| 摘要 |
To turn a thyristor, particularly a high-voltage thyristor, ON, and to connect the thyristor and the utilization circuit to a power source, a charge capacitor is connected to a charging circuit to charge the capacitor when the thyristor is blocked or in OFF state. A controlled switch, typically a transistor 20, is connected to the charge capacitor 19 and connects the charge capacitor to the gate electrode of the thyristor, when the controlled switch is turned ON; a control circuit is connected to the controlled switch which includes an opto-coupler 28 to control its conduction. Preferably, a threshold sensitive element such as a Zener diode 25, or a four-layer diode 30, is included in the controlled switch transistor base circuit to provide for sharp turn-on characteristics. Since the conduction characteristics of the controlled switching transistor 20 will depend on the charge state of the capacitor 19, the controlled switching transistor will be conductive only when the capacitor has a sufficiently high charge for reliable firing of the thyristor.
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