WO2020049787A1 - Transient voltage protection device - Google Patents

Abstract

A transient voltage protection device (101A, 101B) is provided with: one common terminal (Pc); a plurality of input/output terminals (P1, P2); and a transient voltage limiting element (10) of which a first end (T1) is connected to the common terminal (Pc) directly or indirectly. Between a second end (T2) of the transient voltage limiting element (10) and the plurality of input/output terminals (P1, P2), reverse-flow prevention circuits (11, 12) are connected which have a breakdown voltage higher than a breakdown voltage of the transient voltage limiting element (10) and of which a forward direction corresponds to a direction in which a breakdown current of the transient voltage limiting element (10) flows. This configuration affords appropriate protection against transient voltage with respect to a plurality of terminals of the transient voltage protection device.

Description

Transient voltage protection device

(4) The present invention relates to a transient voltage protection device for protecting an electronic circuit from a transient voltage due to electrostatic discharge or the like.

Patent Document 1 discloses a semiconductor integrated circuit including an electrostatic discharge protection circuit for protecting an electronic circuit from electrostatic discharge (ESD: Electrostatic Discharge). The semiconductor integrated circuit disclosed in Patent Literature 1 includes a connection path connecting an external pad for inputting / outputting a signal and an internal circuit, and two protection circuits connected to the connection path. The first protection circuit includes a diode connected between the connection path and the ground line, and the second protection circuit is connected between the connection path and the power supply line or between the connection path and the ground line. It consists of a diode.

JP 2009-54851 A

The semiconductor integrated circuit described in Patent Document 1 is a circuit that protects an internal circuit against electrostatic discharge from the outside with respect to a single input / output terminal, but protects a plurality of input terminals from transient voltages such as electrostatic discharge. When a circuit for protection is constructed, the following problems occur.

FIG. 11 is a circuit diagram of a transient voltage protection device having two input / output terminals P1 and P2 and a common terminal Pc configured to explain the problem of the present invention. This transient voltage protection device includes zener diodes ZD0, ZD1, ZD2 between input / output terminals P1, P2 and common terminal Pc. Usually, the input / output terminals P1 and P2 are external terminals, and the common terminal Pc is a ground terminal. The anode of Zener diode ZD1 is connected to input / output terminal P1, the anode of Zener diode ZD2 is connected to input / output terminal P2, the anode of Zener diode ZD0 is connected to common terminal Pc, and the cathodes of Zener diodes ZD1, ZD2, ZD3. Are commonly connected.

However, in such a circuit in which a transient-voltage-suppressor (TVS) such as a Zener diode is connected between a plurality of input / output terminals and a common terminal, for example, a transient voltage is applied to the input / output terminal P1. Then, when the Zener diode ZD0 breaks down, the Zener diode ZD2 also breaks down. As a result, the transient current i0 flows to the common terminal Pc, and the transient current i2 leaks to the input / output terminal P2. Therefore, the transient voltage protection for the circuit connected to the input / output terminal P2 is not effectively performed. Similarly, when a transient voltage is applied to the input / output terminal P2 and the Zener diode ZD0 breaks down, the Zener diode ZD1 also breaks down. As a result, a transient current flows to the common terminal Pc and leaks to the input / output terminal P1. Therefore, the transient voltage protection for the circuit connected to the input / output terminal P1 is not effectively performed.

Therefore, an object of the present invention is to provide a circuit in which a transient voltage suppressing element is connected between a plurality of input / output terminals and a common terminal, so that a plurality of terminals can be appropriately protected against a transient voltage. It is to provide a device.

A transient voltage protection device as an example of the present disclosure includes:
A single common terminal, a plurality of input / output terminals, and a transient voltage suppressing element having a first end connected directly or indirectly to the common terminal;
A direction in which a breakdown voltage is higher than a breakdown voltage of the transient voltage suppression element and a breakdown current of the transient voltage suppression element flows between a second end of the transient voltage suppression element and the plurality of input / output terminals. Is a forward direction, and a backflow prevention circuit is connected.

According to the above configuration, even when the transient voltage suppressing element breaks down, the transient voltage is not applied from the transient voltage protection device side to the input / output terminal to which the transient voltage is not externally applied by the action of the backflow prevention circuit. Absent. Therefore, the circuits connected to the respective input / output terminals are protected.

According to the present invention, in a circuit in which a transient voltage suppressing element is connected between a plurality of input / output terminals and a common terminal, there is provided a transient voltage protection device capable of appropriately protecting a plurality of terminals against a transient voltage. can get.

