US3200327A

US3200327A - Theater lighting control apparatus

Info

Publication number: US3200327A
Application number: US89956A
Authority: US
Inventors: Joseph W Fleming
Original assignee: ELECTRONIC DIMMER CORP
Current assignee: ELECTRONIC DIMMER CORP
Priority date: 1961-02-17
Filing date: 1961-02-17
Publication date: 1965-08-10
Anticipated expiration: 1982-08-10
Also published as: GB931534A; DE1438429A1

Description

Aug. 10, 1965 J. w. FLEMING 3 00,

THEATER LIGHTING CONTROL APPARATUS Filed Feb. 17, 1961 2 Sheets$heet 1 INVENTOR Joseph W. Fleming 1965 J. w. FLEMING 3,200,327

THEATER LIGHTING CONTROL APPARATUS Filed Feb. 17, 1961 2 Sheets-Sheet 2 l5OA " FIG. 2 [A 7 LE) 2 50A E o :g 3

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0 I50 lggi Conducflon Angles JosePhW-Fleming g ;%TTORNEYS United States Patent 3 200,327 THEATER LIGHTING CONTROL APPARATUS Joseph W. Fleming, Allendale, N.J., assignor to Electronic Dimmer Corporation, New York, N.Y., a corporation of New York Filed Feb. 17, 1951, Ser. No. 89,956 6 Claims. '(Cl. 323- 39) This invention relates to theater lighting control systems and more particularly to improved dimmer apparatus for such systems. 7

Recently devised dimmers utilize so-called controlled silicon rectifiers in combination with saturable reactors (i.e., magnetic amplifiers) for controlling the amount of current supplied to variable intensity incandescent lights. Such dimmers are highly advantageous because they are compact and light-weight and because they have very low heat dissipation requirements. Operating experience with these dimmers has shown, however, that they have overload restrictions which limit their usefulness for stage lighting work.

In normal theater lighting practice, cold lamp loads and heated rated loads are often hot-patched. In either situation, if the connection is made at maximum line voltage, an overload current is expectable for a short amount of time in the lamp or power circuit in which the controlled silicon rectifiers operate. Overcurrent is also expectable when, as sometimes happens, a dimmer is plugged into a rack with everything turned on full, with a rated load or with an overload.

Controlled silicon rectifiers, however, may not be overloaded for any appreciable amount of time or they will burn out. On ordinary 60 cycle power, overload for two successive conducting half cycles is normally sufficient to damage a rectifier. Rectifier ratings are determined on the basis of average or of root mean square current so that a halfcycle of load current is necessary in order to sense the presence of an overload. The time remaining for correction is therefore, only that of the subsequent non-conducting half-cycle (approximately 8 milliseconds for 60 cycle voltage) if a rectifier is to be adequately protected.

A common practice for protecting the rectifiers from overcurrent is to incorporate rapidly responding circuit breakers or fuses in the load circuits. Such protective devices are set very tight, that is, they are set to operate substantially at the rated current of the controlled silicon rectifiers, to assure adequate protection. They do act to remove the dimmer from operation when overload circumstances arise, but this can happen at any time. Should it occur at a crucial moment in a theater performance, the time for developing a desired audience reaction may pass during the interval required to rest-ore operation, and no amount of subsequent technical explanation is sufiicient to restore confidence in the equipment or in the manufacturer who supplied it.

In the controlled silicon rectifier-magnetic amplifier dimmers available to date, the protective devices described have been necessary because the response time for completing a change in the saturation level of a magnetic amplifier core is greater than the permissible rectifier overload time. I have found, however, that slow response is not an intrinsic limitation of magnetic amplifiers but is, instead, a limitation of the way in which magnetic amplifiers have been used.

The purpose of my invention is to provide a dimmer of the controlled silicon rectifier-magnetic amplifier type which is completely reliable for theater use.

I provide a dimmer having means for sensing load current arrangement for rapidly and automatically adjusting rectifier gate signals in order to assure adequate protection from overload. I also provide means for automatically ice limiting initial load voltage to a value which permits no more than rated rectifier current to flow, regardless of the size of the load connected, but which assures that the rectifiers will remain in operation at their rated currents even though the initial load is, in fact, an overload. The voltage limiting means and overload protection means are arranged to cooperate so that control of the rectifiers passes automatically from one to the other as loads are changed or, for example, as cold lamp filaments are heated.

The voltage limiting means of my invention provide a low current to the magnetic amplifier control windings when no load is connected, even though the dimmer is set fully on. This condition is maintained for a brief time after a load, which may be a heavy one, is connected and inrush current is limited to that for which the rectifiers are rated, regardless of the angle in the voltage cycle at which the load is connected. When load current is present, the voltage limiting means permits the amplifier control winding current to increase slowly which in turn advances the firing angle of the controlled silicon rectifiers. If the load is not excessive, load current rises over a few cycles to the desired value and control of the firing angle passes to the over-current protection means.

If the load is excessive, current rise over the next few cycles is limited until the voltage limiting means releases control. In this situation, however, as well as When an excessive additional load may be connected, the overcurrent protection means senses the overload in the next conducting half cycle and responds immediately to retard the rectifier firing angle. Rectifier current is reduced to a safe value during the subsequent conducting half cycle; when that half cycle is over, control winding current is again at the starting or voltage limited value and the control cycle harmlessly repeats.

