JPH03183209A - Drive circuit for voltage driven type semiconductor element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a drive circuit for voltage-driven semiconductor devices such as IGBTs and power MO3FETs, and in particular, to power conversion devices such as inverters, to prevent faults caused by short-circuit accidents. The present invention relates to a drive circuit having an overcurrent protection function that protects these elements from current.

(Prior art) In the power converter as described above, among the overcurrent failures during operation, there are load short circuits and ground faults that lead to element destruction. A simulated circuit at the time of a short-circuit accident in the converter, and the voltage and current waveforms of the elements are shown in FIG. 9 and FIG. 1O.

During the short-circuit period, a short-circuit current flows through the IGBT 2 while substantially a DC circuit voltage is applied thereto. In the figure, 1 is a DC power supply, 3
indicates wiring inductance.

This short circuit current reaches 5 to 6 times the DC rated current (approximately 10 times the DC rated current). Therefore, the instantaneous power applied to the element during the short circuit period is extremely large, and after the short circuit is detected,
It is necessary to cut off the overcurrent by turning off the gate within a predetermined time (about 10 μsec).

A conventional example of a drive circuit having an overcurrent protection function is shown in FIG. 4 is an IGBT as a main switching element, 5 is a photocoupler for signal isolation, 6 and 7 are a voltage source for applying an on-gate voltage and a voltage source for applying an off-gate voltage, respectively. A pair of transistors 9 and 10 which operate complementary to the photocoupler 5 by a signal applied through the transistor 8 are connected. The emitters of these output stage transistors 9 and 10 are connected to the IGBT 4 via a resistor 11, and the midpoint between the voltage sources 6 and 7 is connected to the emitter of the IGBT 4, thereby forming a driving section.

Further, the transistor 14, the Zener diode 13, the diode 15, and the resistor 17 constitute an overcurrent detection section that monitors the voltage at the collector terminal of the IGBT 4 and detects when this voltage exceeds a predetermined value.

Furthermore, a delay circuit is formed by a capacitor 16 at a stage before this overcurrent detection section.

First, normal operation will be explained. When the photocoupler 5 is turned on, the transistor 8 is turned off, and as a result, the transistor 9 is turned on and the transistor 10 is turned off.
An on-gate voltage (1) is applied between the gate and emitter of BT4 via a resistor 11.

At this time, since the transistor 8 is turned off, the resistor 1
2. Transistor 14 via Zener diode 13
However, by providing the resistor 17, the timing at which the transistor 14 operates is delayed. When an on-gate voltage is applied between the gate and emitter of IGBT4, this IGBT4 turns on and the voltage between its collector and emitter becomes on-voltage (VCE<.1
).

Therefore, vzn+ +VLLE >VZ +VCE(ON)+
VF■2I, I: Threshold voltage of Zener diode 13 V8t: Voltage between base and emitter of transistor 14■
By selecting components such that F = forward voltage of diode 15, transistor 14 is kept off when IGBT 4 is on.

Next, when the photocoupler 5 is turned off, the transistor 8
is turned on, and as a result, the transistor 9 is turned off and the transistor 10 is turned on, and an off-gate voltage is applied between the gate I and the emitter of the IGBT 4 via the resistor II, and the IGBT 4 is turned off.

At this time, the capacitor I6 is turned on by the transistor 80.
The charge is discharged to prepare for turn-on operation.

Now, if a short circuit accident occurs during the ON period of IGBT4, as the collector-emitter voltage increases, VZDI + VIE < VZ +
VCE tos+ + "F, the transistor 14 becomes conductive, and an off-gate voltage is applied between the gate and emitter of the IGBT 4, turning off the IC and BT 4, and cutting off the overcurrent.

[Problem to be solved by the invention]

In the overcurrent protection operation of the conventional drive circuit shown in FIG. /dt) is large,
Therefore, there is a risk that an excessive voltage, which is the sum of the voltage (fs-di/dt) induced in the wiring inductance and the DC circuit voltage, will be applied to the IGBT 4.

In addition, since there is a delay circuit made up of the capacitor 16, there is a time delay in detecting overcurrent, and the energy consumed by the element from the time a short circuit occurs until the overcurrent is cut off becomes larger than necessary. was there.

On the other hand, the IGBT 4 has a capacitance between the collector C1 emitter E1 gate G terminals as shown by 13th [1].

