US2690535A - Voltage regulator - Google Patents

Description

Sept- 28, 1954 'r. DOUMA ETAL VOLTAGE REGULATOR 2 Sheets-Sheet 1 Filed May 10, 1952 1:IE E

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Sept. 28, 1954 I T DOUMA ETAL 2,690,535

VOLTAGE REGULATOR Filed May 10, 1952 2 Sheets-Sheet 2 FIIS L FIIEI E| 0 80 9a 100 I50 E0 [40 EL (Va/1 5) 40 INVENTORSI 7j/sA epauma BY Faber/h. l/l a/san ATTORNEYS Patented Sept. 28, 1954 VOLTAGE REGULATOR 'lijiske Douma, San Carlos, and Robert H. Watson, Sunnyvale, Calif., assignors to Sierra Electronic Corporation, San Carlos, Calif, a corporation of California Application May 10, 1952, Serial No. 287,086

Claims.

This invention relates generally to voltage regulators and particularly to electronic voltage regulators for correcting variations in the voltage of an alternating voltage source.

It is an object of this invention to provide a simple electronic A. C. voltage regulator capable of rapidlycorrecting large deviations from the desired voltage and which is compact and light in weight.

It is a further object of this invention to provide a voltage regulator of the foregoing type which is also capable of operating at any frequency over a wide range of frequencies and which is unaffected by rapid variations in the frequency of the source of unregulated voltage.

Other objects of this invention will be better understood from the following description considered in connection with the accompanying drawings:

Figure 1 is a schematic drawing of the basic circuit of the invention.

Figure 2 is a schematic drawing of a circuit equivalent to the circuit of Figure l for purposes of A. C. analysis;

Figure 3 is a plot of the r. m. s. grid voltage of the vacuum tube of Figure 1 as a function of line voltage.

Figure i is a schematic diagram of a modified circuit of the invention including means for changing the stabilized voltage of the regulator.

Figure 5 is a plot of several r. m. s. voltages occurring in the circuit of Figure 4 as a function of line voltage.

Referring to Figure 1, a source of unregulated A. C. voltage II] is shown having one side connected to lead I I and the other to lead I2. Lead II is connected to one side of load resistor I3 which in turn has its other side connected to lead I4. The output winding of transformer I5 is connected in series with resistor I3 between leads I2 and I 4. A bridge comprising resistors I6 and I1 and incandescent lamps I8 and I9 is connected in shunt across source I0, one side of lamp I9 and resistor I6 being connected to lead I I and their other sides being connected to leads in and 2I, respectively. Lamp I8 and resistor I! each have one side connected to lead I2 and their other sides connected to the conductors and 2|, respectively, which are the bridge output leads. The output leads 20 and 2| of the bridge are connected to the input of transformer 22, which supplies amplifier 23, and has one side of its output connected to the negative side of bias supply 24, indicated for convenience as a battery. The other side of the output of transformer 22 is connected to the control grid of vacuum tube 25. The positive terminal of the bias supply and the cathode of tube. 25 are connected to ground. The plate of tube 25 is connected to one side of the input of transformer I5 which has its other side connected to the positive terminal of D. C. voltage source 26, indicated for convenience in Figure l as a battery. The negative side of D. C. voltage source 26 is connected to ground.

The operation of the circuit of Figure l to provide a constant voltage across the load resistor it may be explained as follows: The bridge circuit comprising resistors I6 and I1 and lamps I8 and It produces an A. C. output voltage on leads 2% and 2| which is proportional to the deviation in A. C. voltage of the source It) from a specified voltage at which the bridge is in balance. Each of the lamps I8 and I 9 has a resistance which increases with increasing voltage across it since its resistance increases with increase in temperature, and the temperature is determined by the current through the lamp and hence by the voltage across the lamp. The bridge output voltage is supplied to the amplifier 23 through transformer 22 which is usually a step up transformer. The amplifier 23 then supplies an alternating current to the transformer I5 in series with the load resistor I4. The relative phases of the voltages, the rate of change of bridge output voltage with line voltage, and the tube characteristics may be chosen to provide an alternating current through the transformer I5 of the correct magnitude and phase to exactly compensate for any changes in the voltage from the source of unregulated voltage Ifi. It is to be noted that this regulator does not compensate for changes in the load resistance I3; it is not a servomechanism as are many types of voltage regulators. Although incandescent lamps are indicated in Figure 1, other resistive elements having non-ohmic resistances could as well be used. All that is important is that the resistance of some bridge element should vary with the applied voltage as some continuous function of voltage, such that the change in resistance is in some way proportional to the change in voltage over the desired operating range. In a lamp the resistance increases as voltage is increased, but the bridge works equally well with a non-ohmic resistor which decreases in resistance as voltage increases. Incandescent lamps are simple, readily available, and work satisfactorily, and are therefore indicated in the drawings as the preferred type of non-ohmic bridge resistors.

