JPH02179262A - Gate drive circuit of voltage drive type semiconductor element - Google Patents

Abstract

PURPOSE:To prevent semiconductor elements against destruction and malfunction by operating a constant voltage circuit in which the voltage in a predetermined range is applied to the gate of semiconductor elements to whose output side a reflux diode is connected for a specified time when the semiconductor elements are turned ON. CONSTITUTION:When a photocoupler 201 is turned ON, an FET 202 is turned ON accordingly and a transistor Tr 4 is turned ON through a power source 205 for forward bias of voltage Vcc and a resistor 208, so that the voltage VZD of a constant voltage diode 3 is generated across the collector and base of a Tr 203 and the Tr 203 becomes a constant voltage source. The VGE of an insulating gate type bipolar Tr (IGBT) 100 is turned out VGEapprox.=Vcc-VZD. Since a Tr 2 is turned ON to short a series circuit between the constant voltage diode 3 and the Tr 4 while an FET is OFF, the generation of voltage VZD is only during the period the FET 7 is ON. In the FET 7 after the photocoupler 201 was ON, the voltage VGS discharges the current through a resistor 6 and when it is dropped lower than the threshold value, it is turned OFF. The destruction of the IGBT and malfunction can thereby be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to IGBT (Insulated G
ate BipolarTransistor: Insulated gate type bipolar transistor) and power MO8FE
The present invention relates to a gate drive circuit for a voltage-driven semiconductor device such as T.

(Prior Art) Voltage-driven semiconductor devices, such as IGBTs, have the advantages of bipolar transistors, such as high breakdown voltage and easy increase in capacity, and power MO8FETs, which enable high-speed switching, have simple drive circuits, and require low drive power. Recently, it has been attracting attention as a new device that has the advantage of being easy to use. Fifth
The figure shows the equivalent circuit of a tonotechnical GBT.
1 is an N-channel MOS FET, 102 is an NPN transistor, 103 is a PNP transistor, 104 is a short-circuiting resistor between the base and emitter of the transistor 102, and these connect the gate G, collector C, and emitter E.
An IGBTloo is configured. Here, the transistors 102 and 103 constitute a parasitic thyristor circuit.

FIG. 6 shows an example of a drive circuit for the IGBT 100, in which 201 is a photocoupler for signal isolation connected to a control circuit such as a PWM circuit (not shown), 202 is an N-channel/L/MO3FET, and 203 is an NPN)-transistor, 204 is a PNP transistor, 205 is a forward bias power supply, 206 is a reverse bias power supply, 207,
208 and 209 are resistors.

The on/off operation of IGBTloo by this drive circuit will be described below. When the 'li current flows through the primary side of the photocoupler 201, the photocoupler 201 turns on, thereby causing F
E T 202 is turned off. When the FET 202 is turned off, the transistor 204 is turned off and the transistor 203 is turned on. When the transistor 203 is turned on, the voltage of the forward bias power supply 205 becomes IGBTlo through the resistor 209.
Since it is added between the gate and emitter of
too turns on.

The off operation of IGBTloo is opposite to the above-mentioned on operation, and when the primary current of the photocoupler 201 is cut off, the photocoupler 201 is turned off and the FET 202 is turned on. As a result, the transistor 203 is turned off and the transistor 204 is turned on, and the voltage of the reverse bias power supply 206 is applied between the gate and emitter of the IGBTloo through the resistor 9, so that the IGBTloo is turned off. Note that the resistor 209 in the figure limits the gate current of IGBTloo, and prevents the gate from losing its control ability and being unable to cut off the current due to the latch-up phenomenon in which the internal parasitic thyristor turns on when IGBTloo turns off. It is for the purpose of

Further, FIG. 7 shows another example of the IGBTloo drive circuit. In the figure, 210 is a constant voltage diode,
211 is a resistor, 212 is an NPN transistor, and the other configurations are the same as in FIG.

The operation of this drive circuit is also substantially the same as that of the circuit shown in FIG.
It has the effect of

(Problems to be Solved by the Invention) This type of IGBT is mainly used as a switch for turning on and off the current flowing in an inductive load such as a vvVF (variable voltage variable frequency) inverter. The basic operation is equivalent to the chopper operation in the inverter circuit shown in FIG.

