US2740936A

US2740936A - Voltage stabilizer and reference circuit therefor

Info

Publication number: US2740936A
Application number: US401314A
Authority: US
Inventors: Ray E Anderson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1953-12-30
Filing date: 1953-12-30
Publication date: 1956-04-03
Anticipated expiration: 1973-04-03
Also published as: GB791236A; JPS313591B1

Description

April 3, 1956 R. E. ANDERSON 2,740,936

VOLTAGE STABILIZER AND REFERENCE CIRCUIT THEREFOR Filed Dec. 30, 1953 Ihven tor: Ray E. An derson,

y His Attorney.

United States Patent'O VOLTAGE STABILIZER AND REFERENCE CIRCUIT THEREFOR Ray E. Anderson, 'Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application December 30, 1953, Serial No. 401,314

19 Claims. (Cl. 323-66) This invention relates to voltage stabilizing systems and to thereference circuits for such systems, and more particularly to an alternating-current voltage stabilizer utilizing a bridge-type reference circuit.

There are many applications which require an alterhating-current voltage more stable than the available line voltage. In the past, many alternating-current voltage stabilizing systems have been devised, these systems generally using a reference circuit and adjusting the output voltage in response to deviations of the input voltage from the ref ence value. Bridge circuits have been used for the refererence, however, such circuits have been severely affected by temperature changes and drift caused primarily by theme of rectifiers for. demodulation in the direct path of the reference signal and the random drift of directcurrent devices such as glow tubes.

It is desirable that magnetic amplifiers be utilized in voltage stabilizing systems since they are much more sturdy than vacuum tube amplifiers. The use of magnetic amplifiers however, requires that a low frequency or direct-current control signal be provided by the reference circuit. Furthermore, since an alternating current input and output is involved, it is necessary that the reference circuit detect deviations in the input voltage from the preselected desired value and convert these deviationsinto a direct-current signal suitable for controlling a magnetic amplifier. It is further. desirable that the system not be effected by ambient temperature changes and that reference drift be held to a minimum. It is also desirable that rectifiers be eliminated from the direct path of the reference signal in closed loop feedback systems and that the system be capable of operation over a wide frequency range.

It is therefore an object of this invention to provide an improved voltage stabilizing system incorporating the desirable features set forth above.

Another object of this invention is to provide an improved reference circuit incorporating the desirable features set forth above.

Further objects and advantages of this invention will become apparent and the invention will be better understood by reference to the following description and the accompanying drawing; and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this'specification.

This invention in its broadest aspects provides a bridgetype reference circuit utilizing both fixed linear and nonlinear impedance elements. This bridge circuit has two fixed linear impedance legs and two non-linear impedance legs with a voltage proportional to the input voltage being applied to the bridge to cause circulating current therein and another voltage derived from an independent circuit also being applied to the bridge. Since the impedance of the non-linear legs is a function of the value of the circulating current, the balance or unbalance of the bridge is dependent upon the applied voltage. The other voltage applied to the'bridge provides an output during bridge 2 F unbalance, with a magnitude substantially proportional to the deviation. This output signal can therefore be utilized to control a magnetic amplifier which in turn provides the stabilized output voltage.- Thus, the sensing, comparing, reference-and demodulating functions are all performed by this static network.

In the drawing:

Fig. 1 is a schematic illustration of an improved closed loop feedback alternating-current voltage stabilizing system according to this invention incorporating my improved reference circuit; and

Fig. 2 is a schematic illustration of a modified form of the reference circuit.

Referring now to Fig. 1, the alternating-current voltage to be stabilized is applied across input terminals 1 and 2, terminal 2 being connected to a common bus 3 to which one output terminal 4 is connected. Another output terminal 5 is provided with the autotransformer 6 being connected across output terminals 4 and 5.

Reference circuit 16 is of the bridge type with nonlinear resistance elements 11 being arranged in two opposite legs and with fixed linear resistance elements 1 2 being arranged in the-other two opposite legs. Non-linear resistance elements 11 may be conventional tungsten filament lamps known for their non-linear current characteristic and linear resistance elements 12 may be high quality resistors formed of material such as Nichrome or constantan. Transformers 13 are provided with their-secondary windings 14 respectively connected in series with linear resistance elements 12 and with their primary windings 15 connected in parallel across the output terminals 4 and'S. it will now be seen that a value of an alternatingcurrent voltage proportional to the voltage across output terminals 4 and 5 is applied to the fixed linear legs of the bridge of reference circuit 10, thus causing circulating current to flow in the entire bridge circuit.

