JP2940458B2 - Abnormal voltage protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormal voltage protection circuit in an electronic circuit, and more particularly to an abnormal voltage protection circuit including a photocoupler and a high-speed transistor.

[0002]

2. Description of the Related Art Conventionally, in electronic equipment and the like, a protection circuit using an arrester or a silicon protection device is provided at an input terminal or an output terminal to protect an internal electronic circuit from an abnormal voltage applied by a lightning surge or the like. in use.

Further, a circuit for limiting an electronic circuit to be protected to an output circuit of a transistor and forcibly setting the transistor to 0FF when an abnormal voltage is detected to prevent destruction of the transistor by an overcurrent is disclosed. As shown in FIG. 3, it has already been proposed (Japanese Utility Model Application Laid-Open No. 59-3444).
3).

[0004]

However, in a protection circuit using an arrester or a silicon protection device according to the conventional method, first, a large number of elements are required by multi-stage connection to have sufficient protection capability. . Secondly, there is a problem that an abnormal high voltage passes through the protection circuit and reaches the internal electronic circuit for about 1 microsecond before the arrester starts discharging.

[0005] Further, an electronic circuit to be protected is limited to an output circuit of a transistor, and when an abnormal voltage is detected, the transistor is forcibly set to 0FF to prevent a destruction of the transistor by an overcurrent (actual circuit). Kaisho 59-3
4443) is a general IC with a limited protection target.
Input circuit etc. cannot be protected.

Further, a surge absorbing circuit (Japanese Patent Application Laid-Open No. 61-253926) in which a circuit for absorbing an abnormal voltage is added between an input terminal of an electronic circuit transferred by a photocoupler and ground to avoid noise and induced voltage, and There is a photocoupler with a noise filter (Japanese Unexamined Patent Application Publication No. 5-122044). As shown in FIG. 4, all of them are intended to protect the photocoupler used for transferring the input signal from being damaged by an abnormal voltage. The present invention differs from the present invention in the purpose and the circuit configuration.

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and to completely protect an internal electronic circuit immediately after an abnormal voltage is generated by a relatively simple circuit configuration using a photocoupler and a high-speed transistor. An object of the present invention is to provide an abnormal voltage protection circuit that can be used in a wide range without limiting the circuit to be protected.

[0008]

An abnormal voltage protection circuit according to the present invention comprises an arrestor connected between an input / output terminal of an electronic device comprising an electronic circuit and a ground, and a resistor connected between the input / output terminal and the input / output terminal.
In abnormal voltage protection circuit having a photocoupler high speed operation are connected to, and a NPN transistor of the high-speed operation, to the positive power source through a collector terminal resistance of the output side transistor of the photocoupler, the emitter terminal A first high-speed NPN transistor connected in series between an input / output terminal of the electronic device and an internal electronic circuit;
And a second resistor, a connection point of the first resistor and the second resistor is connected to a collector of the high-speed NPN transistor, and an emitter of the NPN transistor is connected to the ground. It is characterized by the following.

[0009]

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an example of a circuit configuration according to an embodiment of the present invention. In this figure, a positive abnormal voltage applied to the input / output terminal 1 is guided to the input terminal of the photocoupler 3 via the resistor 5, and the output transistor of the photocoupler 3 is set to the ON state. Then, a base current flows from the positive power supply via the resistor 8 to the base of the high-speed NPN transistor 4 connected to the emitter of the output transistor of the photocoupler 3, and the high-speed NPN transistor enters the 0N state. During this time, it is about 0.1 microsecond. That is, when the abnormal voltage rises until the arrester 2 starts discharging, the high-speed NPN transistor 4 quickly becomes 0N, and the connection point between the resistor 6 and the resistor 7 is almost short-circuited to the ground, and the potential drops to 1 V or less. The influence of the abnormal voltage on the internal electronic circuit 9 to be protected, which is connected via the switch 7, is completely cut off. Then, after about 1 microsecond, the arrester 2 starts discharging and limits the abnormal voltage to about 30 V or less.
The internal electronic circuit 9 connected to the input / output terminal including the PN transistor 4 is protected.