Operation such as that last described may be readily detected in a few seconds (lamps are dimmer than expected) and the load can be promptly rearranged. An experienced operator ordinarily knows his equipment and dimmer settings well enough so that excessive loads are not connected intentionally. But if an excessive load is connected to a dimmer incorporating my invention, no damage is done.

On the other hand, if the lamp load is cold, sufficient current is supplied to it with my dimmers to heat the filaments. All the While the rectifiers operate at rated current (or below, if the dimmer setting is very low) and load resistance increases to steady state value within a few cycles. The load circuit is not interrupted by operation of breakers or fuses and dimmer operation is continuous.

These and other features of my invention are explained in detail in the following portion of the specification. For ease of understanding, reference will be made to the accompanying drawings in which:

FIG. 1 is a schematic drawing of lighting control apparatus according to my invention; and

FIG. 2 shows two graphical illustrations of the relations between currents and conduction angles in controlled silicon rectifiers.

In FIG. 1, two controlled silicon rectifiers 2-5 and 26 are connected in a load or power circuit for energizing variable intensity incandescent lamps. As is well known, the controlled silicon rectifiers are solid state devices which offer a controllable conductivity characteristic in their forward or anode to cathode direction. They have a control electrode called a gate, and they may be made conductive when anode voltage is higher than cathode voltage, by supplying a small current flowing through the gate to the cathode.

The controlled silicon rectifiers shown are connected together at their opposite anode and cathode electrodes apnoea? series with a load and a source of alternating voltage in the power circuit. Thus, they are arranged to provide current to a load on each successive h-alf cycle of the source voltage.

A full wave rectifier It) provides a dire-ct volt-age across the variable potentiometer 11 for supplying direct current to a control circuit. One lead of the control circuit is connected to the variable tap 12 of the potentiometer so that the direct voltage applied to the control circuit may be adjusted over a range of, for example to 28 volts. The input to the direct current control circuit may be smoothed with a filter, and a choke indicated at 13 may also be used. A filter is desirable to reduce variations in the DC voltage resulting from the full wave rectification. A choke is desirable for further reducing ripple without altering average voltager It improved linearity of response in the control circuit signal to changes in the potentiometer setting.

A first transistor, shown at 15, is connected in seriesin the control circuit. the transistor to be normally conducting when the potentiometer setting is above zero. A resistor 14 is provided to limit the control circuit current to desired values. The resistor 13 is connected in the collector-base circuit of transistor 15 to maintain a constant reflected impedance to the control windings 19, 21 of the magnetic amplifier enclosed in broken lines in FIG. 1. The output signal transistor 15 appears across control windings 19 and 21 of magnetic amplifiers 2t and 22.

The control circuit shown in the drawing further comprises a low wattage warm-up circuit, generally indicated at 23, and a current limiting circuit generally indicated at 24. The purpose and operation of these two circuits will be explained subsequently. a

The magnetic'amplificr means further comprises saturable cores 2t) and 22, gate windings 3t) and 31 and bias windings 32. and 3'3. Each magnetic amplifier means thus has three windings on its saturable core. These 7 windings are utilized to initiate and control rectifier gate currents.

A resistance 17 is provided to bias I ings 30 and 31.

Resistors

44 and 45 are also provided in the gate circuits to limit current to desired values.

There are several feasible arrangements for supplying current of desired magnitudes and direction to the magetic amplifier bias windings to establish the desired saturation level in the amplifier cores. Separate, regulated sources of voltage may be used for each bias winding, for example. a V i In thisembodiment, I use what isknown as reset or reset control means for biasing each magnetic amplifier during the non-conducting half-cycle of its associated controlled silicon rectifier. In this arrangement, the magnetic amplifier cores are fabricated from high remanencernagnetic material so that a desired saturation level may be, established therein by supplying current to the -bias windings prior to the normally conducting half- A biasing current of desired phase and magnitude is provided in the bias windings to alter saturation'of the the extent desired, and permit the gate windings to V conduct.

The gate windings 3t) and 31 are connected in the gate circuits of the controlled silicon rectifiers. The gate windings are arranged so that they conductduring op.

posite half cycles of the load voltage. When they conduct, current is provided to the gates to initiate current flow or conduction in the rectifiers and thereby energize the load circuit.

A supply transformer 36 has two

secondary windings

37 and 38 arranged to provide power to opposite gate circuits on alternate half-cyclesof load voltage. The primary winding 39 of the supply transformer is also connected to the source of alternating load voltage so that voltageappearing at each secondary winding 37 and 38 is in phase with the voltage applied to the controlled silicon rectifiers in the load circuit. Rectifying means such as diodes are connected in the gate circuits, indicated at 40 and 41, so that gate signals may appear at each controlled silicon rectifier only when its anode potential is higher than its cathode potential.

To obtain optimum performance of the controlled silicon rectifiers it is advantageous to suppress the effects of line transients and other noise which may create spurious signals in the gate circuits and cause the rectifiers to begin conducting at other than the intended times. For this purpose I provide resistors 42 and i and capacitors 46 and 47 connected to shunt to the gate windcycles of the rectifiers.

