JPH0216610A - Constant-voltage power supply circuit - Google Patents

Abstract

PURPOSE:To make satisfactory a ripple rejection even at the time of an action at a non-stabilizing area by removing the ripple of an input and controlling an output transistor through a bias voltage supplying means and a reference voltage supplying means when the input voltage is the prescribed value or below. CONSTITUTION:An input voltage VIN is controlled by an output transistor Q1 fed back and controlled by an error amplifier A and a constant voltage Vo is outputted. When the voltage VIN is reduced to a prescribed value or above, in accordance with the voltage VIN to remove the ripple overlapped by a ripple removing means 300, a bias voltage occurs from a bias voltage supplying means 100, the output of a reference voltage supplying means 200 is supplied to the amplifier A, and even at the time of the action at the non-stabilizing area, the ripple rejection is satisfactorily executed.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a constant voltage power supply circuit suitable for use in audio systems, which has good characteristics in the input voltage stabilization region, and which has good characteristics in the unstabilized region when the input voltage decreases. In order to improve the ripple rejection even when transitioning to the operation of , bias voltage supply means for supplying a bias voltage that changes according to a change in the input voltage when the input voltage is less than a predetermined value, and the error amplifier according to the bias voltage supplied by the bias voltage supply means. A reference voltage supply means for supplying a reference voltage to the input voltage, and a ripple removal means for removing ripples superimposed on the input voltage.
), configured.

[Industrial application field]

The present invention relates to a constant voltage power supply circuit suitable for use in an audio system.

In recent years, there are many devices that can operate at low voltages.

- An example is an in-vehicle audio system that is connected to a car's battery power supply, but in the constant voltage power supply circuit that supplies power to these devices,
It is desirable that the input voltage maintains a predetermined value for stable operation.

However, the input voltage of the constant voltage power supply circuit may drop below the predetermined value, such as when the car's battery power drops. Even in such a case, it is necessary to maintain the operating state of the audio system connected to the following.

In this case, as the input voltage of the constant voltage power supply circuit drops, the output voltage of the constant voltage power supply circuit also drops, but it is necessary to prevent characteristics such as ripple rejection from decreasing at this time.

[Conventional technology]

FIG. 5 shows an example of a conventional constant voltage power supply circuit.

In the constant voltage power supply circuit shown in the figure, when the input voltage V is equal to or higher than the predetermined value V,
IN(S) Output voltage V when in the chemotaxis region. resistors R1 and R
The voltage divided by 2 and the reference voltage vREF are input to the error amplifier A, and the output of the error amplifier A is fed back to the output transistor Q1, thereby supplying a constant voltage. However, in the constant voltage power supply circuit shown in FIG. 5, no consideration is given to the usage condition in the unstabilized region when the input voltage V drops below the predetermined voltage V. and the output voltage V is approximately equal to the input voltage V1N.
However, when operating in the non-stabilized region, the output transistor Q1 becomes saturated, which deteriorates the ripple rejection.

Figure 7 shows a case where the conventional constant voltage power supply circuit shown in Figure 5 is applied to the power supply circuit of a general audio system, and a large ripple component is superimposed on the input voltage v1N of the constant voltage power supply circuit. Therefore, when the input voltage decreases by 1-1 and shifts to an operating state in the non-stabilized region, the ripple component appears in the output voltage V0 of the constant voltage power supply circuit. The small signal amplifier connected to the next stage of the constant voltage power supply circuit has similarly deteriorated ripple rejection due to a drop in its input voltage, and oscillation (motor poding) occurs in the path that passes through the small signal amplifier and is input to the power amplifier. The problem arises that the message is sent @). Therefore, when the input voltage V1N of the constant voltage power supply circuit decreases and the operation state is about to shift to an unstabilized region, the above problem is avoided by immediately turning off the constant voltage power supply circuit. However, when a constant voltage power supply circuit is applied to an audio system, there are many problems in that when the circuit is turned off, the sound cuts out2, causing discomfort to the listener.

FIG. 8 shows another conventional example of a constant voltage power supply circuit. During operation in the unstabilized region, the ripple component superimposed on the input voltage VO is removed by the resistor R and capacitor C2.
The configuration is such that the ripple component is removed by a ripple component filter consisting of the following. Therefore, ripple rejection is improved, but conversely, since the configuration is a non-feedback type using a Zener diode ZD,
Due to variations in the characteristics of D, there is a problem in maintaining the characteristics in the stabilization region.

[Problem to be solved by the invention]

Therefore, if the constant voltage power supply circuit is configured with emphasis on operating characteristics when it operates in the stabilization region, ripple rejection will worsen when the operating state shifts to the non-stabilization region, and conversely, it will become unstable. If the circuit configuration is designed to improve ripple rejection during operation in the stabilization region, there is a problem in that the constant voltage operation characteristics in the stabilization region deteriorate.