In order to supply a direct-current voltage for the bridge reference circuit 10 so that a direct-current output may be provided thereby, a bridge rectifier circuit 17 has its output connected to opposite corners 18 of bridge reference circuit 10. A variable resistance 19,-potentiometer 20 and resistance 21 are connected in series with the sliding element 23 of variable resistance 19 being connected to the autotransformer tap 8 in the output circuit and the extreme end of resistance 21 beingconnected to output terminal 4. It is thus apparent that the voltage across the resistance

circuit including resistances

19, 20 and 21 is proportional to the output voltage across terminals 4 and 5. The input to rectifier 17 is taken across sliding element 24 of potentiometer 20 and the common bus 3. It is thus seen that a small, constant direct-current voltage is applied to opposite corners 18 of bridge reference circuit 10. The other two opposite corners 25 constitute the output terminals of the bridge reference circuit 10 and are connected to control windings of the magnetic amplifiers of the closed-loop feedback voltage stabilizer system which will be hereinafter described.

It will now be seen that the voltage. rises and drops caused by the circulating alternating-current in the bridge reference circuit 10 completely cancel in the bridge and act to adjust the resistances of thenon-linear resistance elements 11, the resistances of these elementsbeing dependent upon the current flow therethrough, which in turn depends upon the voltages'applied by the transformers 13. It is thus seen that. the reference bridge circuit 10 can be balanced by means of resistors 12 so that no directcurrent voltage appears across output terminals 25 at a desired reference voltage. Under these conditions, the alternating-current voltage applied by transformers 13 will result in the resistance of non-linear resistance elements 11 being such that thebridge is completely balanced.

Nowassuming that the'output voltage across theoutput terminals 4 and 5 of the voltage stabilizing system tends to increase thus producing a proportional increase in the voltage applied by transformers 13. This will result in a corresponding increase in the circulating alternating-current in the reference bridge circuit thus producing a corresponding change in the resistance of non-linear elements 11. This causes the bridge to be unbalanced and produces a direct-current voltage across output terminals with a polarity des termined by the polarity of the voltage applied across corners 18 by the rectifier circuit 17. As the voltage across output terminals 4 and 5 tends to deviate further in the same direction, the direct-current voltage appearing across output terminals 25 of bridge circuit 10 will show a further increase.

Assuming that the voltage across output terminals 4 and 5 decreased from the selected value, the voltage applied to the reference bridge circuit by the transformers 13 would decrease thus causing the circulating alternat ing-current in the reference bridge circuit 10 to decrease and a resultant change in the opposite direction in the resistance of non-linear resistance elements It. This again unbalances the bridge producing a direct-current voltage across output terminals 25 with the polarity now being reversed from that existing when the output voltage across output terminals 4 and 5 was above the preselected value. It is thus seen that the direct-current voltage across output terminals 25 of bridge reference 10 is a direct-current voltage substantially proportional to the deviation of the alternating-current output voltage across output terminals 4 and 5 from the preselected value with the polarity being dependent upon the direction of the deviation from the pre-selected value. Thus, it is seen that this bridge circuit acts as a demodulator as well as a reference.

In order to correct the deviation in output voltage across terminals 4 and 5, output terminals 25 of the bridge reference circuit 10 are connected to the directcurrent control windings 26 and 27 of push-pull

magnetic amplifiers

28 and 29. The power windings 30 and 31 of magnetic amplifier 28 are respectively connected between bus 3 and bridge rectifier 32 and

power windings

33 and 34 of magnetic amplifier 29 are respectively connected between bus 3 and bridge rectifier 35. Bridge rectifiers 32 and 35 are connected for energization from the output voltage across output terminals 4 and 5 by

conductors

36 and 37; and their

opposite corners

38 and 39, and 4t) and 41, are respectively connected to direct current control windings 42 and 43 of output magnetic amplifier 44.- Power windings 45 and 46 of output magnetic amplifier 44 are connected between input terminal 1 and a tap 7 on the autotransformer 6 in the output circuit with rectifiers 58 and 49 being respectively interposed in series therewith. Resistor 56 is placed to protect rectifiers 48 and 49 during transient conditions.

