JPS582153Y2 - Gate control circuit of gate turn-off thyristor - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a gate control circuit for a gate turn-off thyristor.

As is well-known, gate turn-off silicon (hereinafter referred to as GTO silicon) is a semiconductor that has the property of becoming conductive when a positive gate control signal is applied between the gate terminal G and the cathode, and non-conductive when a negative gate control signal is applied between the gate terminal G and the cathode. It is element.

To change the GTO thyristor from a conductive state to a non-conductive state, apply a negative gate current of about 1/2 to 1/4 of the main circuit current Ia flowing between the anode and cathode of the G'ID thyristor by several tens of tens of times. It is necessary to flow between usec, but GT
When the O thyristor begins to recover its forward voltage blocking characteristics, the impedance between the gate terminal G and the cathode terminal increases.

When the impedance between the terminal G- and the terminal G- increases, a negative overvoltage is generated between the terminal G- and the negative gate current that is 1/2 to 1/4 of the main circuit current as described above.

The GTO will be destroyed if the negative voltage applied to the terminal G- is not suppressed to a few volts or less.

In order to suppress the negative overvoltage, as shown in FIG.
There is one in which a series circuit of a diode 12 and a constant voltage diode 13 is connected between the gate terminal G and the cathode terminal of the thyristor 11.

This series circuit includes a series circuit of the gate power supply E1 with the polarity shown - an OFF switch OFF - 8W, and an ON switch ON.
-8W- Gate power supply E2 (inserted with opposite polarity to the gate power supply E1.

) are connected in parallel.

In this circuit, when the ON switch 0n-8W is turned on, a positive gate current flows between the gate terminal G and the cathode terminal of the GTO thyristor 11.
1 is turned on, and conversely, when the off switch OFF-8W is turned on, it is turned off.

However, the main circuit current flowing through the GTO thyristor 11 is on the order of several 100 to 100 OA, and the negative gate current is on the order of several 10 OA.

Therefore, when a circuit having the configuration as shown in Fig. 1 is used in a high frequency circuit such as an inverter circuit, a negative gate current of several tens of OA as described above is generated in the constant voltage diode 13 for each turn-off operation of each GTO thyristor for several seconds to several tens of us.
This causes problems such as the current width being shunted between ec and the width of the shunted current changing between light and heavy loads.

In other words, the configuration of the conventional gate control circuit for GTO Cyrisk has the following drawbacks during turn-off operation.

(1) A protection element such as a constant voltage diode 13 is inserted between terminals G- to keep the voltage below a predetermined negative voltage.
When the capacity of the thyristor 11 increases, the rating of the protection element also becomes excessive, making its design difficult.

(2) The negative gate current flowing through the protection element is more current than necessary for the actual turn-off operation, resulting in a loss.

This invention was devised to eliminate such drawbacks, and the purpose is to provide a control circuit for gate turn-off risks that can reduce the rating of the protection element and effectively utilize the energy left over from the turn-off operation. .

An embodiment of this invention will be described below with reference to FIG.

A series circuit including a diode 12 and a constant voltage diode 13 is connected between the gate terminal G and the cathode terminal of the GTO thyristor 11.

A capacitor 14 is connected to the cathode side of this diode 13, and this capacitor 14 and the voltage regulator diode 13
Resistor 15 - semiconductor switch 16 - resistor 17 between
series circuit is connected.

One end of a resistor 18 and a diode 19 are connected to the connection point between the resistor 17 and the semiconductor switch 16, respectively, and the other end of the resistor 18 is connected to the connection point between the diode 12 and the voltage regulator diode 13. The other end of 19 is connected to resistor 17.

A collector of a transistor 20 is connected to the resistor 15, an emitter of the transistor 20 is connected to the resistor 17, and a base thereof is connected to a connection point between the semiconductor switch 16 and the resistor 17.

A series circuit of a resistor 21 and a semiconductor switch 22 and a gate power supply 23 are connected in series to the transistor 20, respectively.

One end of a semiconductor switch 24 is connected to the connection point between the gate power supply 23 and the semiconductor switch 22, and the base of a transistor 26 is connected to the other end via a resistor 25, and the emitter of the transistor 26 is connected to the emitter of the transistor 20. The collector of the transistor 26 is connected to the collector of the transistor 20 via an impedance element 27.

In such a configuration, the GTO thyristor 11
To conduct, the semiconductor switch 22 is turned on at time t1 as shown in FIG.
2-Resistor 21-Capacitor 14-GTO Cyrisk 1
1- A positive gate current is caused to flow in the loop of the gate power supply 23 to turn on the GTO thyristor 11.

