This unique circuit allows use of either
dual-voltage AC mains, such as 120/240 volt operation, or dual output voltages
with a fixed input supply. This is accomplished by switching between a full-wave
doubler configuration, or a full-wave bridge configuration, with a simple SPDT
switch or relay. Note the lower end of the AC source, in this case represented
by a transformer, must be switched to either the junction of C1 and C2 to form a
doubler, or the lower end of the input source is switched to the bridge terminal
to form a bridge system. Both systems are full-wave rectified.