FIG. 14 shows an equivalent circuit of the switching process, in which the input capacitor C4es is charged and discharged. Furthermore, in the ON state of a semiconductor device, the device characteristics depend on the charged voltage value of this input capacitor, so in order to keep the device characteristics constant,
A predetermined voltage value must be charged.

Since the load of the gate drive circuit is capacitive in this way,
Due to the characteristics of the output stage transistors 9 and 10, there is a possibility that the output voltage may not reach the predetermined gate voltage value, and as a result, the gate voltage decreases and the on-voltage of the IGBT 4 increases, which may lead to an increase in generated loss. be.

Further, the pulse current rating of a transistor is generally about twice the DC current rating, which is not very large. Therefore,
IGBT that can be driven by the output stage transistor rating
capacity class is limited. In addition, all I.G.
A transistor that can drive a BT has a large shape, which leads to a problem of increasing the size of the drive circuit.

By the way, when a short-circuit accident occurs while the IGBT4 is in a conductive state, the current increases and the element voltage (CE) also increases rapidly, and as shown in Figure 15, the collector (C) Junction capacitance CC between and gate (G)
I have C and it flows into the gap.

In the conventional overcurrent protection operation, the charge charged in the gate/emitter of the IGBT 4 is discharged through the resistor 11 (gate resistor) and the transistor IO.
1, the impedance of the drive circuit as seen from the IGBT 4 side is high, so the displacement current directly charges between the gate and emitter rather than flowing from the resistor 11 to the transistor 10.

Therefore, due to this charging operation, the voltage between the gate and emitter of the IGBT 4 no longer matches the voltage in front of the resistor 11 (voltage on the drive circuit side).

As a result, the voltage no longer decreases, and the short circuit current also no longer decreases. When the displacement current disappears in this state, the voltage between the gate and the vine rapidly decreases. As a result, the short-circuit current decreases rapidly, and the rate of change of the short-circuit current (d
t/dt) increases, the voltage (/!5-di/dt) induced in the wiring inductance in the main circuit cannot be suppressed, and an excessive voltage that exceeds the withstand voltage of the element is generated, destroying the element. There is a possibility that it will be stored away. Furthermore, since the short circuit current is not reduced, there arises a problem of increased energy consumption of the element. Further, as the element capacitance (voltage, current rating) increases, the CCC increases, so the displacement current also increases, and these problems become more significant.

Furthermore, since IGBT4 turns off from a large current state in several μs or less, the current change at turn-off (di/d
t) becomes a very large value, and the wiring inductance (L
), there is a possibility that a voltage exceeding the withstand voltage of the element may be applied between the collector and emitter (drain and source in MO and 5FET).

An object of the present invention is to eliminate the disadvantages of the conventional example, to suppress the jump voltage at the time of overcurrent cutoff, to reduce the energy consumption of the element, to reliably protect the element from overcurrent, and to maintain a predetermined gate voltage. It is an object of the present invention to provide a drive circuit for a voltage-driven semiconductor device that can reduce the loss generated by applying voltage to the device.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides a driving section including a pair of output transistors that operate complementary to at least a photocoupler for signal connection, and a voltage driving section for driving. In a drive circuit for a voltage-driven semiconductor device, which includes a protection section that protects the device from overcurrent that occurs in the event of a short-circuit accident, the protection section protects the input side of the voltage-driven semiconductor device when a drive signal is present. A detection means that monitors the voltage at the terminal and detects when this voltage exceeds a predetermined value, and a variable voltage source that gradually lowers the voltage over time while the detection means is operating. a diode is connected between the variable voltage source and the base terminal of the output transistor such that the base terminal side serves as an anode; The collector terminal of the transistor that becomes conductive when it is detected that the voltage of the main terminal exceeds a predetermined value and the collector terminal of the photocoupler for signal isolation are connected to the transistor side via a forward diode, and the collector terminal is further driven. As a pair of output transistors that operate complementary to each other,
An FET is used as an on-state transistor, and a bipolar transistor is used as an off-state transistor, and the positive terminal of a capacitor serving as a variable voltage source constituting a protection part is connected to a voltage-driven semiconductor element. The gate terminal is connected through a diode, and a forward bias transistor applies a forward voltage between the gate and cathode of the voltage-driven semiconductor element to turn the element on, and a forward bias transistor turns the element on by applying a reverse voltage. A drive section includes a pair of output transistors consisting of a reverse bias transistor, and a drive section that monitors the voltage at the input side main terminal of the voltage-driven semiconductor element when a drive signal is present, and when this voltage exceeds a predetermined value. a detection means for detecting that the forward bias transistor is in an inoperable state and removes the application of forward voltage when the detection means detects the forward bias; A resistance that is effective when no reverse voltage is applied due to non-operation of the transistor,
A resistor forming a shunt between the gate and cathode of the voltage-driven semiconductor element is provided, and the variable voltage source and the gate terminal of the voltage-driven semiconductor element are connected via a transistor. It is.

