JPH098620A - Overcurrent protective circuit for insulated gate type bipolar transistor - Google Patents

Abstract

PURPOSE: To surely protect an IGBT from an overcurrent by using a thin film coil for an overcurrent protective circuit and utilizing a voltage, which is generated at the thin film coil by a high di/dt when the overcurrent is generated, as the gate voltage of the IGBT. CONSTITUTION: One terminal of a thin film coil 2 and a gate terminal 33 of an MOSFET 3 are connected to an emitter terminal 12 of an IGBT 1, and a source terminal 32 of the MOSFET 3 is connected with the other terminal of the thin film coil 2. Then, a drain terminal 31 of the MOSFET 3 is connected with a cathode terminal 42 of a usual diode 4, an anode terminal 41 of this diode 4 is connected with an anode terminal 51 of a Zener diode 5, and a cathode terminal 52 of the Zener diode 5 is connected with a gate terminal 13 of the IGBT 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated gate bipolar transistor (IGBT) which has an overcurrent limit for limiting the overcurrent when the overcurrent occurs in the insulated gate bipolar transistor (IGBT) to prevent the latch-up breakdown of the IGBT. Regarding a current protection circuit.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional IGBT overcurrent protection circuit. The IGBT 1 of the main circuit has a current detection terminal 16, one terminal of the resistor 6 is connected to the current detection terminal 16, and the other terminal of the resistor 6 is connected to the emitter terminal 12 of the IGBT 1. One terminal of the resistor 6 is a MOS
It is connected to the gate terminal 33 of the FET 3, and is connected to the other terminal of the resistor 6 and the source terminal 32 of the MOSFET 3. MO
The drain terminal 31 of the SFET 3 is connected to the cathode terminal 42 of the normal diode 4, and the anode terminal 41 of this diode 4 is connected to the gate terminal 13 of the IGBT 1.
The area within the dotted line is the overcurrent protection circuit 7. This operation will be described below. When an abnormality occurs in the main circuit and an overcurrent flows, the current flowing through the current detection terminal 16 and the voltage generated by the resistor 6 connected in series with the current detection terminal 16 cause the IGBT 1
The gate of the MOSFET 3 arranged between the gate and the emitter of the. Applied between the sources, MOSFET3 turns on, I
The gate-emitter voltage of the IGBT 1 drops to a voltage that is the sum of the on-voltage of the diode 4 and the on-voltage of the MOSFET 3, and the collector current of the IGBT 1 is a current value determined by the gate-emitter voltage and the output characteristics of the IGBT 1. And protects the IGBT1 from latch-up breakdown.

[0003]

In a conventional IGBT overcurrent protection circuit, a main IGBT for supplying a collector current to an IGBT chip and a sense IGBT for current detection are formed. The sense IGBT for detecting this current (this sense IG
The output characteristics and VGE (th) characteristics of the BT's emitter are connected to the current detection terminal 16) and the main IGBT (IGBT through which the collector current flows) are different in each chip. Due to the difference in the ratio of the currents flowing through the IGBTs, the limiting current during overcurrent protection varies. Further, due to the variation in the resistance value of the resistors that form the protection circuit (hereinafter referred to as the variation in resistance), the voltage across the resistor caused by the current flowing through the sense IGBT also varies, and the voltage across the resistor is between the gate and emitter of the IGBT. Since the MOSFET is turned on to limit the current, the limit current varies during overcurrent protection.

As described above, the sense IGBT and the main IGBT
Due to the characteristic variation between T and the variation in resistance, a large variation occurs in the limiting current at the time of overcurrent protection, so that the accuracy of the overcurrent protection circuit is low. Further, in order to improve the accuracy, it is necessary to individually adjust the IGBT and the resistance, which increases the cost. In order to solve the above problems, the present invention provides a high-precision insulated gate bipolar transistor overcurrent protection circuit that directly detects a main current with a thin-film coil and does not cause the above-described variations. And

[0005]

To achieve the above object, the cathode terminal of the Zener diode is connected to the gate terminal of the insulated gate bipolar transistor of the main circuit, and the anode terminal of the Zener diode is connected to the anode terminal of the diode. The diode cathode terminal is M
Connected to the drain terminal of the OSFET, connected to the gate terminal of the MOSFET and the emitter terminal of the insulated gate bipolar transistor of the main circuit, and this emitter terminal and the MOS
A thin film coil is connected between the source terminals of the FET.

Further, it is preferable that one end is connected to the emitter electrode of the insulated gate bipolar transistor of the main circuit and a thin film coil is formed on the emitter electrode via an insulating film.
The inductance of this thin film coil is 10 pH to 10
The pH is preferably 00 pH, more preferably 10 to 100 pH.

[0007]

The main current (collector current) flowing through the IGBT is
As the current value increases, the change (di / dt) in the main current also increases. Therefore, by connecting the thin film coil to the emitter terminal of the IGBT of the main circuit, the change of the main current (di / d
t) is a voltage (L × di
If the main current becomes too large, this voltage will also become large by controlling the gate of the MOSFET of the overcurrent protection circuit by this voltage.
The main current of BT is suppressed. Further, the detection variation of the main current between the respective elements as in the conventional case does not occur in this protection circuit.

By forming the thin-film coil on the same semiconductor substrate as the IGBT and wiring the thin-film coil and the collector terminal of the IGBT on the semiconductor substrate, variations in wiring inductance can be made extremely small, resulting in high precision. It becomes an overcurrent protection circuit.

