JPH05260723A - Gate circuit for thyristor - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a thyristor gate circuit which has a simple structure and which can prevent or reduce a forward gate current flowing at the time of reverse recovery of a main thyristor. A gate power supply unit having a main switching element 1 for controlling a gate current supplied to a main thyristor 7 and a current limiting resistor 2 and a pulse transformer 3 for insulating the main thyristor 7 from each other are provided. A reverse gate current prevention diode 4 for preventing a reverse current from flowing from the gate between the pulse transformer 3 and the gate of the main thyristor 7, and an excitation prevention diode 4 connected in antiparallel to the secondary side of the pulse transformer 3. In the gate circuit of the thyristor equipped with, the gate current supply path between the gate of the main thyristor 7 and the pulse transformer 3 is normally kept in the ON state and turned off in synchronization with the reverse recovery when the main thyristor 7 is reversely recovered. The switching element 5 for preventing the gate current is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thyristor gate circuit which suppresses a forward gate current flowing when a thyristor is reversely recovered and used.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional thyristor gate circuit similar to, for example, Japanese Utility Model Laid-Open No. 56-129188. In the figure, 1 is a main switching transistor of a gate circuit,
Reference numeral 2 is a current limiting resistor, 3 is a pulse transformer, 4 is an anti-excitation diode connected in antiparallel to the secondary side of the pulse transformer 3, 6 is a reverse gate current prevention diode, and 7 is a main thyristor.

Next, the operation will be described. The main switching transistor 1 of the gate circuit is turned on, and a current determined by the power source limiting resistor 2 is made to flow from the gate power source Eg to the primary side of the pulse transformer 3. As a result, the gate current flows from the secondary side of the pulse transformer 3 through the reverse gate current prevention diode 6 to the main thyristor 7. As a result, the voltage between the anode and cathode of the main thyristor 7 becomes
When positive (when the anode side has a high potential), the main thyristor 7 is turned on by this gate current.

Here, the pulse transformer 3 insulates the main thyristor 7 from the gate power source section and has an effect of preventing noise, and the diode 6 serves as the main thyristor 7.
A reverse current is prevented from flowing from the gate of the above-mentioned gate. Further, the excitation prevention diode 4 is normally connected to the pulse transformer 3 and has a role of preventing direct-current excitation of the pulse transformer.

[0005]

Since the gate circuit of the conventional thyristor is configured as described above, when the main thyristor 7 reversely recovers and a reverse current flows, the order shown by the dotted line in FIG. Directional gate current i _A flows. This is because the reverse recovery current of the thyristor 7 is divided into a current i _A to the gate circuit portion and a current i _B from the cathode of the thyristor 7 to the anode thereof.

The peak value I _G2 of the forward gate current generated during the reverse recovery is mainly determined by the peak value of the reverse recovery current, and when the reverse recovery current flows, for example, 700 to 800 amperes, the characteristics of the diodes 4 and 6 are determined. It depends, but 10A
It flows to some extent. An example of the measured value is shown in FIG.

Therefore, the value of I _G2 exceeds the specified value of the peak gate forward current specified by the thyristor,
In the worst case, the gate of the thyristor is destroyed. Further, this forward gate current flows when the anode-cathode voltage of the main thyristor 7 is negative (when the cathode side is at a high potential), and thus becomes a charging current to the junction that is reversely recovered, and this is the This leads to a local increase in leakage current, and in particular, when a high voltage is applied in the reverse direction, there is a problem that the element is destroyed in the worst case.

On the other hand, for example, Japanese Unexamined Patent Publication No. 52-116160 discloses a gate cutoff structure at the time of reverse voltage. However, the gate cutoff structure gives a wide pulse signal as a gate signal. It was built in the arc device to have both the wide pulse function of the gate signal and the gate cutoff function at the time of reverse voltage, and the circuit configuration was complicated.

The present invention has been made in order to solve the above problems, and has a simple structure, which can prevent or reduce the forward gate current flowing at the time of reverse recovery of the main thyristor. Aim to get the circuit.

[0010]

According to claim 1 of the present invention
The gate circuit of the thyristor that supplies the main thyristor
Main switching element for controlling gate current and current limit
Gate power supply unit with a resistor for use, the main thyristor and the gate
And a pulse transformer that insulates it from the power supply
The gate is between the transformer and the gate of the main thyristor.
Reverse gate current prevention die to prevent reverse current flow
Connect the anti-parallel to the secondary side of the pulse transformer
Of a thyristor with a diode for preventing excitation
In the circuit, the gate of the main thyristor and the pulse
Always on in the gate current supply path to the transformer
Hold and synchronize with the reverse recovery during the reverse recovery of the main thyristor.
Switching element for gate current prevention that turns off
It is provided.

