JPH0744248A - Constant voltage circuit - Google Patents

Abstract

PURPOSE:To provide the constant voltage circuit which is hardly affected by the fluctuation of an input voltage or an output current. CONSTITUTION:A resistor R3 for current limitation is connected between the output of an input voltage stabilizing circuit 1 and the input of a reference power source 2, a capacitor C is connected between the input of the reference power source 2 and the ground, and a voltage Vi at both the terminals of the capacitor C is supplied to the reference power source 2. Thus, even when an input power supply voltage Vin is instantaneously fluctuated, since the fluctuation can be absorbed by the serial circuit of the resistor R3 for current limitation and the capacitor C, an output voltage Vout can be stabilized by reducing an influence to be exerted upon a reference voltage Vc outputted from the reference power source 2. Therefore, even when the input power supply voltage Vin is instantaneously fluctuated, the influence to be exerted upon the reference voltage Vc to be the reference of the output voltage Vout can be reduced, and the output voltage can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage circuit, and more particularly to a circuit that keeps an output voltage constant even when an input voltage changes.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional constant voltage circuit.
In the figure, reference numeral 1 is an input voltage stabilization circuit that stabilizes an input power supply voltage Vin and outputs a voltage Ve to a reference power supply, which will be described later, and that supplies an output current i to an output terminal, 2 is stabilized by an input voltage stabilization circuit 1. The reference power supply that inputs the converted voltage Ve and outputs the highly accurate reference voltage Vc, 3 is the output current control circuit that controls the output current i, 4 is the output voltage Vout obtained at the output terminal, and the output voltage is Detection voltage proportional to Vout
The output voltage detection circuit 5 that outputs Vr compares the reference voltage Vc output from the reference power supply 2 to the non-inverting input terminal with the detection voltage Vr output from the output voltage detection circuit 4, and the output obtained at the output terminal. It is an amplifier (operational amplifier) that controls the output current control circuit 3 so that the voltage Vout is stabilized.

Here, both the input voltage stabilizing circuit 1 and the reference power source 2 are circuits which output a constant voltage. However, when comparing both circuits, the input voltage stabilizing circuit 1 shows a slight output voltage. The reference power supply 2 is a circuit that is configured to supply a predetermined output current to the output terminal even if it fluctuates and to output a voltage higher than the output voltage Vo of the amplifier 5. Increase the output impedance,
Highly accurate reference voltage by reducing the input / output current of the circuit
It is a circuit configured to output Vc. In the conventional example, the output current control circuit 3 is composed of Darlington-connected NPN transistors Q1 and Q2, the collectors of the NPN transistors Q1 and Q2 are connected to the output of the input voltage stabilizing circuit 1, and the emitter of the NPN transistor Q2 is It is connected to the output terminal and the base of the NPN transistor Q1 is connected to the output of the amplifier 5. In the conventional example shown in FIG. 3, the output voltage detection circuit 4 is composed of a series circuit of resistors R1 and R2, and a detection voltage Vr proportional to the output voltage Vout obtained at the voltage dividing point is obtained.
This circuit outputs (Vr = R2 / (R1 + R2)) to the inverting input terminal of the amplifier 5.

By configuring the constant voltage circuit as described above, even if the output voltage Vout fluctuates, the fluctuation of the output voltage is detected by the output voltage detection circuit 4, and the detection voltage Vr and the reference voltage proportional to the output voltage Vout are detected. By comparing Vc and controlling the output current i by the output current control circuit 3, the output voltage Vout can be stabilized. Further, when a load is applied to the output terminal, the output drive current increases, causing an output voltage drop, but the voltage drop can be suppressed.