In addition, in the same figure, 100 a and 100 b are IG
BT, 301 is a DC power supply (voltage Ed), 302, 304
is a freewheeling diode.

303 is a wiring inductance, 305 is a load, and the snubber circuit is omitted.

In the figure, when IGBTlooa of the upper arm is turned off due to the operation of the drive circuit as described above, the load current I
L continues to flow through the freewheeling diode 304 in the lower arm. When IGBTlooa is turned on in this state, the DC power supply 30 is turned on until the freewheeling diode 304 is turned off.
1. Since a short circuit is formed between the IGBTlooa and the freewheeling diode 304, resulting in a DC short-circuit state, a high-speed diode is usually used as the freewheeling diode 304 and 302.

When IGBTlooa is turned on, its collector current Ic and load current I gradually increase as shown in FIG. 9, but the time when IGBTlooa turns on is reached. Before and after , the current Io flowing through the free wheel diode 304 rapidly decreases and then increases as shown in the figure. The current Io and the voltage Vo across the free-wheeling diode 304 at this time are shown in FIG.
The period (t□ to ti) from which the value reaches the maximum value at time t0 (corresponding to time t0 in FIG. 9) until it becomes zero again at time t is the so-called reverse recovery time. Note that this reverse recovery time is usually 1
This is a very short time of less than μS.

In conventional semiconductor devices, the switching time is longer than the reverse recovery time, and therefore, steep changes in voltage or current within this reverse recovery time are suppressed by this switching time. However, since the switching time of a voltage-driven semiconductor element such as an IGBT is approximately the same as the reverse recovery time of a diode, changes in voltage and current during the reverse recovery time are not suppressed and tend to increase further.

During the period (tz to ti) in FIG. 10 of this reverse recovery time, the reverse current (reverse recovery current) rapidly decreases within a short time, so dI/dt (rate of change in current) increases,
In particular, the higher the speed of the diode, the shorter this period of time becomes, so d I/d t becomes larger. Therefore, a voltage ΔV of the same polarity as the DC power supply voltage Ed generated by this dI/dt and the wiring inductance 303.
a s-d I / d t (II s is the inductance value of the wiring inductance 303) is superimposed on the DC power supply voltage Ed, and the voltage V across the freewheeling diode 304
n becomes very high as shown as Vρ in FIG.

In some cases, this voltage Vo exceeds the withstand voltage of the element,
IGBT connected in parallel with freewheeling diode 304
There is a risk that the loob may be destroyed or accidentally turned on.

Furthermore, after time t2, the voltage VD increases rapidly in an extremely short period of time, so its dV/dt also becomes very large, for example, 10XIO' (V/μS) or more. There has been a problem that the photocoupler 201 of the drive circuit shown in FIG. dt
If a photocoupler that is resistant to damage and has a high signal transmission speed is used, there is a problem in that the IGBT drive circuit becomes expensive, leading to an increase in manufacturing costs.

The present invention was proposed in order to solve the above problems, and its purpose is to suppress the reverse recovery current of the freewheeling diode, the transient overvoltage across the freewheeling diode, and the increase in the voltage change rate, thereby reducing the voltage. It is an object of the present invention to provide a gate drive circuit for a voltage-driven semiconductor element that can be realized with a simple configuration and at low cost, which prevents damage to the driven semiconductor element and malfunction of the drive circuit and control circuit.

(Means for Solving the Problems) In order to achieve the above object, a first invention provides a gate drive circuit for a voltage-driven semiconductor device in which a freewheeling diode is connected in series and in a reverse direction to the output side. a constant voltage circuit that applies a voltage higher than the threshold voltage of the semiconductor element and lower than the applied voltage in steady state to the gate of the semiconductor element; The system is equipped with a timer that operates until the reverse recovery time of .

In addition, the second invention is characterized in that among a pair of complementary switching elements provided in the output stage of the gate drive circuit, the switching element for turning on the semiconductor element has a shorter switching time than the switching element for turning off the semiconductor element. A period is provided during which the pair of switch elements are simultaneously turned on when the semiconductor element is turned on. This simultaneous on period is at least longer than the reverse recovery time of the freewheeling diode,
Also, during this period, since the voltage applied to the gate of the semiconductor element is determined by the partial voltage of the resistors connected in series to the pair of switch elements, this voltage is set higher than the threshold voltage of the semiconductor element. In addition, the applied voltage is set to a value lower than the applied voltage during steady state.

