JPS6395730A - Drive circuit for igbt having overcurrent protective function - Google Patents

Abstract

PURPOSE:To contrive the exparsion of the application range of an IGBT (Insu lated Gate Bipolar Mode Transistor) by providing a resistor variable means bringing the resistance of a latch up prevention resistor at normal state different from that at overcurrent state so as to apply overcurrent protection without losing high speed switching capability. CONSTITUTION:When the conduction of overcurrent is detected by a detector 5, its output is given to the gate of a transistor (TR) 4c and given to a control circuit (not shown). As a result, an off command is given to a terminal T and the TR 4c is turned on, then a TR 4b cannot be turned on and a resistor 2a is inserted to the off gate circuit of the IGBT 1 including the power supply 3. Thus, high speed turn-off is applied by a comparatively small resistance decided by the parallel resistance of the resistors 2a, 2b a normal turn-off and the turn-off at overcurrent is executed slowly by a compartively large resistance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an r
GBT (Insulated Gate Bipol)
The present invention relates to a drive circuit for an ar mode '['transistor] element, and particularly to a drive circuit equipped with an overcurrent protection function.

[Conventional technology]

The equivalent circuit of IGET is shown in Figure 2, which consists of a power MO3FET II and two bipolar transistors 1.
It is a monolithic switching device composed of 2.13 and has the following features.

(1) Like the power MO3FET, the on/off state can be controlled by a voltage signal.

(2) Due to the operation of the built-in bipolar transistor,
A larger current can flow than a power MOSFET.

(3) High-speed switching is possible through manufacturing innovations.

These features of IGBTs are extremely favorable for device applications. In addition, IGBT is IGT.

They have been commercialized under trade names such as C0MFET and BIFET. Moreover, when IGBT is represented as a symbol, it becomes as shown in FIG. 2A.

However, such IGBTs also have major drawbacks. This will be explained below.

As shown in FIG. 2, two bipolar transistors 12 and 13 inside the I GET constitute a thyristor circuit. This thyristor circuit is unnecessary for the original switching operation of the IGBT, and therefore, as shown in the figure, a low resistance 14 is connected between the base and emitter of the NPN transistor 13 to prevent the thyristor circuit from operating. We are working on this. In order to prevent the Cyrisk circuit from operating under any operating condition, the above N
PN ) Base-emitter resistance 14 of transistor 13
It is possible to set the value to OΩ, but this is extremely difficult due to the structure of the IGBT. As a result, the IGBT has the following drawbacks.

(1) When the collector current in the on state exceeds a certain value, the thyristor circuit operates and cannot be turned off.

(2) When the collector current exceeds a certain value, the thyristor circuit operates during the turn-off process and cannot be turned off.

In this way, the collector current that causes a thyristor circuit to operate is usually called a latch-up current, and the thyristor circuit that operates is called a rough-up current, but such latch-up is more likely to occur during the turn-off process than in the on state. It has been pointed out that the faster the power MOS FET inside the IGBT is turned off, the easier it is to latch amplifier. Since the occurrence of latch-up in IGBTs leads to element destruction, it is essential to devise ways to avoid this in application.

By the way, among the above-mentioned drawbacks, latch-up in the on state can be solved by a significant improvement in latch-up current due to advances in technology for lowering the resistance between the base and emitter of the NPN transistor.
It has become possible to coordinate the output characteristics of IGBTs, and it has become possible to manufacture elements that do not substantially latch up in the on state. That is, the output characteristics of the IGBT are of the saturated output type as shown in FIG. 3, and the element itself limits the current. In an overcurrent state, in the worst case, a DC power supply voltage is applied across the device, but if the collector current at this time is less than the latch-up current,
At least during the on period, the problem disappears. In this way, rough lumps during the on period are avoided, but the IG
In order to prevent BT from being destroyed by overcurrent, it is necessary to cut off the collector current before thermal damage occurs.

On the other hand, the ruff stub at turn-off has not been completely solved at present, and it is said that the IGBT must not be turned off at a speed higher than a predetermined speed even during switching operation at a normal collector current level. Therefore, I
Conventionally, as an off-gate circuit for slowly turning off a GBT, a method of applying an off-gate voltage 3 through a resistor 2, as shown in FIG. 4, has been exclusively used. In other words, since there is an input capacitance between the gate and collector of IGBTl, inserting resistor 2 reduces the gate and collector.
The voltage between the collectors begins to decrease slowly, and the IGB
The turn-off speed of T also becomes slower.

