JPH0818417A - Power element drive protective circuit and mosfet drive protective circuit - Google Patents

Abstract

PURPOSE:To prevent the destruction of a MOSFET driving circuit at the time of the destruction of a MOSFET. CONSTITUTION:An overcurrent limiting bypass route 16 is constituted of a second overcurrent limiting resistor 14 and an NPN transistor 15 whose base is connected through a resistor 12 for base current control to the contact point of a Zener diode 3 and a first overcurrent limiting resistor 13, in which collector is connected through the second overcurrent limiting resistor 14 to the emitter of a PNP transistor 6 and emitter is connected to the source of the MOSFET 1. When an overcurrent is made flow to the MOSFET driving circuit 2, the overcurrent limiting bypass route 16 is turned to a closed state. Thus, the overcurrent is limited by the first overcurrent limiting resistor 13 and the second overcurrent limiting resistor 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power element drive protection circuit or a MOSFET drive protection circuit which prevents the power element drive circuit from being destroyed by the destruction of a power element such as a MOSFET.

[0002]

2. Description of the Related Art A MOSFET drive circuit as an example of a conventional power element drive circuit will be described with reference to FIG. FIG.
FIG. 3 is a circuit diagram in which a MOSFET drive circuit 2 is connected to an n-channel type MOSFET 1. In the figure, the Zener diode 3 and the first
The gate voltage control resistors 4 are connected in parallel. This Zener diode 3 has a MOSF anode
Connected to the source of ET1 and the cathode is MOSFET1
Connected to the gate. The emitter of the PNP transistor 6 is connected to the gate of the MOSFET 1 via the second gate voltage control resistor 5, and the collector of the PNP transistor 6 is connected to the source of the MOSFET 1. Furthermore, the base of the PNP transistor 6 is the first
It is connected to the high potential side of the control power supply 8 via the off-voltage holding resistor 7, and the emitter of the PNP transistor 6 is connected to the high potential side of the control power supply 8 via the second off-voltage holding resistor 9. The low potential side of the control power supply 8 is connected to the source of the MOSFET 1. A load 10 and a high voltage power supply 11 are connected between an output terminal a to which the drain of the MOSFET 1 is connected and an output terminal b to which the source of the MOSFET 1 is connected.

The operation of the circuit shown in FIG. 3 will be described. When the control power supply 8 outputs a positive voltage pulsed drive voltage, the pulsed drive voltage is composed of the first gate voltage control resistor 4, the second gate voltage control resistor 5, and the second off-voltage holding resistor 9 in series. The first gate voltage control resistor 4 is divided by the circuit.
Is applied between the gate and source of the input of the MOSFET 1 to turn on the MOSFET 1, and power is supplied from the high voltage power supply 11 to the load 10. The Zener diode 3 is for making the gate-source voltage of the MOSFET 1 constant. In addition, while the control power source 8 is outputting a positive pulsed drive voltage,
The PNP transistor 6 is reverse-biased by the voltage applied to the second off-voltage holding resistor 9 and is in the off state.

Next, when the output of the control power source 8 becomes 0V,
The charge accumulated in the gate of MOSFET 1 is MOSFE.
The current flows to the T drive circuit 2 side, and the PNP transistor 6 is driven by the voltage applied to the second off-voltage holding resistor 9.
Is forward-biased and turned on, and the charge accumulated in the gate of MOSFET 1 is discharged.

[0005]

The MOSF shown in FIG.
In the ET drive circuit 2, when the element of the MOSFET 1 is destroyed, the drain and the source are short-circuited, or the drain and the gate are short-circuited, and a high voltage on the drain side of the MOSFET 1 is applied to the MOSFET drive circuit 2 connected to the gate of the MOSFET 1. When applied, a sudden voltage change occurs in the MOSFET drive circuit 2 and an overcurrent flows in. Therefore, there is a problem that the Zener diode 3, the PNP transistor 6, the control power supply 8 and the like are destroyed.

The present invention has been made in view of the above problems,
An object of the invention is to provide a structure of a power element drive protection circuit or a MOSFET drive protection circuit which can prevent the power element drive circuit or the MOSFET drive circuit from being destroyed when the power element such as the MOSFET is destroyed.

[0007]

In order to achieve the above object, the power element drive protection circuit according to claim 1 is incorporated in a power element drive circuit to protect the power element drive circuit when the power element is destroyed. In the element drive protection circuit, a Zener diode in which a cathode is connected to a high potential side input of the power element and an anode is connected to a low potential side input of the power element through a first overcurrent limiting resistor, and a zener diode of the power element And an overcurrent limiting bypass path that is closed when a high voltage is applied to the high-potential-side input due to breakdown and the predetermined voltage applied to the first overcurrent limiting resistor is detected. It is a feature.