Of course, as indicated by the drawing, a conducting half-cycle for one controlled silicon rectifier is a nonconducting half-cycle for the other. The supply transformer windings are arranged so that the gate winding of one magnetic amplifier may conduct while the other magnetic amplifier is being reset. Thus, for example above, as anode potential of rectifier 25 becomes greater than'its cathode potential secondary Winding 37 is energized so that the potential of gate 34 becomes higher than the firing threshold voltage with respect to the rectifier cathode potential, as soon as the core becomes saturated and gate winding 36) becomes conducting. At the same time, the voltage appearing across potentiometer 52 has a polarity such that the bias winding 33 is energized to establish the desired saturation level in the core of the magnetic amplifier 22, associated with the nonconducting rectifier 26.

Theofi time of each rectifier is therefore controlled by the saturation level previously established in the core of its associated magnetic amplifier during the rectifiers previous non-conducting half-cycle. The firing angle of each rectifier, during this Subsequent. half-cycle then depends only on the magnitude of the control signal provided by first transistor 15 which varies the degree of reset and consequently the point at which the core saturates.

For proper control of the controlled silicon rectifiers with the magnetic amplifier means, it is of course necessary that the bias windings be properly energized before voltageis applied to the gate circuits to prevent the rectifiers from becoming conductive at undesired times. As shown in the drawing, bias Voltage for the magnetic amplifiers is obtained from the same voltage source that is provided for the supply transformer.

The circuit is arranged so that the bias windings are energized immediately the power is applied and during the first few cycles thereafter the windings are energized to drive the cores of the magnetic amplifiers in the off direction. The purpose of this is to present a very high impedance across the gate windings during this time so that the currents which might otherwise be induced in the gate windings do not cause the rectifiers to become conductive. By this means the magnetic amplifiers approach their equilibrium state from the off direction.

To accomplish the result just described a potentiometer 52 is connected in the primary circuit of the supply transformer and voltage is supplied directly to the bias windings 32, 33 of the magnetic amplifiers through a circuit connected to the variable tap of the potentiometer and to the junction between potentiometer 52 and resistance 53. The resistance 53 is connected in series primary winding 39. A resistance-capacitance combina tion comprising the resistor 49 and the capacitor 51 connected in parallel is connected across the other two opposite junctions of the four diodes 50. Resistance 54 is also provided as a current divider so that current in potentiometer 52 and hence voltage available for the bias windings will also be limited to desired values. A resistance 49 is provided across capacitor 51 for controlling capacitor discharge time. A small light may also be connected, as shown at 55 in the drawing, across the supply transformer primary circuit. Such a light is con venient for indicating when the supply transformer cir- .Cuit is energized.

I Both bias windings 32, 33 are energized from the previously described connections at the potentiometer 52. Rectifying means, such as diodes 56 and 57 are connected in series with the bias windings so that one bias winding draws current only when line voltage is positive and the other draws current only when the line voltage is negative. Resistance 58 and potentiometer 5? are provided in the bias winding circuits so that the gross current limited to desired values by the resistance and the impedance of the two bias windings may be matched by the potentiometer. The magnitude of bias winding currents and, therefore, the off condition of the rectifiers may be controlled by adjustment of potentiometer 52. Adjustment of trimmer potentiometer 59 permits the characteristics of the individual bias winding circuits to be varied sufiiciently to insure that the firing angles of the rectifiers are equalized. Use of the trimmer potentiometer is advantageous because compensation for slightly different magnetic amplifiers is possible and as a result the expense of constructing or selecting precisely matched amplifiers may be avoided.

Thus, in the normal course of operation, as the voltage at the anode of controlled silicon rectifier 25 swings positive, the bias winding 32 which develops flux in opposition to the fiuX of the gate winding is first energized 180 before the gate winding is energized. Voltage subsequently appears 180 later at the secondary winding 37 of the supply transformer, but a signal is not induced in the gate circuit of the rectifier until the signal at the control winding 19 counteracts the bias flux and unbalances the flux in the core suificiently to permit the core to saturate and to permit current to flow through the amplifier gate winding.

A high-frequency choke may also be connected in the load or power circuit, as indicated at 6t) in the drawing, to suppress line transients. The choke may be desirable if other apparatus is supplied from the same power source as the dimmer. The reason for this is that switching time for the controlled silicon rectifiers is very short, i.e., of the order of one to five, microseconds. Such a short switching time creates high-frequency line transients which, unless suppressed, may have sufiicient energy to interfere with the other apparatus on the line.

I also provide a current transformer 61 for sensing load current and providing feedback signals to the warmup and current-limting circuits 23 and 24, mentioned. The primary winding 62 of this transformer is connected in series in the power circuit of the controlled silicon rectifiers.

As has been mentioned, as soon as the direct current control circuit is energized it provides a signal to the con trol windings of the magnetic amplifiers. This signal is obtained because resistor 17 biases transistor on when the setting of potentiometer 11 is above zero. The

intial or no-load signal to control windings 19 and 21 is limited to a predetermined value, however, so that when load is connected starting current does not exceed rectifier ratings.

I provide a second transistor 65' to limit the intial out- I put of the first transistor 15. The emitter and collector of second transistor 65 are connected across the emitter and base of transistor 15. The base of the second transistor is connected to bias resistor 66. Thus, as soon as the DC. control circuit is energized, second transistor 65 is also biased on. It conducts through biasing resistor 17 for first transistor 15 tending to turn the first transis tor off. The circuit is arranged so that the first transistor is not fully off under this condition and a predetermined small signal is passed to the magnetic amplifier control windings.