FIG. 1A is a circuit diagram of a transient voltage protection device 101A according to the first embodiment. FIG. 1B is a circuit diagram of the transient voltage protection device 101B according to the first embodiment. FIG. 2 is a circuit diagram showing a main part of an electronic circuit to which the transient voltage protection device 101B is connected. FIG. 3 is a cross-sectional view of a main part of the semiconductor integrated circuit when the transient voltage protection device 101B is configured by a single semiconductor integrated circuit. FIG. 4 is a circuit diagram of a transient voltage protection device 101C having three input / output terminals P1, P2, and P3. FIG. 5 is a circuit diagram of the transient voltage protection device 102 according to the second embodiment. FIG. 6 is a circuit diagram of the transient voltage protection device 103 according to the third embodiment. FIG. 7 is a circuit diagram of the transient voltage protection device 104 according to the fourth embodiment. FIG. 8 is a circuit diagram of the transient voltage protection device 105 according to the fifth embodiment. FIG. 9 is a circuit diagram of a transient voltage protection device 106A according to the sixth embodiment. FIG. 10 is a circuit diagram of another transient voltage protection device 106B according to the sixth embodiment. FIG. 11 is a circuit diagram of a transient voltage protection device having two input / output terminals P1 and P2 and a common terminal Pc configured to explain the problem of the present invention.

First, some aspects of the transient voltage protection device according to the present invention will be described.

In the transient voltage protection device according to the first aspect of the present invention, one common terminal, a plurality of input / output terminals, and a transient voltage suppression element whose first end is directly or indirectly connected to the common terminal. , Is provided. Then, between the second end of the transient voltage suppressing element and the plurality of input / output terminals, the breakdown voltage is higher than the breakdown voltage of the transient voltage suppressing element, and the breakdown current of the transient voltage suppressing element flows in the forward direction. A backflow prevention circuit is connected to the direction. According to this configuration, even when the transient voltage suppressing element breaks down, the transient voltage protection device does not apply the transient voltage to the input / output terminal to which the transient voltage is not externally applied due to the operation of the backflow prevention circuit. Therefore, the circuits connected to the respective input / output terminals are protected.

In the transient voltage protection device according to a second aspect of the present invention, the transient voltage suppression element is a Zener diode that breaks down a circuit connected to the input / output terminal with a voltage to be protected. According to this configuration, the transient voltage suppressing element that breaks down at a relatively low voltage can be provided, and the transient voltage protection can be performed in an electronic device with a low power supply voltage.

In the transient voltage protection device according to a third aspect of the present invention, the backflow prevention circuit is a MOS-FET having a gate and a drain connected to each other. According to this configuration, since the voltage drop in the forward bias state is small and the on-resistance is low, the voltage of the input / output terminal during the transient voltage protection operation can be further suppressed.

In the transient voltage protection device according to a fourth aspect of the present invention, the backflow prevention circuit is a PN junction diode formed at a junction between the P layer and the N layer. According to this configuration, the backflow prevention circuit can be configured with a simple circuit and a simple element structure, and a small-sized and low-cost transient voltage protection device can be obtained.

In the transient voltage protection device according to a fifth aspect of the present invention, the backflow prevention circuit is a Zener diode. According to this configuration, a backflow prevention circuit whose breakdown voltage is higher than the breakdown voltage of the transient voltage suppression element can be configured with a simple circuit and a simple element structure, and a small-sized and low-cost transient voltage protection device can be obtained.

In the transient voltage protection device according to a sixth aspect of the present invention, the backflow prevention circuit further includes an inductor connected in series to a path through which the breakdown current flows. According to this configuration, the high-frequency component of the breakdown current is suppressed, and the high-frequency component of the voltage applied to the input / output terminal is suppressed. In addition, the upper limit of the current flowing through each element in the path of the breakdown current is limited, and destruction of those elements can be prevented.

Hereinafter, a plurality of embodiments for implementing the present invention will be described with reference to the drawings and some specific examples. In the drawings, the same parts are denoted by the same reference numerals. Although the embodiments are shown separately for the convenience of explanation in consideration of the explanation of the main points or the ease of understanding, partial replacement or combination of the configurations shown in different embodiments is possible. From the second embodiment onward, description of matters common to the first embodiment will be omitted, and only different points will be described. In particular, the same operation and effect of the same configuration will not be sequentially described for each embodiment.

