JPH01278256A - Gate driving circuit for gto thyristor - Google Patents

Abstract

PURPOSE:To prevent the switching element of an OFF gate current output circuit from damaging due to an overvoltage by constructing not to turn OFF the element even at the time of an output short-circuiting state. CONSTITUTION:The gate driving circuit 2 of a GTO thyristor 1 has a reverse bias voltage detector 18 of the thyristor 1, and is composed of an anti-parallel connection circuit of a photodiode of a photocoupler 16 and a series connecting circuit of a Zener diode 8 and a resistor 12. A pulse width comparator 20, a monostable circuit 19, and an OR circuit 22 are provided as comparing means. When an output (f) from the comparator 20 becomes H, the OR circuit 22 outputs to feed a gate signal to a FET 6. Accordingly, the FET 6 is not continuously turned ON to break the excess OFF gate current, and prevented from damaging due to an overvoltage. A FET 7 for breaking the input current from an OFF. gate power source 3' as a switch is turned OFF when the thyristor is malfunctioned, thereby preventing an overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gate drive circuit for a GTO thyristor (gate turn-off thyristor) as a semiconductor switching device used in an inverter or the like as a power conversion device.

[Conventional technology]

FIG. 4 is a circuit diagram showing an example of the connection between the GTO thyristor 1, its gate drive circuit 2, and gate power supply 3, and FIG. 5 shows an example of the waveforms of the output voltage Vg and output current ig of this gate drive circuit 2. Output current Ig++1gz and fg
s is the semiconductor switch SI+S in the gate drive circuit 2! +
and is output by closing s3.

Of these, fg+ and igz are on-gate currents for turning on GTO thyristor 1, and their peak values are limited by resistors R and R2. *1gz is the ON gate current for turning on GTO thyristor 1.
This is the off-gate current for turning off the gate of the O-thyristor 1, and R8 shown in FIG.
and the internal resistance of capacitor C2 and switch s3-
This is the sum of the wiring resistance of the closed loop of the capacitor C and the -GTO thyristor l, and this is a sufficiently small value compared to the resistance Rt and the resistance R5.

In addition, the reactors L and Lt are connected to a pulsed current i
t and g are the inductances of the gate lead wire of the GTO thyristor l.

Output voltage V1 of gate power supply 3. V2 and v3 are all DC, which is the power supply for 1g++1gg and ig.

FIG. 6 shows an equivalent circuit of the off-gate current output section of such a gate drive circuit 2, and FIG. 7 shows its operating waveforms.

Gate current ig, gate drive circuit output voltage Vg and GTO when the gate of GTO thyristor 1 is turned off
Assuming that the gate and cathode junction voltage of thyristor 1 is g', the gate current ig is after the accumulation time ts tgO determined by the element from the time when the off-gate current of the gate drive circuit 2 is output.
It is cut off by GTO thyristor 1.

At this time, the element generates a breakdown voltage V□ at the gate and cathode junctions, which becomes V□〉■, and this voltage difference is the inductance L
g is applied, the slope of ig is reversed, and ig eventually becomes zero.

[Problem to be solved by the invention]

However, in the above-described off-gate current output circuit, for example, element damage occurs, and when the gate drive circuit 2 is in an output short-circuit state, a problem arises in that the switching element S is destroyed by overvoltage. That is, when the equivalent circuit and gate current voltage waveform at this time are shown in FIGS. 8 and 9, the gate current ig is no longer cut off by the GTO thyristor as it was when GTO thyristor 1 is healthy, and the off-gate When the gate drive circuit inputs an off-gate voltage output stop command, that is, a command to turn off the semiconductor switch S and opens the semiconductor switch S in such a state, the value becomes an excessive value determined by the impedance of the current output circuit. ig is cut off by S and I, and the voltage Vs2 of S3 becomes an excessive value due to the inductance Lg, causing S to be destroyed by overvoltage.

An object of the present invention is to eliminate the disadvantages of the conventional example, and to provide a GT that does not damage the switching element of the off-gate current output circuit due to overvoltage even if the GTO thyristor is damaged and the output is short-circuited.
An object of the present invention is to provide a gate drive circuit for an O thyristor.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a detection circuit that detects the reverse bias voltage of the junction between the gate and cathode of the GTO thyristor, and a period from the start of off-gate current output until the detection means detects the reverse bias voltage. and a comparison means for comparing the time width with a set maximum accumulation time of the element, and when the period detected by the comparison result by the comparison means is longer than the set time, the semiconductor switch of the off-gate current output circuit is The gist of this is to keep it in the on state.

[Effect]

According to the present invention, the period from the off-gate current output to the detection of the reverse bias voltage of the gate-to-cathode junction of the GTO thyristor is compared with a preset maximum accumulation time of the element, and the maximum accumulation time is If the reverse bias voltage at the junction between the gate and cathode cannot be detected even after the period of Avoid doing this.

〔Example〕

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

FIG. 1 is a circuit diagram showing one embodiment of a gate drive circuit for a GTO thyristor according to the present invention, and shows a portion of an off-gate current output circuit corresponding to FIG. 6 showing the conventional example.

