US3922596A

US3922596A - Current regulator

Info

Publication number: US3922596A
Application number: US387838A
Authority: US
Inventors: David L Cave; Walter R Davis
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1973-08-13
Filing date: 1973-08-13
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25
Also published as: DE2438702A1; JPS5045950A

Abstract

A current regulator circuit for providing a regulated, temperature compensated current to a load. The current regulator circuit includes a unity-gain amplifier stage having a feedback circuit connected thereto. The output of the unity-gain amplifier drives an emitter follower, which drives an output transistor. The collector of the output transistor is connected to the load. The feedback circuit includes a transistor having its emitter connected in series with a diode, which in turn is connected to the input of the unity-gain amplifier stage. The circuit provides a well regulated output current and reduced power dissipation.

Description

United States Patent [191 Cave et al.

1 CURRENT REGULATOR [75I lnventors: David L. Cave, Mesa; Walter R.

Davis, Tempe, both of Aria.

[73] Assignee: Motorola, Inc., Chicago, 111.

[22] Filed: Aug. 13, 1973 [2]] Appl. No: 387,838

[ 1 Nov. 25, 1975 OTHER PUBLICATIONS "Another Entrant in Op-Amp Sweepstakes. Electronics, Apr. 28, 1969, pp. 139-141.

Primary Examiner-A. D. Pellinen Attorney, Agent, or Firm\"incent J. Rauner; Charles R. Hoffman [57] ABSTRACT [52] US. Cl 323/4; 323/19 U G0 F 3/ 8 A current regulator circuit for providing a regulated, Field f Search y y 07/ 97; 323/1, 4, temperature compensated current to a load. The cur- 323/16, 19, 22 T rent regulator circuit includes a unity-gain amplifier stage having a feedback circuit connected thereto. [56} References Cited The output of the unity-gain amplifier drives an emit- UNITED STATES PATENTS ter follower. which drives an output transistor. The 3 303 413 NW6.) Warner e 323/4 collector of the output transistor is connected to the 3:392:344 7/1968 2 UX load. The feedback circuit includes a transistor having 3529256 9/1970 Crabbe H 323/ its emitter connected in series with a diode, which in 3,588,672 6/l97l Wilson 323/4 turn is Connected to the input of the unity-gain ampli- 3,648,154 3/1972 Frederiksen et al. 323/22 T fier stage. The circuit provides a well regulated output 3.631.623 Z H m n et l r r 323/4 X current and reduced power dissipation. 3,731,181 5/1973 Cecilet a1 323/4 7 3 7/1973 6 Claims, 1 Drawing Figure l T lj "l 2O M i 1Q I l 1 l l l I I l I l l 22 l l l l l I l l a l l I 24 l0 1 i l l l l T l I I l CURRENT REGULATOR RELATED APPLICATION This patent is related to the application entitled Constant Current Regulating Circuit" by James B. Cecil et al., Ser. No. 294,723, now US. Pat. No. 3,777,251 filed Oct. 3, I972 and assigned to the as signee of the present invention.

BACKGROUND OF THE INVENTION This invention relates generally to circuitry for pro viding a constant output current and more particularly to circuit configurations for providing the constant output current with a low temperature coefficient and for providing reduced power dissipation.

Often, when it is required to provide a relatively constant reference current or the like to a load, such as for example, circuitry in an operational amplifier, the magnitude of the current from the current source circuit varies, either because of the variation in the voltage powering the constant current source or because of the variation in the ambient temperature. When the latter occurs, the performance of the operational amplifier circuitry may be adversely affected. This is especially true when the current produced by the constant current source circuit is being used for biasing circuitry in an operational amplifier.

Regulating circuits which attempt to maintain the current to the load at a constant value are known in the art. However, these circuits are sensitive to changes in temperature and in power supply voltage, and further dissipate an unacceptably high amount of power.

The present invention provides improved current regulator circuitry which provides relatively large values of regulated current, reduced power dissipation, and requires a relatively small number of components.

SUMMARY OF THE INVENTION In view of the foregoing considerations, it is an object of this invention to provide improved current regulating circuitry.

