US3538421A

US3538421A - Temperature stabilized voltage regulator

Info

Publication number: US3538421A
Application number: US657962A
Authority: US
Inventors: Jack Charles Young
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1967-08-02
Filing date: 1967-08-02
Publication date: 1970-11-03
Anticipated expiration: 1987-11-03

Description

Nov. 3, 1970 J. c. YOUNG TEMPERATURE STABILIZED VOLTAGE REGULATOR Filed Aug. 2, 196"? fi, ALTEFINATOR DARLINGTON TEMPERATURE COMPENSATING usrwoax LATOR IRCUIT INVENTOR. Jack C. Young ATTYS.

United States Patent 3,538,421 TEMPERATURE STABILIZED VOLTAGE REGULATOR Jack Charles Young, Phoenix, Ariz., assignor to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed Aug. 2, 1967, Ser. No. 657,962 Int. Cl. H02j 7/10; H02p 9/30 US. Cl. 322-28 13 Claims ABSTRACT OF THE DISCLOSURE where on is the temperature coefficient of resistance of the input transistor, K is a constant equal to the voltage division of the resistance network, 7 is the temperature coefficient of resistance of the breakdown diode and AT is the change in ambient temperature at the regulator.

BACKGROUND OF THE INVENTION This invention relates generally to voltage regulators and more particularly to an improved voltage regulator featuring temperature compensation.

Voltage regulator circuits employing an output transistor stage and one or more input transistors cascaded thereto for controlling the current in the output stage are well known. The current in the output stage is controlled, for example, to regulate proportionately a DC voltage level at a given point. However, the biasing of the input transistor (or transistors) in prior art regulators made the regulated DC voltage at said given point temperature dependent. It would be desirable to provide a voltage regulator circuit capable of regulating a DC supply voltage either independently of temperature or with some predictable dependence on temperature.

SUMMARY OF THE INVENTION An object of this invention is to provide an improved voltage regulator circuit operative to regulate voltage either independently or dependently of variation in temperature.

Another object of this invention is to provide an improved temperature compensated voltage regulator of sim ple construction, which is relatively low in cost and which consumes little power.

Another object of this invention is to provide a novel, temperature compensated voltage regulator, the temperature vs. regulated voltage characteristic of which may be easily adjusted to a desired positive or negative slope.

A further object of this invention is to provide a new and improved temperature compensated voltage regulator circuit which produces a square wave voltage waveform during regulation.

In the drawings:

FIG. 1 is a schematic diagram of one circuit embodiment according to this invention, and

FIG. 2 illustrates a modification of FIG. 1 and is a second embodiment of the invention.

3,538,421 Patented Nov. 3, 1970 DESCRIPTION OF THE INVENTION Briefly described, the present invention is embodied in a voltage regulator circuit including an output Darlington transistor stage driven by an input transistor which controls the amount of current flowing in the Darlington stage in accordance with a regulated DC voltage applied to the input transistor. A temperature compensating network including a voltage divider in series with a reverse breakdown diode is connected between the input transistor and an output or sense terminal at which a DC voltage is regulated. The resistance values of the voltage divider may be selected so that this voltage divider fuctions in combination with the reverse breakdown diode and the emitter-base portion of the input transistor to temperature compensate the regulated DC voltage at the sense terminal.

Referring to the accompanying drawing, there is shown a regulator circuit 9 which is operative to regulate the DC voltage level, for example, at a DC voltage supply 34. The voltage supply 34 may be an automobile battery connected to a field winding 32 of alternator 29. In a typical alternator connection to an automobile voltage regulator, the stator windings of the alternator 29 (represented as an AC current source 31) are connected via a full wave bridge circuit 33 to the load 35 is the automotive load on the alternator and will vary. Therefore, variations in load current will produce variations in the charge current to the DC supply 34 and these variations are regulated in accordance with this invention.

The regulator circuit 9 includes an output transistor stage It) with transistors 12 and 14 cascaded in the wellknown Darlington connection, and a pull down resistor 16 is connected between the emitter and base of transistor 14. The collector of an input transistor 18 is connected to the base of the transistor 12 in the Darlington stage, and a common current source resistor 40 provides an input current path to the Darlington stage 10 and to the input transistor 18 when the terminal 42 is energized by the DC voltage supply 34 upon closing switch 43.

A temperature compensating network 20 is connected to the base of transistor 18 and includes a voltage divider consisting of first and

second resistors

22 and 24 serially connected to a reverse breakdown diode 26 between an output or sense terminal 44 and ground potential.

