JPH05218836A - Driving circuit for insulated gate element - Google Patents

Abstract

PURPOSE:To provide a driving circuit which contains a function when the load is short-circuited and to increase the time before the gate element is broken. CONSTITUTION:The current corresponding to the overcurrent flowing to an insulated gate element IGBT 1 is detected by a current detecting resistance 31 via the emitter of an auxiliary IGBT 21. Then an auxiliary transistor TR 5 is turned on based on the detected voltage of the resistance 31 and the collector potential of the TR 5 is reduced. Thus the gate potential of the IGBT 1 connected to the collector of the TR 5 is reduced. Then the overcurrent is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated gate element used for switching a main circuit in a power converter such as a motor control inverter device (that is, a power MOSFET such as a power MOSFET which is turned on and off depending on the presence or absence of a gate applied voltage) IG as an insulated gate element of this type.
The present invention relates to a gate drive circuit of a BT (typically referred to as an IGBT hereinafter), and a drive circuit having a high noise margin function of limiting a short-circuit current (element current) when a main circuit is short-circuited.

[0002]

2. Description of the Related Art In the following figures, the same reference numerals indicate the same or corresponding parts. Logic or level High
Low is simply described as “H” and “L”. Figure 5 shows I
A conventional drive circuit of this type having a gate voltage cutoff function of a GBT is shown. In the figure, 1 is an I inserted in the main circuit.
The IGBT, 44 drives the gate of this IGBT 1 to drive the IGBT.
A driving circuit for repeatedly connecting and disconnecting T1 is a current transformer 42 for detecting the main circuit current i0 of the IGBT. Reference numeral 43 denotes a comparison circuit which, when the main circuit current i0 detected through the current transformer 42 exceeds a predetermined value, outputs a current I through a drive circuit 44.
Has a role to turn off GBT1. As described above, in the related art, the main circuit short circuit protection is performed by how quickly the gate voltage for driving the IGBT 1 is turned off when the main circuit short circuit current i0 flows.

[0003]

However, in the main circuit short-circuit protection method as described above, it is necessary to speed up the comparator 43 and the drive circuit 44, but on the other hand, such a circuit is apt to malfunction due to noise. is there. Therefore, an object of the present invention is to provide an IGBT drive circuit having a function of suppressing an excessive current flowing in the IGBT when the load is short-circuited by lowering the gate voltage of the insulated gate element, and thereby increasing the time until the IGBT is destroyed. To provide a peripheral control circuit that is robust against noise and does not have to be very fast.

Therefore, for example, when the load is short-circuited, the gate voltage of the IGBT may be turned off by the peripheral control circuit resistant to this noise.

[0005]

Means for Solving the Problems In order to achieve the above-mentioned object, the means taken by the present invention is "a control terminal (such as a gate G) and first and second main terminals (such as an emitter E and a collector C). ) And applying a drive voltage (based on the gate drive power supply 10 or the like) between the control terminal and the first main terminal, the first and second main terminals Between the main terminals is blocked when the drive voltage is cut off.
In a drive circuit such as T1), at least a current detection unit that detects a current corresponding to a main current flowing between the main terminals and a zener voltage that is provided in a polarity that blocks the drive voltage and is lower than the drive voltage. A series circuit of a Zener diode and an auxiliary transistor having the drive voltage in the forward direction is connected between the control terminal and a first main terminal, and a detection output of the current detection means is used for driving the auxiliary transistor. In addition to the terminals, the auxiliary transistor is configured to be turned on when the main current between the main terminals exceeds a predetermined value ", and" the current detecting means has one end of the main terminal as the first gate of the insulated gate element ". A controllable semiconductor device having a drive terminal connected to the drive terminal of the insulated gate element and a main terminal of the controllable semiconductor device connected in series to the other end of the main terminal. The detection output is a voltage generated in the current detection resistor, and is applied against the voltage between the driving terminals of the auxiliary transistor or the sum of the voltage and the Zener voltage. "

[0006]

[Operation] When the main circuit is short-circuited, an overinsulated gate element for obtaining an overcurrent flowing between the main terminals of the insulated gate element and a current corresponding to the insulated gate element and a current detection connected in series to this auxiliary insulated gate element The current is detected by a current detecting means composed of a resistor, and the auxiliary transistor is turned on by the detection output. At this time, the drive voltage of the insulated gate element is clamped to the zener voltage of the zener diode. Therefore, the main circuit current of the insulated gate element is limited, and the time until the breakdown of the IGBT becomes long, and the speed is not so high.
That is, the main circuit short circuit can be protected even if a gate voltage cutoff circuit resistant to noise is used.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 4 are circuit diagrams showing the structure of the essential parts of different embodiments. In FIG. 1, reference numeral 10 is a DC power supply of, for example, 15V for driving the gate G of the IGBT 1, (hereinafter referred to as gate drive power supply), 8 and 9 are auxiliary transistors for connecting and disconnecting the voltage of the gate drive power supply 10, and eD is the IGBT 1 Is the drive signal voltage for.