The control windings, which are connected in series in the output circuit of transistor 15, are arranged so that the flow of direct current through them establishes a flux 1n the core of each magnetic amplifier that opposes the flux also established therein from energizing of the bias windings. The magnitude of control winding current thus determines net bias of the magnetic amplifiers. This in turn determines the angle in the applied voltage cycle at which the gate circuits become conducting, when a lamp load is connected, to fire the controlled silicon rectifiers. When transistor 15 is nearly off, as described, and load is connected, the small current permitted to fiow in the control windings is sufficient to cause the rectifiers to fire or begin conducting late (near 60) in their conducting half-cycles of applied voltage. This permits a small starting voltage to be applied to the load and startmg current is restricted to a low value.

By limiting the initial load voltage in this fashion in my invention, initial load current may be readily limited to a value at or below the ratings of the particular rectifiers being used in the power circuit. The current limitation is effective for any initial load which may be connected regardless of Whether the load is actually connected at a time of maximum line voltage. The limitatron is also effective regardless of the setting of dimmer control potentiometer 11, unless the potentiometer setting is very low. In the latter case the potentiometer setting may establish a load current limitation lower than that permitted by the warm up circuit.

The current transformer has two secondary windings 63 and 6d. Winding 63 is connected to influence bias applied to the second transistor 65. The primary winding ea has a small number of turns as compared to the secondary winding 63 so that the warm up circuit 23 is sensitive to current in a small load such as, for example, a watt load on a 10,000 watt dimmer.

There is of course, no signal in the current transformer primary before load is connected in the power circuit, and transistor 65 conducts as has been described. After a load is connected, a signal appears at the secondary 63 of the current rectifier 67, limited by series resistor 68, smoothed or filtered by shunt capacitor 69 and applied to the bias resistor 66 at the base of transistor 65. The polarity of the rectified signal is such as to tend to bias transistor 65 off and transistor 15 is biased on by resistor 17. As this occurs, output of transistor 15 and the signal to the control windings of the magnetic amplifiers increase, the rectifier conduction angles increase, load current increases, and so on until the bias voltage at resistor 65 is sufiicient to turn off transistor 65.

After a few cycles transistor 65 is biased off and the control function passes to the over-current protection circuit 24-. According to my invention the over-current protection circuit is intended to be sensitive to much higher load currents than those to which the warm-up circuit initially responds. Also the over-current protection circuit is reactive and a short time with nearly steady state load current is required for it to stabilize and be ready to assume the control function. To be certain that this circuit is stabilized before the warm-up circuit is released, I provide a capacitance at '70 across the emitter and collector of second transistor 65. This capacitance is charged by the time the bias voltage at resistor 66 drives the transistor to cut-off. After that point, discharge of the capacitance is suificient to maintain a conducting condition across the emitter and base of transistor 15 and keep the first transistor from becoming fully on for one or two more cycles. p

Now with rated full load of, for example, 10,000 watts, the magnitude of the signal. being provided in the warmup circuit is very large. Obviously a signal large enough to operate that circuit with only a 100 watt load is going to be about 100 times larger than necessary with a 10,000 watt load. Reverse bias voltage at transistor 65' I must be limited, therefore, to protect the emitter to base junction of the transistor from being damaged. I provide a voltage limiter consisting of a silicon diode 7?. across the emitter to base of transistor 65 for this purpose. The diode has a constant forward voltage drop of about 0.6 to 0.9 of a volt. I

I also provide blocking means such as a rectifier at 72 in the output circuit of transistorofi. A rectifier connected as shown to permit current flow only in the direction of bias resistor 17, serves as a blocking diode to decouple the over-current protection circuit 24 from the warm-up circuit 23 during normal operation.

In the over-current protection loop, the signal from the secondary winding 64 of the current transformer is applied across potentiometer resistance S0, changed to DC. by a full wave rectifier 81, and then supplied to a resistive load 82. The average value of this signal, of course, varies with the amplitude and conducting angle of load current. Using resistors at 80 and $2 assures good presentation of this signal.

The voltage appearing across resistor 32 in turn pro vides a signal whi h is fed to a capacitance through an appropriate limiting resistance 85 and a Zener diode 35. One side of the filter and storage capacitor 84 is connected to the emitter and the other side to the junction of diodes S6 and 87. The polarity of the voltage appearing across resistance 32 is arranged so that with an increase in voltage at capacitor 84, the transistor is biased oil. By connecting one tap of the rectifiers 81 to the movable tap 83 of the potentiometer, the current level at which circuit 24 responds may be adjusted.

The diode ss serves to block the signal to the capacitor 84 until voltage across the resistance 82 is at or above a predetermined minimum. The so-called Zener diode is a particularly convenient device for this purpose because it does not conduct until voltage across it exceeds a rated, value. I

In this overcurrent protection circuit of my invention I also provide rectifier means 87 connected between capacitor 84 and the base of transistor 15. Its purpose is analogous to that of rectifier 72 in the warm-up circuit. That is, rectifier 8'7 serves as a blocking diode. t isolates the overcurr'ent protection circuit so that its action is not influenced by operation of second transistor 65.

