US3018431A - Alternating current voltage regulator - Google Patents

Description

H. L. GOLDSTEIN ALTERNATING CURRENT VOLTAGE REGULATOR Jan. 23, 1962 4 Sheets-Sheet 1 Filed Jan. 4, 1960 SENSING CIRCUIT M/VERTER 0 cowvrsn 700 UHF/00x6.

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m 181 ,7 I 6 0 U7\6 06 own IN VE N TOR By H. L. GOLDSTE/(V A TTORNEV United States Patent 3,018,431 ALTERNATING CURRENT VOLTAGE REGULATOR Hans L. Goldstein, Hanover Township, Morris County,

NJ., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Filed Jan. 4, 1960, Ser. No. 329 9 Claims. (Cl. 323-45) This invention relates to regulator systems and particularly to voltage regulators for alternating current power supply.

One type of system for providing voltage regulation for alternating current power supply employs boosting or bucking transformers, or both, having their secondaries connected in series between the main source and the load. Switching circuits are provided for connecting the primary windings of these transformers to the source as the auxiliary voltages provided by their secondaries are required to hold the output voltage to its normal value. In such circumstances it has been the practice to employ boosting or bucking transformers which contribute to the load voltage on a unitary or step-by-step basis. It is also more usual to employ electromagnetic switches or relays for controlling the switching of the transformers.

It is an object of the present invention to increase the range and speed of regulation of alternating current power supply systems.

'It is a further object of the invention to provide a voltage regulator giving reliable operation at high powers with high efliciency and low wave form distortion.

In accordance with this invention a regulator for an alternating voltage supply system is provided with auxiliary transformers which contribute to the output voltage, components that are related on the basis of a numerical system. Since the binary system is readily adaptable to the use of electronic switching, the transformers can be designed to provide steps such as 1, 2, 4, 8, et cetera percentages of the output voltage. By arranging the con trol circuit to select various combinations of these auxiliary transformers, a wide range of regulation may be provided with a very small number of transformers. In particular, the output voltage of the regulator is provided with a sensing unit or comparator which periodically produces an error voltage that is a measure of the deviation of the output voltage from the nominal or standard value. This error voltage is transformed from an analog representation to a digital representation in which it comprises a train of pulses, the number of which is proportional to the value of the error voltage. This train of pulses is impressed upon an electronic binary counter, the various stages of which are associated with the appropriate one of the auxiliary transformers. As a result of the activation of the various stages of the counter by the train of pulses there will be switched into circuit those auxiliary transformers appropriate for making the proper correction in the output voltage. All of the control circuits and the transformer switching circuits are of the electronic type particularly employing magnetic or solid state components. Thus the use of moving parts or vacuum tubes is avoided and rapid regulation with reliability of operation is achieved.

This invention may be more readily understood by reference to the following detailed description in connec tion with the drawing, in which:

FIG. 1 is a block schematic of a specific embodiment of an alternating current voltage regulator in accordance with the present invention;

FIG. 2 is a schematic circuit diagram of one of the auxiliary transformers and its magnetic amplifier switching control;

FIG. 3 is a block schematic diagram of a timer circuit which may be employed in the system of FIG. 1;

FIG. 4 is a schematic circuit diagram of the sensing circuit employed in FIG. 1;

FIG. 5 is a schematic circuit diagram of the inverter of the regulator system;

FIG. 6 is a schematic circuit diagram of the encoder employed in the regulator;

FIG. 7 is a block schematic diagram of the counter used in the regulator; and

FIG. 8 is a schematic circuit diagram of a typical counter stage.

FIG. 1 shows in block schematic form the preferred embodiment of the present invention in a regulator for an alternating current voltage supply. The other circuits show in more detail various component elements of the system of FIG. 1 and the same reference numerals are used for corresponding circuit components, throughout the drawing.

The regulator of FIG. 1 provides a constant voltage supply to the load 112 from an alternating current source of 60 cycles, for example, 103. Connected in series between the source 103 and load 112 are the secondary windings of auxiliary transformers 101, 102, 104, and 108. These transformers are of the step-down type and provide across their secondary windings voltages related in value by the denominational orders of a binary system. For example, transformer 101 may provide a voltage of one percent of the nominal value of the output voltage, in which case that of transformer 102 is two percent, transformer 104 four percent, and transformer 108 eight percent. The primary winding of each of the auxiliary transformers is provided with two switches. Thus, the primary of transformer 101 has a switch 105 which, when closed, short-circuits the primary winding and a switch 106 which, when closed, connects the primary winding to the source 103 on the regulated side of the regulator circuit. (The relative polarities of the transformer windings in this and other figures of the drawing are indicated by dots in accordance with the usual convention.)