<< 1st Embodiment >>
FIG. 1A is a circuit diagram of a transient voltage protection device 101A according to the first embodiment. FIG. 1B is a circuit diagram of a transient voltage protection device 101B according to the first embodiment.

In the transient voltage protection device 101A shown in FIG. 1A, one common terminal Pc, two input / output terminals P1 and P2, and a first end T1 are directly or indirectly connected to the common terminal Pc. And a transient voltage suppressing element 10. Between the second end T2 of the transient voltage suppressing element 10 and the input / output terminals P1 and P2, the breakdown voltage is higher than the breakdown voltage of the transient voltage suppressing element 10, and the breakdown current of the transient voltage suppressing element 10 is Backflow prevention circuits 11 and 12, each having a flowing direction as a forward direction, are connected. In the example shown in FIGS. 1A and 1B, the second end T2 of the transient voltage suppressor 10 is connected to a common connection point CN between the transient voltage suppressor 10 and the backflow prevention circuits 11, 12. .

(4) The transient voltage suppressing element 10 protects a circuit connected to the input / output terminal P1 from a transient voltage caused by electrostatic discharge (hereinafter, referred to as ESD) externally applied to the input / output terminal P1. Similarly, the transient voltage suppressing element 10 protects a circuit connected to the input / output terminal P2 from a transient voltage due to ESD or the like externally applied to the input / output terminal P2.

FIG. 1B is a circuit diagram of an example in which the transient voltage suppression element 10 and the backflow prevention circuits 11 and 12 are configured by specific elements. In the transient voltage protection device 101B shown in FIG. 1B, the transient voltage suppression element 10 is configured by a Zener diode ZD0. The backflow prevention circuit 11 includes a Zener diode ZD1 and a MOS-FET # Q1. The backflow prevention circuit 12 includes a Zener diode ZD2 and a MOS-FET Q2.

The breakdown voltage of the zener diode ZD1 is higher than the voltage applied to the input / output terminals P1 and P2 in a steady state and lower than the upper limit voltage required to protect the circuit connected to the input / output terminals P1 and P2. The breakdown voltage of the Zener diode ZD0 is, for example, a voltage in the range of 7V to 13V, and the breakdown voltage of the Zener diodes ZD1, ZD2 is a voltage in the range of 7V to 13V. The Zener diodes ZD1 and ZD2 are elements formed in one chip together with the Zener diode ZD0, as described later.

In FIG. 1B, a MOS-FET Q1 is an N-channel MOS-FET, and a gate G and a drain D are connected. Similarly, the MOS-FET Q2 is an N-channel MOS-FET, and the gate G and the drain D are connected. In the N-channel MOS-FET $ Q1 in which the gate G and the drain D are connected, the voltage between the gate and the source is equal to the gate threshold voltage (Vth) while the positive voltage is applied to the drain D with respect to the source S. , The MOS-FET $ Q1 turns on. Conversely, when a low voltage is applied to the drain D with respect to the source S of the MOS-FET $ Q1, or when the drain-source voltage is 0, the gate-source voltage becomes the gate threshold voltage (Vth ), The MOS-FET $ Q1 is turned off. In other words, the MOSFET Q1 in which the gate G and the drain D are connected functions as a diode having the drain D as an anode and the source S as a cathode. Similarly, the MOSFET Q2 in which the gate G and the drain D are connected also functions as a diode having the drain D as an anode and the source S as a cathode.

FIG. 2 is a circuit diagram showing a main part of an electronic circuit to which the transient voltage protection device 101B is connected. In this example, the transient voltage protection device 101B is connected between the signal input / output line of the first electronic circuit 51 and the signal input / output line of the second electronic circuit 52 and the ground.

In FIGS. 1B and 2, for example, when a positive ESD is applied to the input / output terminal P1, a forward bias voltage is applied to the Zener diode ZD1. Further, a forward bias voltage is applied to a diode constituted by the MOS-FET # Q1 in which the gate G and the drain D are connected. Therefore, the potential of the cathode of the Zener diode ZD0 with respect to the anode exceeds the breakdown voltage, and the Zener diode ZD0 breaks down. As a result, a current id flows through the path of the input / output terminal P1, the backflow prevention circuit 11, the transient voltage suppressing element 10, and the common terminal Pc. This current id is a breakdown current of the Zener diode ZD0.

