US2983863A - Temperature compensated voltage regulator - Google Patents

Description

y 1951 E. KEONJIAN 2,983,863

TEMPERATURE COMPENSATED VOLTAGE REGULATOR Filed Aug. 15, 1955 F|G.l.

||- SOURCE 2 LOAD mm 2? /RESULTANT 25'c.-5oc. 3 2a a /REF. DIODE soc. uJO o n: -o.3v.f 29 REF. DIODE 250.

9 REVERSE cURRENTm mA 2 3 4 5 s 7 a 9 c 4D|ODES 25 c. 123 & 3p 2?. K? 1 4mooss 60C. -o.3v. coo l-L 2 3 4 5 6 7 B 9 FORWARD CURRENT m mA FIG.4.

SOURCE LOAD l INVENTORI EDWARD KEONJlAN,

HIS ATTORNEY.

United States 2,983,333 Patented May 9, 1961 TEMPERATURE COMPENSATED VOLTAGE REGULATOR Edward Keonjian, Syracuse, N.Y., assignor to General Electric Company, a corporation of New York Filed Aug. 15,1955, SerrNo. $28,172

11 Claims. (Cl. '323-69) The present invention relates to voltage regulators and has as an object thereof to provide an improved voltage regulator wherein the output voltage is insensitive to changes in ambient temperature.

The present invention provides a solution to the temperature instability problem which arises with several types of voltage regulators. In a simple shunt type regulator in which the shunted current flows through a voltage reference device, the output voltage is often found to depend on the ambient temperature. The dependence of the output voltage on temperature is due to a change in the conductivity of the voltage reference device With changing temperature. Voltage reference devices which are sensitive to ambient temperature are semi-conductor diodes of germanium or silicon which are operated in the inverse voltage break-down region and gaseous discharge devices. The invention is generally applicable to regulators in which an increase in the ambient temperature brings about an increase in the voltage developed across the reference device.

The invention provides a voltage regulator temperature compensating circuit that is simpler than previously known arrangements, and one which avoids the disadvantages which have hitherto prevented the use of simple arrangements. The novel temperature compensating circuit here treated provides excellent temperature stability while causing a minimum reduction in regulation and requiring a minimum source voltage to produce a given regulated voltage output.

The compensation circuit further is capable of functioning not only in low voltage and low current ranges but also in high voltage and high current ranges. It is applicable to germanium or silicon diodes having breakdown voltages well below volts as well as to the more common operating voltages of gas discharge tubes. Furthermore, the compensating circuit can be used with voltage reference devices which operate at currents of less than a milliampere without substantial impairment f the voltage-current or regulation characteristic of the compensating network. With larger compensating junction diodes, the range of currents in which temperature compensation can be affected extends to several amperes, permitting application of the invention to regulators employing saturable reactors.

Accordingly, it is a further object of the present invention to provide a temperature stabilized regulator wherein the regulation efficiency of the stabilization circuit is substantially undiminished.

It is still another object of the present invention to provide a temperature compensated voltage regulator capable of stabilizing relatively low output voltages.

These and other objects of the present invention are achieved in a novel voltage regulator circuit employing a voltage reference device exhibiting a positive voltagetempera'ture coefiicient and a temperature compensating network connected in series with it. In accordance with the invention, one or more series connected semi-conductor diodes arranged to conduct in the forward direction form a portion of the compensating network. Since the forward resistance of these diodes diminishes with temperature the connection of a suitable number of properly selected diodes in circuit with a voltage reference source can be used to bring about substantially perfect temperature compensation of the voltage reference source. The illustrative embodiments of the invention employ respectively a semi-conductor diode operated at a large enough inverse voltage to cause break-down as one such reference and a gaseous discharge device as another. In these embodiments very little decrease in the regulation efiiciency is occasioned by the addition of the compensation 7 network.

The features of the invention which are believed to be novel are set'forth with particularity in the appended claims. The invention itself, however, both to its organization and method of operation together with further objects and advantages thereof may be best understood by reference to the following description read in connection with the following drawings wherein:

Fig. 1 shows a schematic diagram of a temperature stabilized voltage regulator employing a reversely poled semi-conductor diode as the reference source;

Fig. 2 is a graph illustrating the conductive properties of p a typical semi-conductor diode operated from the region of inverse voltage break-down to the region of forward saturation;

Fig. 3 is a graph illustrating respectively the separate voltage-current characteristics of the reference device and of the temperature compensating device of the embodiment illustrated in Fig. 1, in addition to the composite voltage-current characteristic of this embodiment illustrating the resultant temperature stabilization achieved; and

Fig. 4 is a second embodiment of the invention employing a gaseous discharge device as the voltage reference source.

