JPH0429558A - Gate drive circuit of voltage driven type semi-conductor element - Google Patents

Abstract

PURPOSE:To reduce a loss (at the time of ON) in a regular time while minimizing a sharp rise of a main circuit voltage at the time of switching, by providing a means of making the absolute value of a gate voltage of a semiconductor element rather low at the time of turn-OFF of the element and increasing this absolute value of the gate voltage gradually when the element turns in an OFF state and a means of increasing the absolute value of the gate voltage gradually at the time of turn-OFF. CONSTITUTION:When a signal input 01 changes from an OFF instruction over to an ON instruction, a reverse bias switch 3-2 turns OFF and a forward bias switch 3-1 turns ON. In this initial state, an equivalent capacity CS being parasitic between a gate G and an emitter E of a voltage driven type semiconductor element 6 is charged with electricity of a voltage -E2. Besides, a voltage E1 of a forward bias power source 1 is impressed between the gate G and the emitter E of the voltage driven type semiconductor element 6. In this case, a gate voltage VGE rises at the initial value -E2, a final achievable target value E1 - VZD1 and a time constant CS XRG. Thereafter, the gate voltage VGE increases, a charging current of the equivalent capacity CS decreases, a Zener diode ZD 1 is thereby put in an OFF state, and the gate voltage rises gradually at a final achievable value E1 and a time constant CS X(RG + R1).

Description

[Detailed description of the invention] [Industrial application field]

This invention is a circuit that drives the gate of a voltage-driven semiconductor element such as I(1, BT, FET, etc.) for switching (turn-on, turn-off) this semiconductor element, and in particular suppresses the rise in main circuit voltage during this switching. The present invention also relates to a gate drive circuit for a voltage-driven semiconductor device that is capable of increasing the on/off stability of the semiconductor device during steady state.The same reference numerals in the following figures indicate the same or corresponding parts.

[Conventional technology]

FIG. 3 shows a conventional gate drive circuit for a voltage-driven semiconductor device. In the same figure, when an on/off command 01 to the voltage-driven semiconductor element 6 is inputted to the logic operation circuit 5 from the outside, the logic operation circuit 5 insulates and amplifies the signal input 01, On/off signal 5a
Communicate as. In the case of an on command, the forward bias switch 3-1 in the forward/reverse changeover switch 3 is turned on, and the voltage E1 of the forward bias power supply 1 is applied to the gate (G) and emitter of the voltage-driven semiconductor element 6 via the gate resistor RG. It is applied as a forward bias voltage between E and E. On the other hand, in the case of an off command, the reverse bias switch 3-2 in the forward/reverse changeover switch 3 is turned on, and the voltage E2 of the reverse bias power supply 2 is applied to the gate G and emitter E of the voltage-driven semiconductor element 6 via the gate resistor RG. Reverse bias voltage between −E2
Join as. However, in the above operation, the logic operation circuit 5 controls so that the forward bias switch 3-1 and the reverse bias switch 3-2 are turned on at the same time and the forward bias power source El and the reverse bias power source E2 are not short-circuited. FIG. 4 shows an example of the gate voltage waveform of the semiconductor element 6 in the circuit of FIG. 3. However, this voltage-controlled semiconductor element 6 is an element that turns on when the gate voltage VGt is a positive voltage. When the signal 01 to the logic operation circuit 5 is turned on, the forward/reverse changeover switch 3 changes the gate voltages v and t to -
Switching from E2 to El, the voltage controlled semiconductor element 6
turns on. However, due to the gate resistance RG and the equivalent capacitance C3 between the gate G and emitter E of the voltage-controlled semiconductor element 6, the gate voltage V
GE switches with a certain time constant. When the signal input 01 becomes an off command, the gate voltage vGx similarly switches from El to -E2 with a certain time constant, and the voltage-controlled semiconductor element 6 turns off.

[Problem to be Solved by the Invention 8] However, in the gate drive circuit shown in FIG. 3, the forward bias power supply voltage El and the reverse bias power supply voltage -E2 are fixed,
When this gate voltage is increased, the voltage-driven semiconductor element becomes less susceptible to disturbances such as noise during steady state, and its on-state and
The stability of the off-state operating state increases and the switching speed increases, but on the other hand, when the switching speed is high, the voltage jump due to the wiring inductance of the main circuit increases (and may exceed the absolute maximum rated voltage of the element). This is because at turn-off, due to the wiring inductance from the power supply to the voltage-controlled semiconductor element, the current decreases, and the energy of this wiring inductance causes a voltage jump; on the other hand, at turn-on, In the case of a bridge-connected inverter circuit, etc., when a flywheel mode current is flowing through the diode in the opposing arm, when the voltage-controlled semiconductor element turns on, the current is commutated to the turned-on element, and the reverse flow of the diode in the opposing arm occurs. This is because a voltage jump occurs during recovery.Also, if the gate resistance RG is increased, the switching speed will be slowed down, and the voltage jump due to the wiring inductance of the main circuit will be reduced, but due to the effect of slowing the switching speed. This has the adverse effect of increasing switching loss.An object of the present invention is therefore to provide a gate drive circuit for a voltage-driven semiconductor element that can solve this problem.

