| 摘要 |
PURPOSE:To apply the sufficient energy to a control electrode to prevent disabling the trigger even though the sensitivity is reduced for the control electrode of a thyristor at a low temperature, by controlling the increment/decrement of energy of a trigger pulse which is due to a change of the phase control angle of the thyristor. CONSTITUTION:A load 6 is connected to an AC power supply 1 via a phase control switch 7 like a thyristor. The ignition phase angle theta of the switch 7 is controlled by a phase control circuit 3. When a full-wave rectification signal is less than the reference level of a reference voltage generating circuit 10, the output of a voltage comparator 11 is set at H. This output H is differentiated by a differentiating circuit 12 and converted into a pulse signal to be supplied to a time constant circuit 13 which decides the phase control timing. The charging voltage of the circuit 13 is compared with the reference voltage by a voltage comparator 16. When it is larger than the reference voltage the output of the comparator 16 is set at H. This output is converted into a pulse signal and supplied to a trigger circuit 18. Then a trigger pulse is supplied to the switch 7. |
