US3742338A

US3742338A - Dc voltage regulator circuit

Info

Publication number: US3742338A
Application number: US00232792A
Authority: US
Inventors: H Sugano; A Tanaka
Original assignee: Matsushita Electronics Corp
Current assignee: Panasonic Holdings Corp
Priority date: 1971-03-15
Filing date: 1972-03-08
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26
Also published as: DE2212275C3; DE2212275B2; FR2130217B1; DE2212275A1; GB1343251A; FR2130217A1; CA980858A

Abstract

A circuit in which the voltage derived from a reference diode or silicon zener diode is fed back through an emitter-follower circuit to the base of a transistor and the constant current flowing through the emitter-collector circuit of the transistor is in turn applied to the reference diode so that such a stabilized output voltage as cannot be attained by the zener diode alone may be obtained.

Description

United States Patent [191 Sugano et al.

[ 1 June 26, 1973 DC VOLTAGE REGULATOR CIRCUIT Inventors: Hitoshi Sugano; Akio Tanaka, both of Takatsuki, Japan Assignee: Matsushito Electronics Corporation,

Osaka, Japan Filed: Mar. 8, 1972 Appl. No.: 232,792

Foreign Application Priority Data Mar. 15, 1971 Japan 46/14481 US. Cl. 323/22 T, 323/1, 323/38 Int. Cl. G05f 1/56 Field of Search 307/297; 323/1, 4,

References Cited UNITED STATES PATENTS 5/1971 Avins 307/297 3,652,922 3/1972 l-lealey et al. 323/22 T OTHER PUBLICATlONS Kesner, Hold That Voltage, Motorola Monitor, Vol. 7, No. 3, November, 1969, pages 33-35.

Primary Examiner-A. D. Pellinen Attorney-S. Delvalle Goldsmith, Lester Horwitz et a1.

[57] ABSTRACT 5 Claims, 2 Drawing Figures PAIENIEDJUHZB 191s 3.742.338

FIG.

PRIOR ART DC VOLTAGE REGULATOR CIRCUIT The present invention relates to a dc voltage regulator circuit which is connected to a dc power supply and which delivers a stabilized output to a load connected thereto even if there is a variation in the voltage of the dc power supply or in the load.

In a transistorized electronic circuit there is need for a power supply as a bias voltage source which can supply a constant output voltage irrespective of the variation in the voltage of the power supply or in the load connected thereto.

For a better understanding of the invention reference may be had to the accompanying drawings in which the same reference numerals are applied to like parts or circuit elements and in which:

FIG. 1 shows a conventional regulator circuit for constant voltage supply; and

FIG. 2 shows a dc voltage regulator circuit according to the invention.

In FIG. 1 which illustrates a prior-art regulator circuit, numerals 1, 2, 3, 4, and 6 respectively designate a terminal connected to a power supply (not shown), a zener diode, a resistor for conducting current to the zener diode, a transistor in emitter-follower configuration, an emitter resistor for the transistor and an output terminal.

In this circuit, current is drawn through the resistor 3 to the zener diode 2. Consequently, a constant voltage is developed across the zener diode 2, and the constant voltage available at a point a in FIG. 1 is put out through an emitter-follower circuit consisting of the transistor 4 and the resistor 5.

Now, even though there is a variation in the voltage applied to the terminal 1 and therefore a variation in the current flowing through the resistor 3, the variation will be absorbed by the diode 2 which has a zener characteristic, so that the change in the voltage at the point a is suppressed.

Further, even if the current drawn from the terminal 6 is changed due to the variation in the load connected to the terminal 6, the change in voltage at the terminal 6 will be suppressed due to the function of the emitterfollower circuit consisting of the transistor 4 and the resistor 5.

As seen from the foregoing description, with the conventional regulator circuit, the variation in the output voltage due to the variation in the voltage of the power supply or in the connected load can indeed be suppressed, but, strictly speaking, there will be a variation, though very small, in the output voltage if there is a variation in the power supply voltage.

Namely, if current flowing through the zener diode is changed, the change in the zener voltage necessarily ensues which is normally very small. As a result, the voltage at the point a and the output voltage available at the terminal 6 vary.

The present invention has been made to solve the problem just mentioned which is often raised with the prior-art regulator circuit, and it is characterized by a circuit for supplying current for the zener diode which current is not affected by the variation in the power supply voltage, the circuit being able to deliver a stabilized output voltage.

The present invention will now be described by way of example shown in FIG. 2 of the attached drawings.