According to another aspect of the MOSFET drive protection circuit of the present invention, the cathode is connected to the gate of the MOSFET.
A Zener diode whose anode is connected to the source of the OSFET, a first gate voltage control resistor connected between the gate and source of the MOSFET, and an emitter are connected to the gate of the MOSFET via a second gate voltage control resistor. A PNP transistor whose collector is connected to the source of the MOSFET and whose base is connected to the high potential side of the control power supply through the first off-voltage holding resistor, and the PNP transistor.
MOSFE including a transistor emitter and a second off-voltage holding resistor connected between the high potential side of the control power supply.
In a MOSFET drive protection circuit for protecting a T drive circuit, an anode of the Zener diode and the MOSF
A first overcurrent limiting resistor connected between the sources of ET and a predetermined voltage applied to the first overcurrent limiting resistor when a high voltage is applied to the gate of the MOSFET due to destruction of the MOSFET. And an overcurrent limiting bypass path that is detected and is in a closed state.

A MOSFET drive protection circuit according to a third aspect of the present invention is the MOSFET drive protection circuit according to the second aspect, wherein the overcurrent limiting bypass path is a second overcurrent limiting resistor and the base is a base current controlling resistor. Is connected to a connection point between the Zener diode and the first overcurrent limiting resistor, a collector is connected to the emitter of the PNP transistor via a second overcurrent limiting resistor, and the emitter is the MOSF.
It is composed of an NPN transistor connected to the source of ET.

A MOSFET drive protection circuit according to a fourth aspect is the MOSFET drive protection circuit according to the second aspect, wherein the base current control resistor and the base are connected to the zener diode and the first via the base current control resistor. The collector is connected to the base of the PNP transistor and the emitter is connected to the connection point with the overcurrent limiting resistor.
An NPN transistor connected to the source of T,
The PNP transistor is used as the overcurrent limiting bypass path.

[0011]

By connecting the first overcurrent limiting resistor between the anode of the Zener diode which is connected between the gate and the source of the MOSFET to make the voltage between the gate and the source of the MOSFET constant, and the source of the MOSFET,
When the FET is destroyed and the drain and the gate are short-circuited and an overcurrent flows into the gate, the current flowing through the Zener diode can be limited, so that the Zener diode can be protected.

Further, when the MOSFET is destroyed, the drain and the gate are short-circuited, a high voltage is applied to the gate, and a predetermined voltage is applied to the first overcurrent limiting resistor, an overcurrent provided between the gate and source of the MOSFET. Since the current limiting bypass path is closed, it is possible to bypass the overcurrent to the source of the MOSFET and protect the control power supply and the like.

FIG. 1 shows an embodiment of a circuit incorporating the MOSFET drive protection circuit according to claim 3. However, FIG.
The same reference numerals are given to the same configurations as those shown in FIG. In the MOSFET drive protection circuit according to claim 3,
The second overcurrent limiting resistor 14 is connected to the overcurrent limiting bypass path.
And the base is connected to the connection point between the Zener diode 3 and the first overcurrent limiting resistor 13 via the base current controlling resistor 12, and the collector is connected to the PNP transistor 6 via the second overcurrent limiting resistor 14. The NPN transistor 15 is connected to the emitter, and the emitter is connected to the source of the MOSFET 1. This allows the MOS
When the FET1 is destroyed and the drain and the gate are short-circuited, a high voltage is applied to the gate of the MOSFET1, and the positive voltage of the high voltage power supply 11 causes the load 10 and the MOS.
A circuit that reaches the negative electrode of the high-voltage power supply 11 via the FET 1, the Zener diode 3, and the first overcurrent limiting resistor 13.
And from the positive electrode of the high voltage power supply 11 to the load 10, MO
An overcurrent flows into the circuit reaching the negative electrode of the high-voltage power supply 11 via the SFET 1, the Zener diode 3, the base current control resistor 12, and the base and emitter of the NPN transistor 15 for the bypass path. Here, since the overcurrent in this transition period is limited by the first overcurrent limiting resistor 13, the element breakdown of the Zener diode 3 can be prevented. Further, the base current is supplied to the NPN transistor 15 for the bypass path via the base current limiting resistor 12, the NPN transistor 15 is turned on, and the overcurrent limiting bypass current is limited by the second overcurrent limiting resistor 14. A path is formed. Since the overcurrent can be bypassed to the source of the MOSFET 1 via this path, the control power supply 8 and the like can be protected.

