JPH10304650A - Gate drive circuit of voltage-driven switching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To turn off a voltage-driven switching device stably by reducing a delay of the gate voltage, caused by a gate input capacity of the switching device. SOLUTION: If negative command voltage vg is applied between the gate and the emitter through a gate resistor 6 when the voltage-driven switching element 7 is in a continuity, the voltage-driven switching device 7 starts an on/off operation and the gate voltage vge is kept at the mirror voltage of a positive polarity, until the collector current becomes zero and it is biased negative when the collector current becomes zero. When the gate voltage vge becomes the mirror voltage or lower, a turn-off judgement section 30 outputs a judgement signal S and thereby a switch 14 reaches a continuity, and negative voltage -En is applied to a second gate resistor 11 and the gate voltage vge is rapidly biased negative and the turn-off condition of the voltage-driven switching device 7 is kept stable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gate drive circuit for a voltage-driven switch element, and more particularly to a gate drive circuit for a voltage-driven switch element which reduces a gate voltage delay due to a gate input capacitance and stably maintains a state after turn-off. The present invention relates to a gate drive circuit for a voltage-driven switch element as described above.

[0002]

2. Description of the Related Art An insulated gate transistor (hereinafter referred to as I) is used as a switch element in a power converter such as an inverter for driving an induction motor by converting DC power into AC power.
A voltage-driven switch element such as a GBT) is used, and the circuit shown in FIG. 9 is used as a gate drive circuit.

When a switching command vin for turning the IGBT 7 into a conductive state (ON) or a non-conductive state (OFF) is input to the gate drive circuit, the transistor 3,
4 and a gate voltage v corresponding to a switching command vin between the gate and the emitter of the IGBT 7 via the gate resistor 6.
ge is added, and a switching operation such as turning on or turning off the IGBT 7 is performed.

That is, when a positive switching command vin is input from a gate control circuit (not shown) as shown in FIG. 10, the transistor 3 is turned on, the transistor 4 is turned off, and the output voltage vg becomes a positive voltage. , Gate resistance 6
Is positively biased, and the IGBT 7 is turned on. When the switching command vin becomes negative, the transistor 3 is turned off, the transistor 4 is turned on, the output voltage vg becomes negative, the gate voltage vge is negatively biased, and the IGBT 7 is turned off.

Reference numeral 1 denotes a forward bias gate power supply of a voltage Ep, 2 denotes a negative bias gate power supply of a voltage En, and 5 denotes a limiting resistor. The limiting resistor 5 may be connected between the gate power supply 2 and the transistor 4, or both.

[0006]

As shown in FIG. 11, an IGBT generally has equivalent capacitances 8 to 10 of Cge, Ccg, and Cce between the gate, emitter, and collector terminals. According to Toshiba's semiconductor data book “IGBT” (1996 edition), since the collector and emitter are short-circuited at high frequency by an external circuit, the input capacitance Cies between the gate and emitter of the IGBT is Ccg + Cge. Exists. Therefore, in order to perform the switching operation of the IGBT, it is necessary to charge and discharge the charge of the input capacitance Cies via the gate resistor 6. In the conventional gate drive circuit (FIG. 9), when the charge is determined by the gate resistance 6 and the input capacitance Cies. A delay of the constant (R6.Cies) may occur, which may cause a failure in the switching operation of the IGBT.

For example, as shown in FIG.
The BTs 25 and 26 are bridged to a DC voltage source,
A PWM inverter in which the BTs 25 and 26 are turned on and off alternately is formed, and the IGBT 26 is turned on in a state where the current I0 circulating from the output side flows as shown in the figure and is regenerated to the DC power supply side via the diode 27. IGBT 25 erroneously fires and an excessive short-circuit current flows,
The BT may be damaged.

That is, in such a state, the IGBT 25
IGBT 26 is supplied with a negative gate voltage vgu, and IGBT 26 is supplied with a positive gate voltage vgx.
When 0 is commutated from the diode 27 to the IGBT 26,
As shown in FIG. 12B, a time delay occurs due to the above-described time constant until the gate voltage vgu applied to the IGBT 25 shifts to a sufficient negative bias state, and the IGBT 26
Turns on quickly, the collector of IGBT25
The emitter-to-emitter voltage vu rapidly rises, and an induced voltage due to electrostatic coupling is generated in the gate voltage vgu by the dv / dt, so that the IGBT 25 may be re-ignited (misfired).