The timer 300 controls the cyclic operation of the regulator. As will be explained in more detail in the discussion of FIG. 3, this timer derives from the 60 cycle power supply controlly or command signals for initiating the various steps in the cyclic operation of the regulator. The first is a sensing command signal S which is a negative voltage step lasting for one cycle of the 60 cycle current and recurring every 8 cycles of the 60 cycle supply. The second is the encoding signal E which is a negative voltage step generated in the cycle following that in which the sensing pulse is produced.

The sensing circuit 400 produces an error voltage which is proportional to the deviation of the output voltage of the regulator from its normal or standard value; This error voltage is produced during each sensing command signal from the timer 300. The error voltage e is positive when the output voltage is too high (above its normal value) and negative when the output voltage is too low. These positive or negative voltages are supplied from the sensing unit 400 to the inverter 500.

Two functions are performed by the inverter 500. First, it produces a voltage equal to the absolute value le] of the error voltage e from the sensing unit 400. The second function of the inverter is to supply control voltages to the up bus 109 and the down bus 110 which control voltages to the up bus 109 and the down bus 110 which control the direction in which the counter 700 will count. Thus, as will be explained in more detail in connection with the description of FIG. 5, when the error voltage is zero or negative the up bus 109 is clamped to positive 18 volts and the down bus is at zero voltage. As will be later explained in detail, this causes the counter to count up. When the error voltage is positive the up bus will be at zero volts and the down bus at plus 18 volts and the counter will count down.

The encoder '600 is essentially an analOg-to-digital converter. It is controlled by the absolute value of the error voltage lel and operates to produce a train of 100 kilocycles per second pulses, the number of pulses of the train being proportional to the value of the error voltage. This train of pulses is supplied to the binary counter 700.

The counter 700 is basically a conventional transistor binary counter employing a series of stages of transistor flip-flop circuits with controls for providing reversible counting (up or down). Each of the counter stages is interconnected to a corresponding switching circuit for the transformers 101, 102, 104, and 108.

The simplest arrangement for the transformer circuits would be that in which their secondaries are connected so that :all of their voltages will be additive. With such a connection the only correction in the output voltage which could be made would be in the positive direction and the regulator could only compensate for negative deviations in the source voltage. With this type of circ'uit the connections of the switches to each of the counter stages would be the same and woufd be such that when "the counter stage is in the position the shortcircuiting switch 105 would be c.os:d and the connecting switch '106 open, while when the counter is in the 1 position the short-circuit switch 105 would be open and the connecting-switch 106 closed.

However it is possible, by connecting one or more of the transformers 101, 102, 104, 108 in a bucking direction, to cover a range of voltages including negative values. In the circuit shown in FIG. 1 the transformer 104 is connected so that the voltage of its secondary is opposite to and bucks the voltage supplied by the other transformers. Accordingly it is necessary that the switches for contro'ling transformer 10.4 be connected to counter stage IV in the opposite manner to which the other "switches are connected to their respective counter stagesl Thus the shorting switch 115 is connected so that his closed when the counter stage IV is in the 1 position and the connecting switch 116 is connected so that it willbe closed when the counter stage IV is in the 0 position.

FIG. '2 shows schematically the circuit for one of the transformers 1 01and its switching circuits 105 and 106. These circuits are of the so-called doubler magnetic amplifier type as described in Magnetic Amplifiers, by H.1F. Storm, John Wiley and Sons, 1955, page 245, or Patent "2,126,790 to Logan, August 16, 1938. The magnetic amplifier '105 for example comprises the magnetic windings 201 and 202 connected in series with the respective diodes 223 and 224 which are oppositely poled to provide conducting paths for both the positive and negative cycles of the alternating current. The wind ings 201 and 202 are each provided with control windings 203 and 204 respectively.

In addition there are provided bias windings (not shown) to which is supplied current of such magnitude and directionas to keep the switch in the open condition when no current is flowing in the control windings. Direct currentis'supplied from amplifiers associated with andcontrolled by thecounter circuitto the control windin'gs'20'3 and 204 to operate each magnetic amplifier in only one of two conditions. The switch 105 is either fully on when it acts as a 'short circuit across the primaryof the transformer 101 or fully olf when it forms a substantial open circuit across primary windings. The switch is on when the current is supplied to the windings 203 and 204 from the respective counter stage.

