JPH0352256B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Description of the Technical Field The present invention relates to a gate circuit for a self-extinguishing semiconductor device that enables switching of an on-gate current supply transistor using a low breakdown voltage photocoupler. It is.

(b) Description of prior art The gate circuit of a conventional turn-off thyristor (hereinafter abbreviated as GTO) will be explained with reference to Figure 1.
The switching power supply 2 supplies gate power to an on-gate circuit 17 that supplies gate current for turn-on to the GTO 16 via the pulse transformer 1, and a negative bias circuit 21 that biases the gate electrode negatively during the turn-off period of the GTO 16. supply. The on-gate circuit 17 is rectified and smoothed by the diodes 3 and 4 and the smoothing capacitor 7, and is turned on and off by the NPN transistor 12.
An on-gate current is supplied through the resistor 13.
The NPN transistor 12 is controlled to be turned on or off by a base signal given by the photocoupler 11. The negative bias circuit 21 is rectified and smoothed by diodes 5 and 6 and a smoothing capacitor 8, and negatively biases the gate electrode of the GTO 16 via a resistor 15. GTO 16 is controlled by a gate signal shown in FIG. When the ON command is input, the NPN transistor 12 is connected via the photocoupler 11.
A base signal is applied to the on-gate current. After an on command is output for a certain period of time, an off command is given and an off gate current is supplied after a time Td determined by taking into account the switching time of the photocoupler 11 and transistor 12 has elapsed.

The GTO 16 is turned off by an off-gate current applied by an off-gate circuit 18 via a pulse transformer 19 in response to an off-command.
The impedance between the gate electrode and cathode electrode of GTO16 remains constant even after off-gate current supply starts.
During the accumulation time when GTO16 is still conducting, the impedance is almost zero, but GTO1
6 is turned off, an induced reverse spike voltage of about 20 to 30 V is generated between the gate electrode and the cathode electrode. FIG. 3 shows an equivalent circuit at this time.
Components that are the same as those in FIG. 1 are given the same reference numerals, and their explanations will be omitted. The pulse transformer 19 for supplying off-gate current generates an output voltage V _p with the polarity shown. Due to the partial voltage between the gate electrode and cathode of GTO16, due to the wiring inductance 20
An induced reverse spike voltage V _GK is generated. At this time, transistor 12 is off, so V _Tr
A voltage is applied. At the same time, a voltage V _PC that is approximately the same as V _Tr is applied to the photocoupler 11 . Here, V _Tr and V _PC are added to the on-gate power supply voltage E _ON charged in the capacitor 7 with V _GK superimposed. That is, V _PC V _Tr =E _ON +V _GK . As mentioned above, when the off-gate circuit operates, the on-gate power supply voltage E _ON and the induced reverse spike voltage generated when the GTO 16 is turned off are superimposed on the NPN transistor 12, which has already been turned off, but at the same time, almost the same voltage is applied to the photocoupler 11. A voltage is applied. Normally E _ON is 10 to 10-odd V, V _GK is 20
~30V, resulting in a voltage of V _Tr V _PC =35 to 45V. The voltage rating of the transistor 12 and photocoupler 11 is generally selected to have a withstand capacity several times higher than the applied voltage.

However, most commercially available photocouplers have collector-emitter voltage ratings of 30 to 50 V or less. If a voltage exceeding the maximum rating is applied to the photocoupler, the photocoupler 11 may break down, causing damage to the photocoupler, or causing damage to the transistor 1.
2 turned on, causing the GTO16 to fire incorrectly.

(c) Purpose of the Invention The present invention has been made in order to eliminate the above-mentioned drawbacks, and includes a photocoupler element in a position where the reverse voltage induced between the gate electrode and the cathode does not form an electric path superimposed on the on-gate power supply. The purpose of this arrangement is to prevent malfunctions of the transistors that would result in breakdown of the photocoupler.

(d) Structure and operation of the invention FIG. 4 shows an embodiment of the invention. Components that are the same as those in FIG. 1 are designated by the same reference numerals, and their description will be omitted. 12 is a PNP transistor, resistor 9
Its control pole is driven by a photocoupler 11 consisting of a combination of an electric/electrical conversion element and an optical/electrical conversion element. FIG. 5 is an equivalent circuit corresponding to FIG. 3. The induced reverse spike voltage generated between the gate electrode and the cathode of the GTO 16 is superimposed only between the emitter E and the collector C of the transistor 12, and as shown in FIG. Since no voltage is applied to the photocoupler, the voltage rating of the photocoupler can be selected with respect to the on-gate power supply voltage _EON , which is approximately ten or more V, and the voltage rating can be significantly reduced.

(e) Other Embodiments FIG. 6 is a circuit diagram showing another embodiment of the present invention. The same or equivalent parts as in FIG. 4 are given the same reference numerals. By configuring the photocoupler 11 to drive the PNP transistor 121 and the NPN transistor 12 via the resistor 9, the same effect as in the embodiment shown in FIG. It is possible to operate the photocoupler without any interference.

(f) Overall effect As explained above, according to the present invention, the voltage applied to the photocoupler is significantly reduced, so it is possible to use a photocoupler with a low withstand voltage.
This has great practical effects, such as preventing transistor malfunctions due to photocoupler breakdown.

[Brief explanation of drawings]

Fig. 1 is a gate circuit diagram of a conventional circuit, Figs. 2 and 3 are diagrams explaining the operation of the conventional circuit, Fig. 4 is a circuit diagram showing an embodiment of the present invention, and Fig. 5 is a gate circuit diagram of a conventional circuit. FIG. 6 is a circuit diagram for explaining another embodiment of the present invention. 1...Pulse transformer, 2...Switching power supply,
3 to 6...diode, 7,8...smoothing capacitor,
9, 13, 15...Resistor, 11...Photocoupler,
12,121...transistor, 16...GTO.

Claims (1)

[Claims] 1. A switching element having a cathode of a self-arc-extinguishing semiconductor element connected to the negative electrode side of a DC power source, and a control pole provided between the positive electrode side of the DC power source and a gate electrode of the self-arc-extinguishing semiconductor element, an on-gate circuit that supplies an on-gate current to the self-extinguishing semiconductor device by driving it through an optical coupling device consisting of a combination of an electric/optical conversion element and an optical/electrical converting element; In the gate circuit of a self-arc-extinguishing semiconductor device, the gate electrode of the self-arc-extinguishing semiconductor device is provided with an off-gate circuit whose other end is connected to the cathode of the self-arc-extinguishing semiconductor device and supplies an off-gate current to the self-arc-extinguishing semiconductor device. 1. A gate circuit for a self-extinguishing semiconductor device, characterized in that one terminal of the optical/electric conversion device is connected to the negative electrode side of the DC power supply, and the other terminal is connected to the control pole of the switching device.