JPH0317480Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a gate circuit for a GTO that supplies gate signals for turning on and turning off the GTO.

GTO turns on when gate forward current flows,
It is a switching element with a self-extinguishing ability that turns off when a reverse current is applied, and its switching characteristics are closely related to the gate current. As shown in Figure 1, the gate current initially has a large peak value.
I _GP and then a constant value (minimum ignition gate current)
There is an on-gate current I _G that holds I _GT for a certain period of time, and an off-gate current I _GQ that has a large current rise rate. This ensures stable operation even under loads with lagging or leading power factors. Note that during turn-off, it is necessary to apply a reverse bias voltage to prevent re-ignition after turn-off.

Conventionally, the gate circuit that supplies the gate current and gate voltage as described above is a circuit as shown in Figure 2, that is, the forward current (on-gate current) I _G is passed from the on-power supply 1 to the GTO 3 via the switch 2, etc. The configuration is such that a reverse current (off-gate current) I _GQ is supplied from the off-power supply 4 to the GTO 3 via a switch 5 or the like. As the switches 2 and 5, transistors are usually used.

The on-gate current I _G is when the switch (transistor) 5 is in the off state.
When 2 turns on, the on power supply 1 to transistor 2
It flows through the path of ~gate of GTO3~cathode electrode of GTO3~power supply 1. Also, the off-gate current I _GQ
When transistor 2 is turned off and transistor 5 is turned on, the off power supply 4 ~ the cathode electrode of GTO 3 ~ the gate electrode of GTO 3 ~ the transistor 5 ~
It flows through the path of power supply 4.

In this way, by alternately turning on and off switches (transistors) 2 and 5, the on-gate current
I _G and off-gate current I _GQ are supplied, and GTO3 operates normally.

However, in the circuit shown in FIG. 2, transistor 5 as an OFF switch may be turned on before transistor 2 is completely turned off due to its carrier accumulation effect. In this case, a short circuit current flows in the path from the on power supply 1 to the transistor 2 to the transistor 5 to the off power supply 4 to the on power supply 1, and the transistors 2 and 5 may be destroyed.

This invention was made taking the above points into consideration.
A high-speed recovery diode is inserted in the on-gate current supply path, and a photodiode is connected between both ends of the diode.
By connecting the light emitting part of the photo coupler and using the output of this photo coupler as a control signal for the off switching element, the GTO can reliably prevent the off switching element from turning on while the on switching element is in the on state. The purpose is to provide gate circuits.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 3 shows an embodiment of the present invention, in which the basic circuit supplies an on-gate current from an on-power supply 1 to a GTO 3 via a transistor 2, and supplies an off-gate current from an off-power supply 4 via a transistor 5. The configuration is the same as the conventional one (Fig. 2), but in this embodiment, the on-gate current (forward current) supply path,
For example, one or more high-speed recovery diodes 6 are inserted between the transistor 2 and the GTO 3 (if more than one is connected in series), and the light emitting part of the photocoupler 7 is connected between both ends of this diode 6. . An inverter (inverting amplifier) 8 is connected to the output side of the photo coupler 7, and a control signal for the transistor 5 is obtained at its output terminal.

Next, the operation will be described. When the ON transistor 2 is in operation, a forward voltage drop occurs across the diode 6, and this voltage
is applied to coupler 7, and photo coupler 7 is in the on state. The output of the photo coupler is inverter 8
The control signal is at the transistor non-drive level, and the off transistor 5 is in the off state.

In this state, when the base signal _S1 of the on-gate transistor 2 is eliminated as shown in FIG. 4a, the on-gate current decreases rapidly, and when the transistor 2 is completely turned off, the photocoupler 7 The input voltage ν becomes zero, and the photo coupler 7 is turned off. As a result, the output of the inverter 8 becomes at the transistor driving level, and is applied to the transistor 5 as the transistor base signal _S2 as shown in FIG. 4c, so that the transistor 5 is turned on. That is, after the on transistor 2 is turned off, the off-gate current is supplied to the GTO 3 through t _S , and the GTO 3 is turned off.

In the above embodiment, an inverter 8 is provided on the output side of the photo coupler 7, but when the photo coupler is used as a buffer, an inverter for inverting the level (polarity) of the signal becomes unnecessary.

As described above, according to the present invention, a high-speed recovery diode is inserted in the on-gate current supply path,
Since the photo coupler is driven by the voltage drop to control the base of the off transistor, the off transistor is turned on after the on transistor is completely turned off, which reduces short-circuit current due to overlapping operation. This reliably prevents generation and destruction of transistors, thereby improving operational reliability.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram of the GTO gate current, Fig. 2 is a circuit diagram showing a conventional example of a GTO gate circuit, Fig. 3 is a circuit diagram showing an embodiment of the present invention, Figs. 4 a, b, c is a time chart for explaining the operation of the same embodiment. 1...On power supply, 2...On switch (transistor), 3...GTO, 4...Off power supply, 5...
...off switch (transistor), 6...high-speed recovery diode, 7...photo coupler,
8...Inverter.

Claims (1)

[Scope of utility model registration request] In the gate circuit that supplies the on-gate current from the gate-on power supply to the GTO via the on-switching element, and the off-gate current from the gate-off power supply to the GTO via the off switching element, one or more high-speed recovery diodes are installed in the on-gate current supply path. A gate circuit for a GTO, characterized in that a light emitting part of a photocoupler is connected between both ends of the diode, and the output of the photocoupler is used as a control signal for the off switching element.