JPH05252654A - Protective circuit against input of ac excessive voltage - Google Patents

Abstract

PURPOSE:To prevent the breakage of a circuit to be protected by a method wherein a power supply line for the circuit to be protected is cut automatically when the circuit is connected to an AC power supply having a high voltage higher than a predetermined voltage. CONSTITUTION:When the input terminals 1a, 1b of a rectifier 1 are connected to an AC power supply, whose voltage exceeds a predetermined level, the DC voltage between output terminals 1c, 1d exceeds a predetermined voltage whereby a first switching transistor 3 is put ON and an electric current, being conducted through a second switching transistor 8, flows through the first switching transistor 3. As a result, the second switching transistor 8 is put OFF and the exciting of a circuit 100 to be protected is stopped. According to this method, the breakage of the circuit 100 to be protected can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC overvoltage protection circuit for protecting an electric circuit or an electronic circuit against an abnormal AC high voltage input.

Electric circuits and electronic circuits are damaged when a voltage or current significantly exceeding the ratings is applied. Therefore, it is necessary to protect the circuits so that such a situation does not occur.

[0003]

2. Description of the Related Art Conventionally, fuses have been widely used for circuit protection against high current.

However, since it is considered unlikely that the commercial AC power supply will have an abnormally high voltage, no protection circuit has been used to protect the circuit against the input of the AC high voltage.

[0005]

However, there are some commercial AC power supplies having different voltages such as 100 V and 200 V, and a device (circuit) for 100 V is provided as 20 V.
When connected to a 0 volt power supply, the circuit is often completely damaged.

Therefore, conventionally, the occurrence of an accident due to such an incorrect connection has been a problem. Therefore, it is an object of the present invention to provide an AC overvoltage input protection circuit capable of preventing the circuit from being damaged when it is accidentally connected to a high-voltage AC power supply.

[0007]

In order to achieve the above object, the AC overvoltage input protection circuit of the present invention rectifies an AC input into a DC as shown in FIG. 1 for explaining an embodiment. When the voltage between the output terminals 1c and 1d of the rectifier 1 which is output as
Connected between the first switching transistor 3 connected between the output terminals 1c and 1d of the rectifier 1 and the output terminals 1c and 1d of the rectifier 1 so as to turn on when the voltage between the 1d exceeds the predetermined level. A collector and an emitter are connected in series to the protected circuit 100, and a second switching transistor 8 whose base is connected to the collector of the first switching transistor 3 is provided. To do.

[0008]

When the input terminals 1a and 1b of the rectifier 1 are connected to an AC power source exceeding a predetermined level, the DC voltage between the output terminals 1c and 1d exceeds a predetermined voltage and the first switching transistor 3 turns on, Second switching transistor 8
The current flowing in the base of the first switching transistor 3 flows to the first switching transistor 3 side. As a result, the second switching transistor 8 is turned off, and the power supply to the protected circuit 100 is stopped.

[0009]

Embodiments will be described with reference to the drawings.

In FIG. 1, 1 is a rectifier for rectifying an AC input into a DC and outputting it, and 1a and 1b are 100
AC input terminals 1c and 1d connected to a commercial AC power source of Volt are DC output terminals for outputting rectified DC. Reference numeral 2 is a smoothing capacitor connected between the DC output terminals 1c and 1d.

Reference numeral 3 denotes a first switching transistor, the base of which has DC output terminals 1c and 1d of the rectifier 1.
The voltage between them is divided and applied by the first and second resistors 4 and 5. As the first resistor 4 and the second resistor 5, for example, resistors having a resistance value of a ratio of 330: 1 are used.

Further, the first switching transistor 3
The emitter of is connected to the low potential side 1c of the DC output end of the rectifier 1, and the collector is connected to the high potential side 1d of the DC output end of the rectifier 1 via the third resistor 6. The resistance value of the third resistor 6 is, for example, 270 kΩ.

Therefore, the DC output terminal 1c of the rectifier 1,
When the voltage of 1d is, for example, about 160 volts or less, the first
The base voltage is not sufficient to turn on the switching transistor 3 of 1., and the first switching transistor 3 is turned off.

The DC output terminals 1c and 1d of the rectifier 1
When the voltage of the voltage exceeds about 200 V, the first switching transistor 3 is turned on.

Reference numeral 100 denotes a protected circuit, one end of which is connected to the high potential side 1d of the DC output end of the rectifier 1 and the other end of which is connected to the collector of the second switching transistor 8.

The emitter of the second switching transistor 8 is connected to the low potential side 1c of the DC output terminal of the rectifier 1. The base of the second switching transistor 8 is directly connected to the collector of the first switching transistor 3, and is connected to the high potential side 1d of the DC output end of the rectifier 1 via the third resistor 6. ing.

Therefore, when the first switching transistor 3 is off, a base current sufficient to turn on the second switching transistor 8 flows to the second switching transistor 8 and the second switching transistor 8 is turned on. Then, when the first switching transistor 3 is turned on, the current that was being directed to the base of the second switching transistor 8 is directed to the first switching transistor 3 side, so the second switching transistor 8 is turned off. ..

Therefore, in this embodiment, the AC voltage input to the AC input terminals 1a and 1b of the rectifier 1 is 1
At 00 volts, the first switching transistor 3 is off, so the second switching transistor 8
Is turned on and a DC voltage of 100 V is applied to the protected circuit 100, the AC input terminals 1a and 1b of the rectifier 1 are
When the AC power supply of 200 V is accidentally connected to the first switching transistor 3, the first switching transistor 3 is turned on, so that the second switching transistor 8 is turned off, and the protected circuit 100 is not applied with voltage.

[0019]

According to the AC excessive voltage input protection circuit of the present invention, when the AC power supply of a high voltage higher than a predetermined voltage is erroneously connected, the power supply line to the protected circuit is automatically disconnected and It is possible to prevent damage to the protection circuit,
Moreover, it can be realized with an extremely simple configuration.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment.

[Explanation of symbols]

 1 Rectifier 1c, 1d DC output terminal 3 First switching transistor 8 Second switching transistor 100 Protected circuit

Claims (1)

[Claims] 1. A rectifier (1) which rectifies an AC input into DC and outputs the same is turned off when a voltage between output terminals (1c, 1d) of the rectifier (1) is lower than a predetermined level, and between the output terminals (1c, 1d). The first connected between the output terminals (1c, 1d) of the rectifier (1) so as to turn on when the voltage exceeds the predetermined level.
The switching transistor (3) and the protected circuit (100) connected between the output terminals (1c, 1d) of the rectifier (1) are connected in series with the collector and the emitter, and the base is A second connected to the collector of the first switching transistor (3)
And a switching transistor (8) for protecting the excessive AC voltage input circuit.