Another object of the invention is to provide improved current regulating circuitry which provides a constant current having a low temperature coefficient.

Another object of the invention is to provide improved current regulating circuitry of the type described which dissipates minimum power, yet provides relatively large regulated currents.

Briefly described, the invention provides a current regulator circuit which includes a unity-gain amplifier including a first transistor in series with a diode-com nected transistor, which acts as a load device thereof. A current source device coupled between the second diode-connected transistor and a supply voltage line determines the current through the unity-gain amplifier stage. Feedback circuitry, including a third transistor and a fourth diode-connected transistor in series therewith coupled between the collector of the second diode-connected transistor and the input of the unitygain amplifier insures that variations in the current source device are cancelled, allowing a relatively constant, temperature compensated voltage to be provided at the output of the unity-gain amplifier. An emitter follower stage driven by the unity-gain amplifier drives an output transistor, which has its collector coupled to the output of the current regulator circuit. By providing a 2 relatively large current through the feedback circuitry and a relatively small amount of current through the emitter follower, a low temperature coefficient for the regulated current at the current regulator output is achieved for regulated currents substantially larger than the current through the feedback circuit.

BRIEF DESCRIPTION OF THE DRAWINGS The single FIGURE of the drawing is a schematic diagram of a preferred embodiment of the invention.

DESCRIPTION OF THE INVENTION Referring to the single FIGURE in the drawing, current regulator circuit 10, outlined by dotted lines, is connected to a first power supply source 28 and to a current source device 26 (which may be a constant cur rent source) and to load 40. Current regulator 10 is also coupled to a second supply voltage line indicated by the ground symbols in the FIGURE.

Current source device 26 in the FIGURE is depicted as a junction field-effect transistor, which may be advantageously used in an integrated circuit implementation of the invention. Junction field-effect transistor 26 may be an epitaxial junction field-effect transistor which is readily implementable in a bipolar integrated circuit. Device 26 may also be a resistor or other resistive device. Output lead 39 is connected to load 40, which may, for example, be operational amplifier cir cuitry.

Current regulator 10 includes an amplifier stage 12, feedback stage 18, an emitter follower driver stage 31, and an output stage 35. Amplifier circuit stage 12 includes first NPN transistor 14 having its emitter connected to ground, (i.e., to the second voltage supply line) and its collector connected to the emitter of second diode-connected transistor 16, which has its base and collector connected to source 17 of field-effect transistor 26. Feedback circuit 18 includes

NPN transistors

20 and 22 and first resistor 24 connected in series. The base of transistor 20 is connected to the collector and base of transistor 16, and the collector of transistor 20 is connected to power supply line 28, and the emitter of transistor 20 is connected to a base and collector of diode-connected NPN transistor 22. The emitter of transistor 22 is connected to the base of transistor l4 and also to one terminal of resistor 24, which has its other terminal connected to ground. Output 30 of amplifier stage 12 is connected to the input (i.e., the base of transistor 32) of first emitter follower drive circuit 31, which includes fifth NPN transistor 32 and second resistor 34. The collector of transistor 32 is connected to power supply line 28, and the emitter thereof is connected to one terminal of resistor 34, which has another terminal connected to ground. The emitter of transistor 32 is also connected to the input of output circuit 35, which includes sixth NPN transistor 36 and third resistor 38 which together form a second emitter follower. The collector of transistor 36 is connected to output node 39, and the base thereof is connected to the emitter of transistor 32, and the emitter of transistor 36 is connected to one terminal of third resistor 38, the other terminal thereof being connected to ground.

