Thyristor switching circuit - operated on HV side of load rather than LV side, using biassed diode circuit with resistors

摘要

When thyristors are used to switch power to a load, they are usually connected between the load and the neutral, or earthy supply line. This is done because the gate signal which triggers conduction is usually at a low potential w.r.t. earth. The main disadvantage of this method is that the load is live whether or not the thyristor is conducting. The modified thyristor switching circuit switches the 'live' supply to the load but still uses a low voltage gating signal. This is achieved by using a diode in series with a resistor between the gate generator and the gate. The diode is biased by the series resistor and another resistor between the thyristor cathode and the gate electrode.