Switch control device, power supply device comprising the same and switch control method

PURPOSE: A switch control device, a power supply device including the same, and a switch control method are provided to accurately detect the zero crossing time without influence to noise. CONSTITUTION: A power switch(M) operates switching according to gate signals delivered from a switch control device(30). The power switch is formed into NMOSFET(n-channel metal oxide semiconductor filed effect transistor). A power supply apparatus(40) comprises a power switch, a bridge diode(10), a diode(FRD), an inductor(L), and a switch control device. The switch control device and the power switch can be formed into one chip. The bridge diode is composed of four diodes(11-14).