The operation of the current regulator 10, in conjunction with current source field-effect transistor 26 and load 40, may be understood by assuming an increase in current through fieldeffect transistor 26. Or. equivalently, it can he assumed that there is an increase in the power supply voltage applied to line 28, which in turn may cause an increase in the current through de vice 26, especially if device 26 is a resistor or other such resistive device. The dynamic admittance of diode-connected transistor 16 is chosen to be substantially equal to the transconductance of transistor 14. It should be noted that the gain of an amplifier stage including a transistor and a load resistance in its collector circuit is equal to the transconductance of the transistor divided by the admittance of the load resistance, which is the dynamic admittance of diode-connected transistor 16 in this case. Transistor and diode-connected transistor 22, connected in series in the feedback path, correspondingly cause the base-to-emitter voltage of transistor 14 to increase, thereby increasing the current flowing through the collector and emitter of transistor 14 and through diode-connected transistor 16, which tends to reduce the voltage at the collector of diode-connected transistor 16. Thus, the increase in voltage at the collector of diode-connected transistor 16 is effectively cancelled, as is the corresponding variation in voltage at the output of unity-gain amplifier circuit stage 12. It is a characteristic of the operation of unity-gain amplifier l2 and feedback circuitry 18 that regardless of changes in the power supply voltage on line 28 or the changes in current source 26, the output voltage appearing at output 30 is maintained substantially constant at a given temperature. Stated differently, feedback transistor 20 detects a variation in the voltage on its base electrode, and transmits this variation two base-to-emitter voltage drops to the base of transistor 14. Note that resistor 24 establishes the biasing current through

transistors

20 and 22.

It is seen from the FIGURE that the voltage at output node 30 of unity-gain ammplifier 12 is equal to the sum of the base-to-emitter voltage drops of

transistors

14, 22, and 20 minus the base-to-emitter voltage drop of diode-connected transistor 16. Since

transistors

14 and 16 are chosen to have the same dynamic transconductance for a given current (i.e., they are chosen to have the same dynamic transconductance characteristic), and since, as will be recognized by those skilled in the art, this base-to-emitter voltage drop will be equal, the voltage at the output node 30 is equal to the sum of the base-to-emitter voltage drops of

transistors

20 and 22.

The regulated voltage at output node 30 is applied across the base-to-emitter junction of transistor 32 and resistor 34.

According to the invention, the value of resistor 24 is chosen such that the current through

transistors

20 and 22 is much larger than the current through transistor 32 and resistor 34. It is then seen that the base-to-emitter voltage drops of

transistors

20 and 22 are each appreciably larger than the base-to-emitter voltage drop of transistor 32. (A more comprehensive discussion of the base-to-emitter voltage characteristics of transistors may be found in Transistor Engineering, by Alvin B. Phillips, McGraw Hill, 1962, and in Analysis and Design oflntegrated Circuits, Editors Linn, Meyer, and Hamilton, McGraw Hill, 1967, and also in Physics and Technology of Semiconductor Devices, A. S. Grove, John Wiley & Sons, lnc., 1967.) Therefore, more voltage is available to be applied across the base-to-emitter junction of transistor 36 and resistor 38 than if the base-toemitter voltage drop is the same for transistor 32 as for

transistors

20 and 22.

Assuming that resistor 38 is sufficiently small in value, and that the geometries of transistors l4, I6, 20, 22, 32, and 36 are matched, it is clear that substantially 4 more current may flow through output transistor 36 than through

transistors

20 and 22.

It has been found that if the geometries of

transistors

14, 16, 20, 22, 32, and 36 are closely matched, (for example, if they are all minimum geometry devices) and if the current densities in

transistors

20 and 22 are substantially greater than in transistor 32, relatively good temperature coefficients are obtained for the output current of current regulator 10.

Since the output current through transistor 36 may be substantially larger than the current through

transistors

20 and 22, according to the invention, a considerable power dissipation advantage over the circuit in the aforementioned related application by Cecil et al. is realized, because the current in the feedback transistor of the circuit in the Cecil et al. patent application then is necessarily larger than that in the output transistor.

It should be recognized that increasing the geometry size of the output transistor 36 would be another way of increasing the output current, but in some cases the resulting additional collector-to-substrate capacitance would be deleterious to the performance of the load circuitry. For example, if the current source is used as a biasing source of an operational amplifier having a high slew rate, the additional capacitance would be prohibitive to obtaining the desired performance.

