US3652922A

US3652922A - Constant current series regulator with control of bias current energizing control circuit of the regulator

Info

Publication number: US3652922A
Application number: US90731A
Authority: US
Inventors: Robert Joseph Healey; Helmut Stocker
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1970-11-18
Filing date: 1970-11-18
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28
Also published as: CA918751A

Abstract

The regulation of the current output of a series type current regulator is significantly improved by closely regulating the bias currents required by the control and reference elements of the regulator. These regulated bias currents may be coupled to the output circuit and form part of the output load current. The regulated bias currents are utilized to energize a reference voltage source and a voltage comparison circuit which in turn control the series regulating device of the current regulator.

Description

United States Patent [1 1 Healey et al. [451 Mar. 28, 1972 CONSTANT CURRENT SERIES [56] References Cited REGULATOR WITH CONTROL OF BIAS UNITED STATES PATENTS CURRENT ENERGIZING CONTROL 3,434,038 3/1969 Vette.- .323/4 CIRCUIT OF THE REGULATOR Inventors: Robert Joseph Henley, Morris Township, Morris County; Helmut Stocker, Randolph Township, Morris County, both of NJ.

Appl. No.: 90,731

U.S. Cl ..323/4, 323/22 T, 323/38 Int. Cl. ..H02j 1/04, G05f1/56 Field oi Search ..323/4, 9, 22 T, 38

3,182,246 5/1965 Lloyd Primary ExaminerGerald Goldberg Att0rney-R. J. Guenther and E. W. Adams, Jr.

[57] ABSTRACT voltage source and a voltage comparison circuit which in turn control the series regulating device of the current regulator.

v 5 Claims, 3 Drawing Figures PATENTEDMAREB r972 3,652,922

FIG (PRIOR ART) FIG. 2 (PRIOR ART) MR V FIG. 3

(loo

R. J. HE ALE Y uvvawrms STOCKER ATTORNEY BACKGROUND OF THE INVENTION This invention relates to series regulators which supply a constant current output. The invention is specifically 'concerned with the regulation and efficient utilization of the bias currents required by the control and reference circuitry of the series regulator.

A typical constant current regulator, such as shown in FIG. 1, includes a breakdown diode l3, energized by an input power source coupled to the input terminals 1 and 2, to derive a reference voltage utilized to control the regulator. The regulated output current is transmitted through the series regulator transistor 20 and a current sensing resistor 11 to an output load 100. The reference voltage developed across the breakdown diode 13 controls the emitter-to-base voltage of the transistor 20. It is apparent from examination of the circuit in FIG. 1 that the transistor 20 transmits a current having a controlled magnitude which maintains the voltage across the current sensing resistor 11 proportional to the voltage across the breakdown diode 13.

This circuit, while simple in operation and reliable, is limited in the precision of regulation it can achieve. The portion of the input current utilized to energize the breakdown diode 13 is directly transmitted to the load 100. The current energizing the breakdown diode 13 is unregulated since it bypasses the current sensing resistor 11. Hence the output current supplied to the load 100 tends to vary in response to changes in the input voltage applied to input terminals 1 and 2 and to changes in the output load 100.

Another typical constant current regulator of the prior art is shown in FIG. 2. In this regulator the breakdown diode 13, which establishes the reference voltage, shunts the input terminals I and 2. Hence the current energizing the breakdown diode l3 bypasses the output load 100 and does not adversely affect the precision of regulation. This regulation arrangement is less efficient than the regulation disclosed in FIG. 1. The current which energizes the breakdown diode 13 is dissipated and does not contribute to the output load current.

It is, therefore, an object of the invention to improve the precision of regulation of a series current regulator by regulating the bias current energizing the reference voltage breakdown diode.

' It is another object of the invention to maintain a constant output current in a series regulator essentially independent of changes in the input voltage or changes in the output load.

It is yet another object of the invention to improve the efficiency of a series current regulator by utilizing the regulated bias currents as part of the load current.

SUMMARY OF THE INVENTION The above enumerated objects are achieved in the invention by regulating the currents utilized to energize the series regulating transistor and the breakdown diode which,

transistor by draining the bias current in excess of its require-v ment from its control electrode. The excess bias current is transmitted to the current sensing resistor and forms part of the regulated output current.

The current energizing the breakdown diode is regulated to significantly limit its detrimental effect on the precision of regulation. The breakdown diode current is regulated by a control transistor and a current measuring resistor. .T he current measuring resistor shunts the base-emitter junction of the control transistor which junction voltage in turn controls the voltage drop across the measuring resistor. The current through the current measuring resistor is proportional and essentially equal to the current through the breakdown diode.

The current measuring resistor hence regulates the current energizing the breakdown diode.

The current traversing the collector-emitter path of the control transistor is advantageously limited by coupling the collector of the transistor to the base electrode ofthe current bypass transistor. This advantageously limits the unregulated bias current transmitted to the output load of the series current regulator.

