JPH10198443A - Serial stabilized power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably set the 1st pole of negative feedback amplifier by freely setting the gain of error amplifier while using a constant current source for a load for preventing the influence of voltage fluctuation from the input side. SOLUTION: A constant current source 1 can be easily provided in configuration with which a transistor is serially arranged between a non-stable input terminal and a stable input terminal, for example, a current to be controlled is let flow to a fixed resistor and the difference between its voltage drop and a reference voltage is amplified and negatively fed back. Thus, since the gain of system is increased by using the constant current source 1, a variable resistor R8 is inserted between the base and emitter of transistor Tr1 and constituted so as to control the gain. The voltage between both the terminals of variable resistor R8 for gain control is the VBE of transistor Tr1 such as about 0.6V, for example, and a current to flow through the resistor R8 becomes 0.6V/R8 and gets extremely reduced so that the selection range of resistance value can be made extremely wide and large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a series-type stabilized power supply circuit, and more particularly to a series-type stabilized power supply circuit in which the gain of an error amplifier can be easily set and the setting of a first pole of a negative feedback amplifier is stable. Things.

[0002]

2. Description of the Related Art First, a series-type stabilized power supply circuit will be described with reference to FIG. FIG. 5 is a diagram of a conventional series-type stabilized power supply circuit. The series stabilized power supply circuit
Programmable controllers, video tape recorders,
It supplies a DC constant voltage to an electronic device such as a television. The power supply circuit is an important part related to the reliability of these electronic devices. Generally used in the prior art are a series stabilized power supply in which a control transistor is connected in series to a load, and a parallel stabilized power supply in which a control transistor is connected in parallel to a load. . In the series-type stabilized power supply circuit, the output voltage is stabilized by controlling the control transistor by applying negative feedback using the divided output voltage of the output voltage, and the performance is very stable. Most of the power supply circuits adopt this method.

With reference to FIG. 5, a series stabilized power supply circuit will be described. In FIG. 5, the control transistor Tr1
The DC input terminal 21 is connected to the collector of the transistor Tr1 (hereinafter simply referred to as a transistor Tr1), and the stabilized voltage output terminal 22 (hereinafter simply referred to as the output terminal 22) is connected to the emitter. The unstable voltage supplied to the DC input terminal 21 (hereinafter simply referred to as the input terminal 21) is supplied to the output terminal 22 through the transistor Tr1, and the output voltage is supplied to the load. The output terminal 22 is connected to a voltage dividing circuit including a voltage dividing resistor R5, a voltage dividing variable resistor R6, and a voltage dividing resistor R7, and a constant voltage diode ZD is connected via a resistor R4.

A base of the transistor Tr1 is connected to a collector of an error amplifying transistor Tr2 (hereinafter simply referred to as a transistor Tr2). The base is connected to an input terminal 21 via a constant current source 1.
The emitter of the transistor Tr2 is connected to the cathode of the constant voltage diode ZD, while the base is connected to a voltage dividing circuit in which a voltage dividing resistor R5, a voltage dividing variable resistor R6, and a voltage dividing resistor R7 are connected in series. It is connected to the sliding point b of the variable resistor R6. An output capacitor C is connected to the output terminal 22.
1 is connected.

In the constant voltage power supply circuit having such a configuration, when the input voltage to the input terminal 21 decreases, for example, and the output voltage from the output terminal 22 decreases, the sliding point b of the voltage dividing variable resistor R6 Voltage at the same time. On the other hand, since the reference voltage by the constant voltage diode ZD is constant,
The base-emitter differential voltage of the transistor Tr2 decreases, and the collector current decreases accordingly. As a result, the collector potential of the transistor Tr2 increases, that is, the base potential of the transistor Tr1 increases, and therefore, the emitter potential of the transistor Tr1 also increases. As a result, the previous decrease in the output voltage is canceled. When the output voltage rises, the operation opposite to the above occurs, so that the output voltage is kept constant irrespective of the fluctuation of the input voltage to the input terminal 21 and the load. Has become.

[0006]

In the conventional series stabilized power supply circuit shown in FIG. 5, the gain of the error amplifier is substantially equal to the ratio of the output resistance R1 on the emitter side of Tr2 to the load resistance of the constant current source 1. Since it is necessary to supply the base current of the output transistor Tr1 to R1, there is a limitation in the case of a high resistance, and when the operating load of the constant current source 1 is reduced, the current flowing to the transistor Tr2 increases. In addition, there is a problem that a large capacity is required for both the operation load of the constant current source 1 and the Tr2.