A capacitor 28 is connected in parallel with the first voltage divider resistor 22 and integrates the voltage variations at the base of the input transistor 18. The sharply rising and falling voltage at the base of transistor 18 causes transistor 14 to be rapidly switched into and out of conduction to produce a square wave voltage at winding 32.

A suppression diode 36 is connected between the output of Darlington stage 10 and the voltage supply terminal 38, and this diode clamps the voltage across the alternator field winding 32 to the positive voltage of the DC supply 34 when the output transistor 14 in the Darlington stage 10 is turned off. The output transistor 14 has one pin connection or terminal 35 connected to ground (or some reference) potential and another pin connection or output terminal 37 to which winding 32 is connected.

DESCRIPTION OF OPERATION In order to understand the operation of the voltage regulator circuit according to this invention, assume initially that the voltage at the DC supply 34 has just dropped below a desired level. This voltage transition is coupled to the base of the input transistor 18 and turns off the NPN transistor 18 when it falls below the transistor V With transistor 18 turned off, all current through resistor 40 flows through the Darlington transistors 12 and 14, and output transistor 14 completes the current path from the DC supply 34 and through the alternator field winding 32 to ground. With transistor 14 drawing current through the alternator field winding 32, the stator windings produce a current (represented as current source 31) that is rectified by the bridge circuit 33 and charges the DC supply 34. As the voltage at sense terminal 44 causes the voltage at the base of the transistor 18 to rise above V this transistor turns on and current now flows through the current source resistor 40 and into the collector of transistor 18. With current flowing in transistor 18, the Darlington stage 10 is turned oil and current flowing in field winding 32 is momentarily interrupted as transistor 14 is turned off. As the regulated voltage at the DC supply 34 is reduced due to the current drain through load 35, transistor 18 is again turned off as previously described. Current now flows into the base of transistor 12 and into the output transistor 14 of the Darlington stage 10 to again complete a path from the DC supply 34 and through the alternator field winding 32 to ground. The DC supply is again charged by the current source 31 and the cycle repeats.

The schematic diagram in FIG. 2 illustrates an alternative connection for the integrating capacitor 28a between the collector and base of the input transistor 18. Capacitor 28a integrates the collector voltage of the transistor 18 to stabilize the loop phase-gain characteristics of the regulator circuit.

The temperature compensating features of the present invention may best be understood by examining the following relationships between the voltage divider network 20 and the input transistor 18. These relationships will be described with the reference to the regulated voltage V at the sense terminal 44 and the temperature induced voltage changes across the base emitter portion of transistor 18 and across the breakdown or Zener diode 26.

Consider first the Zener voltage V across the Zener diode 26 which may be expressed as:

Bn= BEo+ AT where V is the base-emitter voltage of transistor 18 at room temperature and a is the temperature coefficient of resistance of the base-emitter portion of transistor 18. Since the base current flowing in transistor 18 is negligible, i.e., very small when compared to current flowing in resistor 22, then V may also be written as:

where R and R are resistance values for

resistors

24 and 22 respectively.

For simplicity, let

equal a constant K. Then V may be written as:

VBE:KVREG KVZ and the regulated voltage may be written as:

V BE K 2 REG K Substituting the values of V and V as defined in Equations 1 and 2 into Equation 5, the following expression for V may be derived:

VREG K 6) VREG [VBEO +VZD] d-71 The first term in Equation 7, i.e.,

is not dependent upon temperature and does not affect the slope of the V versus temperature characteristic of the circuit. The second term of Equation 7 is temperature dependent but can be adjusted to a desired value by varying K. The temperature coefiicients of resistance 'y and a have opposite signs and tend to cancel each other in the second term of Equation 7, e.g., 7 may be in the order of +4 millivolts per degree centigrade and 0c may be in the order of 2 millivolts per degree centigrade. Thus, if it is desired that V remain constant over a given change in temperature AT, then the value of K can be selected so that 'y/K=ot and the second term in Equation 7 will be zero. On the other hand, the value of V can be made to vary with temperature to a degree in accordance with the selected value of K., where 0 K l. The temperature coefficient of resistance (7) of the Zener diode 26 is dependent upon the value of V so that the value of K for the second term in Equation 7 must be selected in accordance with the desired value of the first term in Equation 7 and the V of the Zener diode 26.

The following table identifies the components values for a voltage regulator circuit of the type described above which has been built and successfully tested.

TABLE Resistor (R) Value R16 Ohms. R or (R 200 ohms. R or (R 500 ohms. R 22 ohms. Capacitor (C) C28 .1 ,ufCl. C .1 ,ufd. Supply voltage 34 14 volts. V 11 volts.