A capacitor 88 is also shown connected across the emitter to base of transistor in FIG. 1. Such a capacitor may be desirable as a damping filter to smooth the signals appearing at bias resistor 17 and minimize the influence of surges or of any remaining DC. ripple at that point.

In FIG. 2, values of maximum average current, maximum root mean square current and maximum peak current (ordinates) are plotted to illustrate their relation to conduction angle (abscissas) for a particular controlled silicon rectifier known commercially as Type C and manufactured by the General Electric Co. The characteristics for different types of controlled silicon rectifiers are quite similar, except for the power levels at which theyoperate. That is, for example, percent change in maximum average current for equal changes in the conduction angle isthe same for rectifiers of different ratings, although, of course, numerical change in maximum average current is not.

Curve A of FIG. 2 shows the relation between maximum average per unit current and conduction angle.

Curve C shows the relation between maximum peak per unit current and conduction angle. Curve B shows a similar relation for maximum per unit root mean square current.

From FIG; 2, it is apparent that the maxima of average and peak currents go in opposite directions with Now, controlled silicon rectifier ratings are conven-v tionally given in terms or a maximum permissible average current. From FIG. 2, it may be appreciated that a control circuit which provides safe constant average current regulation cannot, therefore, maintain rectifier operation at rated maximum average current. Also, a control circuit which provides safe constant peak current regulation would drive both R.M.S. and average current far below rated maxima at small conduction angles.

First, the basic reason for prescribing current ratings is to keep rectifier heating and temperature rise within safe limits during operation; temperature rise is directly related to root mean square current and curve B shows root mean square current to be constant over a wide range of conduction angles. Second, this range of conduction angles, namely 30 to 180, encompasses the range of controlled silicon rectifier firing angles for most normal dimmer. settings in theater lighting practice.

In my invention, I provide means for sensing both peak and average load current signals and balancing these two signals in the overcurrent protection circuit so that the resultant signalprovides substantially constant root mean square current regulation over the' principal range or controlled silicon rectifier conduction angles, viz., 30

sense peak currents only, and regulate to a constant peak value determined by the setting of potentiometer 83.

Capacitor 84 serves as a peak voltage storage device and Zener diode as prevents any voltage from reaching this capacitor unless the voltage appearing across resistor 82 exceeds a predetermined minimum value (which valuein turn determines the ratingof the Zener diode to be mstalled at 85). For effectively controlling bias on first transistor 15', this voltage value (and Zener diode rating) may be, forexample, 4.5 volts. And, as mentioned, the polarity of the voltage is such. that an increase in voltageacross capacitor 84 turns transistor 15 ofi, blocking control current to the magnetic amplifiers and reducing dimmer output. Capacitor 84 therefore gives peak voltage sensing. It also provides damping to pre 'vent overshoot and oscillation. Without it, circuit 24 would sense average currents only and regulate to a constant average determined by the setting of potentiometer 83.

.The size of capacitor 84 determines the ratio of peak to averagecurrent to which the circuit responds and,

was resistor M, a good approximation to constant R.M.S.

current regulation over a range of 30 to in conduction angles is obtained. Suchregulation, with the proper capacitance at 84, maintains rectifier operation at nearly rated maximum currents over a wider range of Curve B is significant for two very important reasons;

9 conduction angles than can be obtained with either peak regulation or average regulation only.

Of course, when conduction angles are below 30, circuit 24 clearly peak limits if it is controlling. From the standpoint of maintaining operation at rated maximum current, this is of small importance because, as a practical matter, the current limit established by the warm-up circuit 23 (or by the dimmer control potentiometer 11) is then normally controlling. But, if overload conditions are present, the overcurrent protection circuit will peak limit as soon as it cuts in.

The Zener diode 8% gives a high gain threshold feed back loop which gives a sharp knee to the current regulation curve. This means that even with less than rated loads, there is no regulation and no feed-back coupling. Changing the setting of potentiometer 80 permits adjustment of the position of the knee of the regulation curve according to the size of the load to be controlled.

With my invention, maximum dimmer output consistent with controlled silicon rectifier temperature rise limitations is maintained. By utilizing transistor 15 as shown, in series with control windings 19 and 21, the magnetic amplifiers have a high input impedance which provides for very rapid magnetic amplifier response.

The overcurrent protection circuit requires only onehalf cycle to effect substantial reduction in load current. Combined with the Warm-up circuit the controlled silicon rectifiers can be made to operate continuously at maximum rated current and, in fact, can be made to operate continuously with large overloads. If an overload condition such as previously described does occur, the overload protection circuit responds to reduce dimmer output as soon as there is one-half cycle of overload current.

The control circuit holds the current at a safe value until the load is rearranged or until the overload situation corrects itself. Operation is not interrupted by load changes which may be made and the dimmer of my invention is fully reliable for theater lighting work.

Typical components for the embodiment illustrated in FIG. 1 are given in the following table.

Transistors, diodes and rectifiers- Reference numeral:

Type

15, 65 2N65l. 25, 26 GE#(I60. 40, 4-1 PA305. 50 PTS 10. 56,57,81 1N43A. 6'7 6X!). 71, 72, PA315. 86 Motorola M452.

