JPH0216611A - Constant-voltage power supply circuit - Google Patents

Abstract

PURPOSE:To make satisfactory the action specification at a stabilizing area and to make satisfactory a ripple rejection characteristic at the non-stabilizing area by changing a reference voltage and controlling an output transistor in accordance with the fact whether the input voltage to remove a ripple is the prescribed value or above or the prescribed value or below. CONSTITUTION:An output transistor Q1 is fed back and controlled by an error amplifier A and an action characteristic becomes satisfactory at the stabilizing area. On the other hand, when an input voltage VIN to remove the ripple overlapped by a ripple removing means 300 becomes the prescribed value or above or the prescribed value or below, the reference voltage of the voltage different by first and second voltage supplying means 100 and 200 occurs, is supplied to the amplifier A and the ripple rejection at the non-stabilizing area is also 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 stabilization region, and which shifts to operation in the non-stabilization region when the input voltage decreases. The purpose of the present invention is to provide a constant voltage power supply circuit with good ripple rejection characteristics even when a first reference voltage supply means that supplies a predetermined reference voltage to the error amplifier when the input voltage is above a predetermined value; and a reference that changes according to the input voltage of the error amplifier when the input voltage is below the predetermined value. It is comprised of a second reference voltage supply means for supplying a voltage to the error amplifier, and a ripple removal means for removing ripples superimposed on the input voltage.

[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 subsequent stage. 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 ■ 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 VRE1 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 situation when the input voltage V drops below the predetermined voltage V, that is, when it is used in an unstabilized region. 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.A large ripple component is superimposed on the input voltage V1N of the constant voltage power supply circuit. Therefore, when the input voltage (1N) decreases and shifts to an operating state in the non-stabilized region, the ripple component becomes the output voltage V of the constant voltage power supply circuit. appears in 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 boarding oscillation) occurs in the path that passes through the small signal amplifier and is input to the power amplifier. ). Therefore, when the input voltage v1N of the constant voltage power supply circuit decreases and the constant voltage power supply circuit is about to enter an operating state in 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 out, causing discomfort to the listener.

FIG. 8 shows another conventional example of a constant voltage power supply circuit. When operating in the unregulated region, the input voltage vIN
The configuration is such that the ripple component superimposed on the ripple component is removed by a ripple filter consisting of a resistor R8 and a capacitor C2. Therefore, ripple rejection is improved, but since it is a non-feedback configuration using a Zener diode, it is difficult to stabilize and maintain the characteristics in the region due to variations in the characteristics of the Zener diode. There is a problem with this point.

[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 an explanatory diagram of the principle of the present invention. In order to derive an output voltage Vo having the relationship shown in FIG. 3 with respect to the input voltage vIN by the output transistor Q1,・An error amplifier A that controls the transistor Q1, a reference voltage supply means 100 that supplies a predetermined reference voltage vREF to the error amplifier A, and a reference voltage supply means 100 that supplies a predetermined reference voltage vREF to the error amplifier A, According to the reference voltage vRE
Reference voltage control means 200 for changing F and input voltage ■
The above problem was solved by configuring a constant voltage power supply circuit with ripple removal means 300 for removing ripples superimposed on 1N.

[Effect]

According to the present invention having the above configuration, the input voltage V1N is in a stabilization region equal to or higher than a predetermined value (in FIG. 3, v1N≧vIN(s
), the first reference voltage supply means 100
A constant reference voltage vREF is supplied to the error amplifier A, and a constant voltage corresponding to the feedback constant determined by the reference voltage vREF and the resistors R1 and R2 is output voltage V. Derive it as In the unstabilized region IN IN(S) where the input voltage V has dropped below the predetermined value V (region of ■≦V in Figure 3), IN
IN(S) is controlled by the input voltage V by the reference voltage control means 200 so that the system of the output transistor Q1 and the error amplifier A is not saturated.
1-Reference voltage vRE according to the change in the error amplifier A
and the output ■ according to the change in input voltage v1. Let's derive it. The ripple component superimposed on the input voltage VIN is removed by the ripple removal means.

〔Example〕

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

FIG. 4 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 shows a specific circuit of buffer amplifier B in FIG. In Figure 2, the output terminal of error amplifier A is connected to the base of output transistor Q1, and the emitter of output transistor Q1 is connected to the input voltage source (V 1N).
The output voltage V is connected to the collector. is derived.

A resistor R is connected between the collector of the output transistor Q1 and the ground.
1 and R2 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. However, 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 (VREF) is connected to the non-inverting input terminal of the error amplifier A, and this reference voltage VR
Although the output voltage Vo was determined by the feedback constant determined by EF and the resistors R1 and R2, the present example differs in this point.

In this embodiment, a buffer amplifier B for controlling the reference voltage is coupled to the inverting terminal of the error amplifier A. The non-inverting input terminal of buffer amplifier B has resistors R4, Rs and R6 connected between the input power supply V1N and ground.
The voltage V divided by the resistor R of the resistor string consisting of
A is applied to the inverting input terminal of the buffer amplifier B, and a fixed reference voltage source (VREF) is applied via a resistor R.
is connected. One end of capacitor C1 is connected to the connection point between resistors R and R5, the other end is grounded, and resistor R4
and capacitor C1 constitute a ripple filter.

