular embodiment oE the invention here presented is by way of illustration only, and is meant to be in no way restrictive; therefore, numerous changes and modifications may be made, and the full use of equivalents resorted to, without departing from the spirit or scope of the invention as outlined in the appended claims.
Claims (8)
1. A power supply for producing at least one stable DC
voltage from an AC line voltage, said power supply including rectifying means connected to said line voltage for producing a DC voltage proportional to said line voltage, a first transformer, switching means for selectively connecting said first transformer across said DC voltage, said first transformer having a primary winding and at least one secondary winding, said secondary winding including rectifying means for preventing current flow in said secondary winding while said primary winding is connected to said DC voltage by said switching means, characterised by control means for controlling said switching means for varying the length of time said primary winding of said first transformer is connected across said DC voltage, and a start-up means for said power supply, said start-up means including a second transformer having a primary winding connected across said line voltage and a secondary winding for producing a voltage proportional to said line voltage, circuit means for providing said voltage proportional to said line voltage to said control means for controlling said switching means, and means for disconnecting said second transformer from said line voltage after said power supply is producing said stable DC voltage.
voltage from an AC line voltage, said power supply including rectifying means connected to said line voltage for producing a DC voltage proportional to said line voltage, a first transformer, switching means for selectively connecting said first transformer across said DC voltage, said first transformer having a primary winding and at least one secondary winding, said secondary winding including rectifying means for preventing current flow in said secondary winding while said primary winding is connected to said DC voltage by said switching means, characterised by control means for controlling said switching means for varying the length of time said primary winding of said first transformer is connected across said DC voltage, and a start-up means for said power supply, said start-up means including a second transformer having a primary winding connected across said line voltage and a secondary winding for producing a voltage proportional to said line voltage, circuit means for providing said voltage proportional to said line voltage to said control means for controlling said switching means, and means for disconnecting said second transformer from said line voltage after said power supply is producing said stable DC voltage.
2. A power supply as claimed in claim 1, characterised by a positive coefficiient resistor in series with said primary winding of said second transformer for limiting the power supplied to said transformer.
3. A power supply as claimed in claim 2, characterised in that said means for disconnecting said second transformer from said line voltage includes normally closed relay contacts, said relay means being operable from said power supply so that said relay means will open said normally closed relay contacts only when said power supply is producing a voltage.
4. A power supply as claimed in claim 1, characterised in that said control means for controlling said switching means includes a third transformer having a primary winding and a secondary winding, said secondary winding of said third transformer being connected to said switching means so that said switching means is on for the length of time said third transformer is energized, said primary winding of said third transformer being connected to an output of said power supply, and pulse responsive means for allowing current to flow through said primary winding of said third transformer, and snubbing means for said switching means.
5. A power supply as claimed in claim 4, characterised by a fourth transformer having a primary winding and a secondary winding, said primary winding of said fourth transformer being connected in series with said primary winding of said first transformer, a current limiting circuit connected across said secondary winding of said fourth transformer, said current limiting circuit providing an adjustable signal proportional to the current in said primary winding of said first transformer for varying said pulse responsive means for allowing current to flow through said primary winding of said third transformer.
6. A power supply as claimed in claim 4, characterised by a first voltage supply to said primary winding of said third transformer, said first voltage supply being from said start-up means and a second voltage supply to said primary winding of said third transformer, said second voltage supply being from said secondary winding of said first transformer.
7. A power supply as claimed in claim 6, and further characterised by a positive coefficient resistor in series with said primary winding of said second transformer for limiting the power supplied to said transformer.
