Patent ID: 6842353

Claim:
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) an a.c.-to-d.c. converter circuit connected to the pair of a.c. input terminals for translating the input a.c. voltage into d.c. voltage, the a.c.-to-d.c. converter circuit having power factor improvement means including an a.c.-to-d.c. converter switch; (c) a first switch control circuit connected to the a.c.-to-d.c. converter switch for driving the a.c.-to-d.c. converter switch at a repetition frequency higher than the frequency of the input a.c. voltage; (d) a d.c.-to-d.c. converter circuit connected to the a.c.-to-d.c. converter circuit for translating the d.c. voltage output of the a.c.-to-d.c. converter circuit into desired d.c. voltage, the d.c.-to-d.c. converter circuit having a d.c.-to-d.c. converter switch; (e) a second switch control circuit connected to the d.c.-to-d.c. converter switch for driving the d.c.-to-d.c. converter switch at a repetition frequency higher than the frequency of the input a.c. voltage; (f) a voltage detector circuit connected to the a.c.-to-d.c. converter circuit for providing a voltage output indicative of the d.c. voltage output from the a.c.-to-d.c. converter circuit; (g) a voltage decision circuit connected to the voltage detector circuit for ascertaining whether the voltage output of the voltage detector circuit is higher than a predefined value or not; and (h) a starter circuit connected to the voltage decision circuit and the second switch control circuit for causing the second switch control circuit to start driving the d.c.-to-d.c. converter switch when the voltage output from the voltage detector circuit grows higher than the predefined value.