FIG. 2 shows an embodiment of a circuit incorporating the MOSFET drive protection circuit according to claim 4. However, in FIG.
The same reference numerals are given to the same configurations as those shown in FIG. The MOSFET drive protection circuit according to claim 4 is P
The NP transistor 6 is also used as an overcurrent limiting bypass path.
To be turned on as an overcurrent limiting bypass path, a base current controlling resistor 17 and a connection point between the base and the Zener diode 3 and the first overcurrent limiting resistor 13 via the base current controlling resistor 17. Connected to the
It is connected to the base of NP transistor 6 and has an emitter of M
The NPN transistor 17 connected to the source of the OSFET 1 is provided. With this configuration, when the MOSFET 1 is broken down and the drain and the gate are short-circuited, a high voltage is applied to the gate of the MOSFET 1, and the load 10, the MOSFET 1 and the zener are fed from the positive electrode of the high voltage power supply 11. Circuit for reaching the negative electrode of the high-voltage power supply 11 via the diode 3 and the first overcurrent limiting resistance 13, and from the positive electrode of the high-voltage power supply 11 to the load 10, MOSFET 1, Zener diode 3, and base current control An overcurrent flows into the circuit reaching the negative electrode of the high-voltage power supply 11 via the resistor 17 and the base and emitter of the NPN transistor 18. Here, since the overcurrent in this transition period is limited by the first overcurrent limiting resistor 13, the element breakdown of the Zener diode 3 can be prevented. Further, the base current is supplied to the NPN transistor 18 via the base current limiting resistor 17,
The PN transistor 18 is turned on, the PNP transistor 6 is forward-biased and turned on, and the high voltage power supply 11 passes from the positive electrode of the high voltage power supply 11 through the load 10, the MOSFET 1, the second gate voltage control resistor 5, and the PNP transistor 6. Overcurrent flows through the circuit to the negative electrode of 11
Since the overcurrent can be bypassed to the source of the OSFET 1, the control power supply 8 and the like can be protected.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the power element drive protection circuit of the present invention will be described below with reference to FIG. However, the same components as those shown in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. In the figure, a series circuit including a Zener diode 3 and a first overcurrent limiting resistor 13 and a first gate voltage control resistor 4 are connected in parallel between the gate and source of the MOSFET 1. The Zener diode 3 has an anode connected to the source of the MOSFET 1 through a first overcurrent limiting resistor 13 and a cathode M
It is connected to the gate of OSFET1. Also, MOS
The gate of the FET 1 is connected to the emitter of the PNP transistor 6 through the second gate voltage control resistor 5,
The collector of the P-transistor 6 is connected to the source of the MOSFET 1. Further, the base of the PNP transistor 6 is connected to the high potential side of the control power supply 8 via the first off-voltage holding resistor 7, and the emitter of the PNP transistor 6 is connected to the control power supply 8 via the second off-voltage holding resistor 9. Connected to the high potential side of. The low potential side of the control power supply 8 is a MOS
It is connected to the source of FET1. Further, the base of the NPN transistor 15 is connected to the zener diode 3 and the first overcurrent limiting resistor 1 via the base current controlling resistor 12.
3, the emitter of the NPN transistor 15 is connected to the source of the MOSFET 1, and the collector of the NPN transistor 15 is connected to the emitter of the PNP transistor 6 via the second overcurrent limiting resistor 14. Output terminal a to which the drain of MOSFET 1 is connected
The load 10 and the high-voltage power supply 11 are connected between the output terminal b and the output terminal b to which the source of the MOSFET 1 is connected.

In the circuit shown in FIG. 1, the MOSFET drive protection circuit includes a first overcurrent limiting resistor 13 for limiting the current flowing through the Zener diode 3, a base current controlling resistor 12, and a second overcurrent limiting resistor. Current resistance 14 and NPN transistor 15 to prevent the NPN transistor 15 from turning on during normal operation.
3 and the base current control resistor 12 are set.

Next, the operation of the circuit shown in FIG. 1 will be described. During normal operation, the NPN transistor 15 does not turn on, and the overcurrent limiting bypass path formed by the second overcurrent limiting resistor 14 and the NPN transistor 15 is open. Therefore, the circuit shown in FIG. The circuit is equivalent to the circuit shown in FIG. 3 in which only the first overcurrent limiting resistor 13 for limiting the current flowing through the Zener diode 3 is added to the conventional circuit shown in FIG. If the Zener voltage of the Zener diode 3 is adjusted in consideration of the voltage applied to the first overcurrent limiting resistor 13, the circuit operates in the same manner as the conventional circuit shown in FIG. It will be omitted.