Typical values for the currents flowing through

transistors

20, 14, and 32 are, respectively 200 microamps, 50 microamps, and 50 microamps in order to obtain an output or load current of approximately 2 milliamperes. For this example, typical values of

resistors

24, 34, and 38, respectively, may be 1 Kohm, 15 Kohms, and 20 ohms. For the above mentioned current values, the following table indicates the relation between the temperature coefficient and the ratio of the load or output current to the current through transistor 20.

TABLE wan 1o TC of 1 The above-described current regulator has utility in linear integrated circuits, and particularly in integrated operational amplifiers, wherein the circuit design power dissipation may be very close to the limits of the thermal capability of the package In such situations, the current regulator of the invention provides a capability of producing a relatively large, temperature compensated regulated current having excellent line rejection with minimum power dissipation.

While the invention has been described in relation to a particular embodiment thereof, it will be recognized by those skilled in the art that variations in arrangement of components may be made within the spirit and scope of the invention.

What is claimed is:

l. A regulator circuit comprising:

first and second voltage supply means for providing first and second voltages, respectively;

first electronic control means having a control electrode, a first main electrode and a second main electrode, said first main electrode of said first electronic control means being coupled to said second'voltage supply means;

second electronic control means having a first main electrode and a second main electrode, said first main electrode of said second electronic control means being coupled to said second main electrode of said first electronic control means;

first current source circuit means coupled between said first voltage supply means and said second main electrode of said second electronic control means;

third electronic control means having a control electrode, a first main electrode, and a second main electrode, said control electrode of said third electronic control means being coupled to said second main electrode of said second electronic control means, and said second main electrode of said third electronic control means being coupled to said first voltage supply means;

fourth electronic control means having a first main electrode, and a second main electrode, said second main electrode of said fourth electronic control means being coupled to said first main electrode of said third electronic control means, said first main electrode of said fourth electronic control means being coupled to said control electrode of said first electronic control means;

first resistive means coupled between said first main electrode of said fourth electronic control means and said second voltage supply means;

fifth electronic control means having a control electrode, a first main electrode and a second control electrode, said control electrode and said second main electrode of said fifth electronic control means being coupled, respectively, to said first main electrode of said second electronic control means and said first voltage supply means;

second resistive means coupled between said second voltage supply means and said first main electrode of said fifth electronic control means;

sixth electronic control means having a control electrode, a first main electrode and a second main electrode, said control electrode and said second main electrode of said sixth electronic control means being coupled, respectively, to said first main electrode of said fifth electronic control means and to an output terminal of said regulator circuit; and

third resistive means coupled between said second voltage supply means and said first main electrode of said sixth electronic control means.

2. The regulator circuit as recited in claim 1 wherein said first, second, third, fourth, fifth. and sixth electronic control means are NPN transistors, each said control electrode being a base electrode, each said first main electrode being an emitter electrode, and each said second main electrode being a collector electrode.

3. The regulator circuit as recited in claim 2 wherein said first, second, and third resistive means are resistors.

4. The regulator circuit as recited in claim 3 wherein said first current source means, said first resistive means, said second resistive means, and said third resistive means are selected to produce a ratio of current in said sixth transistor to current in said third transistor in the range from 1 to 3.

5. The regulator circuit as recited in claim 2 wherein said first, second, third, and fourth NPN transistors are selected to have substantially the same current densities therein, and said fifth transistor is selected to have a current density substantially lower than the current density of said third transistor.

6. An integrated current regulator circuit for providing a regulated current at an output terminal to a load comprising:

first and second voltage supply means;

first current source circuit means, said first current source circuit means being an epitaxial junction field-effect transistor having a drain electrode coupled to said first voltage supply means, a source electrode, and a gate electrode connected to said source electrode;

a first NPN transistor having a first emitter, a first base, and a first collector, said first emitter being connected to said second voltage supply means;

a second diode connected NPN transistor having a second emitter, a second base, and a second collector, said second base being connected to said second collector, said first collector being connected to said second emitter, and said second base and said second collector being connected together and also connected to said first current source circuit means;

a third NPN transistor having a third emitter, a third base, and a third collector, said third base being connected to said second collector and said second base, and said third collector being connected to said first voltage supply means;