(Function) According to the first invention, when turning on the voltage-driven semiconductor element, the voltage-driven semiconductor element is turned on for a certain period of time determined by a timer (a period longer than the reverse recovery time of the freewheeling diode connected to the output side of the semiconductor element). , a relatively low constant voltage is applied between the gate and emitter of the semiconductor element by a constant voltage circuit. As a result, the output current of the semiconductor element is suppressed to a small value, the rate of change of the reverse recovery current of the free-wheeling diode connected in series on the output side is reduced, and overvoltage generation across the diode is prevented, thereby reducing the rate of change of voltage. Since the voltage is also small, there is no risk of erroneous turning on or destruction of the semiconductor element, malfunction of the drive circuit, etc.

Furthermore, after a certain period of time has elapsed according to the above timer, the application of the low voltage to the gate of the semiconductor element by the constant voltage circuit is released, the voltage between the gate and emitter becomes the normal value, and the output current of the semiconductor element becomes sufficient. growing. At this time, since the freewheeling diode has recovered its reverse blocking ability, no current flows through the diode, causing no problem.

Further, according to the second invention, when turning on the semiconductor element, a period is provided in which the on and off switching elements of the output stage of the gate drive circuit are simultaneously turned on, so that the voltage between the gate and emitter of the semiconductor element is changed to the voltage between the gate and emitter of the semiconductor element. The voltage is higher than the threshold voltage of , and lower than the steady state voltage. By reducing the gate-emitter voltage to a low value in this way, the output current (collector current) can be suppressed to a low value due to the output characteristics of the semiconductor element, and by reducing the reverse recovery current of the freewheeling diode connected in series with the semiconductor element. Similarly to the above, it is possible to suppress the transient voltage across the freewheeling diode and reduce the rate of voltage change.

In addition, by making the above simultaneous on period at least as long as the reverse recovery time of the freewheeling diode, only the on switch element is turned on when the simultaneous on period ends, so that the voltage between the gate and emitter of the semiconductor device is normally value, and the output current of the semiconductor element becomes sufficiently large.

(Example) The present invention will be described in detail below with reference to FIG.

First, FIG. 1 is an embodiment of the first invention, and shows a drive circuit for I (3BT) as a voltage-driven semiconductor element. In the same figure, 100 is an IGBT, and 2
01 is a photocoupler, 202 is N-channel MO8FE
T, 203 is an NPN transistor, 204 is a PNP
205 is a forward bias power source, 206 is a reverse bias power source, and 207 to 209 are resistors.

This embodiment includes a circuit that operates the output stage transistor 203 as a constant voltage source, and a timer that operates this circuit for a predetermined period of time. In other words, the circuit operated as a constant voltage source includes an NPN transistor 4 whose base is connected to the base of the output stage transistor 204 and whose emitter is connected to the base of the transistor 203, and whose collector is connected to the 7 nodes. It is composed of a constant voltage diode 3 whose cathode is connected to the positive electrode of the forward bias type g205, and the resistor 208. The timer also includes a resistor 1 connected between the positive electrode of a forward bias power source 205 and the drain of an N-channel MO8FET 7, which will be described later, a collector and a base connected to both ends of the resistor 1, and an emitter connected to a transistor 4.
An NPN transistor 2 connected to the emitter of the FET 2, a FET 7 whose drain is connected to one end of the resistor 1, and whose source is connected to the negative electrode of the reverse bias power supply 206, and the gate of the FET 202 is connected between its gate and the gate of the FET 202.・The transistor 2 is composed of a resistor 6 and a diode 5 connected in parallel to the resistor 6 with its cathode facing the gate of the FET 7. It acts to short-circuit the series circuit of voltage diode 3 and transistor 4, and the timer also connects resistor 6 and FET 7.
depending on the gate input capacitance and gate threshold voltage (threshold level).

This works so that the times at which FET 202 and FET 7 are turned off are slightly different from each other. Note that diode 5 is FET2
This is to equalize the on time of 02.7.

Next, the operation of this circuit will be explained with reference to FIG.