Switch 106 is of similar construction and is controlled by'thesaturating windings 213 and 214.

'FIG. '3 shows the timing circuit 300 which provides thetiming pulses for controlling the cycling of the regulator. This comprises a conventional pulse generator 303 which produces a pulse at the beginning of each cycle of the 60 cycle voltage supplied to its input. The resulting output pulses are supplied to a conventional three stage binary counter comprising three stages of transistor flip-flops, 301, 302 and 304. As is typi al of binary counters, a carry pulse is supplied from one stage to the next through a differentiating circuit when any stage switches from its "1 position to its 0" position. The zero side of each of the counter stages is connected to an AND circuit 305. As a result there will appear in the output of the AND circuit 305 a negative signal each time that all counter stages are in their zero positions (corresponding to the binary numeral 0 0 0). This command signal S in the output of the AND circuit 305 will last for one cycle of the 60 cycle voltage and will appear once every eight cycles of that supply. The AND circuit 306 is connected to the 1 side of the binary stage 301 and to the 0 sides of the stages 302 and 304. Consequently a negative signal will appear at the output of tthe AND circuit 306, on each cycle of the 60 cycle input current following that at which a signal appears in the output of the AND circuit 305 (binary number 001). This signal also lasts for one cycle and is the eucoding command signal E.

FIG. 4 shows in detail the sensing circuit 400 of FIG. 1 which operates to produce'an error voltage proportional to the variation in the output voltage of the regulator from its standard value. The general principle of operation of this circuit will be described first. At the beginning of a sensing cycle a switch comprising the transistors 401 and 402 is-cl-osed and a current proportional to the output voltage of the regulator obtained from the rectifier 403 starts to charge the capacitor 404. At the same time there is supplied to the capacitor 404 a discharging current obtained from the constant current 'source 405. The value of this constant current is the standard for the regulator so that when the output voltage is of the required magnitude the ultimate voltage-on the capacitor is zero. Under other conditions the ultimate voltage of the capacitor 404 will have a value e of magnitude and polarity dependent upon the variation of the output voltage of the regulator from its required or standard value. At the end of the sensing cycle charging 'switch (401--402) is opened and a second switch comprising the transistors 406 and 407 is closed to discharge the capacitor 404 and prepare the circuit for the next sensing cyc e. a

The operation of the circuit of FIG. 4 by meansof which these functions are performed will now be described in detail. The output voltage of the regulator issupplied through the input transformer 408 to the full wave rectifier 403. When the'nega'tive sensing signal S is applied to the input terminal 409 the transistor 410 is shifted from OFF to ON. The resulting positive voltagestep is supplied through the blocking condenser 411 to the right hand terminal of the primary winding of transformer 412. The resulting voltages developed across the secondary windings 413 and 414 are in sucha direction as 'to cause the transistors 401 and 402 to turn ON. This effectively closes the switch for supplying charging and discharging current to the capacitor 404, transistor '401 providing a path in one direction and transistor 402 in the opposite direction. Aspreviously discussed, the capacitor 404 will charge from the rectified current supplied by the rectifier 403. At the same time discharging current of constant amplitude from the constant current source 405 is also connected to the capacitor 404 through the same paths. At the end of a fixed period determined by the length of the sensing command S, the voltage across the capacitor 404 will accordingly be proportional to the variation between the voltage supplied to the primary of trans- :fo'rmer 408 and a standard voltage determined by the. value ofthe current from the constant current source 405, that is, the error in the output voltage of the regulator.

At the termination of the sensing'command signal S the transistor 410 will turn OFF due to the positive 18 volts from battery 415. The resulting negative voltage step is applied to the right hand terminal of the primary of transformer 412, inducing in the secondary windings 416 and 417 voltages in such a direction as to turn transistors 406 and 407 ON, providing a path for the discharge of a charge of either polarity on the capacitor 404, thus preparing the circuit for the next succeeding sensing cycle.

Each of the transistors 401, 402, 406, and 407 is provided with a diode connected in series in its collector lead. Each such diode blocks voltages which otherwise might bias the collector junctions in the forward direction causing the respective transistor to conduct even when its emitter junction is reverse biased as is required for the open switch condition. A sufiiciently high bias voltage at the bases of the transistors cannot be used because this would exceed the emitter-base reverse voltage rating of the transistors.