[0005]

As described above, in the conventional constant voltage circuit, if the reference voltage Vc is stabilized, the output voltage Vout is stabilized even if the output voltage Vout or the output current i fluctuates. However, if the input power supply voltage Vin fluctuates instantaneously, the input voltage stabilization circuit 1 can maintain the output current i supplied to the output terminal substantially constant, but the constant voltage Ve However, there is a problem that the output voltage Vout is fluctuated because the fluctuation of the input power supply voltage Vin is transmitted to the reference power supply 2 without being able to output. Further, as a method of preventing the fluctuation of the output voltage Vout, there is a method of externally attaching a large-capacity capacitor for charging / discharging to the output terminal of the constant voltage circuit, but it has a drawback that it is not suitable for miniaturization and IC implementation. .

The present invention has been made in view of the above problems, and an object of the present invention is to provide a constant voltage circuit which is not easily affected by fluctuations in input voltage and output current.

[0007]

In order to solve the above-mentioned problems, a constant voltage circuit according to the present invention includes a reference power source for generating a reference voltage and an input power source voltage which is made a constant voltage and supplied to the reference power source. An input voltage stabilizing circuit that supplies an output current to an output terminal, an output current control circuit that controls the output current from the input voltage stabilizing circuit to the output terminal, and an output voltage obtained at the output terminal Then, an output voltage detection circuit that outputs a detection voltage according to the output voltage is compared with the reference voltage output from the reference power supply and the detection voltage to stabilize the output voltage obtained at the output terminal. In a constant voltage circuit having an amplifier for driving the output current control circuit, a current limiting resistor is inserted between the output of the input voltage stabilizing circuit and the input of the reference power supply. To the input of the reference power source to ground via a capacitor, it is characterized in that to supply the voltage across the capacitor to the reference power.

[0008]

As shown in FIG. 1, a current limiting resistor R3 is connected between the output of the input voltage stabilizing circuit 1 and the input of the reference power source 2,
By connecting a capacitor C between the input of the reference power supply 2 and ground and supplying the voltage Vi across the capacitor C to the reference power supply 2, even if an instantaneous fluctuation of the input power supply voltage Vin occurs, that fluctuation is used for current limiting. Since it can be absorbed in the series circuit of the resistor R3 and the capacitor C, the influence on the reference voltage Vc output from the reference power supply 2 can be reduced and the output voltage Vout can be stabilized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. The same components as those in the conventional example are designated by the same reference numerals. Input power supply voltage Vin
Is entered. The input power supply voltage Vin is stabilized by the input voltage stabilization circuit 1, and the current limiting resistor R3 and capacitor
Applied to the series circuit of C. This input voltage stabilization circuit 1
Is configured to be capable of outputting a predetermined output current i to the output terminal, and is also configured to be capable of outputting a voltage Ve higher than the voltage Vo output from the amplifier 5. Voltage Ve applied to the series circuit of current limiting resistor R3 and capacitor C
The capacitor C is charged accordingly. The reference power supply 2 is configured to output a highly accurate reference voltage Vc although it has a small current supply capability. The output current control circuit 3 is a circuit for controlling the output current i in order to stabilize the output voltage Vout, and is composed of Darlington-connected NPN transistors Q1 and Q2 in this embodiment, but is limited to the embodiment. Not a thing. The output voltage detection circuit 4 is a circuit that outputs a detection voltage Vr according to the output voltage Vout. In the present embodiment, the resistance R1,
The detection voltage Vr is output from the voltage dividing point of R2. The amplifier 5 compares the reference voltage Vc input to the non-inverting input terminal with the detection voltage Vr input to the inverting input terminal, and when the reference voltage Vc is higher, the output current control circuit 3
To drive a current to supply a current to the output terminal and stabilize the output voltage Vout.