First, when the control circuit causes a current to flow through the primary side of the photocoupler 201 and turns on the photocoupler 201 at time T1, F E 7202 first turns on at time T.

Turn it on. When this FET 202 is turned off, a current flows to the base of the transistor 4 via the forward bias power supply 205 and the resistor 208, and when the transistor 4 is turned on, the voltage Vzo of the voltage regulator diode 3 is changed from the collector to the base of the transistor 203. Occurs between. This voltage causes the transistor 203 to operate as a constant voltage source,
Its collector-emitter voltage VC! + is VcE=Vng+Vzp+Vct' given Vzo=V,
−(1). Note that VB[l is the transistor 203
The voltage between the base and emitter of , Vat' indicates the voltage between the collector and emitter of transistor 4. Therefore,
Gate-emitter voltage Vaa of IGBT 100
If the voltage of the forward bias power supply 205 is Vcc, then
Va[1=Vcc-V, 4Vcc-Vzn-(2)
The voltage V zn (
The period during which V, ) is occurring is as shown in Figure 2.
This is the period during which FET7 is on.

On the other hand, in the FET 7, after the photocoupler 201 is turned on, the gate-source voltage V a s is discharged through the resistor 6, and at the time T when this voltage V (18 falls below the threshold voltage)
1 turns it off. That is, due to the action of the timer described above, it is turned off a certain period of time later than FET 202.

When this FET 7 is turned off, a base current flows to the transistor 2 via the forward bias power supply 205 and the resistor 1, so the transistor 2 is turned on and the series circuit of the constant voltage diode 3 and the transistor 4 is short-circuited, so that viL:
:0, and the voltage Voa is the conventional forward bias voltage V.
It becomes equal to cc.

As described above, in this embodiment, during the fixed period T from time T2 to T3 secured by the timer, the IGB
The gate-emitter voltage V of Tloo is maintained at a constant voltage Vcc-V, which is lower than the power supply voltage Vcc.

In addition, the above-mentioned fixed period T is a freewheeling diode (not shown) connected in series and in the opposite direction to the output side of IGBTloo.
It is necessary to make the reverse recovery time longer than the reverse recovery time. Also,
It goes without saying that the voltage Vcc-V□ is higher than the threshold voltage of the IGBT 100.

In this way, when IGBTl and OO are turned on, the gate-emitter voltage Van is held at a relatively low value, so as shown in the IGBT output characteristics in Figure 3, the IGBT
The collector current Ic of Tloo can be suppressed to a low level. Therefore, by suppressing the reverse recovery current of the freewheeling diode connected in series with IGBTloo, the current change rate dI/dt
As a result, it is possible to reduce the voltage Vo across the freewheeling diode and to reduce the voltage change rate dV/dt.

Furthermore, as is clear from FIG. 3, when the voltage VGII is set to a low value, the on-voltage of IGBTloo increases. , this period T
The on-voltage can be kept sufficiently low during steady state after passing through.

Next, FIG. 4 shows an embodiment of the second invention. In this FIG. 4, the same components as those shown in FIG. 1 or FIG.
The differences will be mainly explained below. That is, in this embodiment, a P-channel MO8FETl0 is used as a turn-on switching element of IGBTloo, and its source is connected to the positive electrode of the forward bias power supply 205.
The drain is connected to the emitter of a transistor 204 via a resistor 11, and the collector of the transistor 204 is connected via a resistor 12 to the negative electrode of a reverse bias power source 206.

Further, the collector of the transistor 212 is connected to the transistor 9.
, 204, and the collector of the transistor 9 is connected to the positive electrode of a forward bias power source 205 via a resistor 8. Furthermore, the collector of transistor 9 is FE
Connected to the gate of Tl0.

The operation of this gate drive circuit will be explained below.

First, the on operation of IGBTloo will be explained.

When the photocoupler 201 is first turned on, the transistor 2
12 turns off, which turns transistor 9 on. By turning on the transistor 9, the gate of the FET 10 is connected to the negative electrode of the reverse bias power supply 206, and the gate and source are forward biased to turn on the FET 10.

Also, when the photocoupler 201 is turned on, the transistor 2
04 is turned off, but since FETs generally have a shorter switching time than transistors, FET10 is turned on before transistor 204 is turned off, so transistor 204 is turned off.
FET10 and transistor 204 are turned on at the same time until FET04 is turned off.