It is an object of the present invention to provide a constant voltage power supply circuit that has good characteristics in the stabilization region and also has good ripple rejection characteristics even when the input voltage decreases and the operation shifts to the non-stabilization region. With the goal.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention, in which an error amplifier A is used to control the output transistor Q1 in order to derive an output voltage V having the relationship shown in FIG. 3 with respect to the input voltage vIN. and a bias voltage supply means 10 for supplying a bias voltage that changes according to a change in the input voltage v1 when the input voltage is less than or equal to a predetermined value.
0 and the reference voltage ■R to the error amplifier A through the bias voltage path supplied by the bias voltage supply means 100.
8, and ripple removal means 30 for removing ripples superimposed on the input voltage.
0 constitutes a constant voltage power supply circuit and solves the above problem.

[Effect]

According to the present invention having the above configuration, the system of the output transistor Q1 and the error amplifier A is saturated in the unstabilized region where the input voltage 1N has dropped (region 1N≦vIN(S) in FIG. 2). In order to prevent this, the bias voltage of the reference voltage supply means 200 is changed in accordance with the input voltage VIN, and as a result, the reference voltage applied to the error amplifier A is changed in accordance with the input voltage v1N. Input voltage V1N
The ripple component superimposed on the image is removed by a beam tool removing means.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 shows a specific circuit of buffer amplifier B in FIG. In FIG. 2, the output terminal of the error amplifier A is connected to the base of the output transistor Q1, the emitter of the output transistor Q1 is connected to the input voltage source (1N), and the output voltage V is output from the collector. is derived. A resistor R1 is connected between the collector of the output transistor Q1 and the ground.
and R are connected in series, and the connection point of resistors R1 and R2 is connected to the non-inverting input terminal of error amplifier A. The configuration of 0 or more is the same as the configuration of the conventional constant voltage power supply circuit shown in FIG. Although they are the same, the embodiment according to the present invention differs from the conventional example in the following points. That is, in the conventional example shown in FIG. 5, a fixed reference voltage source (REF) is connected to the non-inverting input terminal of the error amplifier A, and this reference voltage "REF
The output voltage V is determined by the feedback constant determined by the resistors R and R2.
o has been determined, but this embodiment is different in this respect.

In this embodiment, a diode D1, resistors R3, R4, and a diode D2 are connected in series in this order between the input voltage power supply (VIN) and the ground, and the connection point between the resistors R and R is connected to the base of the transistor Q2. connected to the The collector of transistor Q2 is connected to the input voltage power supply (vlN), and the emitter is connected to the bias terminal of buffer amplifier B, which will be described later.

A bias voltage supply means is constituted by the diode/resistance array consisting of the diodes D 1 and D 2 and the resistors R3 and R4, and the transistor Q2.

A reference voltage vR[F is applied to the non-inverting input terminal (Y) of the buffer amplifier B, and the voltage obtained by dividing the output of the buffer amplifier B by a resistor string consisting of resistors R5 and R6 is applied to the inverting input terminal (Y). X). This buffer amplifier B constitutes a reference voltage supply means and provides a reference voltage vR8 to the error amplifier A.

A capacitor C is connected between the connection point of the resistors R3 and R4 and the ground, and the resistor R3 and capacitor C1 constitute ripple removal means for removing ripples superimposed on the input voltage.

Next, the operation of the circuit shown in FIG. 2 will be explained.

The input voltage V versus the output voltage V that is sought to be achieved by the circuit shown in FIG. Figure 3 shows the characteristic diagram of IN, where the input voltage V is greater than the predetermined value V.
IN(S) If (V>V), that is, the input voltage is stable IN
In the IN(S) region, the reference voltage VR8 and the feedback resistor R,
A constant voltage V determined by R. Input voltage “IN”
On the other hand, if the input voltage V is larger than the predetermined value V, IN IN(S) (V ≦v), that is, the input voltage v1 - non-safe IN
1 old S) When in the constant region, the input voltage v1N, J, is always outputted as a voltage lower by a predetermined voltage va.

In order to obtain such characteristics, the input voltage vIN is set to a predetermined value vI
If higher than N(S) (v>v), then IN
IN(S) The reference voltage ■RB applied to the error amplifier A is changed to the reference voltage ■RB applied to the non-inverting input terminal of the buffer amplifier B. is determined by the resistance values of resistors R5 and R6.

As a result, the output voltage ■. is determined by the reference voltage V applied to the error amplifier A and the resistance values of the resistors R1 and R2, RB, and a constant voltage is output.

That is, the reference voltage vR8 given to the error amplifier A becomes the output voltage V. becomes as follows.

