Patent ID: 8369110

Claim:
A half-wave rectification current resonance type switching power supply device comprising: a serial connection body having a first switching element and a second switching element connected between a pair of terminals of a direct current power source in series, a serial connection body having a primary winding of a transformer and a current resonant capacitor having the second switching element connected in parallel; a half-wave rectifying circuit connecting to a secondary winding of the transformer; and a gate control circuit designing to gradually lengthen an on period of the first switching element in the process of a start operation and designing to gradually shorten the on period of the second switching element in the process of a start operation, wherein the gate control circuit comprises, a comparing means configured to compare a reference voltage with the voltage of a sawtooth signal, both changing gradually form a start or a restart to generate an output signal; and a sawtooth signal generating circuit designed to generate the sawtooth signal having a frequency determined by a feedback signal corresponding to an output voltage from the half-wave rectifying circuit, wherein the gate control circuit on-off controls the first and second switching elements based on the output signal from the comparing means, and wherein the sawtooth signal generating circuit comprises a constant current charge and discharge circuit designed to generate the sawtooth signal by charging and discharging a capacitor via a constant current source.