DESCRIPTION OF THE DRAWINGS In the drawings, FIG. I is a schematic diagram of a typical constant current regulator existing in the prior art and described hereinabove;

FIG. 2 is a schematic diagram of a typical constant current regulator existing in the prior art also described hereinabove and which has a greater precision of regulation and less efficiency than the regulator shown in FIG. 1; and

FIG. 3 is a schematic diagram of a constant current series regulator embodying the principles of the invention to improve the precision of regulation of the output current and more efficiently utilize the bias current energizing the control circuitry.

DETAILED DESCRIPTION OF THE INVENTION A current regulator, as shown in FIG. 3', embodying the principles of the invention regulates a current supplied by an input voltage source coupled to the input terminals 1 and 2. This regulated current is controlled by two compound connected

series regulating transistors

10 and 20. The combined transconductive impedance of

transistors

10 and 20 is controlled in response to a voltage generated across the current sensing resistor 55. A current bypass transistor 40 responsive to the regulation control circuitry controls the bias current applied to the

series regulating transistors

10 and 20 by draining controlled amounts of current away from the control electrode 22. This excess drained current is transmitted to the current sensing resistor 55 and forms part of the regulated output load current.

The invention may be explained by describing the operation of the series current regulator shown in FIG. 3. In the operation of this circuit, a DC voltage source is coupled to the input terminals 1 and 2. A portion of the input current from this source is applied to the collector 13 and the collector 23 of the

series regulating transistors

10 and 20, respectively. A portion of the input current is also transmitted, via the resistor 51, to base electrode 22. This signal biases the compound connected

transistors

10 and 20 into a conductive state. The output current traversing the transconductive path of

transistors

10 and 20 flows through the current sensing resistor 55. The voltage drop across the current sensing resistor 55 is directly proportional to the combined current flow through the transconductive paths of

transistors

10 and 20.

A portion of the input current is also applied via resistor 51 and the transconductive or collector-emitter path of the current bypass transistor 40 to a reference voltage breakdown diode l5 and to the current sensing resistor 55. A portion of the input .current is also applied via resistor 51 and the emitter-base path of transistor 40 44 the control transistor 30. The transistor 30 in response to this current develops a substantially constant voltage across its base-emitter junction. A current measuring resistor 50 shunts the base-emitter junction of transistor 30 and is connected in series with the breakdown diode 15. The bias current energizing the breakdown diode 15 is regulated by the controlled voltage drop across the resistor 5 The current energizing the breakdown diode 15 is applied to the output 'load 100. This bias current may be advantageously optimized to operate the breakdown diode 15 in its most stable region. The current traversing the collectoremitter path of transistor 30 is supplied via the emitter-base junction of transistor 40. This particular connection minimizes the current flowing through transistor 30 and hence reduces the unregulated bias current transmitted to the 100.

It is apparent from the foregoing that the main component of the load current supplied to the output load 100 is derived from current transmitted by the regulating transistors and 20 and from current transmitted by the current bypass transistor 40. The current transmitted by the current bypass transistor 40 is applied in parallel to the current sensing resistor 55 and the breakdown diode 15. The current applied to the current sensing resistor 55 becomes part of the regulated load current. The current traversing the breakdown diode is regulated by the voltage drop across the current measuring resistor 50 controlled by the base-emitter junction voltage of transistor 30. This current is applied to the load 100. Since the current traversing the breakdown diode 15 is regulated, the total output current applied to the output load 100 is very precisely regulated.

The transconductive impedance of transistors 10 and is regulated to keep the current flow therein constant. If, for example, the load current increases, the voltage drop across the current sensing resistor 55 increases in response thereto. This increase in voltage increases the current flowing into the base 31 of the control transistor 30. This increased current biases transistor 30 into a higher conductive state and increases the base current of the current bypass transistor 40. The current bypass transistor 40 is biased into an increased state of conductivity and due to this increased conduction shunts current away from the base 22 of the transistor 20. The transconductive impedance of

transistors

10 and 20 is accordingly increased, reducing the current output at the emitter 11. This reduces the load current applied to the output load 100 to its regulated value. It is apparent that if the regulated current output at emitter 11 decreases, the voltage across the current sensing resistor 55 will decrease and the converse regulation will operate to increase the load current to its regulated value.

The temperature stability of the regulator may be advantageously improved by selecting a breakdown diode 15 with temperature characteristics complementary to the temperature characteristics of the base-emitter junction of transistor 30. In this instance a breakdown diode 15 should have a positive temperature characteristic wherein its voltage drop increases with temperature in order to counteract the negative temperature characteristic of the base-emitter junction. This temperature compensation scheme improves the precision of regulation of the regulator with respect to temperature changes.