FIG. 5 shows in schematic circuit form the details of a circuit that may be used to perform the operations of the inverter 5 00. This circuit comprises two sections operating essentially independently of each other and comprising the inverter proper enclosed in the dash-dot lines 501 and the polarity indicator enclosed in the dash-dot lines 502.

As discussed in connection with the block schematic of FIG. 1, the function of the inverter proper is to produce a voltage |e| equal to the absolute value of the error voltage e obtained from the sensing unit 400, that is of positive polarity independent of the polarity of the error voltage. Each of the transistors 503 and 504 has its base connected to the lead 505 through which the error voltage is supplied from the sensing unit. When error voltage e is negative, transistor 503 is OFF and the transistors 506, 507, 508, and 504 act like a conventional series regulator. In this regulator circuit transistor 506 is the series transistor and supplies to the output lead 509 a positive voltage the value of which is determined by the magnitude of the negative input voltage e. In performing this function transistors 507 and 503 operate as a differential amplifier controlling the transistor 506. The input voltage e from the lead 505 is applied through the transistor 504, operating as an emitter follower, to this differential amplifier. and serves as a negative reference voltage for regulating the value of the output voltage on the lead 509.

When the error voltage 2 is positive, transistor 504 is OFF and transistor 508 is saturated, resulting in the cut-off of transistors 506 and 507. For this positive value of e transistor 503 is ON, operating as a conventional emitter follower with a voltage gain of unity and supplying the error voltage to the output lead 509.

The polarity indicator 502 comprises the transistors 511, 512, and 513 and their associated circuits. As previously indicated, the function of the polarity indicator is to provide the proper voltages on the up and down busses 109 and 110, respectively, to control the operation of the counter 700 in accordance with the polarity of the error voltage e. Actually the busses 109 and 110 are alternately switched between the voltages of plus 18 volts and 0. An examination of the circuit of the polarity indicator' with the interconnection of the transistors and bias voltages as shown will readily indicate the following conditions with respect to the polarity of the error voltage e on the input lead 505.

With the error voltage e either zero or negative, transistors 511 and 512 will be OFF due to the bias voltages on their respective bases. On the other hand transistor 513 will be ON. As a result the up bus 109 will be connected directly to plus 18 volts through the low collector to emitter resistance of transistor 513 in its ON condition, clamping the up bus 109 to positive 18 volts. At the same time the down bus 110 will be at 0 volt.

When a positive error voltage appears on the lead 505 the transistor 511 goes ON, drawing current from the base of the transistor 511, so that the transistor 512 will go ON. The resistor 517 limits the current through the transistor 511 to a safe value. The current through the resistor 516 which serves to bias the transistor 512 OFF when the transistor 511 is OFF can be neglected when both transistors are ON. As a result diode 518 is biased in the forward direction and the base of transistor 513 rises above the positive 18 volts of its emitter causing the transistor 513 to go to the OFF condition. The up bus 109 will therefore drop to 0 volt while the down bus 110 will rise to a positive 18 volts supplied through the collector emitter path of transistor 512.

FIG. 6 is a schematic circuit diagram of a circuit that may be used for the encoder 600. This unit is essentially an analogto-digital converter and other circuits well known in the art could alternately be used. In essence it comprises a pulse generator including two transistors 601 and 602 connected as a conventional freerunning multivibrator. This generator is normally biased OFF, but in response to an encoding command signal E from the timing generator applied to the terminal 603 and the joint presence on the input terminal 604 of an error voltage lel, of at least the minimum value for which the regulator is adjusted to compensate, the pulse generator is turned ON. When the pulse generator operates it delivers an array of pulses of a frequency of kilocycles per second through the emitter-follower transistor 605 to an output terminal 606. This array of pulses is supplied to the counter as described in connection with FIG. 1. At the same time that the pulse generator starts, the capacitor 607 begins to charge with a constant current furnished by the transistor 608 and its associated feedback circuit. When the voltage on the capacitor 607 reaches the magnitude of the error voltage 1e] (supplied through the emitter-follower transistor 609) the comparison circuit including the transistor 610 will operate to stop the oscillator, thus terminating the train of pulses. In this way the number of pulses generated during any encoding period will be proportional to the error voltage for which correction is required.