FIG. 2 is a diagram showing a circuit configuration of another embodiment of the present invention. A negative abnormal voltage applied to an input / output terminal 1 is applied to an input terminal of a photocoupler 3-1 via a resistor 5. The output transistor of the photocoupler 3-1 is 0
The state becomes the N state. Then, a base current flows from the minus power supply via the resistor 10 to the base of the high-speed PNP transistor 11 connected to the collector of the output transistor of the photocoupler 3-1, and the high-speed PNP transistor is set to the ON state. During this time, it is about 0.1 microsecond. That is, when the abnormal voltage falls until the arrestor 2 starts discharging, the high-speed PNP transistor 11 quickly becomes 0 N, and the connection point between the resistor 6 and the resistor 7 is almost short-circuited to the ground, and the potential drops to 1 V or less. The effect of the abnormal voltage on the internal electronic circuit 9 to be protected connected via the resistor 7 is completely shut off.

Therefore, in the case of the embodiment shown in FIG. 2, the internal electronic circuit connected to the input / output terminal, including the input circuit of the photocoupler and the high-speed transistor, can be operated for any abnormal voltage of plus or minus. 9 is protected.

[0013]

As described above, according to the present invention, only by using a high-speed photocoupler and a transistor, the abnormal voltage can be suppressed immediately after the occurrence of the abnormal voltage. Since the circuit is not limited, it is effective for use in a wide range.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit configuration diagram showing a conventional known example.

FIG. 4 is a circuit configuration diagram showing another known example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 I / O terminal 2 Arrester 3, 3-1 High-speed operation photocoupler 4 High-speed operation NPN transistor 5-8, 10 Resistor 9 Internal electronic circuit to be protected 11 High-speed operation PNP transistor

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02H 9/04 H02H 9/06

Claims (3)

(57) [Claims] An arrestor connected between an input / output terminal of an electronic device constituted by an electronic circuit and a ground, and the input / output terminal
High-speed photocoupler connected to the
In abnormal voltage protection circuit having La, and a NPN transistor of the high-speed operation, the to the positive supply via the collector terminal of the output side transistor of the photo coupler resistance, the emitter terminal connected to the base of the high-speed NPN transistor A first resistor and a second resistor connected in series between an input / output terminal of the electronic device and an internal electronic circuit, and a connection point between the first resistor and the second resistor is An abnormal voltage protection circuit, which is connected to a collector of a high-speed NPN transistor, and an emitter of the NPN transistor is connected to the ground. 2. An arrestor connected between an input / output terminal of an electronic device constituted by an electronic circuit and a ground, and the input / output terminal
High-speed photocoupler connected to the
In abnormal voltage protection circuit having La, and a PNP transistor of high speed operation, the negatively power source via the emitter terminal of the output side transistor of the photo coupler resistance, the collector terminal is connected to the base of the high-speed PNP transistor A first resistor and a second resistor connected in series between an input / output terminal of the electronic device and an internal electronic circuit, and a connection point between the first resistor and the second resistor is An abnormal voltage protection circuit, which is connected to a collector of a high-speed PNP transistor and an emitter of the PNP transistor is connected to the ground. 3. An arrester and a photocoupler connected between an input / output terminal of an electronic device constituted by an electronic circuit and a ground .
Positive input terminal is connected to the input / output terminal via a resistor
High-speed operation first photocoupler and photocoupler
The negative input terminal of the plastic is connected to the input / output terminal via a resistor.
An abnormal voltage protection circuit having a high-speed operation second photocoupler and a high-speed operation NPN transistor and a high-speed operation PNP transistor , wherein the output-side transistor of the first photocoupler has the positive supply via the collector terminal resistor is connected emitter terminal to a base of the high-speed NPN transistor, said second negative power emitter terminal via the resistance of the output side transistor of the photocoupler collector terminal said A first resistor and a second resistor connected to a base of a high-speed PNP transistor and connected in series between an input / output terminal of the electronic device and an internal electronic circuit; Is connected to the high-speed NPN
An abnormal voltage protection circuit, which is connected to a collector of a transistor and a collector of the high-speed PNP transistor, respectively, and an emitter of the NPN transistor and an emitter of the PNP transistor are connected to the ground, respectively.