Further, the pole of the series stabilized power supply circuit is
A transistor determined by the emitter output resistance R3 of the transistor Tr1 and the output capacitor C1,
Some are determined by the input capacitance of r1 and the operating load of the constant current source 1, and there is a problem that both approaches and become unstable. For this reason, the emitter output resistor R3 is reduced to be proportional to the current flowing through the transistor Tr1,
The output capacitor C1 had to be large. The capacitance of the output capacitor C1 fluctuates under the influence of the ambient temperature, but in order to operate the circuit stably under various conditions, it is necessary to increase the value of C1 and set the pole sufficiently low. It becomes necessary. For this reason, there has been a problem that the frequency band that can be controlled by the circuit system is narrowed.

In the conventional series stabilized power supply circuit, a constant current circuit is used for the load of the error amplifier in order to prevent the influence of power supply fluctuation from the input side, so that the operating resistance of the constant current source is high. As a result, the gain of the error amplifier becomes too large, and the operation of the negative feedback amplifier becomes unstable. Further, the first pole of the negative feedback amplifier is constituted by an output resistance of an output transistor which varies with respect to an output current and an output capacitor whose capacitance varies with temperature (in practice, an electrolytic capacitor is often used depending on the capacitance). Therefore, there is a problem that the performance as the negative feedback amplifier must be set low.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem. To prevent the influence of voltage fluctuation from the input side, the gain of an error amplifier can be freely adjusted by using a constant current source as a load. It is an object of the present invention to provide a series-type stabilized power supply circuit capable of setting a first pole of a negative feedback amplifier and stably setting the first pole.

[0010]

In order to solve the above-mentioned problems, a series-type stabilized power supply circuit according to the present invention comprises a series-type stabilized power supply circuit having a constant current source as a load resistor. A control transistor inserted between the terminals, a constant current load inserted between the base and collector of the control transistor, an error amplification transistor connected in series with the constant current load, and a base connected to the error amplification transistor A voltage dividing resistor for error detection, a Zener diode serving as a reference power supply connected to an emitter of the error amplifying transistor, and an emitter of the control transistor.
A gain adjusting resistor connected between a connection point between the base of the control transistor and the collector of the error amplifying transistor, and a constant voltage bias connected between an emitter of the control transistor and an emitter of the error amplifying transistor. It is characterized by comprising a resistor and an output capacitor connected to the output terminal. In the series stabilized power supply circuit according to the preceding paragraph, a Zener diode is disposed between a connection point between the base of the control transistor and the constant current load, and a connection point between the collector of the error amplification transistor and the gain adjustment resistor. It is characterized by having been provided. In the series-type stabilized power supply circuit according to the preceding paragraph, an output capacitor connected to the output terminal is removed, and a connection point between the gain adjustment resistor, the base of the control transistor, the collector of the error amplification transistor, and the ground. And a capacitor is disposed in the second portion.

In the above-described series stabilized power supply circuit, the first pole of the negative feedback amplifier is constituted by the above-described gain adjusting resistor and capacitor.
This is to reduce the effects of load current and temperature. When the first pole is brought to the gain adjustment resistor and the capacitor, it is possible to eliminate the large-capacity electrolytic capacitor normally put on the output side, so that there is no problem of the life related to the electrolytic capacitor and the like. A high system can be built.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. 1 to 4, a series stabilized power supply according to the present invention will be described. In the description of the series-type stabilized power supply according to the present invention, the description of the parts common to the related art will be omitted because it is complicated, and the characteristic parts will be described in detail.

[Embodiment 1] FIG. 1 is a circuit diagram of a series stabilized power supply according to an embodiment of the present invention. FIG.
In the figure, the constant current source 1 is not shown, but for example,
A known circuit configuration in which a transistor is arranged in series between an unstable input terminal and a stable output terminal, a current to be controlled flows through a constant resistor, a difference between the voltage drop and a reference voltage is amplified, and negative feedback is performed. And can be easily realized. Since the gain of the system is increased by using the constant current source 1, a variable resistor R8 is inserted between the base and the emitter of the transistor Tr1 so that the gain can be adjusted. The voltage across the variable resistor R8 for gain adjustment is the VBE of the transistor Tr1, for example, about 0.6 V, and the current flowing through the resistor R8 is 0.6 V / R8, which is extremely small. The range is very wide and can be large.

[Embodiment 2] Referring to FIG. 2, a series stabilized power supply according to another embodiment of the present invention will be described. FIG. 2 is a circuit diagram of a series stabilized power supply according to another embodiment of the present invention. In the series stabilized power supply shown in FIG. 2, the common parts with the series stabilized power supply shown in [Embodiment 1] of FIG. 1 are omitted, and different parts will be described. As shown in FIG. 2, a diode D1 is connected between the connection point of the base of the transistor Tr1 and the variable resistor R8 for gain adjustment.
Is inserted, the voltage across the variable resistor R8 can be made substantially zero. In addition, the diode D1
If a light emitting diode is used, the operation can be confirmed. The selection range of the variable resistor R8 can be very wide, and the size of the capacitor C1 is also free.