We will now consider the operation of the circuit in more detail. Under normal conditions, that is, when the error voltage [e] is O or lower than the minimum voltage to be compensated, transistor 610 will be ON dueto the positive bias supplied to its base from the 16 volt source 611 through the potentiometer 612. The use of this potentiometer makes it possible to set the value of the error voltage at which the first pulse appears, thus establishing the sensitivity of the regulator. With transistor 610 ON, current is drawn through its collector-emitter path and resistor 613, bringing the base of the transistor 614 down to such a voltage that the transistor conducts and clamps the base of transistor 602 at positive 16 volts preventing the multivibrator from oscillating.

When the error voltage lel applied to the transistor 610 through the emitter-follower transistor 609 reaches such a value that transistor 610 is OFF, current ceases to flow through the resistor 613 and the base of transistor 614 reaches a value close to positive 18 volts. Transistor 614 is accordingly OFF, removing the positive voltage from the base of the transistor 602 and putting the multivibrator in a condition in which it can be started by the application of a positive voltage to the base of transistor 601.

Assuming that the above conditions exist, the multivibrator 601, 602 will be started by an encoding command signal E (a negative voltage step) applied from the terminal 603 to the base of transistor 615. This causes the transistor 615 to conduct, applying a positive bias to the base of transistor 601 through the lead 616. The multivibrator 601, 602 accordingly starts oscillating, applying a train of pulses through the emitter-follower transistor 605 and the dilferentiating circuit 617 to the output terminal 606.

At the same time the positive voltage developed on the lead 616 as a result of the ON condition of the transistor 615 causes the transistor 608 to be ON so that the capacitor 607 begins to charge. Due to the feedback connections for the transistor 608 the capacitor 607 charges with a constant current. As will be recalled, during this period transistor 610 is OFF as a result of the positive error voltage le| supplied to its emitter. When the voltage on capacitor 607 reaches the value of the error voltage iel transistor 610 is switched to the ON condition causing a drop in the voltage at the base of the transistor 614 which becomes ON, clamping the base of the transistor 602 to a positive voltage and stopping the oscillation of the multivibrator 601, 602. This results in the termination of the pulse train.

It will be observed that the operation of the multivibrator (601602) is responsive to tWo separate controls. It will oscillate (be free-running) only when a positive voltage is applied to the base of the transistor 601 and no positive voltage is applied to the base of the transistor 602. The application of the positive voltage to the transistor 601 is controlled by the encoding command pulse for the purpose of starting the oscillator. On the other hand the condition of the base of transistor 602 is controlled by the error voltage so that the multivibrator cannot be started until the error voltage exceeds the minimum value for regulation and will be stopped when the length of the train of pulses corresponds to the error voltage.

FIG. 7 is a block schematic diagram of the counter 700'. Basically it comprises four transistor flip- flop circuits 701, 702, 704, and 708 corresponding to the binary stages 1, 2, 4, and 8 respectively. These flip-flop stages are interconnected through differentiating and inhibiting circuits to permit counting in either direction (up or down). Only the interconnections between stages 701 and 702 will be described in detail since the others are identical in operation. The counter is operated by the train of 100 kilocycle pulses supplied to the input terminal 706 from the encoder. Assuming that the counter starts counting up from the position for all stages, that is, with all flip-flops in the OFF condition, the first pulse then moves the stage 701 into the 1 position. The second pulse moves it back to the 0 position, and for counting up a carry pulse is transmitted through the differentiating capacitor 710 and the inhibiting circuit 711 to the second stage 702. Under this condition the count down bus 110 will be at 0 potential so that the carry pulse is permitted to reach the up carry lead 712. In counting down the pulses are transferred from one stage to the next when the flip-flop moves from the O to the 1 condition, the down carry signal will be transmitted from stage 701 to stage 702 through the differentiating capacitor 717 and inhibit circuit 718. In this case the up bus 109 will be at 0 voltage, permitting the pulse to reach the down carry lead 713 while the down count bus 110 will be at positive 18 volts inhibiting any pulse from reaching the up carry lead 712. When the regulation required to hold the output voltage at its standard value is greater than the range of the regulator as determined by the auxiliary transformer, a spill-over circuit will hold the regulation at the maximum value. If this spill-over control were not provided .a condition requiring a regulation slightly beyond the limit of the circuit would produce an entirely erroneous control. Thus, for a nominal operating binary counter a condition of 16 pulses representing an error of 16 percent when the limit of the regulator is 15 percent, would cause the counter to recycle to a value of 1 percent. This would produce an entirely erroneous regulation. With a spill-over circuit the counter is set ultimately into its maximum position for either an up or a down count. For the 16 percent error the counter will be set ultimately in the 15 percent position giving the maximum correction.