During this period, the gate-emitter voltage Vaa of IGBTloo is.

Here, Vcc' is the voltage of the reverse bias power supply 206.

From the above equation (3), the gate-emitter voltage VaB can be suppressed to a voltage lower than the normal forward bias voltage Vcc. As a result, as shown in Fig. 3, <IGBT
The collector current Ic of loo can be reduced, and an increase in the current change rate and voltage change rate caused by the reverse recovery current of the freewheeling diode can be eliminated.

In addition, to explain the off operation of IGBTIOQ,
When the photocoupler 201 is turned off, the transistor 212 is turned on. This turns off transistor 9 and turns off the FET.
The gate and source of l0 become at the same potential and FET l0 is turned off. On the other hand, when the transistor 212 is turned on, the transistor 204 is also turned on, but since the FET10 turns off faster than the transistor 204 turns on, the FETLO and the transistor 204 turn on as described above.
There is no simultaneous on period with No. 4, and the same on operation as in the prior art is performed.

Although the above embodiments have been described with respect to the IGBT drive circuit, the present invention is also applicable to other voltage-driven semiconductor devices such as power MOS FETs.

(Effects of the Invention) As described above, according to the first invention, when the voltage-driven semiconductor element is turned on, the voltage applied to the gate of the semiconductor element is set to be a relatively low voltage for a certain period of time by the timer, and the second
According to the invention, a pair of switch elements in the output stage of a gate drive circuit have different switching times, and when the semiconductor element is turned on, a period is provided in which each of the switch elements is simultaneously turned on, and the semiconductor element is turned on only during this period. By suppressing the output current of the semiconductor element by applying a relatively low voltage to the gate, it is possible to reduce the reverse recovery current of the freewheeling diode, prevent overvoltage caused by this, and reduce the rate of voltage change.

Therefore, reliability can be improved by preventing damage to the semiconductor element and malfunction of the drive circuit and its control circuit.

In addition, the present invention can be realized by simply adding a few elements without requiring major changes to conventional circuits.
It has the advantage that it can be provided at low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the first invention. FIG. 2 is an operating waveform diagram, FIG. 3 is an output characteristic diagram of the IGBT, FIG. 4 is a circuit diagram showing an embodiment of the second invention, and FIG.
Figures 1 to 10 are for explaining conventional examples. Figure 5 is an equivalent circuit diagram of an IGBT, Figure 6 is a circuit diagram showing an example of a gate drive circuit, and Figure 7 is another example. Circuit diagram, Figure 8 is a circuit diagram of a chopper using IGBT, Figure 9
The figure is a diagram of its operation waveforms, and FIG. 10 is a diagram of current and voltage waveforms of the diode in the circuit of FIG. 1, 6, 8, LL, 12,207,208,20
9,211...Resistance 2, 4, 9, 203.20
4.212... Transistor 3.210... Constant voltage diode 5... Diode? , 10,202...FET
100...I G B T 201... Photocoupler 205... Forward bias power supply 206... Reverse bias power supply

Claims (2)

[Claims] (1) In a gate drive circuit for a voltage-driven semiconductor element in which a freewheeling diode is connected in series and in the reverse direction on the output side, the voltage is higher than the threshold voltage of the semiconductor element with respect to the gate of the semiconductor element, and A constant voltage circuit that applies a voltage lower than the voltage applied during steady state, and a timer that operates this constant voltage circuit at least until the reverse recovery time of the diode elapses when the semiconductor element is turned on. A gate drive circuit for a voltage-driven semiconductor device, characterized by: (2) In a gate drive circuit for a voltage-driven semiconductor device in which a freewheeling diode is connected in series and in the reverse direction on the output side, a complementary circuit is provided at the output stage of the gate drive circuit to turn on or turn off the semiconductor device. Of the pair of switch elements that operate normally, the switch element for turning on the semiconductor element has a shorter switching time than the switch element for turning off the semiconductor element, and when the semiconductor element is turned on, the pair of switch elements Provide a period in which both are turned on, and set this period to be longer than at least the reverse recovery time of the freewheeling diode,
Within this period, a voltage higher than a threshold voltage of the semiconductor element and lower than a voltage applied in a steady state is applied to the gate of the semiconductor element. drive circuit.