In order to reduce the delay, it is conceivable to reduce the value of the gate resistor 6 to shorten the time constant (R6 · Cies), or to increase the voltage En of the gate power supply 2 for giving a negative bias. . However, when the value of the gate resistor 6 is reduced, the turn-off speed of the IGBT 7 increases, the surge voltage increases, and the IGBT may be damaged by an overvoltage. Further, the same problem occurs even when the voltage En of the gate power supply 2 is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the delay of the gate voltage due to the gate input capacitance of a voltage-driven switch element such as an IGBT and to perform a stable turn-off control. Is to provide.

[0011]

In order to achieve the above object, a gate drive circuit of a voltage-driven switching element according to the present invention is provided with a voltage which becomes conductive or non-conductive based on a gate voltage between a gate and an emitter. When performing a switching control by applying a gate voltage to a conductive state or a non-conductive state via a gate resistor to the drive-type switch element, determine turn-off completion of the voltage-driven switch element based on the gate voltage, Gate control means for applying a negative voltage between the gate and the emitter of the voltage-driven switching element via a second gate resistor is provided, and the state after the turn-off is stably maintained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment (basic form) according to claim 1 of the present invention. In FIG. 1, reference numeral 11 denotes a second gate resistance, and 14 denotes a second
A switch 30 for applying a negative voltage (-En) to the gate resistance 11 of the IGBT 7, and a turn-off determining unit 30 for determining the completion of the turn-off of the IGBT 7 based on the gate-emitter voltage vge of the IGBT 7 and outputting a determination signal S. The other components are the same as those of the related art (FIG. 9), and are denoted by the same reference numerals.

In the above configuration, a switching command vin of a positive or negative voltage is issued from a gate control circuit (not shown).
Is input, a voltage vg corresponding to the switching command vin is output via the transistor 3 or the transistor 4, a positive or negative gate voltage vge is applied between the gate and the emitter of the IGBT 7 via the gate resistor 6, and
Switching control for turning on or off the BT 7 is performed in the same manner as in the related art.

In this case, a negative voltage switching command v
is input, the transistor 4 is turned on and the gate power supply 2
A voltage vg corresponding to the negative voltage of the IGBT 7 is output.
Starts the turn-off operation, the gate-emitter voltage vge changes according to the characteristics of the IGBT 7 at the time of turn-off.
As shown in (2), the current flowing through the collector is maintained at a level called mirror voltage (usually about 5 V) until it becomes zero, and when the collector current becomes zero, the state rapidly shifts to a negative bias state. At the time of turn-off, a predetermined current change rate di /
Since the collector current decreases at dt, the larger the interruption current, the longer the mirror voltage generation period. If the interruption current is small, the shorter the mirror voltage generation period, as indicated by the dotted line.
When the gate voltage vge shifts to a negative bias state, a turn-off completion determination signal S is output from the turn-off determination unit 30, the switch 14 is turned on, and the negative voltage (-En) of the gate power supply 2 is changed to the second gate. It is supplied in parallel between the gate and emitter of the IGBT 7 via the resistor 11. As a result, the gate voltage vge is rapidly shifted to the negative side. Therefore, the collector of IGBT7
Even when the emitter-to-emitter voltage rises rapidly and a large dv / dt is applied, the turn-off state can be maintained without re-ignition, and the turn-off operation can be stably completed.

FIG. 3 shows a specific embodiment of the gate drive circuit according to the present invention, and corresponds to claims 2 and 3. In FIG. 3, 12, 13, and 14 are transistors, 15, 16, and 17 are resistors, and 18 is a diode. The other components are the same as those of the related art (FIG. 9), and are denoted by the same reference numerals.

In the configuration shown in FIG. 3, when a negative voltage switching command vin is input from a gate control circuit (not shown), the transistor 3 is turned off, the transistor 4 is turned on, and the voltage of -En is applied to the gate resistor 6. Is input, the transistor 12 is turned off, the transistor 13 and the transistor 14 are turned on, a voltage of −En is input to the second gate resistor 11, and the gate voltage vge supplied from the gate resistor 6 is input.
At the same time, the gate voltage vge is supplied in parallel from the second gate resistor 11.

When the switching command vin changes to a positive voltage from this state, the transistor 4 turns off and the transistor 3 turns on, and the input voltage vg of the gate resistor 6 becomes -En.
To + Ep, and at the same time, the transistor 12 changes from off to on, the transistor 14 turns off, and the second
The input voltage of the gate resistor 11 changes from -En to zero voltage, and the gate voltage vge starts to change in the positive direction at the rate of change of the time constant (R6.Cies). (Refer to FIG. 4.) When the gate voltage vge changes from negative to positive, the transistor 13 is turned off, the gate voltage vge further increases, and the IGBT 7 is controlled to be turned on.