[Effect]

According to the first aspect of the present invention, after overcurrent is detected, the gate-emitter voltage of the semiconductor element gradually decreases over time. Since the value of the short circuit current rcr flowing through the semiconductor element depends on the voltage VGE applied between the gate and emitter as shown in FIG. 12, the short circuit current also decreases in response to a decrease in the voltage between the gate and emitter. . Therefore, -d i /d t when cutting off overcurrent can be suppressed to a small value. Furthermore, if the voltage between the gate and emitter is greater than the threshold voltage of the element, the semiconductor element becomes conductive, so after the transistor in the overcurrent detection section becomes conductive, the voltage between the gate and emitter becomes equal to the threshold voltage. By setting the time to be longer than the turn-on time of the semiconductor element, the delay circuit required in conventional circuits is no longer required. Therefore, even when an overcurrent occurs, protective operation can be performed without delay, reducing the energy consumed by the element. can be reduced.

According to the present invention as set forth in claim 2, in addition to the above action, while the overcurrent detection section is operating, even if an off signal is input to the signal isolation photocoupler, the gate off operation is not performed. Since priority is given to the operation of the variable voltage source without overcurrent protection, the overcurrent protection operation continues.

According to the present invention as set forth in claim 3, since the output characteristic of the FET as an ON device of the gate drive circuit exhibits a resistance characteristic, SWI in FIG. 14 can be regarded as a resistance.

As a result, the input capacity of IGBT is as follows: power supply ■1→SW1→
It is charged along the path from resistance (Ro) to input capacitance, and when the voltage exceeds the threshold, the IGBT is turned on. Furthermore, the input capacitance is, as mentioned above, <SWI can be regarded as a resistance, so
The battery will be charged to a predetermined gate voltage, which is the power supply ■1. In addition, FETs have pulse current ratings of 4 to 4, which are DC ratings.
Since it is five times as large, the gate drive circuit is less likely to be limited by the IGBT capacity class, and can be used in common. On the other hand, turn-off only requires discharging the charge in the human capacitance, and there are fewer restrictions on the output stage device, so bipolar
Just a transistor.

According to the present invention as set forth in claim 4, the gate terminal of the semiconductor element having the gate resistance and the positive terminal of the capacitor serving as the variable voltage source are connected via the diode.
The impedance of the drive circuit as seen from the semiconductor element side becomes low, and the displacement current generated at the time of a short circuit flows to the drive circuit side. As the capacitor voltage is discharged when an overcurrent occurs, the gate-emitter voltage of the semiconductor element also decreases, and the overcurrent protection function effectively operates.

According to the present invention as set forth in claim 5, the space between the gate and emitter of the IGBT (the gate and source of the MOSFET) can be equivalently considered as a capacitor, and the turn-off speed of this element is determined by the speed between the gate and emitter (the gate and source of the MOSFET). Gate Source〉
It changes depending on the time that the charge stored in is discharged. On the other hand, when an accident such as a load short circuit occurs, a high voltage state approximately equal to the power supply voltage is generated between the collector and emitter (gate and source) of the element. Therefore, the IGBT collector (MO
A circuit that compares the potential of the SFET (drain) and a reference voltage determines that a short circuit has occurred when the collector (drain) potential is higher than the reference potential during an on signal, and simultaneously turns off the transistors for applying forward and reverse voltages to the element. , I.G.B.
The gate of T (MOSFET) is in a non-biased state,
By prolonging the discharge time of the charge accumulated in the gate/emitter (gate/source) of the rGBT by using a discharge resistor with a high resistance value, the turn-off speed of the element is slowed down.
The overcurrent can be cut off while preventing overvoltage from being applied to the element.

According to the invention as set forth in claim 6, since the transistor is attached to the voltage-driven semiconductor element side of the gate resistor, this transistor lowers the impedance of the drive circuit as seen from the semiconductor element side. Therefore, the displacement current generated at the time of short circuit flows to the drive circuit side, that is, to the transistor.