Since the GTO thyristor 11 maintains a conductive state when a main circuit current greater than the holding current flows, the semiconductor switch 22 opens after a predetermined time.

At this time, the capacitor 14 that has been charged to the polarity shown is stopped.

To make the GTO thyristor 11 non-conductive, turn on the semiconductor switch 16 at time t2 as shown in FIG.
A negative gate current is applied in the loop by discharging the charge in the capacitor 14.

At this time, the semiconductor switch 24 is turned on at time t2 and turned off at t4 as shown in FIG. 3 so that the conduction period of the transistor 26 and the transistor 20 overlap, and the semiconductor switch 16 is turned on at time t2 as shown in FIG. and time t3
to turn it off.

Therefore, transistors 26 and 20 are both conductive between times 12-13.

In this way, by passing a negative gate current, the GTO thyristor 1
1 turns off and begins to recover the forward voltage blocking characteristic, the negative polarity voltage between the gate terminal G and the cathode terminal increases. The series circuit with GTO
When the voltage between the gate terminal G and cathode terminal of the thyristor 11 reaches a predetermined voltage, the potential at the connection point a between the diode 12 and the constant voltage diode 13 is established, and the resistors 18 and 15 are connected to the base of the transistor 20. A negative bias voltage is applied by the bias of , and the transistor 20 becomes non-conductive.

At this time, since the semiconductor switch 24 is in the on state and the conduction periods of the transistors 20 and 26 overlap as described above, the discharge current of the capacitor 14 is
It flows as a negative gate current in the impedance element 27-transistor 26-〇TO thyristor 11-capacitor 14 loop.

The negative gate current flowing at this time is the impedance element 2
7 and continues to flow for a long time, but GTO thyristor 1
1 has a small dv/dt tolerance in steady state as is well known;
In order to improve this, good characteristics can be obtained by flowing a negative gate current in a steady state, so the charging current of the capacitor 14, which is the surplus energy of turn-off, is used to increase the dv/dt withstand capacity of the GTO thyristor 11. be done.

Thereafter, when the semiconductor switch 22 is turned on again to make the GTO thyristor 11 conductive, the semiconductor switch 22 is operated so that the transistor 26 is turned off.

In this way, when the GTO thyristor 11 is turned off, it is determined that the voltage between the gate terminal G and the cathode terminal has reached a predetermined value. The transistor 20, which is detected by the detector and which flows a negative gate current when a predetermined voltage is reached, becomes non-conductive. No current flows.

Further, when the transistor 20 is non-conductive, the negative gate current is commutated and flows in a loop limited by the impedance element 2T, so a constant voltage diode is connected to the terminal G- of the GTO thyristor 11 to suppress the voltage between the terminals and the terminal G to a predetermined negative voltage or higher. 13
The dv/dt withstand capability is improved by suppressing the current flowing through the gate and continuing to flow the above-mentioned negative gate current.

Therefore, according to this invention, the rating of the protection element that suppresses the voltage between the gate and cathode of the GTO SIRISK to a predetermined value can be significantly reduced in the large-capacity GTO SIRISK.
Excess energy from Cyrisk's turn-off is converted into dv/
Since it can be used to improve dt tolerance, it is possible to provide an economical and compact gate control circuit with little loss.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a gate control circuit for a conventional gate turn-off switch, FIG. 2 is a circuit diagram showing an example of a gate control circuit for a gate turn-off switch according to this invention, and FIG. 3 is a circuit diagram showing the same example. 5 is a time chart for explaining the operation of the semiconductor switch of the embodiment. 11...Gate turn-off sirisk, 12.
19...Diode, 13...Protective element such as constant voltage diode, 14...Capacitor, 16.22°24...Semiconductor switch, 2
0.26...Transistor, 23...
Gate power supply, 27... impedance element.

Claims (1)

[Scope of utility model registration request] Detection that detects when the negative voltage generated between the gate terminal and the cathode terminal reaches a predetermined value at the time of gate turn-off in a gate turn-off circuit in which a protection element such as a constant voltage diode is connected between the gate terminal and the cathode terminal. a first circuit whose closed circuit impedance has a large value and is connected in parallel within the loop through which the negative gate current of the gate turn-off circuit flows;
switch and a second switch with a lower impedance value.
Among the switches, the gate turn-off is characterized in that when the detection output of the detection means exceeds a predetermined value, the second switch is opened and the first switch is closed to reduce the negative gate current. Thyristor gate control circuit.