The above-described embodiment differs from the conventional example shown in FIG. 3 in that a current limiting resistor R3 is connected between the output of the input voltage stabilizing circuit 1 and the input of the reference power supply 2 and the reference power supply 2 is connected. The point is that the capacitor C is connected between the input and the ground and the voltage Vi across the capacitor C is input to the reference power supply 2. The operation of the current limiting resistor R3 and the capacitor C will be described below. When the input power supply voltage Vin is input to the input terminal, the voltage Ve stabilized by the input voltage stabilization circuit 1 is applied to the series circuit of the current limiting resistor R3 and the capacitor C, and via the current limiting resistor R3. Charging current flows through the capacitor C. The voltage Vi across the capacitor C becomes the voltage input to the reference power supply 2. Since the reference power supply 2 has a high input impedance and a small input current, by setting the current limiting resistor R3 to a high resistance, the capacitor C is slowly charged and discharged, and the voltage changes due to fluctuations in the input power supply voltage Vin.
Even if Ve changes instantaneously, the voltage Vi across the capacitor C does not change instantaneously, the influence of the fluctuation of the input power supply voltage Vin on the reference power supply 2 can be reduced, and the output voltage can be stabilized. Further, since the current limiting resistor R3 has a high resistance to the instantaneous fluctuation of the output current i, the fluctuation of the voltage Vi at both ends can be suppressed and the output voltage can be stabilized.

FIG. 2 shows the voltage waveform of each part when the input power supply voltage Vin changes instantaneously in the constant voltage circuit configured as described above. In the figure, (a) shows the voltage Ve output from the input voltage stabilizing circuit 1, (b) shows the voltage Vi across the capacitor C, and (c) shows the output voltage Vout. As shown in the figure, even if the voltage Ve fluctuates instantly, the voltage fluctuation is absorbed by the current limiting resistor R3 and the capacitor C, so the influence on the voltage Vi across the capacitor C is small. . Further, the voltage Vi at both ends is the reference power source 2
Output voltage Vout is the input power supply voltage.
Not affected by Vin fluctuations.

As described above, the output voltage Vout can be stabilized by the constant voltage circuit of the present invention. However, in order to further stabilize the output voltage Vout, even if a capacitor is externally attached to the output terminal, the output voltage Vout can be stabilized. If it is configured like a voltage circuit, the externally attached capacitor can be a small capacitor having a small capacity, and can be miniaturized and integrated into an IC.

The output current control circuit and the output voltage detection circuit are not limited to the embodiments.

[0014]

As described above, in the constant voltage circuit according to the present invention, the output voltage fluctuation of the input voltage stabilizing circuit is configured to be absorbed by the series circuit of the current limiting resistor and the capacitor. Even if it fluctuates instantaneously, it is possible to reduce the influence on the reference voltage that is the reference of the output voltage and stabilize the output voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a constant voltage circuit according to the present invention.

FIG. 2 is an operation waveform diagram of an embodiment of a constant voltage circuit according to the present invention.

FIG. 3 is a circuit diagram of a conventional constant voltage circuit.

[Explanation of symbols]

 Vout Output voltage Vin Input power supply voltage Ve, Vo voltage Vr Detection voltage Vc Reference voltage Vi Both ends voltage R1, R2, R3 Resistor C Capacitor Q1, Q2 NPN transistor i Output current 1 Input voltage stabilization circuit 2 Reference power supply 3 Output current control circuit 4 Output voltage detection circuit 5 Amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazunori Kidera 1048 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (1)

[Claims] 1. A reference power supply for generating a reference voltage, an input voltage stabilizing circuit which supplies a constant voltage to an input power supply voltage and supplies the output current to an output terminal, and the input voltage. An output current control circuit for controlling the output current from the stabilizing circuit to the output terminal; an output voltage detection circuit for detecting an output voltage obtained at the output terminal and outputting a detection voltage according to the output voltage; An amplifier driving the output current control circuit so that the reference voltage output from the reference power supply is compared with the detection voltage to stabilize the output voltage obtained at the output terminal. In the voltage circuit, a current limiting resistor is inserted between the output of the input voltage stabilizing circuit and the input of the reference power supply, and the input of the reference power supply is grounded via a capacitor to connect the A constant voltage circuit, characterized in that a voltage across a capacitor is supplied to the reference power source.