As described above, the breakdown of the Zener diode ZD0 protects the first electronic circuit 51 connected to the input / output terminal P1 from a transient voltage due to ESD. Further, in a state where the positive ESD is applied to the input / output terminal P1, a reverse bias voltage is applied to the diode constituted by the MOS-FET # Q2 in which the gate G and the drain D are connected. Therefore, the Zener diode ZD2 does not break down, and no ESD is applied to the input / output terminal P2. Therefore, the second electronic circuit 52 connected to the input / output terminal P2 is not affected by the ESD.

The above-described example is a case where ESD is applied to the input / output terminal P1, but when an ESD is applied to the input / output terminal P2, similarly, the input / output terminal P2 → the backflow prevention circuit 12 → the transient voltage suppression element 10 → A breakdown current flows through the path of the common terminal Pc. That is, the breakdown of the Zener diode ZD0 protects the second electronic circuit 52 connected to the input / output terminal P2 from a transient voltage due to ESD. Further, the Zener diode ZD1 does not break down, and the ESD is not applied to the input / output terminal P1. Therefore, the first electronic circuit 51 connected to the input / output terminal P1 is not affected by the ESD.

Note that a diode formed by connecting the gate G and the drain D of the MOS-FET has a lower forward bias voltage drop than a PN junction diode, and thus is suitable for protecting against a lower transient voltage. Also suitable. Further, since the on-resistance is lower than that of the PN junction diode, the voltage of the input / output terminal during the transient voltage protection operation can be suppressed lower.

FIG. 3 is a cross-sectional view of a main part of the semiconductor integrated circuit when the transient voltage protection device 101B is constituted by a single semiconductor integrated circuit. In FIG. 3, P-SUB is a P-type semiconductor substrate, and NWELL is an N-type well. P + is a P-type region and N + is an N-type region. OF is an oxide insulating layer.

ツ ェ A Zener diode is constituted by the N-type well NWELL and the P-type region P + and the N-type region N + formed therein. Further, an N-channel MOS-FET is constituted by the P-type substrate P-SUB, the two N-type regions N +, and the oxide insulating layer OF. Metal films corresponding to the drain D and the source S are formed on the surface of the N-type region N +. On the surface of the oxide insulating layer OF, a metal film corresponding to the gate G is formed.

よ う Thus, the transient voltage protection device 101B can be constituted by a single semiconductor integrated circuit.

In the example described above, the transient voltage protection device having two input / output terminals P1 and P2 has been described. However, a transient voltage protection device having three or more input / output terminals can be similarly configured. For example, FIG. 4 is a circuit diagram of a transient voltage protection device 101C having three input / output terminals P1, P2, and P3. The transient voltage protection device 101C shown in FIG. 4 includes one common terminal Pc, three input / output terminals P1, P2, P3, Zener diodes ZD1, ZD2, ZD3, and MOS-FETs Q1, Q2, Q3. The Zener diode ZD1 and the MOS-FET Q1 constitute a first backflow prevention circuit, the Zener diode ZD2 and the MOS-FET Q2 constitute a second backflow prevention circuit, and the Zener diode ZD3 and the MOS-FET Q3. A third backflow prevention circuit is configured.

As described above, one common terminal Pc, a plurality of input / output terminals P1, P2, and P3, and a transient voltage suppressing element (Zener diode ZD0) having a first end connected to the common terminal Pc are provided. Between the second end of the suppression element (Zener diode ZD0) and the plurality of input / output terminals P1, P2, P3, the breakdown voltage is higher than the breakdown voltage of the transient voltage suppression element (Zener diode ZD0) and the transient voltage A transient voltage protection device having three or more input / output terminals can be configured by connecting a backflow prevention circuit in which the direction in which the breakdown current of the suppression element (Zener diode ZD0) flows is the forward direction.

<< 2nd Embodiment >>
In the second embodiment, an example of a transient voltage protection device in which the configuration of the backflow prevention circuit is different from that shown in the first embodiment will be described.

FIG. 5 is a circuit diagram of the transient voltage protection device 102 according to the second embodiment. The transient voltage protection device 102 shown in FIG. 5 includes one common terminal Pc, two input / output terminals P1 and P2, and a Zener diode ZD0 having an anode connected to the common terminal Pc. Backflow prevention circuits 11 and 12 are connected between the cathode of the Zener diode ZD0 and the input / output terminals P1 and P2, respectively.

