JPH02121011A - Constant-voltage power supply circuit - Google Patents

Abstract

PURPOSE:To improve a constant-voltage characteristic in a stabilized area and a ripple rejection characteristic in a non-stabilized area by outputting constant voltage from an output transistor (TR) when input voltage is higher than prescribed voltage, and preventing the saturation of the output TR when the input voltage drops lower than the prescribed voltage. CONSTITUTION:One of a first reference voltage supplying means 2 to supply definte one or more first reference voltages and a second reference voltage supplying means 3 to supply one or more second reference voltages to change corresponding to the input voltage Vin so as not to make the output TR Q1 saturate is selected by a switching means 4, and is connected to an error amplifier 1. Then, a controlling means 5 outputs a control signal which makes the switching means 4 select the first reference voltage supplying means 2 when the input voltage Vin is over the prescribed voltage, and makes it select the second reference voltage supplying means 3 when the input voltage Vin is lower than the prescribed voltage. Thus, the constant-voltage characteristic in the stabilized area and the ripple rejection characteristic in the non-stabilized area are improved.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a constant voltage power supply circuit suitable for use in an audio system, which aims to satisfy constant voltage characteristics in a stabilized region and ripple rejection characteristics in an unstabilized region, and has an output In a constant voltage power supply circuit comprising an error amplifier that controls an output section based on a comparison between an output voltage of the section and a reference voltage, a constant first reference voltage of at least one or more constant voltages is supplied to the error amplifier. a first reference voltage supply means; a second reference voltage supply means for supplying the error amplifier with at least one second reference voltage that changes according to the input voltage; and first and second reference voltages. a switching means interposed between the supply means and the error amplifier to connect either one of the first and second reference voltage supply means to the error amplifier; and control means for outputting a control signal for selecting the second reference voltage supply means to the switching circuit when the voltage is less than a predetermined 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, like when the battery supply voltage drops,
Although the input voltage of the constant voltage power supply circuit may drop below the predetermined value, it is necessary to stably operate the subsequent audio system even in such a case.

[Prior art] A typical power supply circuit for an in-vehicle audio system is
As shown in the figure, the choke coil 12 is connected to the battery 11.
The choke coil 12 is connected to a preamplifier via a constant voltage power supply circuit 13. In such a power supply circuit, a voltage drop occurs between both ends of the choke coil 12 based on the output current of the power amplifier, and a ripple component based on the voltage drop is superimposed on the input voltage of the constant voltage power supply circuit 13. The constant voltage power supply circuit 13 is provided to stabilize the power supply voltage supplied to the preamplifier and at the same time remove this ripple component. That is, this is to eliminate the inconvenience that the audio system becomes oscillated when the ripple component is input to the power amplifier via the preamplifier.

The constant voltage power supply circuit 13 will be explained based on FIG.
The input voltage Vin is applied to the emitter of the output transistor Q20, the output terminal of the error amplifier 14 is connected to the gate, the reference voltage Vref is input to the non-inverting input terminal of the error amplifier 14, and the reference voltage Vref is input to the inverting input terminal. A voltage obtained by dividing the output voltage Vo output from the collector of the output transistor Q20 by resistors R11 and R12 is input.

Then, the error amplifier 14 compares the input voltages of both input terminals, and when the input voltage of the inverting input terminal becomes higher than the reference voltage V ref in the operation in the stabilization region of the constant voltage power supply port W&13, the drive to the output transistor Q20 is performed. The output voltage V by decreasing the current.

When the input voltage of the inverting input terminal becomes lower than the reference voltage V ref, the output transistor Q2
The drive current to 0 is increased to raise the output voltage Vo, and this operation stabilizes the output voltage vO.
Ripple components superimposed on the input voltage Vin are also removed.

However, when the input voltage Vin becomes lower than the predetermined voltage Vins based on the reference voltage vret and enters the unstabilized region shown in FIG. 6, the output transistor Q20 becomes saturated based on the operation of the error amplifier 14. As shown, an output voltage Vo equal to the input voltage Vin is output, and in this state, the ripple component superimposed on the input voltage Vin is also output without being removed by the output transistor Q20.

Therefore, in such a case, oscillation of the audio system is avoided by turning off the constant voltage power supply circuit 13.

Furthermore, a circuit shown in FIG. 7 has been proposed as the constant voltage power supply circuit 13. That is, in this circuit, the Zener diode 15 stabilizes the output voltage Vo, and the input voltage V
Even when in falls below the predetermined voltage vins, the resistance R
A ripple component included in the input voltage Vin is removed by a time constant circuit consisting of the capacitor c2 and the capacitor c2. However, since such a constant voltage power supply circuit 13 is of a non-feedback type, even in a constant voltage region where the input voltage Vin is higher than the predetermined voltage vins, voltage regulation becomes insufficient based on the temperature characteristics of the Zener diode 15, etc. .

