Patent ID: 7068020

Claim:
A step-down DC-DC converter comprising: switching means which includes at least one MOS transistor connected to a direct-current power supply; at least one reactor which is charged by the direct-current power supply during a time interval in which the MOS transistor is turned on; an output capacitor connected to the direct-current power supply through the MOS transistor and the reactor, the output capacitor supplying a current to a load; and a pulse width modulation circuit inputted a voltage corresponding to an output voltage of the output capacitor and applying a pulse signal of a duty according to the voltage to a gate of the MOS transistor, wherein the MOS transistor is an N-channel type, the N-channel MOS transistor and the reactor are sequentially connected in series between a negative side of the direct-current power supply and a negative side of the output capacitor, and a power supply of the pulse signal applied to the gate of the N-channel MOS transistor is supplied between a positive side and the negative side of the direct-current power supply.