JPH0810821B2 - Overcurrent protection drive circuit for IGBT - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an IG which is a kind of switching semiconductor element.
The present invention relates to a drive circuit having an overcurrent protection function for an BT (Insulated Gate Bipolar Transistor) element.

[Conventional technology]

The IGBT element has the high breakdown voltage of the bipolar transistor,
This device is attracting attention as a new device because it has the advantages that it is easy to increase the capacity and that the power MOSFET can perform high-speed switching and is easy to drive.

 Figure 2 shows the equivalent circuit of an N-channel IGBT.

It consists of N-channel MOSFET 1, NPN transistor 2, PNP transistor 3, and base-emitter short-circuit resistor 4 of transistor 2, and the drain-source of MOSFET 1 and the emitter-collector of transistor 2 are connected in parallel to form transistors 2, 3 Can be represented as forming a thyristor circuit.

When the N-channel IGBT is turned on, a forward bias voltage is applied between the gate and the emitter (between G and E). As a result, a channel is formed in the MOSFET 1, the MOSFET 1 becomes conductive, and the emitter and base of the PNP transistor 3 are forward-biased to start conduction.

Conversely, when turning off this device, apply a reverse bias voltage between the gate and emitter. As a result, the MOSFET 1 is turned off, the base current of the PNP transistor 3 stops flowing, the transistor is turned off, and as a result, the IGBT is turned off.

By the way, this element has the parasitic thyristor formed by the transistors 2 and 3 as described above. Therefore, when the collector current exceeds a predetermined value, a latch-up phenomenon (a phenomenon in which the parasitic thyristor turns on) occurs, and the current may not be cut off.

Since this latch-up phenomenon is linked to the breakdown of the IGBT element, it is necessary to prevent this. IGBT
In case of overcurrent protection, the current level must be kept below the latch-up current. In addition, it is necessary to cut off the collector current before thermal destruction.

In FIG. 2, when an off-gate signal is given to the IGBT, the N-channel MOSFET 1 is turned off first. At the time of overload, the collector current cannot suddenly decrease, so that the current of the PNP transistor 3 increases. Therefore, during turn-off, the collector current is latched up with a smaller collector current than in the turn-on state. Further, the charging current of the junction capacitance due to dv / dt applied between the collector and the emitter at the time of turn-off also reduces the latch-up current. For this reason, turn-off during overcurrent must be performed gently.

FIG. 3 shows a conventional example in which such an IGBT drive circuit has a function of overcurrent protection.

The middle point of the forward bias power supply 5a and the reverse bias power supply 5b connected in series is connected to the emitter of the IGBT11.
Switches 10a and 10b are connected in series to the switches 5a and 5b.
The connection point of a and 10b is connected to the gate of the IGBT 11 via the resistor 9a.

The collector of the NPN transistor 8 is connected to the resistor 9c via the resistor 9c.
The emitter is connected to the midpoint of the connection between a and the gate of the IGBT 11, the emitter is connected to the midpoint of the negative electrode of the reverse bias power source 5b and the switch 10b, and the base of the transistor 8 is the Zener diode 7
And the resistor 9b to connect the switch 10a and 10b to the middle point and the resistor 9b.
The middle point of the connection between the resistor 9b and the Zener diode 7 is connected to a and is connected to the collector of the IGBT 11 via the diode 6.

In normal operation, the switch 10a
Is turned on and the switch 10b is turned off. Therefore forward bias power supply
The voltage of 5a is applied as a forward bias voltage between the gate and emitter of the IGBT 11 via the switch 10a and the resistor 9a. On the other hand, when reverse biasing, switch 10a is turned off and switch 10b
Turn on. Therefore, the voltage of the reverse bias power source 5b is applied as a reverse bias voltage between the gate and the emitter of the IGBT 11 via the resistor 9a and the switch 10b.

 On the other hand, the operation at the time of overcurrent is as follows.

When the collector-emitter voltage of the IGBT 11 during forward bias exceeds the voltage obtained by subtracting the voltage of the reverse bias power source 5b from the sum of the forward bias voltage drop of the Zener voltage of the Zener diode 7 and the base-emitter diode of the NPN transistor 8. , The voltage of the power supply 5a is applied between the base and the emitter of the NPN transistor 8 via the switch 10a, the resistor 9b and the Zener diode 7. As a result, the base and the emitter are forward-biased, and the transistor 8 becomes conductive. Therefore, the voltage of the reverse bias power supply 5b is applied between the gate and the emitter of the IGBT 11 as a reverse bias voltage via the transistor 8 and the resistor 9c. Therefore, IGBT11
Collector current is shut off.

[Problems to be Solved by the Invention]

However, in the conventional drive circuit as shown in FIG.
Since a reverse bias voltage is applied between the gate and the emitter when overcurrent is cut off, turn-off becomes faster, and there is a risk of device breakdown due to latch-up at turn-off.

An object of the present invention is to provide an overcurrent protection drive circuit for an IGBT, which eliminates the disadvantages of the conventional example and can prevent element destruction due to latch-up at turn-off.

[Means for solving the problem]

In order to achieve the above-mentioned object, in the drive circuit for applying a reverse voltage between the gate and the emitter at the normal turn-off of the IGBT, a series circuit including a resistor, a transistor and a diode is connected between the gate and the emitter of the IGBT. , The base of the transistor is connected to the collector of the IGBT via a Zener diode, and when the collector-emitter voltage of the IGBT exceeds a predetermined voltage during conduction between the collector and emitter, the transistor turns on and the IG
The gist is to short-circuit the gate-emitter of the BT to discharge the charge between the gate and the emitter of the IGBT, and turn off the IGBT without applying a reverse voltage between the gate and the emitter of the IGBT.