Referring now to Fig. 1, there is shown a voltage regulator embodying the present invention. A source 11 of direct potential has its negative terminal 12 connected to a ground bus 13 and its positive terminal 14 connected to a regulating resistance 15. The load 16 is connected between the terminal 15 of the regulating resistance remote from the source 11 and the ground bus 13. A voltage reference diode is shown at 17 having its cathode connected to the ground bus 13 and its anode connected to one terminal of a temperature compensating network 18. The temperature compensating network 18 is connected in series between the load side of the compensating resistance 15 and positively energized terminal of the diode reference device 17. By this poling of the diode, the source 11 tends to force current through the reference diode 17 with a sense opposite its direction of easy flow. The compensating network comprises four series connected diodes 19, 2t), 21, and 22 chosen so that their temperature coefiicients bring about substantially complete stabilization of the reference voltage appearing across the load 16.

In the constructive embodiment illustrated, the reference diode 17 is a silicon junction diode constructed to have an inverse break-down voltage of approximately 9 volts. The compensating diodes 19, 2t), 21 and 22 are each germanium diodes.

In accordance with the invention it has been determined that by selection of an appropriate number of forward conducting semi-conductor diodes, connected in series with a reversely biased diode, one may obtain essentially perfect temperature compensation of the output voltage. Since the forward conduction temperature coefiicient is usually smaller than the backward temperature coefiicient, this number is usually larger than one.

The method of achieving temperature compensation may be explained by reference to Fig. 2 on which is plotted the voltage-current characteristics of a typical semi-conductor diode. The line 23 which corresponds to operation at a temperature of 25 is distinct from a similar line 24 taken at 60". It may be noted, however, that except in the vicinity of zero applied voltage, that the lines are closely similar in shape and are merely translations of one another along one axis of the graph. It may also be noted that at an arbitrary inverse current point 25 on the graph, that the voltage corresponding to the 25 point is algebraically greater than the voltage corresponding to the 60 point. Likewise, picking an arbitrary forward current at point 26 of equal magnitude to the current of 25 but of opposite sign, it may be seen that the voltage corresponding to the line for 25 temperature is algebraically more than the voltage corre sponding to the 60 temperature. A careful study of the conduction properties of typical semi-conductor diodes indicates that the voltage-temperature coeflicient for conduction in the forward direction and in the reverse direction are not the same, and that they are ofopposite sign, and essentially linear over a wide range of operating conditions. Accordingly, by selection of a sufficient number of forward conducting diodes one may achieve substantially perfect temperature compensation of an inversely operated reference diode.

Fig. 3 illustrates in detail the operation of the temperature compensated voltage regulator illustrated in Fig. 1. Fig. 3 contains five separate curves of voltage versus current. Curve 27 illustrates the resultant curve of the compensated regulator shown in Fig. 1 over the range of from 25 to 60 C. taken across both the regulating semi-conductor 17 and the compensating semi-conductor 18. Curve 28 represents the voltage characteristic taken across the reference diode 17 alone at a 60 C. ambient temperature. Curve 29 represent the latter characteristic at 25 C. Curve 30 represents the voltage drop appearing across four forward conducting germanium diodes (18) at 25 C. Curve 31 represents the voltage drop in these diodes (18) at 60 C. At 2.4 milliamperes, in the experimental embodiment illustrated in Fig. 1, approximately 0.3 volt difference was obtained between the reference diode voltages corresponding to the two temperatures and the compensating diode voltages corresponding to the two temperatures. At the same time, the points corresponding to a temperature of 60 C. were found to be nearly indistinguishable from the points obtained at 25 and hence were plotted as a single line 27. As measured, the voltage was constant to less than 0.01 volt over most of the graph through this temperature range. The forward conduction curves are so nearly parallel and the reverse conduction curves are so nearly parallel throughout the illustrated range of from 1 to 9 milliamperes, that the compensation is excellent throughout. The indicated reduction in regulation in the compensated circuit is only approximately 35 volts per ampere over the range of from 0.6 milliampere to 9 milliamperes. If the range is changed to from 3.6 to 9 milliamperes, the decrease in regulation is 20 volts per ampere.

Noting typical values, the voltage temperature coeflicient in the reverse conduction region for silicon diodes varies from approximately plus 0.01% per degree C. to plus 0.1% per degree C., the former value corresponding to a diode having a break-down potential in the region of volts and a dynamic resistance of approximately ohms in this region of conduction. In general, the magnitude of the temperature coefiicient, the conductance, and the break-down voltage are interdependent, the diodes having the greater break-down voltage having the greater positive temperature coefiicient.