However, the above table should not be construed as limiting the scope of this invention.

I claim:

1. A voltage regulator including, in combination:

(a) an output transistor stage connectable in the current path of a regulated DC voltage supply,

(b) an input transistor connected to said output stage and operatively biased to control the conductivity of said output stage, and

(c) a temperature compensating network connected to said input transistor and further connectable to said voltage supply, said temperature compensating network including first and second resistor portions connected in series with a reverse breakdown diode said input transistor having an input electrode thereof connected to a common node between said first and second resistor portions, the regulated voltage V at said reverse breakdown diode is temperature dependent in accordance with the relation VREGOC [%+7:| AT

where a is the temperature coefficient of resistance of the emitter-base portion of said input transistor, K is a constant determined by the values of said first and second resistor portions, '7 is the temperature co-' efiicient of resistance of said reverse breakdown diode, and AT is a change in ambient temperature at said regulator.

2. The voltage regulator circuit defined in claim 1 wherein:

(a) said output stage is connected as a Darlington transistor stage, and

(b) said first resistor portion being connected between said input electrode of said input transistor and a point of reference potential, said second resistor portion being connected between said input electrode of said input transistor and one side of said reverse diode, and the other side of said reverse breakdown diode being connected to a sense terminal of said regulator.

3. The voltage regulator defined in claim 2 which further includes an integrating capacitor connected in parallel with said first resistor portion for integrating the voltage across said first resistor portion.

4. The voltage regulator circuit as defined in claim 2 which includes a common current source resistor connected to said Darlington stage and to said input transistor, said current source resistor being connectable to said voltage supply and providing input current to either said Darlington stage or to said input transistor as the supply voltage varies about a given level.

5. The voltage regulator defined in claim 4 which further includes a suppression diode connected to the output of said Darlington stage and connectable to said voltage supply, said suppression diode clamping the voltage at the output of said Darlington stage to the level of said voltage supply when said Darlington stage is biased nonconductive.

6. The voltage regulator defined in claim 5 which further includes an integrating capacitor connected in parallel with said first resistor portion.

7. The voltage regulator defined in claim 5 which further includes an integrating capacitor connected between the collector and base of said input transistor.

8. A system for regulating the voltage level at a DC voltage supply to which is connected an alternator field winding, said system including, in combination:

(a) a transistor output stage for providing a current path from said DC voltage supply and through said alternator field winding to a point of reference potential,

(b) an input transistor connected to said output transistor stage and operatively biased to control the conductivity of said output transistor stage,

(c) a temperature compensating network connected to said input transistor and having a sense terminal connectable to said DC voltage supply, said temperature compensating network including first and second resistor portions connected in series with a reverse breakdown diode between said sense terminal and a point of reference potential, said sense terminal having a regulated voltage V which is controlled according to the relationship where AT is the change in ambient temperature at said system, on is the temperature coefiicient of resistance of the base-emitter portion of said input transistor, K is a constant determined by the values of said first and second resistor portions, and q is the temperature coefficient of resistance of said reverse breakdown diode, said first and second resistor portions being adjustable so that V may increase, decrease, or remain constant with changes in temperature AT.

9. The system defined in claim 8 wherein said transistor output stage includes a pair of transistors in a Darlington connection.

10. The system defined in claim 9 wherein said first and second resistor portions form a voltage divider with an intermediate point thereon connected to said input transistors, said first and second resistor portions being variable so that by varying the values of said first and second resistor portions, said value of K can be changed and set at a desired value.

11. The system defined in claim 10 which further includes a capacitor connected in parallel with said first resistor portion for integrating the voltage thereacross and to thereby produce a square wave voltage waveform at the output of said Darlington connection.

12. The system defined in claim 14 which further includes a capacitor connected between the input and output of said input transistor for integrating the voltage applied to said input transistor and thereby producing a square wave voltage waveform at the output of said Darlington connection.

13. The system defined in claim 14 which further includes (a) a common current source resistor connected to a common junction at the input of the Darlington output stage and the output of the input transistor, current flowing in said common current source resistor alternately flowing to either said input transistor or to said output stage, and

(b) a suppression diode connected to the output of said Darlington connection and connectable to said DC voltage supply for clamping the voltage across said alternator field winding to the level of said DC voltage supply when the output transistor in said pair of transistors in said Darlington connection is turned off.

References Cited UNITED STATES PATENTS 4/1961 Conger et al 32228 2/ 1964 Holm et al. 32228 U.S. Cl. XR