PURPOSE: To reduce the weight and volume of an AC adapter and facilitate its integration into an apparatus, by forming a circuit comprising plural capacitors and diodes, and by providing additionally a charge-discharge changeover switching element, in a DC power supply circuit for converting a commercial AC power supply into a low voltage DC one.

CONSTITUTION: A series-parallel capacitor circuit is formed out of the group comprising plural capacitors 1 and series diodes 2 inserted respectively between them and the group comprising two sets of parallel diodes 3. At this point, for performing the charge from an AC input terminal 9 and the discharge from a DC output terminal 8 in different times from each other, a time-changeover switching element 6 is provided, and the base current thereof is introduced into it from the AC input terminal 9 via diodes 11, 12 and a resistor 10 to alternate the charge and discharge operations every half period. By this configuration, the weight and volume of an AC adapter are reduced, and its integration into an apparatus is facilitated, and further, the use of the switching elements generating electric noises can be reduced.