8. A power supply as claimed in claim 7, characterised in that said means for disconnecting said second transformer from said line voltage includes normally closed relay contacts in series with said second transformer, and relay means for selectively opening said relay contacts, and said relay means is operable from said power supply so that said relay means will open said normally closed contacts only when said power supply is producing a voltage.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US914,815 | 1986-10-03 | ||
| US06/914,815 US4686616A (en) | 1986-10-03 | 1986-10-03 | Power supply operable on varying inputs |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1295013C true CA1295013C (en) | 1992-01-28 |
Family
ID=25434803
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000548435A Expired - Lifetime CA1295013C (en) | 1986-10-03 | 1987-10-02 | Power supply operable on varying inputs |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4686616A (en) |
| EP (1) | EP0262581A3 (en) |
| CA (1) | CA1295013C (en) |
Families Citing this family (21)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR890001259B1 (en) * | 1986-06-20 | 1989-04-28 | 주식회사 금성사 | Safety circuit of power supply circuit for switching mode |
| US4860185A (en) * | 1987-08-21 | 1989-08-22 | Electronic Research Group, Inc. | Integrated uninterruptible power supply for personal computers |
| US4890211A (en) * | 1988-02-05 | 1989-12-26 | Mark Telefus | Switching mode power supply start-up circuit |
| US4890217A (en) * | 1988-07-26 | 1989-12-26 | Norand Corporation | Universal power supply, independent converter stages for respective hardware components of a computerized system |
| US4870553A (en) * | 1988-11-04 | 1989-09-26 | Compaq Computer Corporation | Double-switched flyback power-converter |
| US5032970A (en) * | 1989-03-02 | 1991-07-16 | Mark Telefus | Switching mode power supply start-up circuit |
| US4928218A (en) * | 1989-03-06 | 1990-05-22 | Ncr Corporation | Switch mode power supply start-up circuit |
| US5001623A (en) * | 1989-12-22 | 1991-03-19 | Burle Technologies, Inc. | Automatically switching multiple input voltage power supply |
| US5038264A (en) * | 1990-06-11 | 1991-08-06 | General Electric Company | Multiple-output, single-ended, resonant power converter |
| US5513088A (en) * | 1991-06-14 | 1996-04-30 | Williamson; Floyd | Uninterruptable off-line, isolated flyback topology switch-mode power supply |
| US5294839A (en) * | 1992-06-29 | 1994-03-15 | Eaton Corporation | Soft start AC tool handle trigger switch circuit |
| US5359276A (en) * | 1993-05-12 | 1994-10-25 | Unitrode Corporation | Automatic gain selection for high power factor |
| US5499187A (en) * | 1995-04-03 | 1996-03-12 | Arinc Research Corporation | Voltage sensing, autoselecting aircraft power supply interface |
| AU5574396A (en) * | 1995-05-04 | 1996-11-21 | Intel Corporation | Printed circuit board with selectable routing configuration |
| US5729448A (en) * | 1996-10-31 | 1998-03-17 | Hewlett-Packard Company | Low cost highly manufacturable DC-to-DC power converter |
| JP2001175368A (en) * | 1999-12-15 | 2001-06-29 | Nec Shizuoka Ltd | Cpu core voltage switching circuit |
| US6163140A (en) * | 2000-02-01 | 2000-12-19 | Micrel Incorporated | Start-up circuit for voltage regulators |
| US6625044B2 (en) * | 2001-12-03 | 2003-09-23 | Chung Shan Institute Of Science And Technology | Programmed isolating starting system and method of a switching power supply |
| GB2384328A (en) | 2002-01-16 | 2003-07-23 | Mitel Knowledge Corp | Regulated power supply starting circuit |
| US6919747B2 (en) * | 2002-11-14 | 2005-07-19 | International Rectifier Corporation | Circuit for providing resistance to single event upset to pulse width modulator integrated circuit |
| CN106100365B (en) * | 2016-06-30 | 2018-06-22 | 潍坊市跃龙橡胶有限公司 | A kind of large tyre-forming machine is used, under-voltage protecting circuit |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3697854A (en) * | 1972-01-27 | 1972-10-10 | Pioneer Magnetics Inc | Regulated dc-dc power supply |
| DE2349881A1 (en) * | 1973-10-04 | 1975-04-10 | Linde Ag | HV drive cct. for LV motor sets - has static inverter controlled by ignition and quenching ccts. controlled by voltage comparator |
-
1986
- 1986-10-03 US US06/914,815 patent/US4686616A/en not_active Expired - Fee Related
-
1987
- 1987-09-24 EP EP87113936A patent/EP0262581A3/en not_active Withdrawn
- 1987-10-02 CA CA000548435A patent/CA1295013C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0262581A2 (en) | 1988-04-06 |
| US4686616A (en) | 1987-08-11 |
| EP0262581A3 (en) | 1989-08-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed | ||
| MKLA | Lapsed |
Effective date: 19940730 |