JPH0767073B2 - Insulated gate element drive circuit - Google Patents

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 device of this type.
The present invention relates to a gate drive circuit of a BT (typically referred to as an IGBT hereinafter), which has a function of limiting a short-circuit current (element current) when a main circuit is short-circuited with a high noise margin.

[0002]

2. Description of the Related Art In the following figures, the same reference numerals indicate the same or corresponding parts. Also 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 the 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 drive circuit for repeatedly connecting and disconnecting T1 and a current transformer 42 for detecting the main circuit current i0 of this 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 through the drive circuit 44 to I
It 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, the comparator 43 and the drive circuit 44 must be speeded up, 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 drive an IGBT having a function of suppressing an excessive current flowing in the IGBT at the time of load short-circuiting by lowering the gate voltage of the insulated gate element, thereby lengthening the time until the IGBT is destroyed. To provide a peripheral control circuit that is robust against noise and need not be so 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] The means taken by the present invention for achieving the above object comprises a control terminal and first and second main terminals, and the control terminal and the first main terminal are provided. In a drive circuit for an insulated gate element, when a drive voltage is applied to the terminals, the first and second main terminals become conductive, and when the drive voltage is cut off, the main terminals are blocked.
One end of the main terminal is the second main terminal of the insulated gate element,
The driving terminal comprises an auxiliary insulated gate element connected to the driving terminal of the insulated gate element, and a current detection resistor connected in series with the other end of the main terminal of the auxiliary insulated gate element. The output terminal of the resistor is connected to the drive terminal of the auxiliary transistor, and is provided between the control terminal and the first main terminal in a polarity that blocks the drive voltage,
A series circuit of a constant voltage diode having a breakdown voltage lower than the drive voltage and the auxiliary transistor having the drive voltage in the forward direction is connected between the control terminal and a first main terminal, When the main current between the terminals exceeds a predetermined value, the auxiliary transistor is turned on, and the potential of the control terminal of the insulated gate element is set to the sum of the ON voltage of the auxiliary transistor and the breakdown voltage of the constant voltage diode. To configure.

[0006]

[Function] An auxiliary insulated gate element for obtaining an electric current corresponding to the insulated gate element for an overcurrent flowing between the main terminals of the insulated gate element when the main circuit is short-circuited, and a current detection connected in series to the auxiliary insulated gate element The current is detected by a current detecting means composed of a resistor, and the detection output turns on the auxiliary transistor. 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, which is not so fast.
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, 15 V 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 passes 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 gated. 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. This 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 via 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 large enough to be substantially equal to the voltage of the gate drive power supply 10 (15V in this example). 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, and therefore 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 illustrate 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 supply 11 is inserted.

However, the diode 4 in FIG. 2 is a reverse bias power supply 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 an overcurrent flowing in the IGBT 1 is detected by 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 detection means which is obtained by the GBT and takes out the current flowing in the auxiliary IGBT via the current detection 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 coupled to each other and are driven together.

In FIG. 4, the Zener diode 6 is inserted on the emitter E side of the auxiliary transistor 5. In this circuit, the auxiliary IGBT21 is also in the ON state when the IGBT1 is on, and when the main circuit current i01 flows, the 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 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 an FET, the IGBTs 1 and 21 are MOSFETs, and Bi
It may be a MOS. Moreover, 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, an auxiliary insulated gate element for obtaining an overcurrent flowing between main terminals of an insulated gate element when a main circuit is short-circuited and a current corresponding to the current flowing through the insulated gate element, and this auxiliary insulated gate element. It is detected by the current detection resistor connected in series with the gate element, the auxiliary transistor is turned on by this detection output, and the drive voltage of the insulated gate element is set to the sum of the ON voltage of the auxiliary transistor and the breakdown voltage of the constant voltage diode. Since it is clamped, when an overcurrent flows through the insulated gate element, the current limiting function of the insulated gate element works to suppress the overcurrent and increase the time until the insulated gate element is destroyed, It is possible to prevent destruction due to overcurrent. Therefore, it is not necessary to increase the response speed of the peripheral control circuit, that is, it is possible to use the gate voltage cutoff circuit that is resistant to noise.

[Brief description of drawings]

FIG. 1 is a drive circuit diagram showing a configuration of essential parts 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 a main configuration of an embodiment of a 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 (3)

[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 terminals become conductive and the main terminals are blocked when the drive voltage is cut off , one end of the main terminal is
The drive terminal is connected to the second main terminal of the insulated gate element.
Auxiliary device connected to the driving terminals of the insulated gate device
The auxiliary insulated gate element and the main terminal of the auxiliary insulated gate element
It consists of a current detection resistor connected in series with the other end.
The output terminal of the current detection resistor is the driving terminal of the auxiliary transistor.
And a constant voltage diode having a breakdown voltage lower than the drive voltage, the constant voltage diode being connected between the control terminal and the first main terminal and having a polarity for blocking the drive voltage, and the drive voltage in the forward direction. the series circuit of the auxiliary transistor is connected between the control terminal and the first main terminal, and the auxiliary transistor is turned on when the main current exceeds a predetermined value between the main terminals, the insulating to A drive circuit for an insulated gate element, characterized in that the potential of the control terminal of the gate element is the sum of the on-voltage of the auxiliary transistor and the breakdown voltage of the constant voltage diode. 2. An insulated gate device according to claim 1.
In the child, the constant voltage diode and the auxiliary transistor
In the series circuit with the
Characterized in that it is connected to the driving terminal side of the gate element
Insulated gate element drive circuit. 3. An insulated gate device according to claim 1.
In the child, the constant voltage diode and the auxiliary transistor
In the series circuit with the
Characterized in that it is connected to the driving terminal side of the gate element
Insulated gate element drive circuit.