It will now be seen that a direct-current signal of a given polarity appearing across output terminals 25 of bridge reference circuit 10 is applied to control windings 26 and 27 of a push-pull magnetic amplifier 2-8 and 29. This direct current signal will therefore tend to saturate the cores of the

magnetic amplifiers

28 and 29 respectively in a given direction thus increasing or decreasing, dependent upon the polarity of the signal across output terminals 25 of reference bridge circuit 10, the current flowing in control windings 42 and 43 of output magnetic amplifier 44. This of course through the power windings 45 and 46 controls the voltage applied across the output circuit and the output terminals 4 and 5.

It is now seen that this improved circuit provides an alternating-current voltage stabilizing system which can detect on the basis of the R. M. S. value of the alternating current voltage to be controlled; which provides a direct-current signal for controlling the magnetic amplifiers; and which does not have any rectifiers-in the direct path of the reference signal. It will also be apparent that the reference circuit is not subject to changes in ambient temperature since such changes will have a uniform effect upon the bridge reference circuit and will not cause unbalance, and it will also be readily apparent that the device is capable of operation over a relatively wide range of input frequency.

'It will be readily understood that a single transformer having one primary winding and two secondary windings may be utilized instead of the two transformers 13 of Fig. 1. It will also be readily understood that impedances other than resistances may be used for the fixed linear and non-linear legs of bridge reference circuit 10.

Referring now to Fig. 2, there is shown an alternative form of reference circuit utilizing a filter network for impressing an alternating-current voltage upon the bridge rather than the transformers 13 of Fig. 1. Here, nonlinear resistance elements 11 again form two opposite legs of the bridge and linear resistance elements 50 form the other two opposite legs of the bridge. The direct-current input to the bridge is applied to opposite corners 18 and the output is taken from the other two opposite corners 25. Here, serially connected filter capacitors 51 and 52 are connected across correspond ing ends of the non-linear resistance elements 11 while another pair of serially connected filter capacitors 53 and 54 are connected across the other two corresponding ends of the nonlinear resistance elements 11. The alternating-current voltage is applied to terminals 55 connected respectively between the mid points between the

capacitors

51 and 52, and 53 and 54 respectively. It may be found that the filter network means of introducing the alternating current to the reference bridge circuit shown in Fig. 2 is more desirable if higher frequencies are used.

It will be readily apparent that the reference circuit 10 to Fig. 1 or the reference circuit of Fig. 2 may be used independently of the voltage stabilizer system of Fig. 1 in any application where a direct-current reference or modulated frequency signal is desired. Also it will be readily apparent that an alternating-current signal may be applied across the corners 18 of the bridge reference circuit to obtain an alternating current output.

While I have described particular embodiments of this invention, further modifications and improvements will occur to those skilled in the art. I desire it to be understood therefore that this invention is not limited to the form shown and I intend in the appended claims to cover all modifications which do not depart from the. spirit and scope of this invention.

I claim:

1. A reference circuit for supplying a signal proportional to the deviation of an alternating-current voltage from a preselected value comprising a bridge circuit having non-linear impedance elements in a pair of opposite legs and fixed linear impedance elements in the other pair of opposite legs, connections for impressing a voltage on two opposite corners of said bridge circuit, output terminals connected to the other two opposite corners of said bridge circuit, and means for impressing said alternating-current voltage respectively on one of said pair of opposite legs of said bridge circuit thereby producing circulating alternating-current therein, said bridge circuit being balanced at said preselected alternating-current voltage value with the impedance of said non-linear impedance elements varying in response to variations in said alternating-current voltage thereby producing a voltage across output terminals substantially proportional to the deviation in the said alternating current voltage from preselected value.

2. A reference'circuit for supplying a signal proportional to and indicativeof the deviation of analternating-current voltage from a preselected value comprising a bridge circuit having non-linear impedance elements in a pair of opposite legs and fixed linear impedance elements in the other two opposite legs, connections for impressing a direct-current voltage on two opposite corners of said bridge circuit, output terminals connected to the other two opposite corners of said bridge circuit, and means for impressing said alternating-current voltage respectively on one of said pair of opposite legs of direction of said deviation.

3. A reference circuit for supplying a signal proportional to and indicative of the deviation of an alternating-current voltage from a preselected value comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, connections for impressing a direct-current voltage derived from said alternating-current voltage on two opposite corners of said bridge circuit, output terminals connected to the other two op posite corners of said bridge circuit, and means for impressing said alternating-current voltage on said other two opposite legs of said bridge circuit thereby producing circulating alternating-current therein, said bridge circuit being balanced at said preselected alternating-current voltage value with the resistance of said non-linear resistance elements varying in response to variations in said alternating-current voltage thereby producing a directcurrent voltage across said output terminals substantially proportional to the deviation of the said alternating-current voltage from said preselected value and polarized to indicate the direction of said deviation.