[Problem to be Solved by the Invention] Therefore, since the constant voltage circuit 13 shown in FIG. 5 is configured to turn off its operation in the non-stabilized region, the sound of the audio system may be interrupted, which is unpleasant. Yes, in the constant voltage power supply circuit 13 shown in FIG.
There has been a problem in that poor constant voltage characteristics in the stabilization region cause unstable operation of the audio system or deterioration of sound quality.

The purpose of this invention is to have good constant voltage characteristics in the stabilization region,
Further, it is an object of the present invention to provide a constant voltage power supply circuit having good ripple rejection characteristics in an unstabilized region.

[Means for Solving the Problems] FIG. 1 is a diagram illustrating the principle of the present invention. That is, the error amplifier 1 controls the output section based on a comparison between the output voltage of the output section and a reference voltage. A first reference voltage supply means 2 supplies at least one constant first reference voltage, and at least one reference voltage supply means 2 varies in accordance with the input voltage Vin so as not to saturate the output transistor. One of the second reference voltage supply means 3 for supplying two reference voltages is selected by the switching means 4 and connected to the error amplifier 1. Further, the switching means 4 causes the switching means 4 to select the first reference voltage supply means 2 when the input voltage Vin is above a predetermined voltage, and selects the second reference voltage supply means when the input voltage Vin is below the predetermined voltage. A control means 5 is connected to output a control signal for selecting 3. [Function] When the input voltage Vin is above a predetermined voltage, the error amplifier 1 operating based on the first reference voltage outputs a constant voltage from the output transistor Q1, and when the input voltage Vin falls below the predetermined voltage, the input The error amplifier 1 operates based on the second reference voltage that decreases in accordance with the voltage Vin, and saturation of the output transistor Q1 is prevented.

[Embodiment] An embodiment of a constant voltage circuit embodying the present invention will be described below with reference to FIGS. 2 and 3. An input voltage Vin is input to the input terminal Tin, and an output voltage is input to the input terminal Tin. The emitter of the transistor Q1 is connected, and the collector of the output transistor Q1 is connected to the output terminal TO and grounded via resistors R1 and R2.

The input terminal Tin is connected to a transistor Q2. The emitters of Q3 are connected and their bases are connected together.

Further, the base of transistor Q3 is connected to its collector. Transistors Q4, Q5 and Q6. Each pair of Q7 constitutes a differential amplifier, and transistors Q4 . Q
The collectors of transistors Q5.6 are connected to the collectors of transistors Q2, and the collectors of transistors Q5. The collector of Q7 is the transistor Q
3 collector. Also, transistor Q
5. The base of Q6 is connected between the resistors R1 and R2,
The collector of the transistor Q2 is connected via an intermediate amplifier 6 to the base of the transistor Q1. The transistors Q2 to Q7 and the intermediate amplifier 6 constitute an error amplifier that controls the transistor Q1.

The collector of a transistor Q8 is connected to the input terminal Tin, and the base of the transistor Q8 is connected to the base of the transistor Q4 and to a known reference voltage generation circuit 7 as a first reference voltage supply means. A constant first reference voltage Vref1 is input, and the emitter of the transistor Q8 is grounded via resistors R3 and R4. Therefore, transistor Q8 has an input voltage Vi
A constant collector current always flows regardless of fluctuations in n.

The collector of a transistor Q9 is connected to the input terminal Tin, and the emitter of the transistor Q9 is grounded via a resistor R5. Further, the base of the transistor Q9 is connected to the base of the transistor Q7, and is also connected to the input terminal Tin via resistors R6 and R7, and is grounded via a resistor R8. Furthermore, resistance R6
is grounded via capacitor C1. The resistors R6, R7, and R8 constitute a second reference voltage supply means, and the transistors Q7. A second reference voltage V ref2 obtained by dividing the input voltage vin by resistors R6, R7, and R8 is input to the base of Q9, and the collector current of transistor Q9 increases or decreases based on fluctuations in the reference voltage Vref2. ing.

Transistor Q4. The emitter of Q5 is the transistor QI
Q6.O is connected to the collector of transistor Q6. The emitter of Q7 is connected to the collector of transistor Qll, and the emitters of both transistors QIO and Q11 are grounded. Further, the base of the transistor QIO is connected to the emitter of the transistor Q9, and the base of the transistor QIO is connected to the emitter of the transistor Q9.
The base of the transistor Qll is connected between the resistors R3 and R4 and the base of the transistor Q12, and the collector of the transistor Q12 is grounded.