In the circuit shown in FIG. 1, when MOSFET 1 is destroyed and the drain and gate are short-circuited, M
A circuit in which a high voltage is applied to the gate of the OSFET 1 and from the positive electrode of the high-voltage power supply 11 to the negative electrode of the high-voltage power supply 11 via the load 10, the MOSFET 1, the Zener diode 3, and the first overcurrent limiting resistor 13. , And from the positive electrode of the high-voltage power supply 11 to the negative electrode of the high-voltage power supply 11 via the load 10, MOSFET 1, Zener diode 3, base current control resistor 12, and base and emitter of the NPN transistor 15 for bypass path. Overcurrent flows into the circuit leading to. Here, since the overcurrent in this transition period is limited by the first overcurrent limiting resistor 13,
The element breakdown of the Zener diode 3 can be prevented. Further, the base current is supplied to the NPN transistor 15 for the bypass path via the base current control resistor 12, the NPN transistor 15 is turned on, and the overcurrent constituted by the second overcurrent limiting resistor 14 and the NPN transistor 15 is supplied. The current limiting bypass path 16 will be formed. The current flowing through the overcurrent limiting bypass path 16 is limited by the substantially second gate voltage control resistor 5 and the second overcurrent limiting resistor 14. This allows the MOSFE
Since the overcurrent can be bypassed to the source of T1, the control power supply 8 and the like can be protected.

By the way, in the circuit shown in FIG. 1, the overcurrent limiting bypass path 16 is connected between the emitter and collector of the PNP transistor 6, but is not limited to the embodiment. For example, the first gate voltage control It may be connected in parallel with the resistor 4.

A different embodiment of the MOSFET drive protection circuit of the present invention will be described below with reference to FIG. However, in FIG.
The same components as those of the circuit shown in are denoted by the same reference numerals and detailed description thereof will be omitted. The circuit shown in FIG.
In addition to the conventional circuit shown in FIG.
And an NPN transistor 18 are added,
This is a circuit that uses the NP transistor 6 as an overcurrent limiting bypass path. The base of the NPN transistor 18 is connected to the connection point of the Zener diode 3 and the first overcurrent limiting resistor 13 via the base current controlling resistor 17,
The emitter of the PN transistor 18 is connected to the source of the MOSFET 1, and the collector of the NPN transistor 18 is connected to the base of the PNP transistor 6.

In the circuit shown in FIG. 2, the MOSFET drive protection circuit includes a first overcurrent limiting resistor 13 for limiting the current flowing through the Zener diode 3, a base current controlling resistor 17, and an NPN transistor 18. The first overcurrent limiting resistor 13 and the base current controlling resistor 17 are set so that the NPN transistor 18 is not turned on during normal operation.

The normal operation of the circuit shown in FIG. 2 is similar to that of the circuit shown in FIG. In the circuit shown in FIG. 2, when the MOSFET 1 is destroyed and the drain and the gate are short-circuited, a high voltage is applied to the gate of the MOSFET 1 from the positive electrode of the high voltage power supply 11 to the load 10, the MOSFET 1 and the zener diode. 3, a circuit that reaches the negative electrode of the high-voltage power supply 11 via the first overcurrent limiting resistor 13, and from the positive electrode of the high-voltage power supply 11 to the load 10, MOSFET 1, Zener diode 3, base current control resistor 17, high voltage power supply 1 via the base and emitter of NPN transistor 18
An overcurrent flows into the circuit reaching the negative electrode of 1. Here, since the overcurrent in this transition period is limited by the first overcurrent limiting resistor 13, the element breakdown of the Zener diode 3 can be prevented. Also, the NPN transistor 1
8 is supplied with a base current through the base current limiting resistor 17 to turn on the NPN transistor 18. As a result, the PNP transistor 6 is forward-biased and turned on, and the positive polarity of the high-voltage power supply 11 causes the MOSF
An overcurrent will flow in the circuit reaching the negative electrode of the high-voltage power supply 11 via the ET1, the second gate voltage control resistor 5, and the PNP transistor 6. Since the current flowing through this path is limited by the second gate voltage control resistor 5, PN
MOSFET 1 without destroying P-transistor 6
The overcurrent can be bypassed to the source of and the control power supply can be protected.

In the embodiment, the switching element for controlling the open / closed state of the overcurrent limiting bypass path is described as a transistor which is a current control element, but the invention is not limited to this embodiment, and a FET which is a voltage control element or the like. You may comprise using. In the embodiment, the power element is MO
The power element drive protection circuit according to the present invention can be applied to a drive circuit that drives a power element such as a bipolar transistor or a thyristor, for example, although the SFET is described as an SFET.

