JPH1146439A - Surge protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to definitely prevent the break of an element or malfunction of a circuit, by performing a surge protecting operation for controlling the conduction of a protective transistor. SOLUTION: If a terminal-to-terminal voltage of a diode circuit 6 comprising a group of diode elements connected in series is Vn, then a transistor 4 becomes conductive and is turned to ON state when a surge voltage is applied to an input circuit of a semiconductor IC circuit 1 and a voltage higher than VBE+Vn is applied as a voltage between the base and the emitter of the transistor 4. By doing this, a current flows between the emitter and the collector of the transistor 4, and this current flows to the base of the transistor 5 and the transistor 5 becomes conductive. This transistor 5 takes in a surge current which tends to flow to the internal circuits through a surge protection resistor 2, and releases it to the grounding section GND. By a series of these operations, the surge resisting capacity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge protection circuit applied to a semiconductor integrated circuit.

[0002]

2. Description of the Related Art Normally, in a semiconductor integrated circuit, a protection resistor and positive and negative surges are respectively supplied to a power supply and a grounding section G in order to prevent the destruction of an internal circuit due to a surge due to external static electricity or the like.
There is a surge protection circuit composed of a protection diode to escape to ND.

However, for example, when a plurality of semiconductor integrated circuits such as a microcomputer and an ASIC are mounted on a system and each of them is electrically connected, when one power supply is stopped for some reason, the circuit malfunctions. Or the element may be destroyed.

This situation will be described with reference to FIG. 2 showing a conventional surge protection circuit. In FIG. 2, 1 is a semiconductor integrated circuit, 2 is a surge protection resistor, 3 is a diode for protecting against a negative surge, 7 is a surge protection diode, 8 is a semiconductor integrated circuit including a microcomputer or the like, and 9 is its output circuit. .

As shown in FIG. 2, the output current from the output circuit 9 of the semiconductor integrated circuit 8 flows through the surge protection resistor 2 and the surge protection diode 7 to the power supply side, causing a malfunction of the circuit and destruction of the element. It will be. Therefore, usually, the above-mentioned situation is prevented by removing the surge protection diode 7. Thereby, the surge withstand capability is weakened.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surge protection circuit capable of reliably preventing a malfunction of a circuit and destruction of an element.

[0007]

According to a first aspect of the present invention, there is provided a surge protection circuit comprising: a protection transistor having a collector and an emitter connected between an input circuit of a semiconductor integrated circuit and a ground; A control transistor having an emitter and a collector connected to the base of the protection transistor; and a diode circuit connected between the base of the control transistor and a ground. The protection transistor is made conductive by a control operation of the control transistor in response to application of a surge voltage.

[0008] In the surge protection circuit of the second invention,
An NPN transistor having a collector connected to an input circuit of the semiconductor integrated circuit and having an emitter grounded; a PNP transistor having a collector connected to a base of the NPN transistor and having an emitter connected to the input circuit;
A diode circuit connected between the base of the P-transistor and a ground, wherein the NPN transistor is turned on by a control operation of the PNP transistor in response to application of a surge voltage to the input circuit. is there.

In the surge protection circuit according to the third invention,
An NPN transistor having a collector connected to an input circuit of the semiconductor integrated circuit and having an emitter grounded; a PNP transistor having a collector connected to a base of the NPN transistor and having an emitter connected to the input circuit;
A diode circuit connected between the base of the P-transistor and a ground, and configured to conduct the NPN transistor by controlling the PNP transistor in response to application of a surge voltage to the input circuit; And the diode circuit is constituted by a plurality of diode elements.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a circuit diagram showing one embodiment of the present invention. In FIG. 1, 1 is a semiconductor integrated circuit composed of an ASIC, 2 is a surge protection resistor, 3 is a diode for protecting against a negative surge, 4 is a control transistor composed of a PNP transistor, 5 is a protective transistor composed of an NPN transistor, Reference numeral 6 denotes a diode circuit in which a plurality of diode elements are connected in series.

In this circuit, assuming that a voltage between terminals of a diode circuit 6 composed of a series connection of diode elements is Vn, a surge voltage is applied to the input circuit of the semiconductor integrated circuit 1 so that the PNP transistor 4 When a voltage of VBE + Vn or more is applied as a voltage between the base and the emitter, the PNP transistor 4 is turned on and turned on.
State.

