Switching power supply

A switching power supply capable of translating a.c. voltage into d.c. voltage, comprising:

• (a) a pair of a.c. input terminals for inputting a.c. voltage having a known frequency;
• (b) a pair of d.c. output terminals for outputting d.c. voltage;
• (c) a rectifier circuit connected to the pair of input terminals for rectifying the a.c. input voltage, the rectifier circuit having a first output conductor for outputting a first rectifier output voltage, a second output conductor for outputting a second rectifier output voltage which is substantially the same as the first rectifier output voltage, and a third output conductor;
• (d) a transformer having a primary winding;
• (e) a rectifying and smoothing circuit connected between the transformer and the pair of d.c. output terminals for providing the d.c. output voltage;
• (f) an inductor for improvement of the power factor of the input terminals;
• (g) a smoothing capacitor connected between the first output conductor and the third output conductor of the rectifier circuit via at least part of the primary winding and the inductor;
• (h) a switch connected between the first output conductor and the third output conductor of the rectifier circuit via at least the inductor, and in parallel with the smoothing capacitor via the primary winding;
• (i) a switch control circuit connected to the switch for on-off control of the switch at a repetition frequency higher than the frequency of the a.c. input voltage;
• and
• (j) an ancillary charging circuit having an ancillary winding electromagnetically coupled with the primary winding of the transformer, the ancillary winding being connected between the second output conductor of the rectifier circuit and the smoothing capacitor.