The details of the operation of the circuit of the invention shown in Figure i may be most simply explained by reference to Figure 2. In Figure 2 the source of unregulated A. C. voltage it! is shown with one side connected. to lead El and the other to lead 12. Resistor 21 is connected in shunt with source it! and represents the equivalent resistance of the bridge of Figure 1 comprising lamps i3 and i9 and resistors l6 and. il. Resistor 28 and voltage generator 29 are connected in series between leads [2 and it, and represent the effects of the amplifier 23 of Figure l as reflected into the main circuit by transformer 15 of Figure 1. Load resistor i3 is connected between leads H and is. The usual symbolic notation for each element of Figure 2 accompanies the numeral notation referred to above, i. e. the value of the voltage of source i8 is E, the value of resistor 2'! is Rp/n etc. The derivation of this equivalent circuit is made in the usual manner, employing the equivalent plate circuit representation of the tube 25 of Figure 1. Transformer is considered an ideal transformer with turns ratio lzn, as indicated in Figure 1, hence the value of each impedance in the plate circuit of Figure 1 must be divided by n and the value of the voltage of equivalent constant voltage generator 2% must be divided by r. in order to properly insert these elements directly into the main line, as shown in Figure 2. The only important impedances appearing in the plate circuit of tube 23 of Figure l are plate resistance R and the internal impedance of he D. C. voltage source 26. The impedance of the D. C. source may be neglected because usual practical sources provide a low impedance path to ground for A. C. The value of the voltage of eou valent voltage generator is -,LL Eg, where t is me amplification factor of tube 25 and Eg is the A. C. voltage appearing between grid and cathode of tube 25. The minus sign preceding the equivalent generator voltage indicates that reversed in phase from By. The resistance not a constant, but depends on the applied 1t Rh 1 voltage, since the resistance of lamps ES and i9 increases as the voltage across them is increased. The value of load resistor i3, BL, is considered constant.

The value of E9 is determined by the sensitivity of the bridge circuit of Figure l and the turns ratio of transformer 22. For a typical experimental case, the variation of E9 with El followed the strai ht line variation indicated in Figu 3. As indicated in Figure 3, for the range of shown, was accurately given by the equation:

Eg=l.67(Ei-109.5)

Here negative values simply indicate a reversal in phase of the A. C. voltage, positive values corresponding to an Eg having the same phase as Ei.

One further simplification can be made in the circuit of Figure 2. Although the bridge resistance Rb is a function of E1, it is not important that this variation be known. In fact variations in El) may be neglected entirely for present poses, since what is being considered is a ng source of voltage E1. It is, of course, desirable that Rb should be large in comparison with the sum or" R1. and R /n so that most of the pow is delivered to BL and not wasted in the bridge; this requirement can normally be met quite easily.

Now, neglecting Rb, the load current IL in the circuit of Figure 2 will be given by the following equation, the voltage being out of phase with El for positive El according to our sign convention:

Substituting the equation for Eg from Figure 3 in the above equation and solving for It:

For IL to be independent of E1:

Then the voltage across the load, V1,, is:

RL Ri+ Thus the load voltage is independent oi the un regulated voltage, E1, as desired, over the range of voltages for which a is constant and the output of the bridge follows a linear variation as indicated in Figure 3. To the extent that transformers l5 and 22 can be made to approximate ideal transformers, the load voltage is independent of frequency. An entirely satisfactory approximation to ideal behavior can be obtained, for example, from 300 to 500 cycles, so that the elf-eta of the transformer induotances are negligible with respect to other variations over this range of frequencies. This characteristic of the circuit of the invention is of great importance in installations such as aircraft where the source of unregulated A. C. voltage cannot conveniently be designed to maintain precise frequency under varying loads. A further advantage of this circuit over customary methods of regulation employing capacity and saturated iron is the marked reduction in size and weight which is possible.

It should be noted that the regulator disclosed in Figure 1 is limited first to alternating current regulation and second to applications where substantial changes in the load impedance are not contemplated. For example, if the regulator is used to supply filament power to the tubes of some electronic device, a readjustment of the regulator might be required if the tubes were changed and precisely the same filament voltage was desired. For many applications, the additional circuitry required to compensate for changes in load is wasteful, and in such applications the circuit of Figure 1 provides a simple and economical means of regulating an A. C. voltage.