Under normal conditions, when the drive signal voltage eD is "H", the auxiliary transistors 8 and 9 are turned off and on, respectively, and the voltage of the gate drive power supply 10 is passed through the auxiliary transistor 9 and the resistor 7 to the gate of the IGBT1. G / Emitter E
The IGBT 1 is turned on by being applied between them, and the main circuit current i0 as a collector current flows between the collector C and the emitter E of the IGBT 1 via the main circuit power supply and the main circuit load (not shown).

On the contrary, when the drive signal voltage eD is "L", the auxiliary transistors 8 and 9 are turned on and off, respectively, and the gate drive power supply 10 is disconnected from the gate circuit of the IGBT1 and at the same time, the gate of the IGBT1 is turned off. The G and the emitter E are short-circuited via the resistor 7 and the auxiliary transistor 8, and the IGBT 1 is turned off. In this way, the drive signal voltage eD causes the IGBT 1 to be repeatedly connected and disconnected so that the current i0 required for the main circuit load flows.

By the way, the voltage dividing resistors 2 and 3 inserted between the collector C and the emitter E of the IGBT1 and the zener diode 6 and the auxiliary transistor 5 inserted between the gate G and the emitter E of the IGBT1 are provided for protection of the main circuit short circuit. It is newly added in the present invention. That is, when the main circuit current i0 is a normal value, the collector of the IGBT1
The voltage ecE between the emitters is small, and the voltage between the resistors 3 obtained by dividing the voltage ecE through the voltage dividing resistors 2 and 3, and thus the voltage eBE between the base B and the emitter E of the auxiliary transistor 5, is also sufficiently small. Remains off. As a result, the Zener diode 6 also remains non-conductive, and the IGB
The voltage between the gate G and the emitter E of T1 (hereinafter abbreviated as gate voltage) eg is not affected by the Zener diode 6 or the like, and the IGBT1 is substantially equal to the voltage of the gate drive power supply 10 (15V in this example) and is sufficiently large. Gate voltage e
driven by g and its collector-emitter voltage ecE
Can be small enough.

However, when the main circuit current i0 becomes excessive due to the short circuit of the main circuit, the collector-emitter voltage ecE of the IGBT1 also becomes large, so that the base-emitter voltage eBE of the auxiliary transistor 5 also becomes large and this transistor 5
Switches to the on state. As a result, the gate voltage eg of the IGBT 1 is limited to the zener voltage of the zener diode 6 (about 7 V in this example). As a result, the excessive current i0 of the main circuit is reduced in proportion to the decrease in the gate voltage eg of the IGBT1, and the time until the breakdown of the IGBT1 can be lengthened. Therefore, the main circuit short circuit protection can be sufficiently performed even if the gate voltage off circuit having the structure as shown in FIG.

2 and 3 further show the circuit of FIG.
In order to prevent erroneous turn-on (however, v corresponds to the collector-emitter voltage ecE in this example) due to so-called dv / dt when the GBT1 is turned off, this IGBT is used.
1 is off (that is, when the auxiliary transistor 8 is on and the auxiliary transistor 9 is off), a reverse bias voltage (3 to 4 V in this example) is applied between the gate G and the emitter E of the IGBT 1,
This is a circuit in which a reverse bias power source 11 is inserted.

However, the diode 4 in FIG. 2 is a reverse bias power source 11 via an auxiliary transistor 5 and a zener diode 6.
This is a diode for preventing wraparound from. Next, FIG.
Is an embodiment in which the overcurrent flowing in the IGBT 1 is detected by a means different from the voltage detecting means shown in FIGS. 1 to 3, and a current corresponding to the current flowing in the IGBT 1 is supplied to the auxiliary I
It is intended to protect the IGBT 1 by using a current detecting means which is obtained by the GBT and takes out a current flowing in the auxiliary IGBT via a current detecting resistor. 21 is an auxiliary IGBT as an auxiliary insulated gate element with a small current capacity,
31 is a current detection resistor. The series circuit of the auxiliary IGBT 21 and the current detection resistor 31 is connected in parallel with the IGBT1 such that the other of the resistor 31 side is connected to the emitter E of the IGBT1 and each gate G of the IGBT1 and the IGBT21.
Are connected to each other and are collectively driven.