[Embodiment 3] With reference to FIG. 3, a series stabilized power supply according to still another embodiment of the present invention will be described. FIG. 3 is a circuit diagram of a series stabilized power supply according to still another embodiment of the present invention. In the series stabilized power supply shown in FIG. 3, the common parts with the series stabilized power supply shown in [Embodiment 1] of FIG. 1 are omitted, and different parts will be described.

As shown in FIG. 3, in FIG. 1, the variable resistor R8 for gain adjustment and the control transistor Tr1
A capacitor C2 for setting a first pole is added between a connection point between the base of the first transistor and the collector of the transistor for error amplification Tr2 and the ground.
Neglecting the input resistance (generally higher than the variable resistor R8, it can be ignored), the first pole is determined by the capacitor C2 and the variable resistor R8, and the variable resistor R8 is Since the output resistance is larger than the output resistance R3, a capacitor having a small capacity and excellent temperature characteristics can be used as the capacitor C2, and is less affected by the output current and the temperature. As described above, the first pole can be set at a high position by reducing the variation factors, so that the frequency band in which the system can be controlled can be widened, and the transient response characteristics with respect to load fluctuation can be improved.

Next, the frequency response characteristics of the series stabilized power supply circuit shown in FIG. 3 and the series stabilized power supply circuit shown in FIG. 5 will be described with reference to FIG. FIG. 4 is a Bode diagram showing the frequency response characteristics of the series stabilized power supply of FIGS. 3 and 5. In FIG. 4, the horizontal axis represents the frequency and the vertical axis represents the gain. In the series stabilized power supply circuit of the present embodiment shown in FIG. 3, the cutoff frequency and the position of the first pole are different from those of the conventional series stabilized power supply. It can be seen that it exists in a high frequency region as compared with the circuit, and shows good frequency characteristics.

[0018]

As described above in detail, according to the configuration of the present invention, even if a constant current circuit is used as the load of the error amplifier in order to prevent the influence of the voltage fluctuation from the input side, the error amplifier can be used. The gain can be freely set, the first pole of the negative feedback amplifier can be set stably, and a series-type stabilized power supply circuit with improved various characteristics and performance can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram of a series-type stabilized power supply circuit according to an embodiment of the present invention.

FIG. 2 is a series-type stabilized power supply circuit according to another embodiment of the present invention.

FIG. 3 is a circuit diagram of a series stabilized power supply according to still another embodiment of the present invention.

FIG. 4 is a Bode diagram showing frequency response characteristics of the series stabilized power supply circuit shown in FIGS. 3 and 5;

FIG. 5 is a diagram of a conventional series stabilized power supply circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Constant current source R1, R2, R3, R4, R5, R6, R7 ... Each fixed resistance R8 ... Variable resistance for gain adjustment Tr1 ... Control transistor Tr2 ... Error amplification transistor C1 ... Output capacitor C2 ... Capacitor ZD ... Zener Diode D1 ... Diode 21 ... Input terminal 22 ... Output terminal

Claims (3)

[Claims] In a series stabilized power supply circuit using a constant current source as a load resistor, a control transistor inserted between an input / output terminal, a constant current load inserted between a base and a collector of the control transistor, An error amplifying transistor connected in series with the current load, an error detecting voltage dividing resistor connected to the base of the error amplifying transistor, and a zener diode serving as a reference power supply connected to an emitter of the error amplifying transistor. An emitter of the control transistor; a gain adjusting resistor connected between a connection point of the base of the control transistor and a collector of the error amplifying transistor; an emitter of the control transistor and the error amplifying transistor A constant voltage bias resistor connected between the emitters and an output capacitor connected to the output terminal Tandem stabilized power supply circuit, characterized in that it is configured. 2. The series stabilized power supply circuit according to claim 1, wherein a connection point between a base of the control transistor and the constant current load, a connection point between a collector of the error amplification transistor and the gain adjustment resistor. A series-type stabilized power supply circuit, characterized in that a constant voltage element is disposed between the power supplies. 3. The series-type stabilized power supply circuit according to claim 1, wherein an output capacitor connected to the output terminal is removed, and the gain adjustment resistor, the base of the control transistor, and the output of the error amplification transistor are removed. A series-type stabilized power supply circuit comprising a capacitor arranged between a collector connection point and ground.