[Problem that the invention seeks to solve]

By the way, when performing overcurrent protection, it is necessary to turn off the IGBT later than in a normal case. However, in the circuit shown in FIG. 4, since the resistance value of the resistor 2 is selected depending on the overcurrent, a problem arises in that the turn-off operation during normal operation is delayed.

Therefore, it is an object of the present invention to provide overcurrent protection without impairing the high-speed switching ability of the IGBT, and to expand the range of applications of the IGBT.

[Means for solving problems]

A resistance variable means is provided to make the resistance value of the latch-up prevention resistor different between normal times and overcurrent.

[Effect]

By changing the way the off-gate voltage is applied during normal and overcurrent conditions, high-speed turn-off is possible during normal conditions.
In the event of overcurrent, the IGBT is turned off relatively slowly to prevent latch-up, thereby expanding the range of IGBT applications.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which only an off-gate circuit is shown and an on-gate circuit is omitted. In the figure, 1 is IGBT% 2a.

2b is a resistor, 3 is an off-gate power supply (or voltage), 4a
, 4b and 4c are transistors, and 5 is an overcurrent detector.

That is, between the gate and emitter of IGBTI, a resistor 2a is connected via a transistor 4a, and a resistor 2a is connected between the gate and emitter of the IGBTI.
Resistors 2b are connected through terminals b, and transistors 4a and 4b are driven by an off command given from terminal T. Further, a transistor 4c is inserted between the base and emitter of the transistor 4b, and the base of the transistor 4c is connected to the overcurrent detector 5.

Therefore, under normal conditions when no overcurrent flows, the transistors 4a and 4 are
Both resistors 2a and 2b are turned on, and the resistors 2a and 2b are inserted in parallel into the off-gate circuit of the IGBT1 including the power supply 3. On the other hand, when the detector 5 detects that an overcurrent has flowed, its output is given to the gate of the transistor 4c as well as to a control circuit (not shown). An off command is given. As a result, transistor 4C is turned on, transistor 4b cannot be turned on, and therefore power supply 3
Only the resistor 2a is inserted into the off-gate circuit of the IGBT1 including the IGBT1. As a result, during normal turn-off, fast turn-off is performed with a relatively small resistance determined by the parallel resistance value of resistors 2a and 2b, while turn-off in the event of overcurrent is performed slowly with a relatively large resistance of only resistor 2a. and the intended purpose will be achieved.

In the above description, only the resistor 2a is used during overcurrent, but it is also possible to use only the resistor 2b. In addition, two gate resistors are connected in series, and when the overcurrent detection level is lower than the overcurrent detection level, one gate resistor is shorted to supply the off-gate voltage, and when the overcurrent detection level is exceeded, the two gate resistors are connected in series to supply the off-gate voltage. Alternatively, a method of supplying a high off-gate voltage below the overcurrent detection level and a low off-gate voltage above the overcurrent detection level without changing the gate resistance may also be considered.

〔Effect of the invention〕

According to this invention, during normal switching operation, the IG
Being able to turn off the BT as quickly as possible and also ensuring overcurrent protection provides the advantage of making the IGBT applicable to a wider range of applications.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of this invention, Fig. 2 is an IG
Fig. 2A is an equivalent circuit diagram showing a BT, Fig. 2A is a circuit symbol diagram symbolizing an rGBT, Fig. 3 is a characteristic diagram showing the output characteristics of an IGBT, and Fig. 4 is a circuit diagram showing a conventional example of an IGBT drive circuit. . [Explanation of symbols] 1 ・IGBT, 2.2a, 2b, 14-resistance,
3... Off-gate power supply, 4a, 4b, 4c, 13...
・NPN) transistor, 5... overcurrent detector, 6.
...Switch, 11...N-channel MO5FET,
12...PNP) transistor. Agent Patent Attorney Kiyoshi Matsuzaki 12 Hama 2@, y2A Kuni No. 3 Figure c Hiroshi 4 Figure

Claims (1)

[Claims] In a drive circuit that applies an off-gate voltage to an IGBT via a predetermined resistor to turn it off when an off command based on normal operation or an off command based on overcurrent detection is issued, the resistor An IGBT having an overcurrent protection function, which is equipped with a variable resistance means that changes the resistance value of the device to different values in normal times and in the event of overcurrent, and in the event of overcurrent, the resistance value is increased to turn off the IGBT.
T drive circuit.