In this FIG. 1, a power MOS FET 6 is used as an equivalent to the switch 3 in FIG. 6, and a capacitor 4 corresponds to the capacitor C3 in FIG.

In the figure, 18 is a detection circuit for the reverse bias voltage of the junction between the gate and cathode of the GTO thyristor. It is connected between the gate and cathode of the thyristor 1, and the midpoint of the connection between the series-connected circuit of the phototransistor and the resistor 13 of the photocoupler 16 is used as an output terminal.

The series connection circuit ends (A), CB) are connected to the off-gate power supply 3.
' is connected to a circuit end consisting of a resistor 15, a diode 11, a Zener diode 9, and a capacitor 5,
If "H" is set to the (A) potential and "L" is set to the (B) potential for positive logic, the output of the output terminal becomes "H" when the detection circuit detects a reverse bias voltage.

In the figure, 20 is a pulse width comparator as comparison means, 19 is 5
Maximum accumulation time of GTO thyristor 1 from the time when off-gate output command a becomes H'' due to off tstg ma
This is a monoste that generates a pulse of Compare the period ts and tg until the output of the reverse bias voltage detection circuit between the gate and cathode becomes "H", which is the accumulation time of the element, and ts
When tg > tstg max, the output f
-t-Hold at "H".

A concrete example of how to do this is to perform a logical operation on the inputs a, b, and d of the pulse width comparator 20 as shown in FIGS. 2 and 3.

In the figure, F and F indicate flip-flops, and if e in the figure becomes "H" even once, f=F, F, (e) becomes
It is held at "H".

That is, as shown in FIG. 2, when the GTO thyristor 1 is healthy, since ts tg≦tstg wax, e never becomes H'' and r also never becomes H''. However, as shown in FIG. 3, if the GTO thyristor 1 is damaged (element failure), ta tg > ts
Since tg max, e becomes "Hl" for a certain period of time, and as a result, f maintains the "H" state.

In the figure, 22 is an OR circuit whose output side is connected to the gate of the power MOSFET 6 via a non-inverting buffer 21, and the OR circuit 22 receives the off-gate output command a and the output f from the pulse width comparator 20. is input.

As mentioned above, when the output f from the comparator 20 becomes H'',
Since the OR circuit 22 outputs an output and sends a gate signal to the power MO5FET6, the power MO8FET6 continues to be turned on, and the excessive off-gate current (drain current) as shown in FIG. 9 is no longer cut off, causing overvoltage damage to the device. can be prevented from

In the figure, 7 is a power MO3FET as a switch for cutting off the input current from the off-gate power supply 3'.

A transistor 23 was connected between the gate and drain of the power MO3FET 7, and the output of the pulse width comparator 20 was introduced to the gate of the transistor 23 via a resistor 24.

In this way, when a failure of GTO thyristor 1 is detected (f
- “H”) is the output of the pulse width comparator 20 and the power M
Since the OS FET 7 is turned off and the input terminal of the off-gate output circuit of the gate drive circuit 2 is cut off, overcurrent of the off-gate power supply 3' can be prevented.

In addition, since the power MOSFET 7 has an inductance Lt, if it is turned off immediately after the failure of the GTO thyristor 1, a large current will not be cut off.
It is better to set 7↓.

Furthermore, the output f of the pulse width comparator 20 can also be used to stop unnecessary operations of the on-gate circuit shown in FIG.

〔Effect of the invention〕

As described above, the gate drive circuit for the GTO thyristor of the present invention has a configuration that does not turn off the switching element of the off-gate current output circuit even if the GTO thyristor is damaged and the output is short-circuited. It is something that can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a gate drive circuit for a GTO thyristor according to the present invention, FIGS. The figure is a circuit diagram showing a connection example of the gate drive circuit of a GTO thyristor, Figure 5 is an output voltage and current waveform diagram of the drive circuit of Figure 4, Figure 6 is an off-gate current output circuit diagram, and Figure 7 is a diagram of a healthy GTO thyristor. FIG. 8 is an off-gate current output circuit diagram when the GTO thyristor is damaged, and FIG. 9 is an off-gate current and voltage waveform diagram when the GTO thyristor is damaged. 1...GTO thyristor 2...Gate drive circuit 3.
...Gate power supply 3'...Off gate power supply 4.5
... Capacitor 6.7 ... Power MO3FET 8.9 ... Zener diode 10, 11 ... Diode 12-15 ... Resistor 1
6... Photocoupler 17... Voltage clamp type snubber circuit 18... Gate-cathode junction reverse bias voltage detection circuit 19... Monostable circuit 20... Pulse width comparator 21... Non-inverting Buffer 22...O
R circuit 23...Transistor 24...Base resistance

Claims (1)

[Claims] A detection circuit that detects the reverse bias voltage of the junction between the gate and cathode of the GTO thyristor, a period from the start of off-gate current output until the detection means detects the reverse bias voltage, and a preset maximum accumulation time of the element. and a comparison means for comparing widths, and the semiconductor switch of the off-gate current output circuit is held in an on state when the period detected by the comparison result by the comparison means is longer than the set time. GTO thyristor gate drive circuit.