a fourth diode connected NPN transistor having a fourth emitter, a fourth base, and a fourth collector, said fourth base and said fourth collector being connected together and also connected to said third emitter, said fourth emitter being connected to said first base;

a first resistor connected between said fourth emitter and said second voltage supply means;

a fifth NPN transistor having a fifth emitter, a fifth base, and a fifth collector, said fifth base being connected to said second emitter, and said fifth collector being connected to said first voltage supply means;

a second resistor connected between said fifth emitter and said second voltage supply means;

a sixth NPN transistor having a sixth emitter, a sixth base, and a sixth collector, said sixth base being connected to said fifth emitter, said sixth collector being connected to said output terminal; and,

a third resistor connected between said sixth emitter and said second voltage supply means.

Claims

1. A regulator circuit comprising: first and second voltage supply means for providing first and second voltages, respectively; first electronic control means having a control electrode, a first main electrode and a second main electrode, said first main electrode of said first electronic control means being coupled to said second voltage supply means; second electronic control means having a first main electrode and a second main electrode, said first main electrode of said second electronic control means being coupled to said second main electrode of said first electronic control means; first current source circuit means coupled between said first voltage supply means and said second main electrode of said second electronic control means; third electronic control means having a control electrode, a first main electrode, and a second main electrode, said control electrode of said third electronic control means being coupled to said second main electrode of said second electronic control means, and said second main electrode of said third electronic control means being coupled to said first voltage supply means; fourth electronic control means having a first main electrode, and a second main electrode, said second main electrode of said fourth electronic control means being coupled to said first main electrode of said third electronic control means, said first main electrode of said fourth electronic control means being coupled to said control electrode of said first electronic control means; first resistive means coupled between said first main electrode of said fourth electronic control means and said second voltage supply means; fifth electronic control means having a control electrode, a first main electrode and a second control electrode, said control electrode and said second main electrode of said fifth electronic control means being coupled, respectively, to said first main electrode of said second electronic control means and said first voltage supply means; second resistive means coupled between said second voltage supply means and said first main electrode of said fifth electronic control means; sixth electronic control means having a control electrode, a first main electrode and a second main electrode, said control electrode and said second main electrode of said sixth electronic control means being coupled, respectively, to said first main electrode of said fifth electronic control means and to an output terminal of said regulator circuit; and third resistive means coupled between said second voltage supply means and said first main electrode of said sixth electronic control means.

2. The regulator circuit as recited in claim 1 wherein said first, second, third, fourth, fifth, and sixth electronic control means are NPN transistors, each said control electrode being a base electrode, each said first main electrode being an emitter electrode, and each said second main electrode being a collector electrode.

6. An integrated current regulator circuit for providing a regulated current at an output terminal to a load comprising: first and second voltage supply means; first current source circuit means, said first current source circuit means being an epitaxial junction field-effect transistor having a drain electrode coupled to said first voltage supply means, a source electrode, and a gate electrode connected to said source electrode; a first NPN transistor having a first emitter, a first base, and a first collector, said first emitter being connected to said second voltage supply means; a second diode connected NPN transistor having a second emitter, a second base, and a second collector, said second base being connected to said second collector, said first collector being connected to said second emitter, and said second base and said second collector being connected together and also connected to said first current source circuit means; a third NPN transistor having a third emitter, a third base, and a third collector, said third base being connected to said second collector and said second base, and said third collector being connected to said first voltage supply means; a fourth diode connected NPN transistor having a fourth emitter, a fourth base, and a fourth collector, said fourth base and said fourth collector being connected together and also connected to said third emitter, said fourth emitter being connected to saiD first base; a first resistor connected between said fourth emitter and said second voltage supply means; a fifth NPN transistor having a fifth emitter, a fifth base, and a fifth collector, said fifth base being connected to said second emitter, and said fifth collector being connected to said first voltage supply means; a second resistor connected between said fifth emitter and said second voltage supply means; a sixth NPN transistor having a sixth emitter, a sixth base, and a sixth collector, said sixth base being connected to said fifth emitter, said sixth collector being connected to said output terminal; and, a third resistor connected between said sixth emitter and said second voltage supply means.