Resistors and potentiometers Reference numeral: Ohms lid 220 17 150K 13 5.6

K

42, 43, 44, 45 68 49 I. 3000 52, 59, 68, 80, 82, 85 1000 53 470 54 2700 58 1500 66 100K CapacitorsReference numeral: Microfarads 46, 47 2 51 30 69 70 5 84 1 86 .25

10 Transformer windings- Reference numeral: Turns 19, 21 3000 30, 31 1360 32, 33 1500 37, 38 340 39 1700 62. 1 63 1000 64 My invention has been explained with detailed reference to one embodiment thereof. It is to be understood that many changes may be made in that embodiment without departing from my invention. For example, in other applications, the warm-up circuit or the overcurrent protection circuit alone may be adequate for meeting performance requirements. The scope of the invention is as set forth in the following claims.

I claim:

1. Apparatus comprising power circuit means adapted to be connected to an electric load and to a source of alternating voltage; controllable solid state rectifier means serially connected in said power circuit for controlling current condition therein, said controlled solid state rectifier means including a gate for controlling rectifier conductivity; magnetic amplifier means having a saturable magnetic core and control, bias and gate windings wound on said core; gate circuit means connected to said amplifier means and to said gate and adapted to receive voltage from said source of alternating voltage for supplying gate currents of magnitude suificient to initiate conduction in said controlled rectifier means, said gate circuit means including said gate winding for controlling gate current phasing with respect to that of said alternating source voltage; bias circuit means connected to said amplifier and adapted to be energized by alternating voltage for supplying bias currents to said amplifier means, said bias circuit means including a bias winding, said gate and bias circuit means including rectifier means connected in series with each of said bias and gate windings; said bias circuit being operative to drive the saturation level in each said saturable core in one direction during one half-cycle of said source voltage and in the opposite direction during the other half-cycle of said source of energizing voltage, the saturation level in said magnetic amplifier means being increased with current in said gate windings and decreased with current in said bias windings; direct current circuit means connected to a variable source of direct voltage and to said magnetic amplifier means and arranged to supply direct current of desired magnitude and direction to said control winding for counteracting the saturation of said core by said bias circuit means and controlling said phasing, said direct current circuit means including first transistor means connected in series with said control windings for controlling conduction therein, first bias means connected to said first transistor for controlling conductivity thereof, and second transistor means with second bias means connected to said second transistor means for controlling the conductivity thereof, said second transistor means having its output terminal connected to said first bias means such that output from said second transistor means reduces conductivity of said first transistor means, and including feedback circuit means responsive to current in said power circuit means, said feedback circuit means being connected to said second bias means and adapted to bias off said second transistor means when current in said power circuit means exceeds a predetermined value, said first and second bias means being operative to limit output of said first transistor means to a value Within a range having a predetermined maximum when average value of current in said power circuit means is zero.

2. Apparatus comprising power circuit means adapted to be connected to an electric load and to a source of alternating voltage; controllable solid state rectifier means serially connected in said power circuit for controlling curii rent conduction therein, said controlled solid state rectifier means including a gate for controlling rectifier conductivity; magnetic amplifier means having a saturable magnetic core and control, bias and gate windings wound on said core; gate circuit means connected to said amplifier means'and to said gate and adapted to receive voltage from said source of alternating voltage for supplying gate currents of magnitude sufiicient to initiate conduction in said controlled rectifier means, said gate circuit means including said gate winding for controlling gate current phasing with respect to that of said alternating source voltage; bias circuit means connected to said amplifier means and adapted to be energized by alternating voltage for supplying bias currents to said amplifier means, said 'bias circuit means including a bias winding, said gateland bias circuit means including rectifier means connected in series with each of said bias and gate windings; said bias circuit being operative to drive the saturation level in each said saturable core in one direction during one half-cycle of said source voltage and in the opposite direction during thetother half-cycle of said source of energizing voltage, the saturation level in said magnetic amplifier means being increased with current in said gate windings and decreased with current in said bias windings; direct current circuit means connected to a variable source of direct voltage and to said magnetic amplifier means and arranged to supply direct current of desired magnitude and direction to said control winding for counteracting the saturation of said core by said bias circuit means and controlling said phasing, said direct current circuit means including first tran-' sistor means connected in series with said control winding for controlling conduction therein, first bias means connected to said first transistor means for controlling conductivity thereof, first feedback circuit means responsive to current in said power circuit means, said first feedback circuit means being connected to said first bias means and arranged vto reduce conductivity of said first transistor when said power circuit current exceeds a predetermined maximum value, said direct current circuit means also including second transistor means and second bias means connected to said second transistor for controlling conductivity thereof, said second transistor having its output circuit means connected to said first bias means such that output fromsaid second transistor reduces conductivity of said first transistor; and second feedback circuit means responsive to current in said power circuit, said second feedback circuit means being connected to said second bias means and adapted to bias off said second transistor when power circuit current exceeds a predetermined minimum value, said first and second bias means being operative to limit output of said first transistor means to a value within a range having a predetermined maximum when average value of current in said power circuit means is zero.

