Abstract: When an AC power source (1) is turned on, energy is accumulated in a backup capacitor (63) by an energy supply circuit (64). An internal power source (65) supplies the energy accumulated in the capacitor (63) to a control unit (49). Thus, a power factor improvement circuit (40-2) operates. When the power factor improvement circuit (40-2) operates to output a predetermined voltage, an output voltage detection circuit (67) detects the voltage, and switches the internal power source (66) on. The turned on internal power source (66) supplies the energy in the capacitor (63) to a control unit (56) to operate a DC/DC conversion circuit (50). In this way, by operating the DC/DC conversion circuit (50) after operating the power factor improvement circuit (40-2), the capacity of the capacitor (63) can be reduced.

Abstract: When an AC power source (1) is turned on, energy is accumulated in a backup capacitor (63) by an energy supply circuit (64). An internal power source (65) supplies the energy accumulated in the capacitor (63) to a control unit (49). Thus, a power factor improvement circuit (40-2) operates. When the power factor improvement circuit (40-2) operates to output a predetermined voltage, an output voltage detection circuit (67) detects the voltage, and switches the internal power source (66) on. The turned on internal power source (66) supplies the energy in the capacitor (63) to a control unit (56) to operate a DC/DC conversion circuit (50). In this way, by operating the DC/DC conversion circuit (50) after operating the power factor improvement circuit (40-2), the capacity of the capacitor (63) can be reduced.

Abstract: A dc-to-dc converter includes a transformer having a primary winding connected to an input rectifying and smoothing circuit via an FET or like switching device, and a secondary winding connected to an output rectifying and smoothing circuit. A resonance capacitor is connected in parallel with the switching device. A switch control circuit cyclically turns the switching device on and off so as to keep constant the output voltage of the output rectifying and smoothing circuit by feedback control. The switch control circuit drives the switching device in light load mode when a flyback voltage developed by the transformer terminates earlier than each clock pulse, and in heavy load mode, in which each on-off cycle of the switching device is longer than in the light load mode, when the flyback voltage terminates later than each clock pulse.

Abstract: 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.

Abstract: 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.

Abstract: A dc-to-dc converter includes a transformer having a primary winding connected to an input rectifying and smoothing circuit via an FET or like switching device, and a secondary winding connected to an output rectifying and smoothing circuit. A resonance capacitor is connected in parallel with the switching device. A switch control circuit cyclically turns the switching device on and off so as to keep constant the output voltage of the output rectifying and smoothing circuit by feedback control. The switch control circuit drives the switching device in light load mode when a flyback voltage developed by the transformer terminates earlier than each clock pulse, and in heavy load mode, in which each on-off cycle of the switching device is longer than in the light load mode, when the flyback voltage terminates later than each clock pulse.