A thyristor gate circuit according to a second aspect is the thyristor gate circuit according to the first aspect, further comprising a parallel connection body of a resistor and a switch, instead of the gate current preventing switching element. The resistor is input to the gate current supply path in synchronization with the reverse recovery of the above.

[0012]

In the gate circuit of the thyristor according to the first aspect of the present invention, the forward gate current flowing when the main thyristor reversely recovers is prevented by the gate current preventing switching element. Prevent the destruction of the main thyristor.

Further, in the gate circuit of the thyristor according to a second aspect of the invention, the resistor and the parallel connection body of the switch provided in place of the switching element for preventing the gate current are synchronized with each other in reverse recovery of the main thyristor. Is supplied to the gate current supply path, the forward gate current flowing at the time of reverse recovery is reduced.

[0014]

EXAMPLES Example 1. Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 1-4, 6 and 7 are the same as the conventional device. Reference numeral 5 denotes a phototransistor which is normally in the on state and which is in the off state in synchronization with the reverse recovery of the main thyristor 7 to prevent the forward gate current flowing during the reverse recovery.

In the gate circuit configured as described above, the phototransistor 5 is previously turned on before the start time t ₁ of the turn-on gate current of the main thyristor 7 shown in FIG. Thereby, when the main switching transistor 1 of the gate circuit is turned on, a gate current flows through the main thyristor 7.

Due to this gate current, a forward current flows in the main thyristor 7. Next, the time t _{2 at} which the main current of the main thyristor 7 changes direction from the forward direction to the reverse direction is detected,
In synchronization with this, the phototransistor 5 is turned off immediately after t ₂ to prevent the forward gate current flowing during reverse recovery.

Embodiment 2. Although the phototransistor 5 is inserted in the first embodiment, a parallel connection body of the gate current reducing resistor 8 and the switch 9 may be inserted instead, as shown in FIG. In this case, the switch 9 turns on the resistor 8 in the gate current supply path in synchronization with the reverse recovery of the main thyristor, thereby reducing the forward gate current flowing during the reverse recovery.

In the second embodiment, the switch 9
May be removed. In that case, a circuit for synchronizing the phototransistor 5 as shown in FIG. 1 is not required, but the gate power supply voltage Eg is increased to increase the current limiting resistor 2
Must be adjusted so that the peak value I _G1 (see FIG. 4) of the turn-on gate current required for the main thyristor 7 can be obtained even if the resistor 8 is adjusted.

[0019]

As described above, according to the first aspect of the present invention, by inserting the switching element for preventing the gate current, the forward gate current flowing when the main thyristor reversely recovers with a simple circuit configuration. Can be prevented and damage to the main thyristor due to this gate current can be prevented.

According to a second aspect of the present invention, a resistor is inserted in place of the gate current preventing switching element, and similarly, the forward gate current flowing when the main thyristor reversely recovers can be reduced. The same effect can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a thyristor gate circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a gate circuit of a thyristor showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a gate circuit of a conventional thyristor.

FIG. 4 is an operation waveform diagram of each part of FIG.

FIG. 5 is a characteristic diagram showing a relationship example between a peak value I _G2 of a forward gate current and a reverse recovery current.

[Explanation of symbols]

 1 Gate Circuit Main Switching Transistor 2 Current Limiting Resistor 3 Pulse Transformer 4 Excitation Preventing Diode 5 Gate Current Preventing Phototransistor 6 Reverse Gate Current Preventing Diode 7 Main Thyristor 8 Gate Current Reduction Resistor

Claims (2)

[Claims] 1. A gate power source section having a main switching element for controlling a gate current supplied to the main thyristor and a current limiting resistor, a pulse transformer for insulating between the main thyristor and the gate power source section, and this pulse. A gate of a thyristor including a reverse gate current prevention diode that prevents a reverse current from flowing from the gate between the transformer and the gate of the main thyristor, and an excitation prevention diode that is connected in antiparallel to the secondary side of the pulse transformer. In the circuit
In the gate current supply path between the gate of the main thyristor and the pulse transformer, there is provided a switching device for preventing the gate current, which is normally kept in the ON state and turns OFF in synchronization with the reverse recovery during the reverse recovery of the main thyristor. A thyristor gate circuit characterized by being provided. 2. The gate circuit of the thyristor according to claim 1, further comprising a parallel connection body of a resistor and a switch instead of the switching element for preventing the gate current, wherein the resistor is connected to the gate in synchronization with reverse recovery of the main thyristor. A thyristor gate circuit characterized by being applied to a current supply path.