In FIG. 2, circuit elements designated by numerals 1,

2, 4 and 6 are similar to those indicated by the same numerals in FIG. 1; resistors 7 and 8 divide the voltage across a zener diode 2; a transistor 9 and a resistor 10 constitute an emitter-follower circuit; a transistor 11 forms a circuit for delivering a constant current by using the voltage available at the emitter of the transistor 9 as base bias voltage of the transistor 11;

resistors

12 and 13 serve respectively as the emitter and collector resistors for the transistor 11; a diode 14 is inserted for temperature compensation; a transistor 15 and a resistor 16 form a circuit for supplying a constant current for the zener diode 2; and a resistor 17 conducts the initial current to the zener diode 2. The operation of this circuit to obtain a stabilized output voltage is as follows.

When a dc voltage from a power supply (not shown) is applied to the terminal 1, current is drawn to the zener diode 2 through the resistor 17, so that a reference voltage appears at the point b in the emitter circuit of the emitter-follower transistor 4. The voltage at the point b is then applied as bias voltage to the base of the constant current conducting transistor 11 through the emitter-follower transistor 9. Current will flow also through the transistor 15 at the same time.

In this way, immediately the voltage is applied to the terminal 1, a circuit is established which leads current to the zener diode 2 through the transistor 15.

Since the base bias voltage of the transistor 11 depends on the zener voltage of the diode 2, the collector current of the transistor 11 is kept constant, and since the base bias voltage of the transistor 15 also depends on the constant current, the collector current of the transistor 15 and therefore the current to the zener diode 2 is kept constant.

Therefore, the zener voltage of the reference diode 2 is scarcely affected by the variations in current and voltage but assumes a constant value. Consequently, the output voltage appearing at the terminal 6 will not fluctuate notwithstanding the variation in the voltage of the power supply so that a very stable power source can be provided.

It should here be noted that the initial current conducting resistor 17 in the circuit shown in FIG. 2 plays a very important role.

Namely, without the resistor 17 no voltage would appear at the point b and no collector currents would flow through the transistors 11 and 15 since even if a voltage is applied to the terminal 1 no current can flow through the zener diode. And therefore no output could be derived from the output terminal 6. Thus, the resistor 17 serves to conduct the initial current to the reference diode, i.e., silicon zener diode 2, and is considered to be an indispensable circuit element. The value of the resistance which the resistor 17 is to possess, must be very carefully chosen.

Namely, if the resistance value of the resistor 17 is small and therefore if current drawn to the zener diode 2 through the resistor 17 is large, it would be difficult to obtain a highly stabilized output voltage.

Therefore, the resistance value of the resistor 17 should be so chosen such that the current flowing through the resistor 17 may be sufficiently small in comparison with the collector current of the transistor 15.

It is needless to say that in this case the current flowing through the resistor 17 must have at least such a value as can produce an output voltage at the terminal 6 when a voltage is applied to the terminal 1.

As has hithereto been described, the output of the dc voltage regulator circuit according to the invention is not affected by the variation in the voltage of the power supply connected thereto and therefore is effectively used to supply a constant voltage for a transistorized electronic circuit.

We claim:

1. In combination with a voltage regulator having an emitter follower connected between input and output terminals and a zener diode connected to the base of the emitter follower to maintain a substantially constant base voltage, means for stabilizing the voltage at the output terminal, comprising a current control transistor having an input base and an output collector connected to the zener diode for controlling the supply of base current to the base of the emitter follower, bias voltage control means connected to the input base of the control transistor for maintaining said base current constant, means connected to the output terminal for supplying a reference voltage to the bias voltage control means, and initial current conducting means connecting the input terminal to the base of the emitter follower for instantaneously rendering the emitter follower conductive to establish said reference voltage.

2. The combination of claim 1 wherein said reference voltage supply means comprises a voltage divider connected to the output terminal, and an emitter follower circuit connecting the voltage divider to the bias voltage control means.

3. The combination of claim 2 wherein said bias voltage control means comprises a constant current conducting transistor having collector and emitter circuits connected in parallel with said emitter follower circuit and a base connected to an output of the emitter fol lower circuit, the collector circuit of the constant current conducting transistor being connected to the input base of the control transistor.

4. The combination of claim 3 wherein said initial current conducting means comprises a resistor connected to the input terminal.

5. A dc voltage regulator comprising power supply and output terminals, a first transistor having a collector and an emitter connected respectively to said power supply terminal and said output terminal and a base, a reference diode connected between the base of said first transistor and ground, parallel circuits consisting of a resistor and a second transistor, said parallel circuits being connected between the power supply terminal and the base of said first transistor, a voltage divider circuit connected in series with the emitter of said first transistor, a third transistor having an emitter, a collector connected to the power supply terminal and a base connected to said voltage divider circuit, the output from the emitter of said third transistor being coupled to the base of said second transistor to control base bias voltage applied to said second transistor.

Claims

3. The combination of claim 2 wherein said bias voltage control means comprises a constant current conducting transistor having collector and emitter circuits connected in parallel with said emitter follower circuit and a base connected to an output of the emitter follower circuit, the collector circuit of the constant current conducting transistor being connected to the input base of the control transistor.