As a result, a current flows between the emitter and the collector of the PNP transistor 4, and the current flows into the base of the PNP transistor 5. When a current flows into the base of the NPN transistor 5, the NPN transistor 5 conducts. The PNP transistor 5 draws a surge current flowing from an input through the surge protection resistor 2 into an internal circuit from its collector. ,
An attempt is made to escape to the ground part GND.

With this series of operations, the surge resistance can be improved. The operating voltage of the diode circuit 6 can be adjusted by increasing or decreasing the number of diodes in the diode element group connected in series. And a semiconductor integrated circuit 1 composed of an ASIC.
When an output circuit of a semiconductor integrated circuit composed of a microcomputer or the like is connected to the input circuit of, the NPN transistor 5 as a protection transistor does not conduct in this state even if the power supply of the semiconductor integrated circuit 1 is stopped. Because
The output current of the semiconductor integrated circuit such as a microcomputer does not flow to the power supply side through the surge protection circuit, and no malfunction of the circuit or destruction of the element occurs.

Thus, according to this embodiment, N
A malfunction of the circuit is achieved by performing a surge protection operation using a protection transistor including the PN transistor 5 and a control transistor including the PNP transistor 4 that controls the protection transistor including the NPN transistor 5 and controls conduction of the protection transistor including the NPN transistor 5. And a surge protection circuit that can reliably prevent the destruction of the element. Further, by increasing or decreasing the number of diode elements of the diode circuit 6, it is possible to obtain a surge protection circuit capable of appropriately adjusting the operation voltage of the circuit.

[0015]

According to the first aspect of the present invention, the surge protection operation is performed by the protection transistor and the control transistor for controlling the conduction of the protection transistor.
It is possible to obtain a surge protection circuit capable of reliably preventing a malfunction of the circuit and the destruction of the element.

According to the second aspect of the present invention, the surge protection operation is performed by the protection transistor including the NPN transistor and the control transistor including the PNP transistor for controlling conduction of the protection transistor including the NPN transistor. A surge protection circuit that can reliably prevent malfunction and destruction of elements can be obtained.

According to the third aspect of the present invention, it is possible to reliably prevent malfunction of the circuit and destruction of elements, and to appropriately adjust the operating voltage of the circuit by increasing or decreasing the number of diode elements in the diode circuit. A protection circuit can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a conventional surge protection circuit.

[Explanation of symbols]

1 whole semiconductor integrated circuit, 2 resistance of surge protection circuit,
3 Diode for protection against negative surge, 4 PN
P transistor, 5 NPN transistor, 6 series-connected diode group, 7 diode for protection against positive surge, 8 semiconductor integrated circuit such as microcomputer,
9 Output circuit of semiconductor integrated circuit.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H03K 19/018 H01L 27/06 311A H03K 19/092

Claims (3)

[Claims] 1. A protection transistor having a collector and an emitter connected between an input circuit of a semiconductor integrated circuit and a ground, and an emitter and a collector between the input circuit and a base of the protection transistor. A control transistor connected thereto, and a diode circuit connected between a base of the control transistor and a ground portion, and a control operation of the control transistor according to application of a surge voltage to the input circuit. A surge protection circuit, wherein the protection transistor is made conductive. 2. An NPN transistor having a collector connected to an input circuit of the semiconductor integrated circuit and an emitter grounded,
A PNP transistor having a collector connected to the base of the NPN transistor and an emitter connected to the input circuit; and a diode circuit connected between the base of the PNP transistor and a ground portion, wherein a surge to the input circuit is provided. A surge protection circuit, wherein the NPN transistor is turned on by a control operation of the PNP transistor in response to application of a voltage. 3. An NPN transistor having a collector connected to an input circuit of the semiconductor integrated circuit and an emitter grounded,
A PNP transistor having a collector connected to the base of the NPN transistor and an emitter connected to the input circuit; and a diode circuit connected between the base of the PNP transistor and a ground portion, wherein a surge to the input circuit is provided. A surge protection circuit, wherein the NPN transistor is turned on by a control operation of the PNP transistor in response to application of a voltage, and the diode circuit is constituted by a plurality of diode elements.