I'm trying to be more decisive. The bias voltage ■oD of the buffer amplifier B is connected to the diode D1. D2 and resistance R3,
It is provided by a bias voltage supply means composed of a diode/resistance string R4 and a transistor Q2. Here, the base voltage of the transistor Q2 changes according to the change in the input voltage vI- at the connection point of the resistors R3 and R4, and as a result, the bias voltage V of the buffer amplifier B also changes to the input voltage 1-
It will change accordingly. If the base voltage of the transistor Q is v8, and the voltage between the diode and the base-emitter voltage of Q2 are both VD, then the bias voltage 00 of the buffer amplifier B becomes IN IN( S) (V ≦■), the reference voltage IN of the error amplifier A is
The IN(s) voltage V can be expressed as the bias voltage vDO of the buffer amplifier B as RB, and it can be seen that the bias voltage VDO changes according to the input voltage V1N. Bias voltage V
changes according to the input voltage v1N, the error amplifier A
The reference voltage vR8 applied to the input voltage vR8 similarly changes according to the input voltage v1N. Therefore, the output voltage V. Also the input voltage
It will change according to 1N.

A ripple filter is formed by the resistor R3 and the capacitor C1, and removes the ripple component superimposed on the input voltage.

A specific circuit of buffer amplifier B shown in FIG. 2 is shown in FIG.

The emitters of transistors Q14 and Q15 are commonly connected, and their common connection terminal is connected to the collector of transistor Q11, which constitutes a constant current source circuit together with transistors Q12 and Q13. The reference voltage REF shown in FIG. 2 is applied to the base of the transistor Q15, and the base of the transistor Q14 is connected to the connection point between the resistors R5 and R6, also shown in FIG. The collectors of transistors Q14 and Q15 are connected to transistors Q16 and Q1 of a current mirror configuration, respectively, and the base of transistor Q18 is connected to the collector of transistor Q15. The collector of transistor Q18 is connected to the emitter of transistor Q2 shown in FIG. 2 via transistor Q12, which serves as a constant current load circuit.

Similarly, the collector of transistor Q19 is connected to transistor Q.
2, and its base is connected to the collector of transistor Q18. Transistor Q1
The emitter of transistor Q19 is connected to ground via resistor R7, and the reference voltage VR3 to be applied to error amplifier A is derived from the emitter of transistor Q19.

In the buffer amplifier B configured as above, when the input voltage V has fallen below the predetermined value V
IN(S), the reference voltage vRB applied to the error amplifier A is the saturation voltage of the transistor Q. If E(sat), then V−V−(V+V l ・・
・ (4) RB 00 0 CE (sat
), therefore, the output voltage V. Substituting equations (4) and (3) into equation (5), R1+
R2... (5)' Also, the input/output voltage difference va is the saturation voltage V of Ql. E(sat). By setting the resistors R1 and R2 so that the voltage between input and output is larger than 1, deterioration of ripple rejection due to saturation of transistor Q1 is almost eliminated. However, since there is a term that includes "IN" in equation (5)', a ripple component will appear in the output if no measures are taken. Therefore, a capacitor C1 is connected to the connection point of resistors R3 and R4, Together with the resistor R3, a ripple filter is formed to substantially remove ripple components appearing in the output.

〔Effect of the invention〕

As explained above, according to the present invention, even if the input voltage is so low that the constant voltage power supply circuit becomes unstabilized, it is possible to reduce the deterioration of ripple rejection, which contributes to the stable operation of the device. It has the effect of being large.

... (6) This V becomes the emitter-collector voltage of the transistor Q1. This allows the transistor

[Brief explanation of the drawing]

1 is a circuit diagram for explaining the principle of a constant voltage power supply circuit according to the present invention, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is a circuit diagram for explaining the principle of a constant voltage power supply circuit according to the present invention.
Figure 4 is a circuit diagram showing an embodiment of the buffer amplifier shown in Figure 2. Figure 5 is a circuit diagram showing a conventional constant voltage power supply circuit. , Fig. 6 is an input/output characteristic diagram of the circuit shown in Fig. 5, Fig. 7 is a diagram showing the case where the constant voltage power supply circuit of Fig. 5 is applied to the power supply circuit of a general audio system, and Fig. 8 is a diagram showing the case where the constant voltage power supply circuit of Fig. 5 is applied to the power supply circuit of a general audio system. , is a circuit diagram showing another conventional constant voltage power supply circuit. A...Error amplifier, B...Buffer amplifier, Ql...Output transistor, Q2-Q19...Transistor, C1...Capacitor, R1-R7...Resistor. Diagram explaining the principle of the present invention.Figure 1.Figure 2. Characteristics of input voltage vs. output voltage realized.Figure 3.Figure 7. Circuit diagram of buffer amplifier.Figure 4.Figure 6.

Claims (1)

[Claims] A predetermined output voltage (V_0
) and an error amplifier (Q_1) for controlling the output transistor (Q_1).
In a constant voltage power supply circuit comprising A), when the input voltage is below a predetermined value, the input voltage
), and a bias voltage supply means (100) for supplying a bias voltage that changes according to changes in the error amplifier (A) according to the bias voltage supplied by the bias voltage supply means (100). (V_R_B)
a reference voltage supply means (200) that provides an input voltage (V
A constant voltage power supply circuit comprising: ripple removal means (R_3, C_1) for removing ripples superimposed on the voltage (R_3, C_1).