Moreover, since the base terminal of the transistor into which this displacement current flows is connected to the positive terminal of the capacitor of the variable voltage source, when an overcurrent occurs, the voltage across the capacitor is
The difference between the IGBT gate and
It is applied between the emitters, and overcurrent protection works effectively.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of a drive circuit for a voltage-driven semiconductor device according to the present invention, in which the same components as in FIG. 11 showing the conventional example are given the same reference numerals.

That is, for the IGBT 4 as the main switching element, the photocoupler 5 for signal isolation and the photocoupler 5
A pair of transistors 9 and 10 operate complementary to each other via a transistor 8, and a voltage source 6 for applying an on-gate voltage and a voltage source 7 for applying an off-gate voltage are connected in series thereto.
This is the same as in the prior art example in that the driving section is formed by the resistor 11 and the resistor 11.

The present invention consists of the diode 15, the Zener diode 13, the resistor 17, and the transistor 14 in the conventional circuit, and is an overcurrent detector that monitors the voltage on the collector terminal side of the IGBT 4 and detects when this voltage exceeds a predetermined value. Department,
A resistor 18 and a capacitor 20 were connected to a voltage limiting circuit consisting of a variable power source connected to the base of the output stage transistor 9.10 of the drive section.

The capacitor 20 is connected to the positive side terminal via a resistor 19, and the midpoint between the capacitor 20 and the resistor 19 is connected to the output stage transistor 9. IO
diode 21 in that case is connected to the base of transistor 9. The IO side becomes the anode.

On the other hand, the base of the transistor 23 is connected to the base of the transistor 8, and the collector of the transistor 23 is connected to the base of the transistor 8.
It is connected to the midpoint between the Zener diode F13 and the diode 15 of the overcurrent detection section and to the positive side terminal via the resistor 22, and the emitter is connected to the negative side terminal, so that I
We configured a circuit that detects the on-period of GBT4 and transmits this to the overcurrent detection section.

Next, the operation will be explained.

The capacitor 20 is first charged by the voltage source 6°7 through the resistor 19, and the voltages across the capacitor 20 are V, +V,
becomes. The positive terminal of the capacitor 20 and the transistor 9,
As shown in the figure, a diode 2 is connected between the base of
1 is connected so that the base terminal side thereof becomes the anode, so that it has almost no effect on normal operation.

As in the past, when overcurrent is detected, transistor 1
4 is conductive. Accordingly, the charge in the capacitor 2° is discharged via the resistor 18. Then, the voltage difference between the voltage across the capacitor 20 and v2 is applied to the diode 21. It is output via transistor 9.

If the resistance values of resistors 12, 18, and 19 are Rt, Rz, and Rs, by selecting Rt, R3>R2, VG
It can be the low voltage required for E@I G B T 4 to turn off.

The transistor 23 notifies the overcurrent detection section that the IGBT 4 is in the on period. Note that the resistor 18 may be a constant current diode.

By the way, in the drive circuit shown in FIG. 1, the overcurrent detection section detects an overcurrent, the transistor 14 becomes conductive, and the I
Even when the voltage between the gate and emitter of the GBT 4 is decreasing, if an off signal is input, the normal off operation will be performed. As a result, the short circuit current cannot be reduced sufficiently and is cut off, resulting in a decrease rate of current (-di/dt) at the time of cutoff.
becomes large. Therefore, there is a risk that an excessive voltage will be applied to the element.

In the second embodiment shown in FIG. 2, the collector terminal of the signal insulating photocoupler 5 and the transistor 14 are connected via a diode 24 in order to cope with such a problem.

In the circuit shown in FIG. 2 as well, when the overcurrent detection section detects an overcurrent, the transistor 14 becomes conductive. At this time,
When the off signal is input, the photocoupler 5 is turned off.

Therefore, the base-emitter voltage VIIE of transistor 8 or 23 and the collector-emitter voltage VC of transistor 14! If the components are selected so that the relationship between , and the forward voltage of the diode 24 is VIIE > VCE + VF, the current flowing from the voltage source 6°7 through the resistor 25 will flow to the base of the transistor 8.23. Instead, it flows through diode 24 to transistor 14 .

As a result, the overcurrent protection operation is performed without transistors 8 and 23 being turned on.

Further, during normal off-operation, the transistor 14 is not conductive, so that it does not have an effect on the current flowing through the base of the transistor 8.23.

FIG. 3 and FIG. 4 show a third embodiment and a fourth embodiment of the present invention, respectively.

First, referring to FIG. 3, in the first and second embodiments, a pair of output stage transistors 9. Bipolar transistors were used as the IO in both cases, but an FET 26 was used instead of the ON transistor 9.