The spill-over circuit comprises a delay circuit'721 connected to the up and down carry busses 722 and 723 respectively of the final stage 708 of the counter. This delay circuit may conveniently comprise a transistor monosta'ble flip-flop. The purpose of the delay is to assure that the count is complete before the carry signal is passed on to the spillover busses. The outputs of the delay circuit 721 are fed through two inhibitor circuits 724 and 725; the output of the inhibitor circuit 724 is connected to the spill-over up bus 726 and that of the inhibitor 725 to the spill-over down bus 727. When counting up the positive 18 volts on the count up bus 109 actuate inhibitor 725 to prevent any signal from reaching the spill-over down bus 727. The spill-over up bus 726 is connected to the 1 sides of each of the counter flip-flops to set each of the flip-flops into their 1 positions. For counting down similar connections cause each of the flip-flops to be set into its 0 position.

FIG. 8 shows the circuit of a typical counter stage, for example stage 701. This comprises a conventional flip-flop including the transistors 800 and 801; the incoming train of pulses to be counted is supplied from the input terminal 802 to the bases of the flipflop transistors through the diodes 803 and 806 respectively. (For subsequent stage-s there will be two inputs, an up carry and a down carry so that additional diodes 805 and 806 will be required as shown in the dotted line circuit.)

It is assumed for the purpose of this explanation that the 0 condition of the counter stage is that in which the transistor 800 is ON and that the 1 condition is that in which the transistor 801 is ON. Transistor 807 has its base connected to the collector of transistor 800 and has the control windings 203 and 204 of the switch connected to its collector. Thus, when the flip-flop is in the 0 condition, current will be supplied to the windings 203 and 204 to hold the switch 105 closed, short-circuiting the secondary of the transformer 101. Diode 803 is connected in series with the windings 203 and 204 to prevent positive pulses in the magnetic amplifiers from interfering with the counter operation. A transistor 809 is similarly connected between the collector of transistor 801 and the windings 213 and 214 to control the operation of switch 106.

Carry signals are transmitted to the transistor amplifiers 810 and 811. Thus when the transistor 801 shifts from the ON to the OFF condition the potential of its collector carries the base of the transistor 810 to apositive voltage so that transistor 310 goes OFF, producing a negative pulse through the differentiating capacitor 816 on the up carry lead 812. For counting up the carry down lead 813 will be clamped to positive 18 volts by the voltage from the inverter 500 on the count up lead 109'.

For counting down a negative pulse will be applied to the carry down lead 813 through the transistor 811 in a similar fashion. Under these conditions the carry up lead 812 will be clamped to positive 18 volts by the voltage on the count down bus 110.

The spill-over up bus 826 and the spill-over down bus 527 are connected to the transistors 801 and 800 respectively to set the flip-flop in the required 1 or (Y'- condition, as was described in connection with FIG. 7.

What is claimed is: V

1. In a regulator for interconnecting a source of alternating voltage and .a load circuit, a plurality of transformers the voltage ratios of which are different from each other and are related according to a predetermined.

plan, said transformers having their secondary windings connected in series between said source and said load circuit, individual switching means normally short-circuiting the primary windings of each of said transformers, a reference source proportional to the voltage required across said load, means for comparing the output voltage across said load with said reference source to produce an error signal, and means responsive to said error signal in accordance with said plan to selectively open-circuit said primary windings of said transformers and connect them to receive current from said source of alternating voltage.

2. A voltage regulator for association with a source of voltage and a load circuit comprising a plurality of auxiliary sources of voltages of amplitudes differing from each other and corresponding respectively to the denominational orders of a numerical system, means for producing an error signal corresponding to the variation of voltage across said load circuit from a predetermined value, and means responsive to said error signal for actively associating with said source and said load circuit those of said auxiliary sources corresponding to said error signal in said numerical system, in which said auxiliary sources of voltages comprise transformers having their secondary windings connected in series with each other between said source and said load circuit and having their primary windings normally short-circuited and in which the means responsive to said error signal includes switching means associated with each of said transformers for opening the short-circuit connections of the selected primary windings and for connecting said selected primary windings to receive current from said source.