In the transient voltage protection device 101B shown in FIG. 1B, the diodes are respectively constituted by the MOS-FETs Q1 and Q2, but in the present embodiment, the PN junction diodes D1 and D2 are provided in the backflow prevention circuits 11 and 12, respectively. Each is provided. Other configurations are as described in the first embodiment.

According to the present embodiment, the configuration of the diodes D1 and D2 is simplified, and the size of the transient voltage protection device can be further reduced.

<< 3rd Embodiment >>
In the third embodiment, an example of a transient voltage protection device in which the configuration of the backflow prevention circuit is different from that shown in the first embodiment will be described.

FIG. 6 is a circuit diagram of the transient voltage protection device 103 according to the third embodiment. The transient voltage protection device 103 illustrated in FIG. 6 includes one common terminal Pc, two input / output terminals P1 and P2, and the transient voltage suppression element 10 having a first end connected to the common terminal Pc. Backflow prevention circuits 11 and 12 are connected between the second end of the transient voltage suppression element 10 and the input / output terminals P1 and P2, respectively.

で は In the present embodiment, the transient voltage suppressing element 10 is constituted by the Zener diode ZD0. The backflow prevention circuit 11 includes zener diodes ZD1 and ZD21. Similarly, the backflow prevention circuit 12 includes zener diodes ZD2 and ZD22. Other configurations are as described in the first embodiment.

The breakdown voltage of the Zener diodes ZD0, ZD1, ZD2, ZD21, ZD22 is the same.

Since each of the backflow prevention circuits 11 and 12 is configured by a multi-stage connected zener diode as in the present embodiment, the substantial breakdown voltage of the backflow prevention circuit is increased, so that the zener diode ZD0 is first broken down. I do. For example, when ESD is applied to the input / output terminal P1, a breakdown current id flows through the path of the input / output terminal P1, the zener diode ZD1, the zener diode ZD21, the zener diode ZD0, and the common terminal Pc. That is, the breakdown of the Zener diode ZD0 protects the electronic circuit connected to the input / output terminal P1 from a transient voltage due to ESD. At this time, the Zener diodes ZD22 and ZD2 do not break down. Thus, the ESD is not applied to the input / output terminal P2. Therefore, the electronic circuit connected to the input / output terminal P2 is also protected from ESD.

According to the present embodiment, the Zener diode ZD0 constituting the transient voltage suppression element 10 and the Zener diodes ZD1, ZD2, ZD21, ZD22 constituting the backflow prevention circuit can be constituted by Zener diodes having the same breakdown voltage. It can be easily manufactured in the same process without special adjustment of the breakdown voltage.

<< 4th Embodiment >>
In the fourth embodiment, an example of a transient voltage protection device in which the configuration of the backflow prevention circuit is different from that shown in the first embodiment will be described.

FIG. 7 is a circuit diagram of the transient voltage protection device 104 according to the fourth embodiment. The transient voltage protection device 104 illustrated in FIG. 7 includes one common terminal Pc, two input / output terminals P1 and P2, and the transient voltage suppression element 10 having a first end connected to the common terminal Pc. Backflow prevention circuits 11 and 12 are connected between the second end of the transient voltage suppression element 10 and the input / output terminals P1 and P2, respectively.

で は In the present embodiment, the transient voltage suppressing element 10 is constituted by the Zener diode ZD0. The backflow prevention circuit 11 is configured by a Zener diode ZD31. Similarly, the backflow prevention circuit 12 includes a Zener diode ZD32. Other configurations are as described in the first embodiment.

Here, if the breakdown voltage of the Zener diode ZD0 is represented by VB0, the breakdown voltage of the Zener diode ZD31 is represented by VB31, and the breakdown voltage of the Zener diode ZD32 is represented by VB32, the relations are VB0 <VB31 and VB0 <VB32. . The breakdown voltage VB0 of the Zener diode ZD0 is, for example, a voltage in the range of 7V to 8V, and the breakdown voltages VB31, VB32 of the Zener diodes ZD31, ZD32 are all in the range of, for example, 10V to 13V.

That is, the Zener diodes ZD31 and ZD32 connected between the cathode of the Zener diode ZD0 (the second end of the transient voltage suppression element 10) and the input / output terminals P1 and P2 have a breakdown voltage of the Zener diode ZD0. An element whose forward direction is higher than VB0 and in which the breakdown current of the Zener diode ZD0 flows.