The transistors QIO, Qll, and Q12 constitute a switching means, and the base voltage VB of the transistor Q10 varies based on the increase/decrease in the collector current of the transistor Q9, and the base voltage VC of the transistor Q11 varies based on the collector current of the transistor Q8. and remains constant. Then, when VB > VC, transistor QIO is turned on and transistor Q4. Q5 operates and VB≦VC
Then, transistor Qll is turned on and transistor Q6. Q7 is now operational. Therefore, the transistor Q8, the resistors R3, R4, the transistor Q9, and the resistor R5 constitute a control means for controlling on/off of the transistors QIO, Qll.

Next, the operation of the constant voltage power supply circuit configured as described above will be explained.

Now, when the input voltage Vin is in the stabilization region of this constant voltage power supply circuit shown in FIG. ．． Q
5 works. Then, transistor Q2. Q3. Q4
．． Transistor Q1 based on the action of Q5 and intermediate amplifier 6
As a result of the operation, the output voltage vO becomes (R1-1-R2)VO=XVref1, which is a constant value set by the resistor RIR2 and the first reference voltage Vrefl, regardless of fluctuations in the input voltage Vin.

On the other hand, the input voltage Vin is a predetermined input voltage V shown in FIG.
When the voltage drops further below inS and reaches the unstabilized region, VB≦C based on the decrease in the collector current of transistor Q8.
Therefore, transistor Qll is turned on, and transistor Q6. Q7 works. Then, the output voltage vO becomes (R1+R2) vg = x V ref2. That is, since V ref2= Vln (R6+R7+R8), (R1+R2) R8 x XVinR2(R6
+R7+R8) Here, if R1=R7 and R2=R8, then (R1+R2) vO= Vln (R1+R2+R6), and as shown in Figure 3, the output voltage Vo becomes equal to the input voltage Vi.
The voltage is lowered by the voltage drop generated across the resistor R6 with respect to n.

That is, the transistor Q1 always has a voltage drop between its emitter and collector equal to that across the resistor R6 and is never saturated, improving ripple rejection.

In addition, since the input voltage Vin is included in the above equation, the ripple component included in the input voltage Vin cannot be completely removed. To solve this problem, a ripple filter is formed by the resistor R6 and the capacitor C. , which further improves ripple rejection.

Note that the present invention can be similarly implemented even if the output transistor Q1 has a multistage configuration.

[Effects of the Invention] As detailed above, the present invention has the advantage of being able to provide a constant voltage power supply circuit that has good constant voltage characteristics in the stabilized region and good ripple rejection characteristics in the non-stabilized region. It has a great effect.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of this invention, Fig. 2 is a circuit diagram showing an embodiment embodying this invention, Fig. 3 is an input/output voltage characteristic diagram of the embodiment, and Fig. 4 is related to this invention. 5 is a conventional constant voltage circuit diagram, FIG. 6 is an input/output voltage characteristic diagram of the conventional constant voltage circuit diagram, and FIG. 7 is a circuit diagram showing another conventional example. In the figure, 1 is an error amplifier, 2 is a first reference voltage supply means,
3 is a second reference voltage supply means, 4 is a switching means, 5 is a control means, Ql is an output transistor, Fig. 1 Diagram explaining the principle of the present invention 0° Fig. 3 Input/output voltage characteristic diagram of the present invention 9X

Claims (1)

[Claims] 1. Predetermined output voltage (V0) with respect to input voltage (Vin)
an output part (Q1) for deriving
) in a constant voltage power supply circuit comprising an error amplifier (1) that controls the output section (Q1) based on a comparison between the output voltage (V0) of the output unit (V0) and a reference voltage. at least one first reference voltage supply means (2) that supplies one reference voltage to the error amplifier (1); and at least one second reference voltage supply means (2) that supplies one reference voltage to the error amplifier (1). a second reference voltage supply means (3) that supplies a reference voltage; and a first and second reference voltage supply means (2, 3) interposed between the first and second reference voltage supply means (2, 3) and the error amplifier (1). One of the reference voltage supply means (2, 3) is connected to the error amplifier (1).
A switching means (4) connected to the input voltage (Vin) selects the first reference voltage supply means (2) when the input voltage (Vin) is above a predetermined voltage, and selects the second reference voltage supply when the input voltage (Vin) is below the predetermined voltage. A constant voltage power supply circuit comprising: control means (5) for outputting a control signal for selecting the means (3) to the switching circuit (4).