JPH01270118A - Constant voltage power source circuit - Google Patents

Abstract

PURPOSE:To suppress the actual injury at minimum even when an input voltage drops excessively unextectedly by providing a voltage stabilization circuit bypassing circuit. CONSTITUTION:An input voltage detection circuit 2 is provided in a constant voltage power source circuit 1, and the voltage stabilization circuit bypassing circuit 3 is equipped so as to output the input voltage as it is (without being affected by voltage drop) by bypassing the voltage stabilization circuit 1 when the excessive drop of the input voltage is detected by the circuit 2. In such a way, it is possible to suppress the actual injury at minimum even when the input voltage drops excessively unexpectedly due to an unknown reason, and also, to take an appropriate counterpart such as the exchange of a battery for the input voltage, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in constant voltage power supply circuits. In particular, even if the input voltage of the series Dromba type constant voltage power supply circuit drops below a predetermined value, the output voltage will not drop excessively. The present invention relates to an improvement that makes it possible to issue a warning at a necessary time, automatically replace the input power source, etc.

[Conventional technology]

It is well known that NC devices and the like require a controlled power source that generates accurate voltage, but at the same time, it is also well known that NC devices have a certain degree of tolerance in the voltage at which they can operate.
A series Dromba type constant voltage power supply circuit is widely used as a relatively low-cost constant voltage 1g circuit.

An example of this series dropper type constant voltage power supply circuit is shown in the third example.
In the figure 0 shown in the figure, the input voltage is ■.

A constant voltage setting device ZD such as a Zener diode with a specified voltage of It is read directly through the resistor R, and if the input voltage 1H is larger than the voltage v2 specified by the constant voltage setting device ZD, the emitter of the above-mentioned switching element Q and the constant voltage setting device aZD
and the other end, the formula Vou = Vz-Vr where 2 is the voltage drop of the switching element Q.

The device is configured to output a constant output voltage defined by . In a constant voltage power supply circuit with a configuration of
If an extremely high input voltage VIN is applied, the value at which this input terminal VIN exceeds the specified voltage 2 of the constant voltage setting device ZD increases, and the current flowing through the switching element Q also increases, causing the tolerance of the switching element Q to increase. It is natural that there is a maximum permissible input voltage V IN that can be applied to this constant voltage power supply circuit because the current may exceed the current value, but it is widely used because it has the advantage of a simple structure. There is.

[Problem to be solved by the invention]

Constant voltage 1 above! In the source circuit, the input voltage V decreases excessively, resulting in a constant voltage of 1! When the voltage applied to the source 2ZD becomes lower than its specified voltage ■2, the output voltage ■ of the constant voltage power supply circuit. 8. is not controlled by the constant voltage setting device ZD, and the input voltage becomes the value obtained by subtracting the voltage drop in the switching element Q from vIN, resulting in an output of an unpredictable low voltage that is impossible to control. The opportunity as a voltage power supply circuit is lost.

The purpose of the present invention is to reduce the output voltage in such a case. Minimize the voltage difference between ut and the input voltage VIN (voltage drop due to the presence of a constant voltage power supply circuit) to minimize actual damage, and if desired, when the input W source reaches the end of its life and requires its replacement. It is an object of the present invention to provide a constant voltage power supply circuit that makes it possible to issue a warning, etc., or to automatically switch input power sources.

(Means for Solving the Problems) The above purpose is to provide a voltage stabilization circuit (1), an input voltage detection circuit (2) provided on the input side thereof, and a voltage stabilization circuit (2) that detects the input voltage. This is achieved by using a constant voltage power supply circuit including a voltage stabilizing circuit bypass circuit (3) that bypasses the voltage stabilizing circuit (1) when a voltage drop is detected.

Note that when the input voltage detection circuit (2) operates and detects an excessive drop in the input terminal VIN, it issues an alarm to warn of depletion of the input power supply. It goes without saying that you are completely free to add additional functions, such as switching to a healthy input power source, when you need it.

