JPS6395727A - Gate driving circuit for igbt - Google Patents

Abstract

PURPOSE:To increase the dv/dt rating by short-circuiting a latchup preventing resistor when a gete-emitter, voltage is below a prescribed value when an IGBT (Insulated Gate Bipolar Mode Transistor) is turned off. CONSTITUTION:A transistor (TR) 9a is turned on when the condition of E-Ez>=EGE exists, where E is the power supply voltage, Ez is a Zener voltage of a Zener diode 8 and EGE is a voltage of the IGBT 1 between a gate and emitter. Then a TR 9b is turned on and the latchup preventing resistor 2 is short-circuitted. Thus, even if a voltage with a large dv/dt is applied to the collector-emitter of the IGBT1, the gate-emitter voltage rise is suppressed and malfunction such as mis-turning-on or the like is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an I
GBT (In5lated Gate Bipol)
The present invention relates to a gate drive circuit for a (translator) device, and particularly to a gate drive circuit that can prevent malfunctions during off-operation.

[Conventional technology]

IGBT elements have the advantages of bipolar transistors, such as high voltage and easy to increase capacity, and power MO8F.
Recently, it has been attracting attention as a new device that combines the advantages of ET, such as high-speed switching and easy drive, such as IGT, C0MFET,
Each company has commercialized the product under a trade name such as GEMFET or B I FET.

Figure 4 shows such circuits. That is, jGBT is PN
P) transistor 11 and NPN) transistor 12
M connected in parallel to transistor 12
A short-circuit resistor 1 that shorts between the base and emitter of the OSFET (N-channel) 13 and the NPN transistor 12
It is characterized by having a built-in thyristor circuit made up of transistors 11 and 12. Note that the circuit symbol of the IGBT is shown in FIG. 4A.

By the way, in such an IGBTX device, the thyristor circuit as described above turns on, and as a result, the IGBT cannot be turned off, which is a so-called latch-up phenomenon.
It has been pointed out that this occurs more easily at turn-off than at turn-on. Since this latch-up phenomenon is directly linked to destruction of the IGBT element, it is necessary to prevent this phenomenon from occurring.

On the other hand, as one method for suppressing such a latch-up phenomenon at turn-off of an IGBT, a method is conventionally known that delays turn-off of a MOSFET section in an IGBT. This is achieved by turning off the MOSFET section and the PNP transistor almost simultaneously.
This suppresses the rapid increase in current in the transistor, making it difficult for latch-up phenomena to occur.

FIGS. 5 through 7 all show conventional examples of base drive circuits based on this principle.

In FIG. 5, 1 is an IGBT, 2 is a latch-up prevention resistor, 3 is an on switch, 4 is an off switch, and 5 is a DC power source for driving the IGBT.

This turns on the IGBT 1 by closing the switch 3 and opening the switch 4, and turns it off by opening the switch 3 and closing the switch 4. At the time of turn-off, the gate charge is discharged by the resistor 2. This delay suppresses the latch-up phenomenon.

In FIG. 6, a parallel circuit of a latch-up prevention resistor 2 and a diode 6 is connected in series to the gate of the IGBT 1, and turn-on is performed via the diode 6.
Other details are the same as in FIG.

In FIG. 7, the DC power supply has two positive and negative systems of 5 m and 5 b, and voltages of opposite polarity are applied at turn-on and turn-off.

[Problems that the invention is supposed to solve]

However, the fifth, 6r! In the circuit shown in A, I
There is a large dv/dt between the collector and emitter of GBT (
When a voltage with a voltage increase rate (voltage increase rate) is applied, the gate-emitter voltage increases due to the newly inserted latch-up prevention resistor, which may cause the IGBT to turn on. Therefore, the dma/dt tolerance is limited to a small value, and there is a constraint that the operation must be performed so that the dma/dt tolerance does not become large.

On the other hand, the circuit shown in FIG. 7 requires two power supplies, resulting in an increase in size and cost.

Therefore, this invention uses one power source and dv/d
It is an object of the present invention to provide a gate drive circuit that can have a large t tolerance.

[Means for solving problems]

A control circuit is provided that monitors the voltage between the gate and emitter of the IGBT and short-circuits the latch-up resistor when this voltage falls below a predetermined value during turn-off.

[Effect]

The above control circuit prevents the voltage between the gate and emitter from rising even if a large voltage of dv/dt is applied between the collector and emitter at turn-off, and prevents the voltage between the gate and emitter from increasing.
Increase dt tolerance.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention. This is a circuit diagram shown in FIG.
NP transistor 9 and NPN transistor 9
It is constructed by adding b.

Now, the power supply voltage is E1, the Zener voltage of the Zener diode is Ez, and the gate-emitter voltage of IGBTI is Eo.
lt, the transistor 9a turns on when the condition E-EZ≧EGI is satisfied. As a result, the ninth transistor 9b is also turned on, and the latch-up prevention resistor 2 is short-circuited. Therefore, even if a large voltage dv/dt is applied between the collector and emitter of the IGBTI, the voltage rise between the gate and emitter is suppressed, and malfunctions such as erroneous turn-on are prevented.

FIG. 2 is a circuit diagram showing another embodiment of the invention. This corresponds to FIG. 6, and its operating principle is exactly the same as that in FIG. 1, so details will be omitted.

FIG. 3 is a circuit diagram showing still another embodiment of the present invention. This is a PNP transistor 9a in Fig. 2. A P-channel MO8FET 10m is placed in place of the transistor 9a, and a pKN-channel MO8FET 10m is placed in place of the transistor 9b.
The operating principle is exactly the same as that in FIG. 1, so the details will be omitted.

〔Effect of the invention〕

According to this invention, when the gate-emitter voltage of the IGBT falls below a predetermined value when the IGBT is turned off, the latch-up prevention resistor is short-circuited.
There is less risk of malfunction even if a large voltage of dv/dt is applied between the emitters.
The advantage is that the amount of IT can be made larger than that of the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of this invention, FIG. 2 is a circuit diagram showing another embodiment of this invention, FIG. 3 is a circuit diagram showing still another embodiment of this invention, and FIG. 4 is a circuit diagram showing another embodiment of this invention. is an equivalent circuit diagram showing an IGBT, FIG. 4A is a circuit symbol diagram showing an IGBT,
5 to 7 are circuit diagrams showing conventional examples of base drive circuits for IGBTs. Code explanation 1... IGBT, 2... Resistor for latch-up prevention, 3゜4... Switch, s, sa, sb... DC power supply, 6... Diode, 7... Resistor, 9m , 11
...PNP) transistor, 9b, 12...NPN
)? 10m...P channel MO8IT,
10b, 13...N channel MO8FET,
14...Short circuit resistance. Agent Patent Attorney Akio Namiki Agent Patent Attorney Kiyoshi Matsuzaki Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In an IGBT gate drive circuit that turns on or turns off an IGBT and prevents latch-up by performing turn-off via at least a resistor, the gate drive circuit monitors the gate-emitter voltage of the IGBT and detects the voltage at the time of turn-off. A gate drive circuit for an IGBT, comprising a control circuit that short-circuits the resistor when the voltage falls below a predetermined value.