[0024]

As described above, according to the power element drive protection circuit of the first aspect, when the power element is destroyed and a high voltage is applied to the Zener diode of the power element drive circuit, the first overcurrent is generated. Since the current flowing through the Zener diode can be limited by the current limiting resistance, the Zener diode can be protected. In addition, since the overcurrent flows through the Zener diode and the first overcurrent limiting resistance, the overcurrent limiting bypass circuit is closed, and the overcurrent can be bypassed to the low voltage side of the power supply. Can be protected.

MOSFET according to any one of claims 2 to 4.
According to the drive protection circuit, the MOSFET is destroyed and the MO
When a high voltage is applied to the gate of the SFET and an overcurrent flows into the gate, the overcurrent is limited by the first overcurrent limiting resistance, so that the Zener diode can be protected. Further, since the overcurrent flows through the Zener diode and the first overcurrent limiting resistor, the overcurrent limiting bypass circuit is closed and the overcurrent can be bypassed to the source of the MOSFET, so that the MOSFET driving circuit is protected. You can

Furthermore, the MO according to claims 3 and 4
According to the SFET drive protection circuit, the resistance value between the gate of the MOSFET and the high potential side of the control power supply is the same as that of the conventional circuit, so that the MOSFET can be driven without a large operation delay during normal operation. It can be carried out.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a MOSFET drive protection circuit according to the present invention.

FIG. 2 is a circuit diagram showing another example of the MOSFET drive protection circuit according to the present invention.

FIG. 3 is a circuit diagram showing an example of a MOSFET drive circuit.

[Explanation of symbols]

1 MOSFET (power element) 2 MOSFET drive circuit (power element drive circuit) 3 Zener diode 4 1st gate voltage control resistor 5 2nd gate voltage control resistor 6 PNP transistor (in the case of the circuit shown in FIG. 2, overcurrent limiting bypass) Also serves as a path.) 7 1st off-voltage holding resistor 8 Control power supply 9 2nd off-voltage holding resistor 12 Base current control resistor 13 1st overcurrent current limiting resistor 14 2nd overcurrent current limiting resistor 15 NPN transistor 16 Overcurrent Current limiting bypass path 17 Base current control resistor 18 NPN transistor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H03K 17/567

Claims (4)

[Claims] 1. A power element drive protection circuit incorporated in a power element drive circuit to protect the power element drive circuit when the power element is destroyed, wherein a cathode is connected to a high potential side input of the power element. A Zener diode having an anode connected to a low potential side input through a first overcurrent limiting resistor, and the first overcurrent limiting circuit when a high voltage is applied to the high potential side input due to destruction of the power element. A power element drive protection circuit, comprising: an overcurrent limiting bypass path that is closed when a predetermined voltage applied to a resistor is detected. 2. A Zener diode having a cathode connected to the gate of the MOSFET and an anode connected to the source of the MOSFET, a first gate voltage control resistor connected between the gate and the source of the MOSFET, and an emitter being the second. The MOSFET via a gate voltage control resistor
A PNP transistor whose collector is connected to the source of the MOSFET and whose base is connected to the high potential side of the control power source through the first off-voltage holding resistor.
In a MOSFET drive protection circuit for protecting a MOSFET drive circuit including an emitter of the PNP transistor and a second off-voltage holding resistor connected between the high potential side of the control power supply, an anode of the Zener diode and a source of the MOSFET. The first overcurrent limiting resistance connected between the MOSFET and the MOSFET by the destruction of the MOSFET.
An overcurrent limiting bypass path that is closed when a high voltage is applied to the gate of T and detects a predetermined voltage applied to the first overcurrent limiting resistor.
OSFET drive protection circuit. 3. The overcurrent limiting bypass path is connected to a second overcurrent limiting resistor, and a base is connected to a connection point between the zener diode and the first overcurrent limiting resistor via a base current controlling resistor. 3. An NPN transistor, the connected collector of which is connected to the emitter of the PNP transistor via a second overcurrent limiting resistor, and the emitter of which is connected to the source of the MOSFET. MOSFET drive protection circuit. 4. A base current control resistor, a base connected to a connection point between the Zener diode and the first overcurrent limiting resistor via the base current control resistor, and a collector connected to the base of the PNP transistor. 3. The MOSFET drive protection circuit according to claim 2, further comprising an NPN transistor having an emitter connected to a source of the MOSFET, the PNP transistor being the overcurrent limiting bypass path.