4. A reference circuit for supplying a signal proportional to and indicative of the deviation of an alternatingcurrent voltage from a preselected value comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, a rectifier having its input adapted to be connected for energization from said alternating-current voltage and having its output connected across two opposite corners of said bridge circuit, output terminals connected to the other two opposite corners of said bridge circuit, and means for impressing said alternating-current voltage on said other two opposite legs of said bridge circuit thereby producing circulating alternating-current therein, said bridge circuit being balanced at said preselected alternating-current voltage value with the resistance of said non-linear resistance elements varying in response to variations in said alternating-current voltage thereby producing a direct-current voltage across said output terminals substantially proportional to the deviation of said alternating-current voltage from said preselected value and polarized to indicate the direction of said deviation.

5. A reference circuit for supplying a signal proportional to the deviation of an alternating-current voltage from a preselected value comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, connections for impressing voltage on two opposite corners of said bridge circuit, output terminals connected to the other two opposite corners of said bridge circuit, and transformer means having secondary Windings in each of said other two opposite legs and adapted to be energized from said alternating-current voltage for impressing said alternating-current voltage on said other two opposite legs of said bridge circuit thereby producing circulating alternating-current therein, said bridge circuit being balanced at said preselected alternating-current voltage value with the resistances of said non-linear resistance elements varying in response to variations in 6 said alternating-current voltage thereby producing a'voltage across said output terminals substantially proportional to the deviations of said alternating-current voltage from said preselected value.

6. A reference circuit for supplying a signal proportional to and indicative of-the deviation ofan alternatingcurrent voltage from a preselected value comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, connections for impressing a direct-current voltage derived from said alternating-current voltage on two opposite corners of said bridge circuit, output terminals connected'to the other two output terminals of said bridge circuit, and transformer means having secondary windings ineach of said other two opposite legs and adapted to be energized from said alternating-current voltage for impressing said alternatingcurrent voltage on said other two opposite legs of said bridge circuit thereby producing circulating alternatingcurrent therein, said bridge circuit being balanced at said preselected alternating-current voltage value with the resistances of said non-linear resistance elements varying in response to variations in said alternating-current voltage thereby producing a direct-current voltage across said output terminals substantially proportional to the deviations of said alternating-current voltage from said preselected value and polarized to indicate the direction of said deviation.

7. A reference circuit for supplying a signal proportional to the deviation of an alternating-current voltage from a preselectedvalue comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, connections for impressing a voltage on two opposite corners of said bridge circuit, output terminals connected to the other two opposite corners of saidbridge circuit, and filter networks adapted to impress said alternating-current voltage across said non-linear resistance elements thereby producingalternating-current in said bridge circuit, said bridge circuit being balanced at said I preselected alternating-current voltage value with the resistances of said non-linear resistance elements varying in -response to variations in said alternating-current voltage thereby producing a voltage across said output terminals substantially proportional to the-deviation of said alter nating-current voltage from said preselected value.

8. A reference circuit for supplying a signal proportional to and indicative of the deviation of an alternatingcurrent voltage from a preselected value comprising a bridge circuit'having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, connections for impressing a direct-current voltage derived from said alternating-current voltage on two opposite corners of said bridge circuit, output terminals connected to the other two opposite corners of said bridge circuit, and filter networks adapted to impress said alternating-current voltage across said non-linear resistance elements thereby producing alternating-current in said bridge circuit, said bridge circuit being balanced at said preselected alternating-current voltage value with the resistances of said non-linear resistance elements varying in response to variations in said alternating-current voltage thereby producing a directcurrent voltage across said output terminals substantially proportional to the deviation of said alternating-current voltage from said preselected value and polarized to indicate the direction of said deviation.

