JPH05252649A - Regulator output short-circuit protective circuit - Google Patents

Abstract

PURPOSE:To obtain a regulator output short-circuit protective circuit, reduced in the number of components and inexpensive, by a method wherein a voltage difference detecting means, detecting that a difference between an input voltage and the output voltage of a regulator is more than a given value, is provided to forbid the regulator output when the voltage difference is more than a given value. CONSTITUTION:When the output of a four-terminal regulator 10 is short-circuited to OV, the emitter potential of a transistor 14 becomes OV and the base potential of the same becomes a forward saturation voltage between a base and an emitter or about 0.6V. Then, a Zener diode 11 is broken and a base current is conducted between the base and the emitter whereby another transistor 14 is put ON. When the transistor 14 is put ON, a collector potential becomes a saturation voltage between a collector and the emitter or about 0.3V. Accordingly, the output control input terminal CONT of the 4-terminal regulator 10 becomes a L-level and the output of an output voltage 5V is forbidden. This forbidden condition is continued even when the short-circuit between the output voltage 5V and OV is restored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a regulator output short circuit protection circuit for stabilizing an input voltage at a predetermined voltage.

[0002]

2. Description of the Related Art Electronic equipment often uses a three-terminal regulator for stabilizing an input voltage to a predetermined voltage or a four-terminal regulator having an output control input terminal in the three-terminal regulator.

There is no regulator output short-circuit protection circuit, or there is a fuse element.

[0004]

If the regulator output short-circuit protection circuit is not provided, shorting the output of the regulator to the ground will cause the regulator to overheat, the pattern of the printed board will be burnt out, and the case of the device will be deformed by heat. There was an inconvenience.

Even if there is an output protection circuit, it is a protection circuit using a fuse element, and has a drawback that the mounting area is bulky, the price is high, and the fuse is blown even after the short circuit is removed, so that the fuse needs to be replaced. ..

An object of the present invention is to realize an inexpensive regulator output short-circuit protection circuit with a minimum number of parts.

[0007]

Means for Solving the Problems A voltage difference detecting means for detecting that a difference between an input voltage and an output voltage of a regulator is a certain voltage or more is provided, and when the voltage difference is a certain voltage or more, the voltage input to the regulator is adjusted. It is either configured to be prohibited or the output of the regulator is prohibited.

[0008]

According to the present invention, an inexpensive regulator output short circuit protection circuit can be realized with a small number of parts.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A regulator output short circuit protection circuit according to an embodiment of the present invention will be described below.

FIG. 1 is a block diagram of a regulator output short circuit protection circuit according to an embodiment of the present invention.

Reference numeral 1 denotes a switching means, which prohibits the input voltage from being supplied to the regulator 2 when the output of the voltage difference detecting means 3 indicates that the difference between the input voltage and the output voltage of the regulator 2 exceeds a certain voltage. Is a regulator and outputs a stabilized output voltage by inputting a voltage equal to or higher than the output voltage. Reference numeral 3 is a voltage difference detecting means, and whether the difference between the input voltage and the output voltage of the regulator 2 is equal to or more than a certain voltage. To detect. If the voltage exceeds a certain level, the voltage input to the regulator is prohibited.

FIG. 2 shows an example of a concrete circuit of this embodiment. Reference numeral 10 is a four-terminal regulator having an output control input terminal. The input has an input voltage of 6V and the output has an output voltage of 5V.
The output control input terminal is connected to the collector of the transistor 14, the ground is grounded to 0V, and 11 is 3.9.
It is a Zener diode that breaks at V, the cathode is connected to the input voltage 6V, the anode is connected to the resistor 12,
12 is a base current limiting resistor of the transistor 14,
One end is connected to the anode of the Zener diode 11, and the other end is connected to the base of the transistor 14. Reference numeral 13 is a resistor for preventing the transistor 14 from turning on by a leakage current when the Zener diode 11 is not broken, One end is connected to the base of the transistor 14 and the other end is connected to the emitter of the transistor 14. Reference numeral 14 is an npn type transistor, and the collector is a four-terminal regulator 1.
0 is connected to the output control input terminal, the base is connected to the resistor 12, and the emitter is connected to the output of the 4-terminal regulator 10.
Is a resistor that pulls up the output control input terminal of the four-terminal regulator 10, one end of which is connected to the output control input terminal of the four-terminal regulator 10 and the other end of which is connected to the input voltage 6V.

First, the normal operation will be described. In normal operation, when the input voltage 6V is applied, when the input voltage 6V is equal to or lower than the break voltage of the Zener diode 11, the Zener diode 11 does not break and the transistor 14 is in the OFF state, so the potential of the output control input terminal of the 4-terminal regulator 10 Also becomes the same as the input voltage 6V, and the four-terminal regulator 10 becomes the output valid state.

Even if the input voltage 6 V exceeds the break voltage of the Zener diode 11, the four-terminal regulator 10
Is a valid output state, a voltage higher than the break voltage is not applied to the Zener diode 11, and a break does not occur. Therefore, the transistor 14 is in the OFF state, the 4-terminal regulator 10 is in the valid output state, and the input voltage of 6V is applied. At the same time, an output voltage of 5V is output.

Next, the output of the 4-terminal regulator 10 is set to 0V.
The case of short-circuiting to will be described. When the output of the 4-terminal regulator 10 is short-circuited to 0V, the potential of the emitter of the transistor 14 connected to it becomes 0V.

Then, the base potential of the transistor 14 becomes a quasi-direction saturation voltage between the base and emitter of the transistor, which is about 0.6V.

Then, the Zener diode 11 breaks, the base current flows between the base and the emitter of the transistor 14, and the transistor 14 is turned on.

When the transistor 14 is turned on, the collector potential of the transistor 14 becomes a collector-emitter saturation voltage of about 0.3V.

Since the collector of the transistor 14 is connected to the output control input terminal of the four-terminal regulator 10, the output control input terminal becomes the "L" level and the output voltage 5
V output is prohibited.

When the output of the output voltage of 5V is prohibited, even if the short circuit between the output voltage of 5V and 0V is restored, the potential of the output voltage of 5V is maintained at 0V because the load of the device is connected to the output voltage of 5V. ..

When the potential of the output voltage 5V is 0V, the Zener diode 11 is in the break state, the transistor 14 is in the ON state, and the 4-terminal regulator 10 is in the output prohibited state. In this state, the input voltage 6V is temporarily cut off, It continues unless it is turned on again.

Therefore, even if the output of the four-terminal regulator 10 is short-circuited to 0V, the output of the four-terminal regulator 10 is immediately prohibited and the prohibited state continues, so that the overheating of the four-terminal regulator 10 can be prevented.

[0023]

According to the present invention, an inexpensive regulator output short-circuit protection circuit can be realized with a small number of parts.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a regulator output short circuit protection circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific circuit of a regulator output short circuit protection circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 switching means 2 regulator 3 voltage difference detecting means

Claims (2)

[Claims] 1. A regulator having an output control input terminal, and voltage difference detection means for detecting that the difference between the input voltage and the output voltage of the regulator is a certain voltage or more, and the output of the voltage difference detection means has a voltage difference. Is a constant value or more, the regulator output short-circuit protection circuit controls the output control input terminal of the regulator to inhibit the regulator output. 2. A voltage difference detection for detecting that the difference between the input voltage and the output voltage of the regulator is a constant voltage or more, and a switching means for turning on / off the input voltage, a regulator using the output of the switching means as an input. A regulator output short-circuit protection circuit having means for disconnecting the switching means when the output of the voltage difference detecting means has a voltage difference of a certain value or more.