Thereafter, when the switching command vin changes from a positive voltage to a negative voltage while a current is flowing through the collector of the IGBT 7, the transistor 3 is turned off, the transistor 4 is turned on, and the voltage of -En is applied to the gate resistor 6. And the transistor 12 is turned off at the same time. However, when a current flows through the collector of the IGBT 7, FIG.
As shown in the figure, the gate-emitter voltage vge does not immediately become a negative voltage but is maintained at the above-mentioned mirror voltage, so that the transistor 13 does not immediately shift to the on state, and the transistor 14 remains at the base even when the transistor 12 turns off. No current flows and the off state is maintained. Therefore, the IGBT 7 is turned off only by the gate voltage vge supplied from the gate resistor 6. When the collector current becomes zero, the Miller voltage disappears and the gate-emitter voltage vge becomes negative, the transistor 13 turns on, the transistor 14 turns on and the voltage input to the second gate resistor 11 changes from zero voltage to −En. , And a negative gate voltage vge is supplied in parallel from the gate resistor 6 and the second gate resistor 11.

Therefore, according to the present embodiment, after the IGBT 7 completes the turn-off operation, the gate voltage vge has a shorter time constant [Cge. (Rg1.Rg2 / Rg1) than the conventional (dotted line).
+ Rg2))] and is rapidly biased to the negative side. Thereby, the dv / d of the collector-emitter voltage of the IGBT 7 is
Re-ignition due to t can be prevented.

In this embodiment, since the gate voltage is controlled by detecting the completion of turn-off of the IGBT 7, the IGBT 7 is controlled.
The change in characteristics due to the breaking current or the variation due to individual differences does not affect the effect.

FIG. 5 shows another specific embodiment of the gate drive circuit of the present invention, which corresponds to claims 4 and 5. In FIG. 5, 19 and 20 are diodes, 2
Reference numerals 1 and 22 are resistors. Others are the same as those in the above-described embodiment (FIG. 3) and the conventional (FIG. 9), and are denoted by the same reference numerals.

In this embodiment, the transistor 13 is turned on and off by the higher of the input side voltage vg and the output side voltage vge of the gate resistor 6. In the configuration of FIG. 5, a gate control circuit (not shown)
, A switching command vin of a negative voltage is input, the transistor 3 is turned off, the transistor 4 is turned on, a voltage of −En is input to the gate resistor 6, and the transistors 13 and 14 are turned on and the second Gate resistance 1
1 is supplied with the voltage -En, and the negative gate voltage vge is supplied to the IGBT 7 in parallel.

When the switching command vin changes to a positive voltage from this state, the transistor 4 is turned off and the transistor 3 is turned on, and the input voltage vg of the gate resistor 6 becomes -En.
To + Ep, and at the same time, the transistor 13 changes from on to off, and the transistor 14 turns off.
The input side of the gate resistor 11 is opened, and the gate voltage vge
Increases in the positive direction at the rate of change of the time constant (R6 · Cies),
The IGBT 7 is controlled to be turned on. Then, when the switching command vin changes to a negative voltage in a state where a current flows through the collector of the IGBT 7, the transistor 3 is turned off again, the transistor 4 is turned on, and the voltage of −En is applied to the gate resistor 6. Is entered. However, when a current flows through the collector of the IGBT 7, the gate-emitter voltage vge does not immediately become a negative voltage but is maintained at the mirror voltage, so that the transistor 13 immediately shifts to the on state as shown in FIG. And transistor 14
Are kept off. Therefore, the IGBT 7 is turned off only by the gate voltage vge supplied from the gate resistor 6. When the collector current becomes zero, the Miller voltage disappears, and the gate voltage vge becomes negative, the transistor 13 turns on, the transistor 14 turns on, and the voltage input to the second gate resistor 11 changes from zero voltage to -En. Then, a negative gate voltage vge is supplied in parallel from the gate resistor 6 and the second gate resistor 11.

Therefore, according to the present embodiment, after the IGBT 7 completes the turn-off operation, the gate voltage vge is rapidly shifted to the negative side similarly to the above-described embodiment, whereby the collector-emitter voltage of the IGBT 7 is reduced. Dv /
dt can be prevented from being re-ignited.

FIG. 7 shows still another specific embodiment of the gate drive circuit of the present invention, which corresponds to claims 4 and 5. In FIG. 7, 23 and 24 are diodes. Others are the same as in the above-described embodiment (FIG. 5) and the conventional example (FIG. 9).
And the same reference numerals.

In this embodiment, when the switching command vin is given a negative voltage, the input voltage vg of the gate resistor 6 is set to zero voltage to short-circuit the gate and emitter of the IGBT 7 through the gate resistor 6. The other configuration is the same as that shown in FIG.

