Returning to FIG. 6, a change over switch SW is connected between the neutral point of smoothing capacitors C10,C20 for smoothing the output of rectifying circuit BR and common line COM of 'the reference side of the AC source voltage. Switch SW is turned ON
when, for example, the AC source voltage is 110 v, thereby effecting a double voltage rectification. On the other hand, when the AC voltage source is 220 V, switch SW is turned OFF to allow a bridge rectification. Thus, converter is adapted to both 110 V system and 220 V system.