It is, however, often important to be able to adjust the circuit to allow for changes in load or changes in the bridge output characteristic resulting from changing the lamps in the bridge arms. Both types of change correspond to a shift in the line or unregulated voltage for zero bridge output with relation to the range of line voltages over which regulation is required. For example, after a change in bridge lamps it may be found that the line voltage for zero bridge output is changed from 109.5 volts to volts. Now if a 109.5 volt value for E1 is required with the given tube ,u, transformer turns ratios, and load, to give the desired load current, some techiiique is required to permit a convenient readjustment of the value of E1 for zerobridge output. Similarly, if the load resistance is changed, the load current will change and some technique is required to permit an appropriate increase or decrease in the stabflized load voltage. First, it is quite feasible to correct for such changes by changing the values of the resistors in the bridge, I3 and I? in Figure 1. Two other techniques which are somewhat more flexible are illustrated in Figure 4. Referring to Figure 4, the circuit is in all respects the same as Figure 1 with the exception of the transformer 30, potentiometer resistor 3I, their connections to transformer 22 and amplifier 23, and the replacement of bias battery 24 with resistor 32 and capacitor 33. The input of transformer 30 is connected across the main line between leads I I and I2. Potentiometer resistor 3I is connected across the output of transformer 30. A center tap on the output of transformer 30 is connected to ground and a tap 34 on resistor 3| is connected to one side of the output of transformer22. The other side of transformer 22 supplies grid voltage to amplifier 23 by a connection to the control grid of vacuum tube 25. Resistor 32 is connected in series with the cathode of tube 25 and is partly bypassed to ground by capacitor 33 which has an adjustable tap 34 on resistor 32.

Two adjustments are here provided for varying the load current to compensate for a change in load resistance or bridge lamps, taps 34 and 35. The simplest type of adjustment is provided by tap 35 on resistor 32, which changes the value of the unbypassed part of the cathode resistor. If the tap 35 is adjusted to give an unbypassed part of the cathode resistor of a value Bk, an equivalent resistance will be introduced in series with the load of a value (1+u) Ric/n If the normal operating position of tap 35 is near the middle of resistor 32, a fairly wide range of load current variations in either direction can be compensated for by increasing R1; to decrease load current or vice versa. A second adjustment is provided by the tap 34 on resistor 3 I. The operation of this circuit is as follows.

A small A. C. voltage E1 is developed between the center tap of transformer 30 and tap 34 on resistor 3|, if tap 34 is not at the exact center of resistor 3 I. The phase of this voltage is either in phase or 180 out of phase with the bridge output voltage E2 appearing at the output of transformer 22, depending on whether tap 34 is above or below center on resistor 3|. The voltage E1 is zero for zero E1 and is directly proportional to E. A typical curve for E1 vs. E1 is shown in Figure 5, which also shows the values of E1 and E2 over the same range of E1. E2 is the same as Eg in Figure 3. Eg is simply the sum of E1 and E2. Above 109.5 volts E2 and E1 are out of phase and below this value of E1 they are in phase. As seen from Figure 5, the new Eg has a zero at 115 volts. If it is desired to stabilize at a lower voltage than 109.5 volts, it is simply necessary to move tap 33 to the other side of center on resistor 31. Then E1 would be positive, in phase with E2, above 109.5 volts and out of phase with E2 below this value of E1. Thus, it is possible with this circuit to adjust the value of the stabilized voltage, i. e. the line voltage for which the amplifier output is zero, to any value above or below the line voltage for which zero bridge output voltage occurs. Any change in bridge lamps or load can thus be compensated for by a simple adjustment of one potentiometer.

In the discussion thus far it has been assumed that the amplifier 23 is a simple triode voltage amplifier. For many applications this type of amplifier circuit will be most desirable because of its simplicity. Of course more complex amplifier circuits may become of interest in high power regulators where the lower efficiency of a simple tricde circuit is undesirable. In this case standard high efficiency amplifier techniques such as the use of a push pull circuit may be used. The fact that a simple triode amplifier is illustrated in Figures 1 and 5 should not be taken to indicate that this invention is so limited, as this circuit is provided merely as an example of the type of amplifier that may be used.

Circuit element values are given below for a typical regulator using the circuit of Figure l and designed to supply a constant load of 30 watts dissipation.

Tube 6AQ5 (triode connection) Turns ratio of transformer I5:9:1

Turns ratio of transformer 22=l6:1

Bridge lamps (GE #S-6) 3 w. v.