The resistor string consisting of resistors R, R5 and R6 and the buffer amplifier B output the voltage shown in FIG.
1. When the voltage VA applied to the non-inverting input terminal of the buffer amplifier B is smaller than the reference voltage ``REF'', the output Vs of the buffer amplifier B becomes equal to the voltage ■A (■8=■A), Voltage V
When A is larger than the reference voltage vREF (VA≧VREF
', the output ■8 of buffer amplifier B is the reference voltage source voltage V
will be equal to REF. By setting the input voltage v1-range where vA x vREF is equal to or less than vIN(S) in Figure 3, and setting it to vREF, a voltage V is generated at the output transistor Q1 to prevent saturation of the output transistor Q1. let A ripple filter composed of a resistor R4 and a capacitor C1 removes the ripple component superimposed on the input voltage VIN, so that only a DC voltage is applied to the non-inverting input of the buffer amplifier B.

FIG. 4 shows a circuit diagram of buffer amplifier B in FIG. In FIG. 4, the emitters of transistors Q11 and Q12 are commonly connected, and their common connection terminal is connected to the collector of transistor Q13, which constitutes a constant current source circuit together with transistors Q14 and Q15. The input voltage vIN is applied to the base of the transistor Q11.
A voltage VA obtained by dividing the voltage by resistors R4 and R5°R is applied. The collector of transistor Q11 is transistor Q
It is grounded via 16. The base of transistor Q12 is connected to the reference voltage source (VR, ) via resistors R' and R3.
It is connected to the. The cathode of a diode D1 is connected to the collector of the transistor Q12 and the base of the transistor Q16, and the anode of the diode D1 is grounded.

The collector of transistor Q14 is connected to the base of transistor Q18 and the emitter of transistor Q17. The collector of transistor Q18 is connected to the connection point between resistors R3 and R3'. The emitter of transistor Q18 is connected to the base of transistor Q19 and is grounded via resistor R7. The collector of transistor Q is connected to one end of resistor R3' and to the base of transistor Q12.

Next, the operation will be explained.

Now, in the stabilization region where the input voltage VIN is sufficiently high, the voltage V divided by the resistors R, R5, and R6 is set to be sufficiently higher than the reference voltage VREF, and the transistor Q11 is turned off. state. Therefore, the collector voltage of the transistor Q11 drops, the transistor Q1□ turns on, and the current I flows into the transistor Q1□.

Accordingly, transistors Q18 and Q19 are turned off. At this time, the transistor Q12 is in the on state, and the reference voltage source (
A small current flows through VRE, ), and as a result, a voltage Vs equal to the reference voltage ■ is applied to the non-inverting input terminal of the error amplifier A.
will be applied.

EF Next, the potential ■4 decreases to below the voltage vREF of the reference voltage source and shifts to operation in the non-stabilized region, and the collector voltage of the transistor Q11 rises, causing the transistor Q1
7 is in the off state. Along with this, transistor Q1
8 and Q19 are turned on, and the gain of the buffer amplifier B is 1, so the voltage ■ becomes the same potential as the voltage VA.

When operating in the stabilization region (V≦vIN(S)'), the following equation holds true.

Therefore, the output voltage Vo is as follows.

... (3) To simplify equation (3), if we set Rs ''' R1R2, equation ('3) becomes, and when V = V, the voltage difference between the input and output is the resistor I.
N IN (S) is determined only by the voltage developed across resistor R4.

This reduces the deterioration of ripple rejection due to saturation of the output transistor Q1 at low voltages. However, since Equation (4) includes ■IN, if ripples are superimposed on this, ripples will appear in the output.In order to prevent this, a ripple filter is formed by conzante C1 and resistor R4, and a buffer is used. By applying only direct current to the non-inverting input terminal of amplifier B, deterioration of ripple rejection is effectively prevented.

〔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.

[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 shown in Fig. 5 is applied to the power supply circuit of a general audio system, and Fig. 8 The figure is a circuit diagram showing another conventional constant voltage power supply circuit. A...Error amplifier, B...Buffer amplifier, Ql...Output transistor, Q11 to Q19...Transistor, c, c2...Capacitor, R to R, R3'...Resistance. Figure 6

Claims (1)

[Claims] A predetermined output voltage (V_0
) and an error amplifier (Q_1) for controlling the output transistor (Q_1).
A): a reference voltage supply means (100) for supplying a predetermined reference voltage (V_R_E_F) to the error amplifier (A) when the input voltage (V_I_N) is equal to or higher than a predetermined value; , input voltage (V_
When the input voltage (V_I_N) of the error amplifier (A) is lower than the predetermined value, the reference voltage (V_R_E
A constant voltage power supply circuit comprising: a reference voltage control means (200) for changing the input voltage (V_I_N); and a ripple removal means (300) for removing ripples superimposed on the input voltage (V_I_N).