US Patent 6842353 Switching power supply, and a method of driving the same

A switching power supply comprising an a.c.-to-d.c. converter circuit for connection to a source of commercial alternating current, and a d.c.-to-d.c. converter circuit for translating the d.c. output voltage of the a.c.-to-d.c. converter into desired d.c. voltage for application to a load. The d.c.-to-d.c. converter circuit is set into operation only after the output voltage of the a.c.-to-d.c. converter circuit has built up sufficiently, in order to preclude instability in the output voltage of the power supply during a startup period.