3. A dimmer comprising'a power circuit adapted to be connected to a variable intensity electric light load and to a source of alternating voltage; controllable solid state rectifier means having controllable anode to cathode conductivity and gate electrode means'for controlling said conductivity and being serially connected in said power circuit for controlling conduction therein; gate circuit magnetic amplifier means connected in said gate circuit means and responsive to changes in magnitude of unidirectional current signals for controlling the phasing of said gate currents with respect to that of said source voltage; an adjustable source of direct'voltage; control circuit means connected to said adjustable source and to said magnetic amplifier means for supplying thereto direct cur- 'rent control signals of preselected magnitude and direction for controlling said phasing; first transistor means having variable emitter to collector conductivity and being connected in said control circuit means for controlling u conduction therein; first bias means connected to said first transistor means for controlling said emitter to collector conductivity and being connected in said control circuit means to receive biasing voltages from said adjustable source for increasing said conductivity, second transistor means havingvariable emitter to collector conductivity connected in said control circuit means and to said first bias means for supplying thereto biasing voltages for decreasing said first transistor conductivity; second bias means connected to said second transistor means for controlling conductivity thereof and being connected in said control circuit means to receive biasing voltage from said adjustable source for increasing said second transistor conductivity;'feedback circuit means responsive to load current in said power circuit and connected to said second bias means for supplying thereto biasing voltage for decreasing said second transistor conductivity, said feedback circuit means being arranged so that the last named biasing voltage is sufficient to bias said second transistor means off when said load current exceeds a predetermined value, said first and second bias means being operative to limit 7 output of said first transistor means to a value within a range having a predetermined maximum when average current in said power circuit is zero; and voltage limiting means connected to said second transistor means and to said second bias means to limit reverse biasing voltages to a safe operating value.

4. A dimmer comprising a power circuit adapted to be connected to a variable intensity electric light load and to a source of alternating voltage; controllable solid state rectifier means having controllable anode to cathode conductivity and gate electrode means for controlling said conductivity and being serially connected in said power circuit for controlling conduction therein; gate circuit means adapted to be connected to said source of alternating voltage and being connected to said gate electrode means for supplying gate currents of magnitude sufficient to initiate conductionain said controlled rectifier means;

magnetic amplifier means having a gate winding connected in said gate circuit means and responsive to changes in magnitude of unidirectional current signals for controlling the phasing of said gate currents with respect to that of said adjustable source for increasing said conductivity,

first feedback means responsive to current in said power circuit and'connected to said first bias means for supplying thereto biasing voltages for decreasing said first transistor conductivity when said power circuit current eX- ceeds a first predetermined value; second transistormeans having variable emitter to collector conductivity connected in said control circuit means and to said first bias means for supplying thereto biasing voltages for decreasing said first transistor conductivity; second bias means connected to said second transistor means for controlling conductivity thereof and being connected inlsaid control circuitmeans to receive biasing voltages from said ad justable source for increasing said second transistor conductivity; second feedback circuit means responsive to load current in said power circuit and connected to said second bias means forsupplying thereto biasing voltages for decreasing said second transistor conductivity, said second feedback circuit means being arranged so that the last named biasing voltage is suificient to bias said second transistor means off when said power circuit current exceeds a second predetermined value less than said first predetermined value, said first and second bias means being operative to limit output of said first transistor means to a value within a range having a predetermined maximum when average current in said power circuit is zero; and voltage limiting means connected to said second transistor means and to said second bias means to limit reverse bias voltages at said second transistor means to a safe operating value when said power circuit current is greater than said second predetermined value.

5. Apparatus for selectively and variably controlling the intensity of variable intensity, alternating current electric lights and including a power circuit adapted to be connected to at least one of said lights and to a source of alternating voltage, controllable solid state rectifier means having variable anode to cathode conductivity and gate electrode means for controlling said conductivity, said controllable rectifier means being serially connected in said power circuit for controlling conduction therein, magnetic amplifier means including at least a saturable magnetic co-re means with control, bias and gate windings, gate circuit means connected to said gate electrode and to said magnetic amplifier means and adapted to receive voltage from said alternating source for supplying gate currents of magnitude sufiicient to initiate conduction in said controllable rectifier means, each gate circuit means including said gate winding for controlling gate current phasing with respect to that of said source voltage, bias circuit means connected to said amplifier and adapted to receive alternating voltage from said source for supplying bias currents of preselected magnitude to said amplifier means, said bias circuit means including said bias winding, said gate and bias circuit means including rectifier means operative to drive the saturation level in each said saturable core in one direction during one half cycle of said source voltage and in the opposite direction during the other half cycle of said source voltage, and direct current circuit means connected to an adjustable source of direct voltage and to said magnetic amplifier means and arranged for supplying direct current of preselected magnitude and direction to said control windings, a supply transformer having a primary winding and a secondary winding for energizing said gate circuit means, said secondary winding being connected in series with said gate winding therein, a potentiometer to which said bias circuit means is connected, one side of the bias circuit means being connected to the movable tap of the potentiometer for adjusting said preselected magnitude of the bias currents, supply circuit means for connecting said potentiometer in series with said primary winding and adapted to be connected to said source of alternating voltage, and timing means to delay energizing said primary winding until said bias circuit means is energized when said supply circuit means is connected to said source of alternating voltage, which timing means comprises: rectifier means, a capacitance connected in series with said rectifier means, said capacitance and rectifier means being connected in shunt across said primary winding, a first resistance of preselected size connected in said supply circuit means for controlling capacitance charge time and a second resistance of preselected size connected in shunt across said capacitance for controlling capacitance discharge time.