The off transistor 10 has the first. A bipolar transistor is used as in the second embodiment, but transistors 27, 28 are added in combination in multiple stages in order to turn on/off the FET 26 as the ON device, and a diode 29, resistors 30, 31, . 32.33
Add.

Of these, the resistor 30 is connected to the drain side of the FET 26.
1 was inserted into the collector side of the transistor 10, the base of the transistor 28 was connected to the photocoupler 5, and the base of the transistor 27 was connected to the collector of the transistor 14 via a diode 29. Also,
The resistor 32 is connected to the collector side of the transistor 28, and the resistor 33 is connected to the collector side of the transistor 28.
are inserted into the collector side of the transistor 27, respectively.

Next, the on/off operation of this drive circuit will be explained.

When current flows through the primary side of the photocoupler 5, the photocoupler 5 is turned on and the transistor 28 is turned off. When the transistor 28 is turned off, the transistor 27 is turned on, and the FE
The gate and source of T26 are forward biased, and the FET
26 turns on.

When the FET 26 is turned on, the forward bias voltage source 6 is applied between the gate and emitter of the IGBT 4 via the resistor 11, so the TGBT 4 is turned on. Note that when the photocoupler 5 is turned on, the transistor 10 is turned off as before.

The OFF operation of the IGBT 4 is opposite to the above-mentioned ON operation. When the primary side current of the photocoupler 5 is cut off, the photocoupler 5 is turned off. When photocoupler 5 is turned off, transistor 28 is turned on.

When transistor 28 is turned on, transistor 27 is turned off. By turning off the transistor 27, the FET4
is turned off. Further, as in the first embodiment, when the photocoupler 4 is turned off, the transistor 10 is turned on, and the reverse bias voltage source 7 is applied to the IGBT 4 through the resistor 11, so that the IGBT 4 is turned off.

Next, circuit operation during overcurrent protection will be explained. In the same manner as in the first embodiment, when an overcurrent is detected, the transistor 14 is turned on. Here, VIIF) V!
+VCE+VF ■IIE: Transistor 27 novllEVci:) VC of transistor 14! ■If you select the components so that the forward voltage of F = diode 29, you can connect the resistor 32 from the power supply.
The base current of the transistor 27 flowing through is
It does not flow to transistor 27 but flows to transistor 14 via diode 29. As a result, transistor 27
is turned off, and FET26 is turned off. Next, transistor E0 is turned on, and the same protection operation as in the first embodiment operates.

The fourth embodiment shown in FIG. 4 is a modification of the third embodiment.
The on/off operation of ET26 is performed by photocoupler 5,
A transistor 28, a resistor 32, and a resistor 33 are used to turn off the FET 26 when an overcurrent occurs. That is, the gate of the FET 26 is connected to the photocoupler 5 and also to the terminal of a transistor 28 via a resistor 33, and the base of this transistor 28 is connected to the collector of the transistor 14 via a diode 29. shall be.

To explain the on/off operation of the FET 26 in FIG. 4, when the photocoupler 5 is turned on, the gate (G) of the FET 26 is connected to the negative terminal (-) via the secondary side of the photocoupler 5. The gate and source of the FET 26 are forward biased, and the FET 26 is turned on.

When the photocoupler 5 is turned off, the FET 26 is turned off because the gate (G) is connected to the positive terminal (+>) via the resistor 32 and has the same potential as the source (S).

Next, circuit operation during overcurrent protection will be explained.

When an overcurrent is detected and transistor I4 is turned on, transistor 28 is also turned on. When the transistor 28 is turned on, the potential of the gate (G) of the FET 26 is R2□: potential of the resistor 32 Rtff: potential of the resistor 33,: potential of the voltage source 6 V2: potential of the voltage source 7, where Rzz (Rzi By selecting , the gate potential becomes (v, +Vz >), which is the same potential as the source potential (or below the threshold for turning off the FET 26), and the FET26 turns off.
ET26 turns off. After that, normal protection operation will occur.

Note that the resistors 30 and 31, which are added in common in the third and fourth embodiments, are used to control the on-time of the FET 26 and the transistor 1.
This is to suppress the short circuit current that flows due to the difference in the off time of zero.

FIG. 5 shows a fifth embodiment of the present invention, in which a diode 100 is added to the circuit of FIG. 1 showing the first embodiment.