The resistor 53 shunting the collector-emitter path of transistorl0 is included to limit the power dissipation of the

series regulating transistors

10 and 20 to a safe value should the voltage increase significantly. The

resistors

52 and 54 are utilized as collector-base leakage path resistors for the transistor 40 and the transistor 10, respectively. These leakage paths help to provide thermal stability for the operation of the regulator within the normal temperature range in which the circuit operates. The feedback capacitor 61 is included to modify the gain phase characteristics of the series regulator to prevent high frequency instability problems. The

diodes

25 and 35 are included as protection against high voltage surges such as may be caused by lightning striking the load.

lt is understood that the principles of the invention are equally applicable if semiconductor devices of an opposite polarity from those described are used. Such a substitution may involve designing a regulator utilizing PNP-transistors inoutput load stead of NPN-transistors as disclosed herein.

We claim:

l. A constant current supply comprising input and output terminals, a variable impedance current regulator including a control electrode, a current sensing impedance connected in series with said current regulator, a bias current path connecting one of said input terminals to the control electrode of said current regulator, semiconductor breakdown means to establish a reference voltage, means to compare the voltage drop across said current sensing imlpedance with said reference voltage including a contro transistor, means responsive to said means to compare to adjust the impedance of said variable impedance current regulator including a current bypass transistor, the collector-emitter path of said current bypass transistor connecting said control electrode to a junction of said current regulator and said current sensing impedance, the collector-emitter path of said control transistor connecting the base electrode of said current bypass transistor to a junction of said current sensing impedance and said output terminal, said semiconductor breakdown means being connected across the series connection of the collector base junction of said control transistor and the collector base junction of said current bypass transistor, whereby said bypass transistor controls the bias current applied to said control electrode and transmits the excess bias current supplied by said bias current path to one of said output terminals via said current sensing impedance.

2. A constant current supply as defined in claim 1 further including a current limiting resistor in series with said semiconductor breakdown means and being shunted across the base emitter junction of said control transistor.

3. A constant current supply asdefined in claim 2 wherein said variable impedance current regulator comprises a plurality of compound connected transistors.

4. A current regulator comprising a series regulating device including a transconductive path and a control electrode to receive signals to control the conductivity of said transconductive path, a current path comprising a transistor with a controllable transconductive impedance to divert bias signals from said control electrode in order to control the transconductive impedance of said series regulating device, a current sensing device to generate a voltage proportional to the current transmitted by said series regulating device, a source of reference voltage comprising a current energized breakdown diode, a comparison circuit to compare the reference voltage and the voltage generated by said current sensing device, said comparison circuit being coupled to and controlling the trans conductive impedance of the transistor of said current path, said comparison circuit comprising means to regulate the current energizing said source of reference voltage including a second transistor and a current drain control impedance whose voltage drop is controlled by the base-emitter junction voltage of said second transistor, said current drain control impedance being in series with said source of reference voltage, and the collector base of said transistor in said current path and the collector base of said second transistor being series connected with said reference voltage source in a closed loop whereby the current absorbed by said second transistor is limited.

5. A current regulator as defined in claim 4 wherein said breakdown diode has a temperature characteristic complementary to the temperature characteristic of the base-emitter junction of said second transistor.

Claims

1. A constant current supply comprising input and output terminals, a variable impedance current regulator including a control electrode, a current sensing impedance connected in series with said current regulator, a bias current path connecting one of said input terminals to the control electrode of said current regulator, semiconductor breakdown means to establish a reference voltage, means to compare the voltage drop across said current sensing impedance with said reference voltage including a control transistor, means responsive to said means to compare to adjust the impedance of said variable impedance current regulator including a current bypass transistor, the collector-emitter path of said current bypass transistor connecting said control electrode to a junction of said current regulator and said current sensing impedance, the collectoremitter path of said control transistor connecting the base electrode of said current bypass transistor to a junction of said current sensing impedance and said output terminal, said semiconductor breakdown means being connected across the series connection of the collector base junction of said control transistor and the collector base junction of said current bypass transistor, whereby said bypass transistor controls the bias current applied to said control electrode and transmits the excess bias current supplied by said bias current path to one of said output terminals via said current sensing impedance.

3. A constant current supply as defined in claim 2 wherein said variable impedance current regulator comprises a plurality of compound connected transistors.

4. A current regulator comprising a series regulating device including a transconductive path and a control electrode to receive signals to control the conductivity of said transconductive path, a current path comprising a transistor with a controllable transconductive impedance to divert bias signals from said control electrode in order to control the transconductive impedance of said series regulating device, a current sensing device to generate a voltage proportional to the current transmitted by said series regulating device, a source of reference voltage comprising a current energized breakdown diode, a comparison circuit to compare the reference voltage and the voltage generated by said current sensing device, said comparison circuit being coupled to and controlling the transconductive impedance of the transistor of said current path, said comparison circuit comprising means to regulate the current energizing said source of reference voltage including a second transistor and a current drain control impedance whose voltage drop is controlled by the base-emitter junction voltage of said second transistor, said current drain control impedance being in series with said source of reference voltage, and the collector base of said transistor in said current path and the collector base of said second transIstor being series connected with said reference voltage source in a closed loop whereby the current absorbed by said second transistor is limited.