According to the present embodiment, for example, when a positive ESD is applied to the input / output terminal P1, the electronic circuit connected to the input / output terminal P1 is protected from a transient voltage due to the ESD by breaking down the zener diode ZD0. You. Since the breakdown voltage of the Zener diode ZD32 forming the backflow prevention circuit 12 is higher than the Zener diode ZD0 forming the transient voltage suppression element 10, even when the Zener diode ZD0 breaks down, the Zener diode ZD32 does not break down and the ESD is reduced. It is not applied to the input / output terminal P2. Therefore, the electronic circuit connected to the input / output terminal P2 is also protected from ESD. When the ESD is applied to the input / output terminal P2, the electronic circuit connected to the input / output terminal P2 is similarly protected from the transient voltage due to the ESD by breaking down the zener diode ZD0, and the Zener diode ZD31 is broken down. Therefore, the ESD is not applied to the input / output terminal P1. Therefore, the electronic circuit connected to the input / output terminal P1 is also protected from ESD.

<< 5th Embodiment >>
In the fifth embodiment, an example of a transient voltage protection device in which the configuration of the backflow prevention circuit is different from that shown in the first embodiment will be described.

FIG. 8 is a circuit diagram of the transient voltage protection device 105 according to the fifth embodiment. The transient voltage protection device 105 illustrated in FIG. 8 includes one common terminal Pc, two input / output terminals P1 and P2, and the transient voltage suppression element 10 having a first end connected to the common terminal Pc. Backflow prevention circuits 11 and 12 are connected between the second end of the transient voltage suppression element 10 and the input / output terminals P1 and P2, respectively.

で は In the present embodiment, the transient voltage suppressing element 10 is constituted by the Zener diode ZD0. The backflow prevention circuit 11 includes a Zener diode ZD1, a MOS-FET Q1, and an inductor L1. Similarly, the backflow prevention circuit 12 includes a Zener diode ZD2, a MOS-FET Q2, and an inductor L2. Other configurations are as described in the first embodiment.

The transient voltage protection device 105 of the present embodiment is obtained by adding inductors L1 and L2 to the transient voltage protection device 101B shown in FIG. The inductor L1 is connected in series to a path of a breakdown current flowing from the input / output terminal P1 to the common terminal Pc. Similarly, the inductor L2 is connected in series to the path of the breakdown current flowing from the input / output terminal P2 to the common terminal Pc.

For example, when ESD is applied to the input / output terminal P1, the MOS-FET Q1 acts as a forward-biased diode, and the input / output terminal P1 → Zener diode ZD1 → Inductor L1 → MOS-FET Q1 → Zener diode ZD0 → common. The breakdown current id flows through the path of the terminal Pc. At this time, since the reverse bias voltage is applied to the diode constituted by the MOS-FET # Q2 in the backflow prevention circuit 12, the diode remains off.

(4) Since the inductor L1 is inserted in the current path of the breakdown current, the inductor L1 suppresses the high-frequency component of the breakdown current and suppresses the high-frequency component of the voltage applied to the input / output terminal P1. That is, the transient voltage fluctuation of the input / output terminal P1 when the ESD is applied to the input / output terminal P1 and the Zener diode ZD0 breaks down is suppressed. Further, the upper limit of the current flowing through each element in the path of the breakdown current is limited, and destruction of those elements is prevented.

同 様 The same applies to the inductor L2 in the backflow prevention circuit 12. That is, the transient voltage fluctuation of the input / output terminal P2 when the ESD is applied to the input / output terminal P2 and the Zener diode ZD0 breaks down is suppressed. Further, the upper limit of the current flowing through each element in the path of the breakdown current is limited, and destruction of those elements is prevented.

Note that an inductor may be inserted between the second end T2 (the cathode of the Zener diode ZD0) of the transient voltage suppression element 10 and the common connection point CN. According to the configuration, the inductors L1 and L2 are unnecessary.

<< Sixth Embodiment >>
In the sixth embodiment, an example of a transient voltage protection device that protects against a bipolar transient voltage will be described.

FIG. 9 is a circuit diagram of a transient voltage protection device 106A according to the sixth embodiment. The transient voltage protection device 106A illustrated in FIG. 9 includes a common terminal Pc, input / output terminals P1 and P2, and transient voltage suppression elements 10p and 10n whose first terminals T1 are connected to the common terminal Pc. Backflow prevention circuits 11p and 12p are connected between the second end of the transient voltage suppression element 10p and the input / output terminals P1 and P2, respectively. Similarly, backflow prevention circuits 11n and 12n are connected between the second end of the transient voltage suppression element 10n and the input / output terminals P1 and P2, respectively.