This diode 100 is connected to the IGBT 4 side of a resistor 11 that is a gate resistance and to the positive electrode side of a capacitor 20 that is a variable power source of a voltage limiting circuit.

When an overcurrent is detected, the transistor 14 becomes conductive and the voltage of the capacitor 20 is discharged through the resistor 18 and the transistor 14. According to this embodiment, the capacitor 20
Since the diode 100 becomes conductive at the same time as the voltage decreases, the gate-emitter voltage also decreases. Moreover, since the displacement current flows to the drive circuit side via the diode 100, the gate-emitter voltage is not charged. As a result, overcurrent protection is reliably performed.

Further, unless the transistor 14 is turned on, the capacitor voltage is the sum of the power supply voltage V and V□, so the forward bias voltage is not discharged through the diode 100 when the transistor 14 is turned on.

FIG. 6 shows a sixth embodiment of the present invention.

In FIG. 6, vS is a signal (referred to as an opening/closing command signal) that commands opening/closing of the IGBT 4.

As in the first to fifth embodiments, 6 is a voltage source for applying an on-gate voltage for forward biasing between the gate and the IGBT 4 through a forward biasing transistor 9;
is the IGBT4 via the reverse bias transistor 10.
14 is a transistor (referred to as an overcurrent detection transistor) for performing overcurrent detection control, and 45° and 44 are the forward bias This is a front stage transistor for controlling the bases of the reverse bias transistor 9 and the reverse bias transistor 10.

In this embodiment, it is determined that the voltage between the anode and the cathode when the IGBT 4 is turned on has increased to a predetermined voltage (such as the sum voltage of the Zener voltage of the Zener diode 13 and the base-emitter voltage of the overcurrent detection transistor 14). Then, the forward bias transistor 9 is rendered inoperable, and means for removing the application of the forward voltage (resistor 50, 51, 53, capacitor 20, Zener diode 13, transistor 45, 14, etc.) and at least the means are provided. The resistor is a resistor that becomes effective when the forward voltage is not applied through the gate and when the reverse voltage is not applied due to the inoperation of the reverse bias transistor 10, and is a resistance between the gate and cathode of the IGBT 4. A resistor 55 constituting a shunt is provided.

Next, the normal operation shown in FIG. 6 will be described. Opening/closing command signal■
When S becomes II HIT, the front stage transistor 44.4
A base current flows through the resistors 52 and 51 through the resistors 52 and 51, respectively, and the transistors 44 and 45 are turned on.As a result, around 11 the bias transistor 9 has its base current flowing through the resistor 53 and the transistor from the voltage sources 6 and 7. 45, the reverse bias transistor 10 is turned off. Therefore, the voltage source 6 for applying an on-gate voltage is applied between the gate of the IGBT 4 and the terminal via the resistor 11, and the GBT 4 is turned on.

At this time, a charging current flows through the capacitor 20 via the resistor 50, and the terminal voltage VC of the capacitor 20 gradually increases.
Eventually, the diode 15 turns on, and this capacitor terminal voltage VC becomes the off-gate voltage applying voltage source 7.
The voltage is clamped to the voltage obtained by adding the forward voltage drops of the IGBT 4 and the diode 15 to the voltage. However, depending on the capacitor terminal voltage VC in this state, the Zener diode 13
is not conductive and the overcurrent detection transistor 14 is in an off state.

Next, when the opening/closing command signal VS becomes eJ L FF, the front-stage transistors 44 and 45 are turned off, which turns off the forward bias transistor 9, and the reverse bias transistor IO is connected to the base of the voltage source 6 and 7 via the resistor 54. It turns on when current flows. Therefore, the reverse bias power supply 7 is applied between the gate and the gate of the GBT 4 via the resistor 11, and the IGBT 4 is turned off rapidly (for example, in about 1 μs).

At this time, the photoelectric charges in the capacitor 20 are discharged through the resistor 5o to the power supply side of the opening/closing command signal VS (to the left in FIG. 6).

Next, the operation will be described when the main circuit current (collector current) IC of the IGBT 4 abnormally increases due to a load short circuit in the main circuit or the like when the IGBT 4 is in the above-mentioned ON state. In this case, due to the increase in collector current IC,
IGBT4 forward voltage drop (collector-emitter voltage)
also increases.

As a result, the diode 15 switches to the OFF state, and the capacitor terminal voltage VC tries to gradually increase again from the normal clamp voltage to the lamp voltage, but in this embodiment, in the process of this gradual increase, the capacitor terminal voltage VC VC is set so as to reach the sum of the Zener voltage of the Zener diode I3 and the base-emitter voltage of the overcurrent detection transistor 14.