[Means for Solving the Problems] In order to solve the above problems, the circuit of the present invention is a circuit for driving the gate of a voltage-driven semiconductor element that turns on and off depending on two polarities of the r gate voltage. , means for lowering the absolute value of the gate voltage when the semiconductor element is turned off, and gradually increasing the absolute value of the gate voltage when the semiconductor element enters a steady OFF state (Zena diode ZD2, resistor R2, etc.); and a means (Zena diode ZDI, resistor R1, etc.) that lowers the absolute value of the gate voltage when the semiconductor element is turned on, and gradually increases the absolute value of the gate voltage when the semiconductor element enters a steady on state. Let J with . [Operation] FIG. 2 is a waveform diagram of the gate voltage V applied to the voltage-driven semiconductor element according to the present invention. When the signal power 01 switches from the off command to the on command, the gate voltage ■1 rises with a certain time constant τ1, aiming at a value smaller than the final gate voltage E1 (1/2E in FIG. 2). Thereafter, the gate voltage increases from 1/2E before and after turn-on is completed, again with a time constant τ2 (τ,>τI) aiming at El. As a result, the turn-on time is not too fast during turn-on, so the voltage jump is kept within the optimum value, and the high gate voltage during steady-on operation provides a stable on state that is resistant to external disturbances and a low voltage drive type semiconductor device. Saturation voltage (low loss) can be obtained. Similarly, when the signal human power 01 switches from an on command to an off command, the gate voltage VGE has a certain time constant τ. A value whose absolute value is smaller than the final reached gate voltage -E2 at (
In Fig. 2, the target is -t/2Ez). After that, E2 again from 1 1/2 EZ before and after the turn-off is completed.
The absolute value of the gate voltage increases with a certain time constant τ4 (τ4>τ3). As a result, at turn-off, the turn-off time is not too fast, so the voltage jump is within the optimum value, and at steady-state off, the gate voltage has a sufficiently large absolute value, so voltage-driven semiconductor devices can maintain a stable off-state that is resistant to external disturbances. Become.

【Example】

FIG. 1 is a circuit diagram as an embodiment of the present invention, and corresponds to FIG. 3. In FIG. 1, in contrast to FIG. 3, a resistor R1 is inserted in series with the forward bias switch 3-1,
Furthermore, a Zener diode ZDI is connected in parallel with this resistor R1 and has a polarity that blocks the forward bias power supply 1. Similarly, a resistor R2 is inserted in series with the reverse bias switch 3-2, and a Zener diode ZD2 is connected in parallel with the resistor R2 and has a polarity that blocks the reverse bias power supply 2. When the signal 01 given to the logic operation circuit 5 switches from the off command to the on command, the reverse bias switch 3
-2 is turned off, and the forward bias switch 31 is turned on. In this initial state, the equivalent capacitance C5 parasitic between the gate G and emitter E of the voltage-driven semiconductor element 6 is charged to a voltage of -E2. Furthermore, the Zener voltage v2DI of the Zener diode ZDI is set to a lower voltage value than the forward bias power supply voltage E. Therefore, the Zener diode ZDI is initially turned on, and the voltage E of the forward bias power supply 1 is changed to the forward bias switch 3-1. Zener diode ZD1. Passing through the gate resistor R, the gate G and emitter E of the voltage-driven semiconductor element 6
applied in between. In this case, the gate voltage vex is the initial value -E2. Final target value E, -V, □9 time constant c, X
It rises at Re (that is, with a rise time that is not too fast). After that, the gate voltage (2) increases, the charging current of the equivalent capacitance C3 decreases, and when the voltage drop across the resistor R1 due to this charging current becomes less than the Zener voltage (2), the Zener diode ZDI turns off. state, and the gate voltage ■1
is the final reached value Elf time constant C8x (RG + Rυ). On the other hand, when the signal human power 01 switches from the on command to the off command, the forward bias switch 3-1 is turned off and the reverse bias is turned off. The switch 3-2 is turned on, and the equivalent capacitance C5 is reversely charged.In this case, since the Zener voltage v2□ of the Zener diode ZD2 is set to a voltage value lower than the voltage E2 of the reverse bias power supply 2, the Zener voltage V2□ is initially Diode ZD
2 turns on, the gate voltage ■G becomes the initial value E
1. Final reached value - (E2 - V2D,), time constant Cs
Rc T: falls (with a falling time that is not too fast), then when Zener diode ZD2 turns off,
Gate voltage ■1 is the final reached value -E2. time constant c s x
It slowly descends at (RG+R,). In this way, suitable EI + EIV2DI + VZ11Z
If the value of +R1+R2,R, is selected, the time chart shown in FIG. 2 will be obtained.

【Effect of the invention】

According to the present invention, the absolute value of the gate voltage is made low without increasing the rise (fall) time of the gate voltage during switching, and the gate voltage is changed higher than before and after the completion of switching. By simply adding a few components to the circuit, it is possible to minimize the rise in main circuit voltage during switching, reduce the loss (when on) of voltage-driven semiconductor elements in steady state, and provide a gate drive that is resistant to external disturbances. The circuit can be realized.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram as an embodiment of the present invention, FIG. 2 is a gate voltage time chart based on FIG. 1, FIG. 3 is a conventional circuit diagram corresponding to FIG. 1, and FIG. Third
5 is a time chart showing an example of gate voltage based on the figure. 01: Signal input, 1: Forward bias power supply, 2: Reverse bias source, 3: Forward/reverse changeover switch, 3-1: Forward bias switch, 3-2 two reverse bias switches, RG: Gate resistance, 5: Logic operation circuit, 6: Voltage driven semiconductor element, ZDI, ZD2: Zener diode, R1, R2:
Resistance, C5: equivalent capacitance. Figure 3 Figure 4

Claims (1)

[Claims] 1) In a circuit that drives the gate of a voltage-driven semiconductor element that turns on and off depending on two polarities of the gate voltage, the absolute value of the gate voltage is set to a low level when the semiconductor element is turned off. means for gradually increasing the absolute value of the gate voltage when the semiconductor element enters a steady OFF state, and a means for lowering the absolute value of the gate voltage when the semiconductor element is turned on, so that the semiconductor element enters a steady ON state. 1. A gate drive circuit for a voltage-driven semiconductor device, comprising means for gradually increasing the absolute value of the gate voltage when the gate voltage enters a state.