In the case of this embodiment, when the switching command vin changes from a positive voltage to a negative voltage while the IGBT 7 is turned on and a collector current is flowing, the IGBT 7 starts a turn-off operation and the gate voltage vge becomes as described above. Is maintained at the mirror voltage. When the collector current becomes zero and the Miller voltage disappears, the gate voltage vge drops to a negative voltage, and the base voltage vo applied to the transistor 13 via the diode 20 and the resistor 17 becomes negative, as shown in FIG. 13 turns on and the transistor 14
Is turned on, and a voltage of −En is applied to the second gate resistor 11. As a result, the gate voltage vge is rapidly biased to the negative side, and the collector-emitter voltage d of the IGBT 7 is d.
Re-ignition due to v / dt can be prevented.

According to this embodiment, the turn-off operation of the IGBT 7 is performed relatively slowly to suppress the surge voltage due to di / dt, and the gate voltage vge is rapidly biased to the negative side from the time when the turn-off is completed. Can be
Re-ignition due to dv / dt of the collector-emitter voltage of IGBT 7 can be prevented. Note that the diode 24 is for preventing an excessive reverse voltage from being applied between the collector and the emitter of the transistor 4.

[0029]

According to the gate drive circuit of the voltage-driven switch element of the present invention, it is possible to rapidly shift the gate voltage to the negative bias side when the voltage-driven switch element completes the turn-off operation. Circuit voltage dv /
It is possible to perform stable and highly reliable ON / OFF switching control without erroneous ignition at dt.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment according to claim 1 of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment.

FIG. 3 is a configuration diagram of an embodiment according to claims 2 and 3 of the present invention.

FIG. 4 is a waveform chart for explaining the operation of the embodiment.

FIG. 5 is a configuration diagram of an embodiment according to claims 2 and 3 of the present invention.

FIG. 6 is a waveform chart for explaining the operation of the embodiment.

FIG. 7 is a configuration diagram of an embodiment according to claims 4 and 5 of the present invention.

FIG. 8 is a waveform chart for explaining the operation of the embodiment.

FIG. 9 is a configuration diagram of a conventional device.

FIG. 10 is a waveform chart for explaining the operation of the conventional device.

FIG. 11 is a diagram showing an equivalent capacitance of an IGBT.

12A is a main circuit diagram of a power converter using an IGBT, and FIG. 12B is a waveform diagram for explaining a malfunction of the IGBT.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gate power supply (for positive bias) 2 ... Gate power supply (for negative bias) 3, 4 ... Transistor 5 ... Resistance 6 ... Gate resistance 7 ... IGBT 8,9,10 ... Equivalent capacitance 11 ... Second gate resistance 12-14 ... transistors 15-17 ...
Resistors 18-20: Diodes 21, 22 ...
Resistors 23, 24 ... Diodes 25, 26 ...
IGBT

Claims (5)

[Claims] 1. A switching control in which a gate voltage for making a conductive state or a non-conductive state through a gate resistor is applied to a voltage-driven switch element that is made conductive or non-conductive based on a gate voltage between a gate and an emitter. When turning off is performed, a turn-off completion of the voltage-driven switching element is determined based on the gate voltage, and a gate that applies a negative voltage between the gate and the emitter of the voltage-driven switching element via a second gate resistor A gate drive circuit for a voltage-driven switch element, characterized by comprising a control means and stably maintaining a state after turning off. 2. A gate drive circuit for a voltage-driven switch element according to claim 1, wherein said gate control means includes a switch element that is turned on when said gate voltage is equal to or lower than a predetermined value, and said switch element is turned on. A gate drive circuit for a voltage-driven switch element, which determines that turn-off is completed. 3. A gate drive circuit for a voltage-driven switch element according to claim 2, wherein said gate control means is supplied with a gate voltage for making said element non-conductive, and said gate element is made conductive. Second condition to conduct
A gate drive circuit for a voltage-driven switch element, wherein a negative voltage is applied to the second gate resistor through the second switch element. 4. The gate drive circuit of a voltage-driven switch element according to claim 1, wherein said gate control means is configured to set a higher voltage of the voltage applied to said gate resistor or said gate voltage to a predetermined value or less. A gate drive circuit for a voltage-driven switch element, characterized in that the switch element is turned on when the switch element is turned on, and it is determined that turn-off is completed when the switch element is turned on. 5. The gate drive circuit for a voltage-driven switch element according to claim 4, wherein said gate control means includes a second switch element that is turned on when said switch element is turned on. The second through an element
A gate drive circuit for a voltage-driven switch element, wherein a negative voltage is applied to the gate resistance of the switch.