PHASE CONTROL DEVICE

PROBLEM TO BE SOLVED: To provide a phase control device which prevents disorder of a waveform of output current by surely arc-lighting a thyristor in spite of a light load. SOLUTION: The phase control device includes a first phase control circuit 1 having a self arc-extinguishing type control element, a second phase control circuit 2 having the thyristor and connected in parallel with the first phase control circuit, a load current detection means 3, and a control means 4 which turns on the first phase control circuit at zero crossing timing when conducting during the whole period of a half-wave in cooperation with the load current detection means and turns off the first phase control circuit by turning on the second phase control circuit when output current with a designated value or more flows in the first phase control circuit and turns off the second phase control circuit by turning on the first phase control circuit when the load current flowing in the second phase control circuit becomes less than the designated value and turns off the second phase control circuit after the first phase control circuit is turned off when the output is turned off. COPYRIGHT: (C)2009,JPO&INPIT