The forward conduction characteristics of junction diodes can be expressed by the equation:

=lse -1 (1) Where I is the saturation current, k a constant that at room temperature may vary between 30 volts and 20 volts depending on the dimensions of the diode, and v is the junction voltage. The factor k is proportional to the absolute temperature. This variation is so small, however, that it usually can be neglected.

The saturation current 1,, when a junction is biased forwardly, varies exponentially with temperature, being relatively independent of voltage over the intended operating range:

where I, is the saturation current at temperature T I the saturation current at temperature T and 11" a constant. For most germanium and silicon diodes, the coefiicient a equals approximately 0.08 (degrees K).

The total current-voltage characteristics is therefore:

In the forward part of the characteristic under the operating conditions contemplated, the last term of (3) can be normally be neglected so that:

1=1 a('I T1)+irv 4 a 1 I zi ril-b 7:

For a constant current I, we have, therefore:

6V a w r (6) The voltage drop of a diode during forward conduction with constant current changes, therefore, with temperature at a rate of -a/k. A typical value (for k=39 volts a=0.08 (degrees K)-' is 2 millivolts per degree C. It is important to note that the temperature coefficient of the forwardly biased diode is always negative.

In general it may be said that the forward conduction temperature coefficients of germanium and silicon diodes are quite uniform, while the temperature coefficients for backward conduction diifer greatly with different diodes. Since the positive temperature coefiicient goes up with break-down voltage diodes operating at higher breakdown voltages require a larger number of compensating diodes than diodes operating at lower break-down voltages. Since the temperature coefiicients for forward conduction are relatively uniform, it may be desirable in some cases to' employ shaping networks in order to achieve precise compensation for a reference diode whose temperature coefficient would otherwise call for a fractional number of compensating diodes. A simple shaping network may take the form of a resistance connected in shunt with one or more of the compensating diodes. For most purposes, however, the use of the nearest number of compensating diodes brings about compensation to an adequately high degree.

Fig. 4 illustrates another embodiment of the invention in which a gaseous discharge device provides the voltage reference. A source of direct potential is shown at 32 having one terminal connected to a regulating resistance 33. A load 34 is connected to the terminal of the regulating resistance 33 remote from the source 32 and to the other terminal of the source 32. The compensating voltage regulating circuit comprises the gaseous discharge device 35 and the compensating network 36, these elements being serially connected in shunt across the load 34. The compensating network 36 is formed of four forward conducting diodes 37, 3'8, 39, and 40 whose total temperature coefficient is such as to provide compensation of the positive temperature coeflicient of the gaseous discharge device 35. In this manner a typical gaseous discharge device, having a positive temperature coeflicient of 7.5 millivolts per'de-gree can be compensated by four forward conducting diodes each having approximately 1.9 millivolts per degree negative temperature coeflicient.

There are several types of diodes which exhibit the negative temperature coefficient forward conduction characteristic here employed. Silicon and germanium junction diodes have been found to exhibit this property over an extremely wide range of currents. As is true in most junction diodes, the dynamic resistance decreases with increasing current levels, so that the reduction in regulation is greatest at the lower currents and a minimum at the higher currents. By appropriate design, diodes may be made in which the knee of the resistance curve is below a milliampere, thus permitting high regulation when the compensating diode is operated at currents above this point. The upper range of current operation is limited by the size of the diode, but in general the negative temperature coefficient is exhibited throughout the normal current range of the diode.

While particular embodiments of this invention have been shown and described it will of course be apparent that various modifications may be made without depart ing from the invention. Therefore, by the appended claims, it is intended to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What I claim as new and desire to Patent of the United States is:

1. In combination, a voltage reference device having a positive voltage-temperature coefiicient and a compensating element having a negative voltage-temperature coefiicient of substantially equal magnitude to said first recited coefiicient and connected in series therewith, said compensating element comprising a semi-conductor diode oriented for easy conduction in the direction of normal current flow through said reference device.

2. A temperature stabilized voltage regulator comprising a semi-conductor diode adapted to be connected to potentials of such magnitude as to cause inverse breakdown of said diode, the voltage of said breakdown having a positive temperature coefficient, and a temperature compensating element connected in series with said diode and comprising a number of semi-conductor diodes arranged for easy current flow in the direction of normal current flow through said reference semi-conductor diode, said number being selected to provide a voltage drop in said compensating element having a negative temperature coefficient of substantially equal magnitude to said positive temperature coefiicient.

3. A temperature stabilized voltage regulator comprising a semiconductor diode adapted to be connected to potentials of such magnitude as to cause break-down of said diode, the voltage of said breakdown having a positive temperature coeiiicient, and a temperature compensating element having a negative voltage-temperature coefficient of substantially equal magnitude to said positive temperature coefficient, said compensating element being connected in series with said diode and comprising at least one semi-conductor diode oriented for easy current flow in the direction of normal current flow through said reference semi-conductor diode.