[0009]

FIG. 1 shows an IGBT overcurrent protection circuit according to an embodiment. The IGBT 1 of the main circuit has a collector terminal 11, an emitter terminal 12, and a gate terminal 13. One terminal of the thin film coil 2 is connected to the emitter terminal 12, and one terminal of this thin film coil 2 is the gate terminal 3 of the MOSFET 3.
3 and the source terminal 32 of the MOSFET 3 is connected to the other terminal of the thin film coil 2. The drain terminal 31 of the MOSFET 3 is the cathode terminal 4 of the normal diode 4.
2, the anode terminal 41 of the diode 4 is connected to the anode terminal 51 of the Zener diode 5, and the cathode terminal 52 of the Zener diode 5 is connected to the gate terminal 13 of the IGBT 1. The area within the dotted line is the overcurrent protection circuit 7.

2A and 2B are views showing the thin film coil formed on the IGBT. FIG. 2A is a plan view and FIG. 2B is a sectional view taken along the line X--X in FIG. 2A. In FIG.
The gate pad 15, the emitter electrode 14, and the thin-film coil 2 of the IGBT 1 are shown. The thin-film coil 2 is formed on the emitter electrode 14 of the IGBT 1 via an insulating film, one end of the thin-film coil 2 is connected to the emitter electrode 14 at the connecting portion 21, and the other end is a main terminal through which a collector current flows (not shown). ) To. From both sides of the thin film coil 2, coil auxiliary terminals (not shown) are projected. The coil auxiliary terminal is connected to the gate terminal and the source terminal of the MOSFET of the external protection circuit. In FIG. 1B, the IGBT 1 is formed on the semiconductor substrate, the insulating film 22 is selectively formed on the emitter electrode 14, the thin film coil 2 is formed on the insulating film 22, and one end of the thin film coil 2 is an emitter. The electrode 14 and the connection portion 21 are connected. The other end is connected to a main terminal (not shown) through which the collector current flows.

FIG. 3 is an operation waveform diagram when the IGBT is applied to the voltage resonance circuit. FIG. 3A is a collector current waveform diagram of the IGBT, and FIG. 3B is a coil voltage waveform diagram of the thin film coil. (C) shows a gate voltage waveform diagram of the IGBT.
In FIG. 6A, when the collector current increases, the change in the collector current (current increase rate: di / dt) increases. In the same figure (b), the coil voltage generated in the thin film coil is small when the current value is small, and becomes large when the current value becomes large, that is, when an overcurrent occurs. When this voltage exceeds the gate threshold voltage (VGS (th)) of the MOSFET, the MOSFET turns on. In the same figure (c), the gate voltage of the IGBT is MOSFET
Keeps a high gate voltage supplied from the gate drive power supply until the MOSFET turns on, and when the MOSFET turns on, the voltage drops to the sum of the Zener voltage of the Zener diode, the normal diode ON voltage and the MOSFET ON voltage.

This lowered voltage becomes the gate voltage and IG
The collector current of BT is reduced to the collector current determined by the output characteristics. In this way, the overcurrent is limited, and the IGBT is protected from the latchup breakdown due to the overcurrent by setting the overcurrent limitation level to the latchup level of the IGBT or less. The above di / dt is several tens to several thousands A /
On the other hand, since the gate drive voltage of the MOSFET is several V to several tens of V, the inductance required for the thin film coil 4 is 10 to 1000 pH. However, in most cases, di / dt is 100 A / μs or more, and it is difficult to increase the inductance of the thin-film coil in terms of manufacturing.
It is 100 pH.

[0013]

According to the present invention, the thin-film coil is used in the overcurrent protection circuit, and the voltage generated in the thin-film coil due to the high di / dt when the overcurrent is generated is used as the gate voltage. Gate voltage is MOSFET
To turn on the MOSFET without fail,
It is possible to reliably reduce the gate voltage of the IGBT to a predetermined value, limit the overcurrent to a predetermined value, and reliably protect the IGBT from the overcurrent.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an IGBT overcurrent protection circuit according to an embodiment of the present invention.

FIG. 2 is a view showing a thin film coil formed on a semiconductor substrate (a).
Is a plan view, (b) is a cross-sectional view taken along line X-X of (a)

FIG. 3 is an operation waveform diagram when an IGBT is applied to a voltage resonance circuit, (a) is a collector current waveform diagram of the IGBT,
(B) is a voltage waveform diagram of the thin film coil, (c) is a gate voltage waveform diagram of the IGBT

FIG. 4 is a circuit diagram of a conventional IGBT overcurrent protection circuit.

[Explanation of symbols]

 1 IGBT 11 Collector Terminal 12 Emitter Terminal 13 Gate Terminal 14 Emitter Electrode 15 Gate Pad 16 Current Detection Terminal 2 Thin Film Coil 21 Connection Part 22 Insulating Film 3 MOSFET 31 Source Terminal 32 Drain Terminal 33 Gate Terminal 4 Normal Diode 41 Anode Terminal 42 Cathode Terminal 5 Zener diode 51 Anode terminal 52 Cathode terminal 6 Resistance 7 Overcurrent protection circuit

Claims (3)

[Claims] 1. A cathode terminal of a Zener diode is connected to a gate terminal of an insulated gate bipolar transistor of a main circuit, an anode terminal of a Zener diode is connected to an anode terminal of a diode, and a cathode terminal of the diode is a drain terminal of a MOSFET. Connect, MOSFE
An insulated gate bipolar transistor having a thin film coil connected to a gate terminal of T and an emitter terminal of an insulated gate bipolar transistor of a main circuit, and having both ends connected to the emitter terminal and a source terminal of a MOSFET. Overcurrent protection circuit. 2. The insulated gate according to claim 1, wherein the thin film coil has one end connected to the emitter electrode of the insulated gate bipolar transistor of the main circuit, and is formed on the emitter electrode through the insulating film. Type bipolar transistor overcurrent protection circuit. 3. The overcurrent protection circuit for an insulated gate bipolar transistor according to claim 1, wherein the thin film coil has an inductance of 10 pH to 1000 pH.