Current supply circuit with switchable transformer tappings - has triacs in primary tap leads, initially made conducting very briefly, and then for longer periods

摘要

Power semiconductor switches (triacs) controlled by a selector switch are inserted into the leads of transformer taps on the primary side. They are controlled by a starting up control circuit to limit the transformer switch on current. The triacs are made conducting during the second half of a half cycle of the voltage to be switched. Conduction is initially only brief, and then longer and earlier. The start up control circuit may contain an automatic element which puts the triac into continuous conduction when the start of conduction point has reached the voltage max. in a half cycle.