4. A temperature stabilized voltage regulator comprising a regulating resistance adapted to be connected in series between a source of energizing potentials and a load device, and a voltage regulating circuit adapted to be connected in shunt with said load device comprising a constant voltage drop device having a positive voltagetemperature coefficient and a temperature compensating element having a negative voltage-temperature coefiicient or" substantially equal magnitude to said positive voltagetemperature coefiicient, said compensating element being connected in series with said constant voltage drop device and comprising at least one semi-conductor diode oriented secure by Letters 6 for easy current flow in the direction of normal current flow through said constant voltage drop device.

5. A temperature stabilized voltage regulator comprising a regulating resistance adapted to be connected in series between a source of energizing potentials and a load device, and a voltage regulating circuit adapted to be connected in shunt with said load device comprising a semi-conductor diode adapted to operate in the inverse break-down region, said semi-conductor diode having a positive voltage-temperature coefiicient, and a temperature compensating element having a negative voltage-temperature coeflicient of substantially equal magnitude to said positive voltage-temperature coefiicient, said compensating element being connected in series with said diode and comprising at least one semi-conductor diode oriented for easy current flow in the direction of normal current flow through said inversely operated semi-conductor diode.

6. A temperature stabilized voltage regulator comprising a regulating resistance adapted to be connected in series between a source of energizing potentials and a load device, and a voltage regulating circuit adapted to be connected in shunt with said load device comprising a semi-conductor diode connected for operation in the inverse break-down region, said diode having a positive voltage-temperature coefiicient, and a temperature compensating element connected in series with said diode and comprising a number of semi-conductor diodes whose forward resistance decreases with temperature, oriented for easy current flow in the direction of normal current flow through said inversely operated semi-conductor diode, said number being chosen to make the total negative voltage-temperature coelficient of said compensating element substantially equal to the positive voltage-temperature coeflicient of said inversely operated device.

7. A temperature stabilized voltage regulator as set forth in claim 6 wherein said temperature compensating diodes employ a semiconductor material selected from the class of materials including silicon and germanium.

8. A constant voltage source comprising: a source of D.C. potential; a resistor; a pair of silicon diodes, a series circuit including said source of D.C. potential, said resistor and said pair of silicon diodes each of said silicon diodes having a cathode and an anode electrode arranged in juxtaposition so that one electrode of one of said diodes is connected to a like electrode of the other said diode, means to derive a potential across said pair of diodes.

9. In combination a reverse biased semiconductor diode voltage reference device, having a voltage temperature coefficient, and a compensating element, having a negative-voltage-temperature coeficient of opposite sense and of substantially equal magnitude to said first recited coeificient, connected in series therewith, said compensating element including a semiconductor diode oriented for easy conduction in the direction of normal current flow through said reference device.

10. Means for providing a temperature stabilized constant voltage source from a D.C. potential source, comprising a series circuit adapted to be connected to said D.C. potential source and including a resistance, a first semiconductor diode oriented for operation in the inverse break-down region, said first diode having a first tem perature coefficient, and a second semiconductor diode oriented for easy current flow in the direction of normal current flow through said inversely operated first diode, said second diode having a temperature coefficient of opposite sign to that of the temperature coeificient of said first diode, and means to derive a substantially constant D.C. potential across said diodes.

11. A temperature stabilized voltage source comprising a source of D.C. potential, a resistor, a first junction semiconductor diode, and a second junction semiconductor diode, a series circuit including said source of DC. potential, said resistor, said first diode, and said second diode, said first diode and said second diode being connected so as to be oppositely poled, said first diode exhibiting a positive voltage temperature coefiicient and said second diode exhibiting a negative voltage temperature coefiicient, means to derive a temperature stabilized constant potential across a portion of said series circuit including said first and said second diode. A

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 2 983 863 May 9, 1961 EdwerdKeonjian It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 46 for cathode read anode same line 46 for anode read cathode column 4L,

line 23 strike out ioe fl first occurrence,

Signed and Sealed this 3rd day of July 1962o (SEAL) Attest;

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE. OF CORRECTION Patent Ne, 2,,983 86s, May 9 1961 Edward I Keonjian It is hereby certified that errer appears in the above numbered patent requiring correction and that the said Letters Patent should read as eerrected below.

Column 2 line 46 for cathode read anode 5 same line 46 fer Fanode"; read cathode column 4 line 23 strike eat be first oceumeenee.a

Signed and sealed this 3rd day of July 1962,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

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