9. A reference circuit for supplying a signal proportional to and indicative of the deviation of an alternatingcurrent voltage from a preselected value comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance, elements in'the other two opposite legs, connections for impressing .a direct-currentvoltage derived from said alternating-current voltage on two opposite corners of said bridge circuit, outavenues put terminals connected to the other two opposite corners of said bridge circuit, and filter capacitor respectively having one side connected to the ends of said non-linear resistance elements adapted to have their opposite ends connected to said alternating-current voltage for impressing said alternating-current voltage acrosssaid nonlinear resistance elements thereby producing alternatingcurrent in said bridge circuit, said bridge circuit being balanced at said preselected alternating-current voltage value with the resistances of said non-linear resistance elements varying in response to variations in said alter hating-current voltage thereby producing a direct-current voltage across said output terminals substantially proportional to the deviation of said alternating-current voltage from said preselected value and polarized to indicate the direction of said deviation.

10. A closed loop feedback alternating-current voltage stabilizer system comprising a bridge circuit having non-linear impedance elements in two opposite legs and fixed linear impedance elements in the other two opposite legs, an output circuit, an amplifier having its output connected to energize said output circuit, its two opposite corners of said bridge circuit being adapted to be connected to a source of voltage, the other two opposite corners of said bridge circuit being connected to the control element of said amplifier, and means for impressing a voltage taken from said output circuit on said other two opposite legs of said bridge circuit thereby producing circulating alternating-current therein, said bridge circuit being balanced at a preselected alternating current output voltage value with the impedance of said non-linear impedance elements varying in response to variations of said alternating-current output voltage thereby producing a voltage across said amplifier control element substantially proportional to the deviation of said alternating-current output voltage from said preselected value.

11. A closed loop feedback alternating-current voltage stabilizer system comprising a bridge circuit having non-linear impedance elements in two opposite legs and fixed linear impedance elements in the other two opposite legs, an output circuit, an amplifier having its output connected to energize said output circuit, a rectifier hav' ing its input connected for energization from said output circuit and having its output connected across two opposite corners of said bridge circuit, the other two opposite corners of said bridge circuit being connected to the control element of said amplifier, and means for impressing a voltage taken from said output circuit on said other two opposite legs of said bridge circuit thereby producing circulating alternating-current therein, said bridge circuit being balanced at a preselected alternating-current output voltage value with the impedance of said non-linear impedance elements varying in response to variations of said alternating-current output voltage thereby producing a direct-current voltage across said amplifier control element substantially proportional to the deviation of said alternating-current output voltage from said preselected value and polarized to indicate the direction of said deviation.

12. A closed loop feedback alternating-current voltage stabilizer system comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, an output circuit, an amplifier having its output connected to energize said output circuit, a rectifier having its input connected for energization from said output circuit and having its output connected across two opposite corners of said bridge circuit, the other two opposite corners of said bridge circuit being connected to the control element of said amplifier, and transformer means having secondary windings in each of said other two opposite legs and being connected for energization from said output circuit for impressing said ,alternatingcurrent output voltage on'said other two opposite legs of said bridge circuit thereby producing circulating alternatingcurrent therein, said bridge circuit being balanced at a preselected alternating-current output voltage value with the resistance of said non-linear resistance elements varying in response to variations in said alternating-current output voltage thereby producing a direct-current voltage across said amplifier control element substantially proportional to the deviation of said alternating-current output voltage from preselected value and polarized to indicate the direction of said deviation.

1?).- A closed-loop feedback alternating-current voltage stabilizer system comprising a bridge circuit having non linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, an output circuit, an amplifier having its output connected to energize said output circuit, two opposite corners of said bridge circuit being adapted to be connected to a source of voltage, the other two opposite corners of said bridge circuit being connected to the control element of said amplifier, and filter networks impressing a voltage taken from said output circuit across said non-linear resistance elements thereby producing alternating-current in said bridge circuit, said bridge circuit being balanced at a preselected alternating-current output voltage value with the resistance of said non-linear resistance elements varying in response to variations in said alternating-current output voltage thereby producing voltage across said amplifier control element substantially proportional to the deviation of said alternatingcurrent output voltage from said preselected value.

14.- A closed-loop feedback alternating-current voltage stabilizer system comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, an output circuit, an amplifier having its output connected to energize said output circuit, a rectifier having its input connected for energization from said output circuit and having its output connected across two opposite corners of said bridge circuit, the other two opposite corners of said bridge circuit being connected to the control element of said amplifier, and filter networks impressing a voltage taken from said output circuit across said non-linear resistance elements thereby producing alternating-current in said bridge circuit, said bridge circuit being balanced at a preselected alternating-current output voltage value with the resistance of said non-linear resistance elements varying in response to variations in said alternating-current output voltage thereby producing a direct-current voltage across said amplifier control element substantially proportional to the deviation of said alternating-current output voltage from said preselected value and polarized to indicate the direction of said deviation.