Resistors l6 and 11:3300 ohms Regulation within 1% over range E1 from 10 v. to v. and line frequency from 300 cycles to 500 cycles In this circuit the regulation at line voltages above 120 volts was achieved by permitting the rid to draw current and develop an additional bias by means of a conventional grid leak and condenser combination in series with the lead to the grid. The A. C. plate current is somewhat distorted as a result, at high values of E1, but for the desired application this was not important. The use of this technique introduces a time constant into the circuit but it need be no more than a few cycles of line voltage, which is satisfactory for many applications. This use of rectified grid current to extend the range of the regulator permits a considerably smaller and more economical tube to be used than would otherwise be the case.

We claim:

1. An alternating voltage regulator for regulating alternating voltage supply from a source to a load impedance, an essentially resistive bridge circuit having its input terminals connected across said source, said bridge circuit including at least one element having non-ohmic resistance which is a continuous function of the voltage appearing across said element, whereby an alternating output voltage is obtained between output terminals of the bridge circuit, said output voltage having a value directly proportional to deviation of said unregulated voltage from a specified voltage at which said bridge circuit is in balance, means for amplifying said bridge output voltage and means for introducing said amplified bridge output voltage in series between the source and said load to cancel out variations in the amplitude of said unregulated voltage in said load.

2. An alternating voltage regulator for regulating an alternating voltage supplied from a source to a load impedance, the voltage and frequency of the source being subject to variations, said regulator comprising an essentially resistive bridge circuit having first and second input terminals and two output terminals, said bridge circuit including at least one element having a nonohmic resistance, said resistance being a continuous function of the voltage appearing across said element, said first and second input terminals of said bridge circuit being connected across said source, whereby an alternating output voltage is produced between said two output terminals of said bridge circuit having a value directly proportional to the deviation of said unregulated voltage from a specified voltage at which said bridge circuit is in balance, a vacuum tube amplifier having its input connected to the output terminals of the bridge and serving to amplify said bridge output voltage, a load impedance, conductors forming a circuit connecting the source to the load impedance, and means for coupling the output of the amplifier to said circuit, said means being connected between the bridge and said load and in series with the load, whereby the voltage produced across the load is maintained at a constant value independent of fluctuations in the unregulated voltage.

3. A voltage regulator as in claim 2 also including adjustable means for generating an alternating voltage directly proportional to the value of said unregulated voltage and means for combining said alternating voltage and said bridge output voltage to supply an input voltage to said amplifying means, said input voltage having a value directly proportional to the deviation of said unregulated voltage from a specified voltage other than the voltage at which said bridge circuit is in balance, said specified voltage having a value above or below said bridge balance voltage, depending on the adjustment of said means for generating said first alternating voltage.

4. An alternating voltage regulator for regulating alternating voltage supplied from a source to a load impedance comprising an essentially resistive bridge circuit having first and second input terminals, and two output terminals, said bridge circuit including at least four resistive elements, one element per arm of said bridge circuit, at least one of said four resistive elements eing an incandescent lamp, said first and second input terminals of said bridge circuit being adapted to connect to the first and second output terminals of said source of unregulated voltage, whereby an alternating voltage is produced between said two output terminals of said bridge circuit having a value directly proportional to the deviation of said unregulated voltage from a specified voltage at which said bridge circuit is in balance, an electronic amplifier circuit, inductive transformer means for coupling the input of the amplifier circuit to said two output terminals of said bridge circuit, a transformer having an input winding connected to the output of said amplifier circuit and having an output winding having first and second terminals, a load impedance having one side connected to said first output terminal of said source of unregulated voltage and having the other side connected to said first terminal of said transformer output winding, and a connection between said second output terminal of said source of unregulated voltage and said second terminal of said transformer output winding, whereby the voltage pro duced across said load impedance is maintained at a constant value independent of fluctuations in said unregulated voltage.

5. A voltage regulator as in claim 4, including a second transformer having input and output windings, said input winding being connected between said first and second output terminals of said source of unregulated voltage, a first resistor connected across said output winding of said second transformer, a tap on said output winding, an adjustable tap on said resistance, and leads serving to connect said taps in series with the input of the amplifying circuit thereby producing a voltage at said amplifier input comprising the sum of the voltage appearing between said first and second taps and said bridge output voltage, and whereby a voltage is supplied to said amplifier input having a value directly proportional to the deviation of said unregulated voltage from a specified voltage other than the voltage at which said bridge is in balance, said specified voltage having a value above or below said bridge balance voltage, depending on the positions of said first and second taps.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,660,084 Morton Feb. 21, 1928 1,893,768 Fitzgerald Jan. 10, 1933 1,954,680 Morack Apr. 10, 1934 2,351,980 Lee June 20, 1944 2,366,577 Thompson Jan. 2, 1945

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