As a result, when the Zener diode 13 and therefore the overcurrent detection transistor 14 are turned on, the preceding stage transistor 45 is turned on.
is turned off, and thereby the forward bias transistor 9 is also turned off. At this time, the reverse bias transistor IO remains off, and the value of the resistor 55 is set to (gate) resistor 11.
Since the value is sufficiently large compared to the value of , the gate and emitter of the IGBT 4 are almost in a non-biased state. And I.G.
The charge stored between the gate and emitter of BT4 is resistor 1
1.55° and the time when the IGBT 4 is turned off by relatively lightly discharging through the off-gate voltage application voltage source 7 can be selected.

FIG. 7 shows a seventh embodiment, in which an oscillation prevention diode 56 is added to the charging circuit for the capacitor 20 in FIG.
is added. In this case, there is also a diode 5
7 is added so that when the IGBT 4 is off, that is, when the reverse bias transistor 1o is on, the charge in the capacitor 20 is discharged to this transistor IO via the diode 57, and this capacitor 2o is returned to its initial state.

FIG. 8 shows an eighth embodiment, in which the IGBT 4 side of the gate resistor 11 and the positive electrode side of the capacitor 20 are connected via a transistor 200 in the circuit shown in FIG. 1 of the first embodiment. Specifically, the emitter terminal of this transistor 200 and the gate resistor 11 were connected, and the base terminal was connected to the positive terminal of the capacitor 20.

In the circuit shown in FIG. 8, when an overcurrent is detected as in the conventional case, the transistor 14 becomes conductive. transistor 1
When 4 becomes conductive, the voltage on capacitor 20 is discharged through resistor 18 and transistor 14.

The voltage of this capacitor 20 is V of the transistor 200.
Since it is also llF (base-emitter voltage), when the voltage of the capacitor 20 is discharged, the VC of the transistor 200
■ than E (collector-emitter voltage). becomes lower, so the transistor 200 turns on.

When this transistor 200 becomes conductive, there is a voltage across the capacitor 20 between the gate and emitter of the IGBT4.
A difference of 2 will be applied through transistor 200. Moreover, since the displacement current flows through the transistor 200, the gate-emitter voltage is not charged.

As a result, the overcurrent protection operation will be performed reliably.

〔Effect of the invention〕

As described above, the drive circuit for the voltage-driven semiconductor device of the present invention suppresses the jump voltage when overcurrent is cut off in the event of a short circuit accident, reduces the energy consumption of the device, and protects the device from overcurrent. It is something that can be protected.

Furthermore, when an FET is used as a transistor for turning on an element among the output stage transistors, a predetermined gate voltage can be applied to the element, and the loss generated by the element can be reduced. Furthermore, the gate drive circuit can be shared regardless of the capacitance of the semiconductor element, and there is no need to increase the size.

Further, when the voltage-driven semiconductor element is turned on, it is determined that the collector-emitter voltage of the element has exceeded a predetermined voltage due to overcurrent, and the forward bias transistor is turned off.
The voltage-driven semiconductor device can be turned off relatively slowly by slowly discharging the accumulated charge between the gate and emitter through a discharge resistor while maintaining an almost unbiased state between the gate and emitter of the device. The current change (di/dt) in the main circuit of the drive type semiconductor element becomes small, and the voltage applied to the element can be made lower than the element breakdown voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a drive circuit for a voltage-driven semiconductor device of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the same, and FIG. 3 is a circuit diagram showing a third embodiment. 4 is a circuit diagram showing the fourth embodiment, FIG. 5 is a circuit diagram showing the fifth embodiment, FIG. 6 is a circuit diagram showing the sixth embodiment, and FIG. 7 is a circuit diagram showing the seventh embodiment. FIG. 8 is a circuit diagram showing the eighth embodiment,
Figure 9 is a circuit diagram simulating a short-circuit accident in a power converter, Figure 1O is a voltage and current waveform diagram of the same as above, Figure 11 is a circuit diagram showing a conventional example, and Figure 12 is a short-circuit current and gate-emitter voltage. Figure 13 is an equivalent circuit diagram of rGBT capacitance, Figure 14 is an equivalent circuit diagram of the switching process,
FIG. 15 is a voltage waveform diagram at the time of a short circuit, and FIG. 16 is an explanatory diagram of the state of the element at the time of a short circuit. 1...DC power supply 2...I GBT3...
- Wiring inductance 4...I GBT5...Photocoupler 6...Voltage source for applying on-gate voltage 7...Voltage source for applying off-gate voltage 8, 9.10, 14.23...Transistor 11.
12, 17. 18. 19, 22, 25...Resistance 13
...Zener diode 15.21, 24.29...Diode 16.20
... Capacitor 26 - FET 27.28 ... Transistor 30.31, 32.33 ... Resistor 44.45 ... Transistor 50.51, 52, 53, 54.55 ... Resistor 56 ．．
57...Diode 100...Diode 200...Transistor