In FIG. 9, the transient voltage suppression element 10p and the backflow prevention circuits 11p and 12p constitute a transient voltage protection circuit for a positive transient voltage. The transient voltage suppression element 10n and the backflow prevention circuits 11n and 12n provide a negative voltage. A transient voltage protection circuit for the transient voltage is configured. The transient voltage protection circuit including the transient voltage suppression element 10p and the backflow prevention circuits 11p and 12p has the same configuration as that of the transient voltage protection device shown in FIG.

The transient voltage suppressing element 10p is constituted by a Zener diode ZD0p. Similarly, the transient voltage suppression element 10n is configured by a Zener diode ZD0n. The backflow prevention circuit 11p includes a zener diode ZD1p and a MOS-FET $ Q1p, and the backflow prevention circuit 12p includes a zener diode ZD2p and a MOS-FET $ Q2p. Similarly, the backflow prevention circuit 11n includes a zener diode ZD1n and a MOS-FET $ Q1n, and the backflow prevention circuit 12n includes a zener diode ZD2n and a MOS-FET $ Q2n.

The positive transient voltage protection circuit and the negative transient voltage protection circuit have the same circuit configuration except that the direction of each Zener diode and the direction of the MOS-FET are reversed.

{For example, when a positive ESD is applied to the input / output terminal P1, a forward bias voltage is applied to the Zener diode ZD1p. In addition, a forward bias voltage is applied to a diode composed of a MOS-FET # Q1p in which the gate G and the drain D are connected. Therefore, the potential of the cathode of the Zener diode ZD0p with respect to the anode exceeds the breakdown voltage, and the Zener diode ZD0p breaks down. As a result, the current idp flows through the path of the input / output terminal P1, the backflow prevention circuit 11p, the transient voltage suppressing element 10p, and the common terminal Pc. As a result, the input / output terminal P1 is protected from positive ESD.

(4) For example, when a negative ESD is applied to the input / output terminal P1, a forward bias voltage is applied to the Zener diode ZD1n. Further, a forward bias voltage is applied to a diode composed of a MOS-FET # Q1n in which the gate G and the drain D are connected. Therefore, the potential of the cathode of the Zener diode ZD0n with respect to the anode exceeds the breakdown voltage, and the Zener diode ZD0n breaks down. As a result, the current idn flows through the path of the common terminal Pc → transient voltage suppressing element 10n → backflow prevention circuit 11n → input / output terminal P1. Thus, the input / output terminal P1 is protected from negative ESD.

The above example is a case where ESD is applied to the input / output terminal P1, but the same applies to a case where positive or negative ESD is applied to the input / output terminal P2. For example, when a positive ESD is applied to the input / output terminal P2, a breakdown current flows through the path of the input / output terminal P2 → the backflow prevention circuit 12p → the transient voltage suppressing element 10p → the common terminal Pc. As a result, the input / output terminal P2 is protected from positive ESD. Further, for example, when a negative ESD is applied to the input / output terminal P2, a breakdown current flows through the path of the common terminal Pc → the transient voltage suppressing element 10n → the backflow prevention circuit 12n → the input / output terminal P2. Thereby, the input / output terminal P2 is protected from negative ESD.

FIG. 10 is a circuit diagram of another transient voltage protection device 106B according to the present embodiment. This transient voltage protection device 106B is a device that performs transient voltage protection for three input / output terminals P1, P2, and P3. The transient voltage protection device 106B illustrated in FIG. 10 includes one common terminal Pc, three input / output terminals P1, P2, and P3, and zener diodes ZD0p, ZD0n, ZD31p, ZD31n, ZD32p, ZD32n, ZD33p, and ZD33n. Prepare. The Zener diode ZD0p is a transient voltage suppression element for positive transient voltage protection, and the Zener diode ZD0n is a transient voltage suppression element for negative transient voltage protection. The Zener diodes ZD31p, ZD32p, and ZD33p are elements that form a backflow prevention circuit for positive transient voltage protection, and the Zener diodes ZD31n, ZD32n, and ZD33n are elements that form a backflow prevention circuit for negative transient voltage protection. is there.