[Effect]

In the constant voltage power supply circuit according to the present invention, an input terminal detection circuit 2 is provided, and when this detects an excessive drop in the input voltage, the voltage stabilization circuit 1 is bypassed, and the input voltage remains unchanged ( ?!), so even if the input voltage drops unexpectedly for some reason, the actual damage will be relatively minor, and the input power supply Appropriate measures such as replacing the battery can be taken.

〔Example〕

Referring to the drawings below, constant voltage 1 according to an embodiment of the present invention
The 1B circuit will be further explained.

Referring to FIG. 2, a circuit diagram of a constant voltage power supply circuit according to an embodiment of the present invention is shown.

In the figure, reference numeral 1 denotes a voltage stabilizing circuit, which has the same configuration as the constant voltage 78.8 circuit according to the prior art shown in FIG.

2 is an input voltage detection circuit, to which an input voltage V is applied and is connected to a second bipolar transistor Q! through a resistor R! A second Zener diode Z D connected to the base of
This second bipolar transistor Q2 has an input voltage applied between its collector and emitter via a resistor R1. The connection point between the collector of the second bipolar transistor Q8 and the resistor R1 is connected to the base of the third bipolar transistor Q, and the collector of the third bipolar transistor Q is connected to the bypass circuit via the resistor R4. The collector and emitter of the bipolar transistor Q4 forming the bypass circuit are connected to bypass the bipolar transistor Q of the voltage stabilizing circuit 1.

When the input voltage V +w is normal, the Zener diode Z
DZ is conducting and the second bipolar transistor Q
, are conducting, and the third bipolar transistor Q,
Since no current is supplied to the base of Q, the third bipolar transistor Q is non-conducting, the bypass circuit 3 is also inactive, and the voltage stabilizing circuit 1 is operating normally.

However, when the input voltage V 1 N drops excessively, the second Zener diode ZDt becomes non-conductive, the second bipolar transistor Q becomes non-conductive, and the third bipolar transistor Q becomes conductive, so that the bypass circuit 2 The bipolar transistor Q4 becomes conductive and output voltage Vou
As t, the value obtained by subtracting the internal voltage drop of the bipolar transistor Q4 of the bypass circuit 2 from the input voltage VI, l is output. You are free to use this to take measures such as issuing a warning of an excessive drop in input voltage or automatically replacing the power supply with a healthy one.

(Effects of the Invention) As explained above, the constant voltage power supply circuit according to the present invention has the following features:
A voltage stabilization circuit 1, an input voltage detection circuit 2 provided on the input side thereof, and a voltage stabilization circuit that bypasses the voltage stabilization circuit 1 when the input voltage detection circuit 2 detects an excessive drop in the input voltage. Bypass circuit 3 is provided, so when the input voltage drops excessively and loses its function, the voltage stabilization circuit is bypassed and the input voltage remains as it is (without voltage drop). ), so even if the input terminal drops unexpectedly for some reason, the actual damage will be relatively minor, and appropriate measures such as replacing the input power battery will be taken. I can take it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a constant voltage power supply circuit according to the present invention. FIG. 2 is a circuit diagram of a constant voltage power supply circuit according to an embodiment of the present invention. FIG. 3 is a circuit diagram of a constant voltage power supply circuit according to the prior art. 1... Voltage stabilization circuit, 2... Input voltage detection circuit, 3... Voltage stabilization circuit bypass circuit, Q... Bipolar transistor, R... Resistor, ZD... Zener diode, L ...Resistor, Q2 ...Second bipolar transistor, ZD,
...Second Zener diode, R1...Resistor, Q,...Third bipolar transistor, R4...
Resistor, Q,...Bipolar transistor.

Claims (1)

[Claims] A voltage stabilizing circuit (1), and an input voltage (V_I) input to the voltage stabilizing circuit (1).
When the input voltage detection circuit (2) detects an excessive drop in the input voltage (V_I_N), the voltage stabilization circuit (1) detects an excessive drop in the input voltage (V_I_N). ) A voltage stabilizing circuit bypass circuit (3) that bypasses the voltage stabilizing circuit.