Claims (6)

[Claims] (1) Protection that protects the device from overcurrent that occurs in the event of a short-circuit accident between the drive unit, which consists of at least a pair of output transistors that operate complementary to a photocoupler for signal isolation, and the voltage-driven semiconductor device to be driven. In a drive circuit for a voltage-driven semiconductor device, the protection unit monitors the voltage at the input-side main terminal of the voltage-driven semiconductor device when a drive signal is present, and detects whether this voltage exceeds a predetermined value. and a variable voltage source that gradually lowers the voltage over time while the detecting means is in operation, and this voltage source is connected between the variable voltage source and the base terminal of the output transistor. A drive circuit for a voltage-driven semiconductor device, characterized in that a diode is connected so that the base terminal side serves as an anode. (2) A drive section that includes at least a pair of output transistors that operate complementary to a photocoupler for signal isolation, and a voltage drive unit that monitors the voltage at the input side main terminal of the voltage-driven semiconductor element when a drive signal is present. , consists of a detection means for detecting that this voltage exceeds a predetermined value, and a variable voltage source that gradually lowers the voltage over time while this detection means is operating, and the drive signal is In some cases, the voltage at the main input terminal of the voltage-driven semiconductor element is monitored, and when the detection means detects that this voltage exceeds a predetermined value, the collector terminal of the transistor becomes conductive, and the signal isolation photocoupler A drive circuit for a voltage-driven semiconductor element, characterized in that a collector terminal is connected to a transistor side via a forward diode. (3) Protection that protects the device from overcurrent that occurs in the event of a short-circuit accident between the drive unit, which includes at least a pair of output transistors that operate in a complementary manner with a photocoupler for signal isolation, and the voltage-driven semiconductor device to be driven. In a drive circuit for a voltage-driven semiconductor device consisting of a pair of complementary output transistors of the drive section, an FET is used as the on-state transistor of the device, and a bipolar transistor is used as the off-state transistor. A drive circuit for a voltage-driven semiconductor device, characterized in that it uses a voltage-driven semiconductor device. (4) A drive unit that includes at least a pair of output transistors that operate complementary to a photocoupler for signal isolation, and a voltage drive unit that monitors the voltage at the input side main terminal of the voltage-driven semiconductor element when there is a drive signal. It consists of a detection means that detects when this voltage exceeds a predetermined value, and a protection section that consists of a variable voltage source that gradually lowers the voltage over time while the detection means is operating. A drive circuit for a voltage-driven semiconductor device, characterized in that a positive terminal of a capacitor serving as a variable voltage source constituting the protection section and a gate terminal of the voltage-driven semiconductor device are connected via a diode. (5) A pair of output transistors consisting of a forward bias transistor that applies a forward voltage between the gate and cathode of a voltage-driven semiconductor device to turn the device on, and a reverse bias transistor that turns the device off by applying a reverse voltage. a driving section comprising: a driving section; a detecting means for monitoring the voltage at the input side main terminal of the voltage-driven semiconductor element when a driving signal is present and detecting that this voltage exceeds a predetermined value; and the detecting means. a means for disabling the forward bias transistor and removing the application of the forward voltage upon detection of the forward bias transistor; 1. A drive circuit for a voltage-driven semiconductor device, comprising a resistor that is effective and forms a shunt between the gate and cathode of the voltage-driven semiconductor device. (6) A drive section that includes at least a pair of output transistors that operate in a complementary manner to a photocoupler for signal isolation, and a voltage drive unit that monitors the voltage at the input side main terminal of the voltage-driven semiconductor element when there is a drive signal. , a voltage-driven semiconductor consisting of a detection means for detecting that this voltage exceeds a predetermined value, and a variable voltage source that gradually lowers the voltage over time while the detection means is operating. 1. A drive circuit for a voltage-driven semiconductor device, characterized in that the variable voltage source and a gate terminal of the voltage-driven semiconductor device are connected via a transistor.