Further, in FIG. 4, the Zener diode 6 is inserted on the emitter E side of the auxiliary transistor 5. In this circuit, when the IGBT1 is on, the auxiliary IGBT21 is also in the on state, and when the main circuit current i01 flows, a current corresponding to the current i0 of the IGBT1 flows to the current detection resistor 31 via the auxiliary IGBT, and both ends of this resistor 31 are connected. A voltage corresponding to the main circuit current i01 will appear.

When the main circuit current i01 increases and the voltage across the current detection resistor 31 becomes higher than the sum of the zener voltage of the zener diode 6 and the base B-emitter E voltage eBE of the auxiliary transistor 5. , The auxiliary transistor 5 is turned on, and the gate voltage eg of the IGBT 1 drops almost to the Zener voltage of the Zener diode 6. By this action, the current i0 flowing between the main terminals of the IGBT1 can be suppressed, and the power breakdown of the IGBT1 can be prevented.

The circuit of FIG. 4 has an advantage that the Joule heat generated by the current detecting resistor 31 can be made smaller than that of the voltage dividing resistor 2 of FIGS. In each of the above embodiments, the auxiliary transistor 5 may be a FET, the IGBTs 1 and 21 are MOSFETs, and Bi
It may be a MOS. In addition, in FIG.
The auxiliary IGBT 21 and the auxiliary IGBT 21 may be formed on one chip or may be separate chips.

[0017]

According to the present invention, a series circuit of a Zener diode and an auxiliary transistor is provided in parallel with the gate / emitter of the insulated gate element, and an overcurrent flowing between the main terminals of the insulated gate element when the main circuit is short-circuited, Detected by the current detection means consisting of an auxiliary insulated gate element for obtaining a current corresponding to the insulated gate element and a current detection resistor connected in series to this auxiliary insulated gate element, the auxiliary transistor is turned on by this detection output. At this time, the driving voltage of the IGBT is clamped to the Zener voltage of the Zener diode. Therefore, when an overcurrent flows through the insulated gate element, the insulated gate element itself limits the overcurrent and isolates it. The time until the gate element is destroyed can be lengthened. Therefore, it is not necessary to increase the response speed of the peripheral control circuit, that is, it is possible to use a gate voltage cutoff circuit that is resistant to noise.

[Brief description of drawings]

FIG. 1 is a drive circuit diagram showing a main part configuration of an embodiment of a first embodiment.

FIG. 2 is a drive circuit diagram showing a main part configuration of an embodiment of a second embodiment.

FIG. 3 is a drive circuit diagram showing the main configuration of an embodiment of the third embodiment.

FIG. 4 is a drive circuit diagram showing the main configuration of an embodiment of the fourth embodiment.

FIG. 5: Conventional drive circuit diagram

[Explanation of symbols]

1,21: Insulated gate element (1: IGBT, 21: auxiliary IG
BT) 2, 3: Voltage dividing resistor 4: Leakage prevention diode 5, 8, 9: Auxiliary transistor 6: Zener diode 7: Resistor 10: Gate drive power supply 11: Reverse bias power supply 31: Current detection resistance

Claims (2)

[Claims] 1. A control terminal and first and second main terminals. When a drive voltage is applied between the control terminal and the first main terminal, the first and second main terminals are provided. In the drive circuit of the insulated gate element in which the connection between the main terminals is blocked when the drive voltage is cut off, the current detection means for detecting a current corresponding to at least the main current flowing between the main terminals, A zener diode having a zener voltage lower than the drive voltage and having a polarity for blocking the drive voltage between the control terminal and the first main terminal; and an auxiliary transistor having the drive voltage in the forward direction. Is connected between the control terminal and the first main terminal, the detection output of the current detection means is applied to the drive terminal of the auxiliary transistor, and the main current between the main terminals has a predetermined value. When exceeded A drive circuit for an insulated gate element, characterized in that the auxiliary transistor is configured to be turned on. 2. The drive circuit for an insulated gate element according to claim 1, wherein in the current detection means, one end of a main terminal is the first main terminal of the insulated gate element, and the drive terminal is the insulated terminal. The controllable semiconductor device is connected to each of the driving terminals of the gate element, and the current detection resistor is connected in series with the other end of the main terminal of the controllable semiconductor device. A drive circuit for an insulated gate element, which is applied against a voltage generated between the driving terminals of the auxiliary transistor or a sum voltage of the voltage and the zener voltage.