3. A voltage regulator comprising an alternating current source of supply, a load circuit, a plurality of transformers adapted to be energized from said source of supply to produce across their secondary windings voltages lower than that required across said load circuit and related to each other in accordance with the denominational orders of a binary numerical system, a circuit interconnecting said source of supply and said load and including said secondary windings for supplementing the voltage from said source in maintaining the voltage supplied to said load at a predetermined value, means for producing a quantized error signal proportional to the departure of the voltage across said load from said predetermined value, and means responsive to said error signal for rendering operative those of said secondary windings required to restore the voltage across said load to substantially said predetermined value.

4. A voltage regulator comprising an alternating current source of supply, a load circuit, a plurality of transformers adapted to be energized from said source of supply to produce across their secondary windings voltages lower than a predetermined value required across said load circuit and related to each other in accordance with the denominational orders of a binary numerical system, means for periodically producing a train of pulses of number proportional to the departure of the voltage across said load from said predetermined value, a multistage binary counter, connections for supplying said train of pulses to said counter, and switching means controlled by each stage of said counter for operatively associating the respective ones of said secondary windings with said load circuit to restore the voltage across said load circuit to substantially said predetermined value.

5. A voltage regulator for associating with a source of voltage and a load circuit comprising a plurality of transformers adapted to be energized from said source of supply and producing voltages differing from each other and related by the respective denominational orders of a binary numerical system, switching means for each of said transformers for associating the primary winding with said source of supply so that the voltage across the secondary winding supplements the voltage from said source in maintaining the voltage supplied to said load circuit at a predetermined value, means for periodically producing a train of pulses of number proportional to the departure of the voltage across said load from said predetermined value, means for producing a controlsignal determined by the direction of departure of the voltage across said load from said predetermined value, a reversible multistage binary counter means for controlling the direction of operation of said counter in response to said signal, connections for supplying said train of pulses to said counter for operating the same, and means interconnecting each stage of said counter with the switching means associated with the respective transformers for controlling the operation thereof.

6. A voltage regulator in accordance with claim 5 including means responsive to a train of pulses of number beyond the capacity of said counter for maintaining the counter in its maximum or minimum condition depending upon the direction of counting.

7. A voltage regulator comprising an alternating current source of supply, a load circuit, a plurality of transformers each having a primary winding and a secondary winding, said transformers being so proportioned that the voltages produced across their secondary windings are related to each other in proportion to the powers of 2, said secondary windings being connected in series with each other to supplement the voltage supplied from said source to said load, switching means associated with each primary winding for alternatively short-circuiting the winding or connecting it to receive current from said source, means for periodically producing an error voltage proportional to the departure of the voltage across said load from a predetermined value, means responsive to said error voltage for producing a train of pulses of number proportional to said error voltage, a multistage binary counter, means responsive to each stage of said counter for controlling the switching means associated with that one of said secondary windings producing a voltage proportional to the respective denominational order of the counter stage, and means for supplying said train of pulses to said counter for the operation thereof.

8. A voltage regulator comprising an alternating current source of supply, a load circuit, a plurality of transformers each having a primary winding and a secondary winding, said transformers being so proportioned that the voltages produced across their secondary windings are related to each other in proportion to the powers of 2, said secondary windings being connected in series with each other to supplement the voltage supplied from said source to said load, switching means associated with each primary winding for alternatively short-circuiting at the Winding or connecting it to receive current from said source, means for producing an error voltage of absolute magnitude proportional to departure of the voltage across said load from a predetermined value and of sign dependent upon the direction of such departure, means for periodically producing a train of pulses proportional to the absolute value of said error voltage, a reversible multistage binary counter, means for controlling the direction of counting of said counter in accordance with the sign of said error voltage, means for applying said train of pulses to said counter for the operation thereof, and means responsive to the condition of the respective stages of said counter at the end of said count for controlling the switching means associated with that one of said secondary windings producing a voltage of value corresponding to the respective denominational order of the counter stage.

9. A regulator according to claim 8 including means responsive to a train of pulses of number greater than the capacity of said counter for maintaining said counter in the maximum or minimum position depending upon the direction of counting.

References Cited in the file of this patent UNITED STATES PATENTS 2,857,565 Sealey Oct. 21, 1958 2,884,587 Hanthorn Apr. 28, 1959 2,916,734 Spencer Dec. 8, 1959

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