Here, the breakdown voltage of the Zener diode ZD0p is represented by VB0p, the breakdown voltage of the Zener diode ZD31p is represented by VB31p, the breakdown voltage of the Zener diode ZD32p is represented by VB32p, and the breakdown voltage of the Zener diode ZD33p is represented by VB33p, respectively.
VB0p <VB31p
VB0p <VB32p
VB0p <VB33p
It is. Also, when the breakdown voltage of the Zener diode ZD0n is represented by VB0n, the breakdown voltage of the Zener diode ZD31n is represented by VB31n, the breakdown voltage of the Zener diode ZD32n is represented by VB32n, and the breakdown voltage of the Zener diode ZD33n is represented by VB33n, respectively.
| VB0n | <| VB31n |
| VB0n | <| VB32n |
| VB0n | <| VB33n |
It is.

According to the present embodiment, for example, when a positive ESD is applied to the input / output terminal P1, the electronic circuit connected to the input / output terminal P1 breaks down due to the breakdown of the Zener diode ZD0p. Protected. Further, for example, when a negative ESD is applied to the input / output terminal P1, the Zener diode ZD0n breaks down, and the electronic circuit connected to the input / output terminal P1 is protected from a transient voltage due to the negative ESD. Similarly, the input / output terminals P2 and P3 are protected from positive and negative transient voltages.

In the embodiment described above, an example is shown in which the first ends of the transient voltage suppression elements 10, 10p, and 10n are directly connected to the common terminal Pc. However, the first ends of the transient voltage suppression elements 10, 10p, and 10n are common. It may be indirectly connected to the terminal Pc. For example, an inductor may be inserted between the first terminals of the transient voltage suppression elements 10, 10p, and 10n and the common terminal Pc.

(4) The common terminal Pc may not be directly connected to the ground but may be connected indirectly. For example, an inductor may be inserted between the common terminal Pc and the ground. According to this configuration, the high-frequency component of the breakdown current of the transient voltage suppression element is suppressed, and the high-frequency component of the breakdown current is suppressed. Thereby, transient voltage fluctuations of the input / output terminals (P1, P2, etc.) are suppressed. Further, the upper limit of the current flowing through each element in the path of the breakdown current is limited, and the elements are protected from destruction.

Lastly, the description of the above-described embodiment is illustrative in all aspects and is not restrictive. Modifications and changes can be made by those skilled in the art as appropriate. The scope of the present invention is defined by the terms of the claims, rather than the embodiments described above. Further, the scope of the present invention includes modifications from the embodiments within the scope equivalent to the scope of the claims.

CN: common connection point D: drain D1, D2: diode G: gate id, idp, idn: breakdown current L1, L2: inductor P1, P2, P3: input / output terminal Pc: common terminal Q1, Q2: MOS-FET
S Source T1 First end T2 Second end ZD0, ZD1, ZD2, ZD3 Zener diodes ZD0n, ZD1n, ZD2n Zener diodes ZD0p, ZD1p, ZD2p Zener diodes ZD21, ZD22 Zener diodes ZD31, ZD32 Zener Diodes ZD31n, ZD32n, ZD33n Zener diodes ZD31p, ZD32p, ZD33p Zener diodes 10, 10p, 10n Transient voltage suppressing elements 11, 12 Backflow prevention circuits 11n, 12n Backflow prevention circuits 11p, 12p Backflow prevention circuits 51 1st electronic circuit 52 ... 2nd electronic circuit 101A, 101B, 101C ... transient voltage protection device 102,103,104,105 ... transient voltage protection device 106A, 106B ... transient voltage protection device

Claims (6)

A single common terminal, a plurality of input / output terminals, and a transient voltage suppressing element having a first end connected directly or indirectly to the common terminal;
A direction in which a breakdown voltage is higher than a breakdown voltage of the transient voltage suppression element and a breakdown current of the transient voltage suppression element flows between a second end of the transient voltage suppression element and the plurality of input / output terminals. The forward direction, the backflow prevention circuit is connected,
Transient voltage protection device. The transient voltage protection device according to claim 1, wherein the transient voltage suppression element is a Zener diode that breaks down at a voltage to protect a circuit connected to the input / output terminal. The transient voltage protection device according to claim 1, wherein the backflow prevention circuit includes a MOS-FET having a gate and a drain connected to each other. 3. The transient voltage protection device according to claim 1, wherein the backflow prevention circuit includes a PN junction diode formed at a junction between the P layer and the N layer. The transient voltage protection device according to any one of claims 1 to 4, wherein the backflow prevention circuit includes a Zener diode. 6. The transient voltage protection device according to claim 1, wherein the backflow prevention circuit further includes an inductor connected in series to a path through which the breakdown current flows. 7.

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