[Action]

According to the present invention, by connecting a series circuit including a resistor, a transistor and a diode between the gate and emitter of the IGBT, the transistor is turned on at the time of overcurrent protection of the IGBT to short-circuit the gate and the emitter, and The accumulated charge of the junction capacitance between the gate and the emitter is gently discharged through the resistor.

This discharge is gentler than in the case where a reverse bias is applied between the gate and the emitter, so that the collector current can be shut off gently when it is overcurrent, and latchup at the time of interruption can be prevented.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of an IGBT overcurrent protection drive circuit of the present invention, in which the same components as those in FIG. 3 showing the conventional example are designated by the same reference numerals.

That is, the midpoint of connection between the forward bias power supply 5a and the reverse bias power supply 5b connected in series is connected to the emitter of the IGBT 11,
Switches 10a and 10b are connected in series to the power supplies 5a and 5b, and the connection midpoint of the switches 10a and 10b is connected to the gate of the IGBT 11 via a resistor 9a. Further, the collector of the NPN transistor 8 is connected to the middle point of connection between the resistor 9a and the gate of the IGBT 11 via the resistor 9c, and the emitter is connected to the middle point of connection between the forward bias power source 5a and the reverse bias power source 5b via the diode 6b. Is
The base of the transistor 8 is connected to the connection midpoint of the switches 10a and 10b via the Zener diode 7 and the resistor 9b, and the connection midpoint of the resistor 9b and the Zener diode 7 is connected to the collector of the IGBT 11 via the diode 6a. It

The present invention is a drive circuit as shown in FIG. 1, in which the emitter of the transistor 8 is connected to the reverse bias power source via the diode 6b.
5b is connected to the positive electrode and the IGBT 11 is turned on when the transistor 8 is turned on.
A circuit was formed in which the gate and the emitter were connected via a resistor 9c.

 Next, the operation will be described.

During forward bias, switch 10a is turned on and switch 10b is OF
F Therefore, the voltage of the forward bias power supply 5a is the switch 10a,
A forward bias voltage is applied between the gate and emitter of the IGBT 11 via the resistor 9a.

On the other hand, when reverse biasing, switch 10a is turned off.
Turn on 10b. Therefore, the voltage of the reverse bias power supply 5b is
It is applied as a reverse bias voltage between the gate and emitter of the IGBT 11 via a and the switch 10b.

By the way, when the forward bias is applied, the collector-emitter voltage of the IGBT 11 is equal to the Zener voltage of the Zener diode 7 and NP.
If the voltage obtained by subtracting the voltage of the reverse bias power source 5b from the sum of the forward bias voltage drop of the base-emitter diode of the N transistor 8 exceeds the voltage of the NPN transistor 8,
The voltage of the power supply 5a is applied between the emitter, the switch 10a and the resistor 9
b, applied through the Zener diode 7 and therefore forward biased between the base and emitter,
Conducts.

At this time, the gate and emitter of the IGBT 11 are short-circuited by the resistor 9c, the transistor 8 and the diode 6b. The diode 6b provides the transistor 8 with a reverse breakdown voltage. That is, since the switch 10b is turned on during normal turn-off, the voltage of the power supply 5b is applied in the opposite direction between the collector and the emitter of the transistor 8.
Generally, a transistor has a weak reverse breakdown voltage. So the diode
The transistor 8 is protected by applying the voltage of the power supply 5b between the cathode and the anode of 6b.

In this way, the gate and emitter are short-circuited,
The charge between the gate and emitter of the IGBT11 is discharged more slowly than when a reverse voltage is applied.As a result, the collector current is turned off slowly and overcurrent protection is achieved without latchup at the time of current interruption. It can be carried out.

〔The invention's effect〕

As described above, the IGBT overcurrent protection drive circuit of the present invention can perform overcurrent protection without causing latch-up at the time of current interruption, so that the IGBT can be applied to a wider range of applications. Is.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an IGBT overcurrent protection drive circuit of the present invention, FIG. 2 is an equivalent circuit diagram of an IGBT, and FIG. 3 is a circuit diagram showing a conventional overcurrent protection drive circuit. . 1 ... N-channel FET, 2 ... NPN transistor 3 ... PNP transistor, 4 ... Resistor 5a ... Forward bias power supply, 5b ... Reverse bias power supply 6, 6a, 6b ... Diode, 7 ... Zener diode 8 ...... NPN transistor, 9a, 9b, 9c …… Resistor 10a, 10b …… Switch, 11 …… IGBT

Claims (1)

[Claims] 1. In a drive circuit for applying a reverse voltage between a gate and an emitter at a normal turn-off time of an IGBT, a series circuit including a resistor, a transistor and a diode is connected to the IG.
When the IGBT's collector-emitter voltage exceeds the specified voltage when the transistor's base is connected to the IGBT's collector via a Zener diode while connecting between the BT's gate and emitter. The transistor is turned on, the gate and emitter of the IGBT are short-circuited, and the charge between the gate and emitter of the IGBT is discharged.
Without applying a reverse voltage between the gate and emitter of the IGBT
An IGBT overcurrent protection circuit characterized by turning off the IGBT.