6. A controlled rectifier system for variably controlling the application of an alternating voltage to a load by a variable D.-C. control voltage comprising: power input terminals provided to receive A.-C. voltage from a supply source, power output terminals provided to deliver A.-C. voltage to a load, a solid state controlled rectifier having a cathode, an anode and a gate control electrode, a magnetic amplifier including a saturable magnetic core having at least a gate winding connected to the input and output terminals and having a control winding, circuit means connected in series with said gate winding adapted to apply an A.-C. control voltage between the cathode and the control-electrode of said controlled rectifier, means for connecting the anode and cathode terminals of said rectifier between an A.-C. input terminal and an A.-C. output terminal, a D.-C. voltage supply including manually operable means for varying the output voltage of said supply to produce a DC. control voltage, current control means connecting the D.-C. control voltage of said supply to said control winding, first load-current-feedback control means connected to said current control means operable when said load current reaches a predetermined maximum value to reduce the D.-C. current flow through said current control means to said control winding and thereby limit the current flow through said controlled rectifier and load to said predetermined maximum value, second load-current feedback control means connected to said current control means including current limiting means provided to restrict the D.-C. current fiow through said current control means to said control winding to a predetermined maximum value when the load current is small, said limiting means being responsive to load current feedback and being disabled when the load current exceeds a predetermined minimum value thereby permitting the load current to be controlled between predetermined minimum and maximum values by the adjustment of said manually operable means.

References Cited by the Examiner UNITED STATES PATENTS 2,914,720 11/59 Merkel 32l25 2,920,240 1/60 Macklem 32322 X 2,972,097 2/ 61 Dornhoefer 323-89 2,998,547 8/61 Berman 323-22 X LLOYD MCCOLLUM, Primary Examiner. MILTON O. HIRSHFIELD, Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,200,32 August 10, 1965 Joseph W5 Fleming It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 23, for "condition" read conduction Signed and sealed this 3rd day of May 1966.,

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer Commissioner of Patents EDWARD J. BRENNER

Claims

6. A CONTROLLED RECTIFIER SYSTEM FOR VARIABLY CONTROLLING THE APPLICATION OF AN ALTERNATING VOLTAGE TO A LOAD BY A VARIABLE D.-C. CONTROL VOLTAGE COMPRISING POWER INPUT TERMINALS PROVIDED TO RECEIVE A.-C. VOLTAGE FROM A SUPPLY SOURCE, POWER OUTPUTS TERMINALS PROVIDED TO DELIVER A.-C. VOLTAGE TO A LOAD, A SOLID STATE CONTROLLED RECTIFIER HAVING A CATHODE, AN ANODE AND A GATE CONTROL ECLECTRODE, A MAGNETIC AMPLIFIER INCLUDING A SATURABLE MAGNETIC CORE HAVING AT LEAST A GATE WINDING CONNECTED TO THE INPUT AND OUTPUT TERMINALS AND HAVING A CONTROL WINDING, CIRCUIT MEANS CONNECTED IN SERIES WITH SAID GATE WINDING ADAPTED TO APPLY AN A.-C. CONTROL VOLTAGE BETWEEN THE CHAHODE AND THE CONTROL-ELECTRODE OF SAID CONTROLLED RECTIFIER, MEANS FOR CONNECTING THE ANODE AND CATHODE TERMINALS OF SAID RECTIFIER BETWEEN AN A.-C. INPUT TERMINAL AND AN A.-C. OUTPUT TERMINAL, A D.-C. VOLTAGE SUPPLY INCLUDING MANUALLY OPERABLE MEANS FOR VARYING THE OUTPUT VOLTAGE OF SAID SUPPLY TO PRODUCE A D.-C. CONTROL VOLTAGE, CURRENT CONTROL MEANS CONNECTING THE D.-C. CONTROL VOLTAGE OF SAID SUPPLY TO SAID CONTROL WINDING, FIRST LOAD-CURRENT-FEEDBACK CONTROL MEANS CONNECTED TO SAID CURRENT CONTROL MEANS OPERABLE WHEN SAID LOAD CURRENT REACHES A PREDETERMINED MAXIMUM VALUE TO REDUCE THE D.-C. CURRENT FLOW THROUGH SAID CURRENT CONTROL MEANS TO SAID CONTROL WINDING AND THEREBY LIMIT THE CURRENT FLOW THROUGH SAID CONTROLLED RECTIFIER AND LOAD TO SAID PREDETERMINED MAXIMUM VALUR, SECOND LOAD-CURRENT FEEDBACK CONTROL MEANS CONNECTED TO SAID CURRENT CONTROL MEANS INCLUDING CURRENT LIMITING MEANS PROVIDED TO RESTRICT THE D.-C. CURRENT FLOW THROUGH SAID CURRENT CONTROL MEANS TO SAID CONTROL WINDING TO A PREDETERMINED MAXIMUM VALUE WHEN THE LOAD CURRENT IS SMALL, SAID LIMITING MEANS BEING RESPONSIVE TO LOAD CURRENT FEEDBACK AND BEING DISABLED WHEN THE LOAD CURRENT EXCEEDS A PREDETERMINED MAXIMUM VALUE THEREBY PREMITTING THE LOAD CURRENT TO BE CONTROLLED BETWEEN PREDETERMINED MAXIMUM AND MAXIMUM VALUES BY THE ADJUSTMENT OF SAID MANUALLY OPERABLE MEANS.