15. A closed-loop feedback alternating-current voltage stabilizing system comprising a bridge circuit having nonlinear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, an output circuit, an amplifier having its output connected to energize said output circuit, a rectifier having its input connected for energization from said output circuit having its output connected across two opposite corners of said bridge circuit, the other two opposite corners of said bridge circuit being connected with control elements of said amplifier, and filter capacitors respectively having one side connected to one end of said non-linear resistance elements and having their other ends connected to said output circuit for impressing a voltage from said output circuit across said non-linear resistance eiements thereby producing alternating-current in said bridge circuit, said bridge circuit being balanced at a preselected alternating-current output voltage value with the resist ance of said non-linear resistance elements varying in response to variations in the said alternating-current output voltage thereby producing a direct-current voltage across said amplifier control element substantially proportional to the deviation of said alternating-current output voltage from said preselected value and polarized to indicate the direction of said deviation.

16. A closed-loop feedback alternating-current voltage stabilizing system comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, an output circuit, a magnetic amplifier having its output connected to energize said output circuit, a rectifier having its input connected for energization from said output circuit and having its output connected across two opposite corners of said bridge circuit, the other two opposite corners of said bridge circuit being connected to energize the control element of said magnetic amplifier, and means for impressing a voltage taken from said output circuit on said two other opposite legs of said bridge circuit, said bridge circuit being balanced at a preselected alternating-current output voltage value with the resistance of said non-linear resistance elements varying in response to variations in said alternating-current output voltage thereby producing a direct-current voltage across said magnetic amplifier control element substantially proportional to the deviation of said alternating-current output voltage from said preselected value and polarized to indicate the direction of said deviation.

17. A closed-loop feedback alternating-current voltage stabilizing system comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, an output circuit, a magnetic amplifier having its output connected to energize said output circuit, a rectifier having its input connected for energization from said output circuit and having its output connected across two opposite corners of said bridge circuit, the other two opposite corners of said bridge circuit being connected to energize the control element of said magnetic amplifier, and transformer means having secondary windings in each of said other two opposite legs of said bridge circuit and being connected for energizetion from said output circuit for impressing said alternating-current voltage on said other two opposite legs of said bridge circuit, said bridge circuit being balanced at a preselected alternating-current output voltage value with the resistance of said non-linear resistance elements varying in response to variations in said alterhating-current output voltage thereby producing a directcurrent voltage across said magnetic amplifier control element substantially proportional to the deviation of said alternating-current output voltage from said preselected value and polarized to indicate the direction of said deviation.

18. A reference circuit for supplying a signal proportional to the deviation of an alternating-current voltage from a preselected value comprising a bridge circuit having non-linear resistance elements in two opposite legs and fixed linear resistance elements in the other two opposite legs, connections for impressing a voltage on two opposite corners of said bridge circuit, output terminals connected to the other two opposite corners of said bridge circuit, and means for impressing said alternating-current voltage on said other two legs of said bridge circuit thereby producing circulating alternating current therein, said bridge circuit being balanced at said preselected alternating-current voltage value with the resistance of said nonlinear resistance elements varying in response to variations in said alternating-current voltage thereby producing a voltage across said output terminals substantially proportional to the deviation of said alternating-current voltage from preselected value.

19. A closed-loop feedback alternating-current voltage stabilizing system comprising a bridge circuit having nonlinear resistance elements in two opposite legs and linear resistance elements in the other two opposite legs, an out put circuit, a magnetic amplifier having its output connected to energize said output circuit, a rectifier having its input connected for energization from said output circuit having its output connected across two opposite corners of said bridge circuit, the other two opposite corners of said bridge circuit being connected to a control winding of a saturable core reactor, said saturable core reactor being connected for energization from said output circuit and having its output connected to a control winding of said magnetic amplifier, and means for impressing a voltage taken from said output circuit on said two other opposite legs of said bridge circuit thereby producing circulating alternating-current therein, said bridge circuit being balanced at a preselected alternating-current voltage output value With the resistance of said non-linear resistance elements varying in response to variations in said alternating-current output voltage thereby producing a direct-current voltage across said magnetic amplifier control winding substantially proportional to the deviation of said alternating-current output voltage from said preselected value and polarized to indicate the direction of said deviation.

References Cited in the file of this patent UNITED STATES PATENTS