Patent ID: 7635971

Claim:
A DC-DC converter comprising: a capacitor; a resistor; a control IC including; a triangular wave generation circuit which charges and discharges the capacitor and generates a triangular wave by switching between charging and discharging in accordance with a charging voltage; and a PWM control circuit which controls an output of the DC-DC converter by controlling an on duty ratio of a switching element on the basis of the triangular wave; and a synchronizing signal input circuit arranged to apply a synchronizing pulse voltage signal to the capacitor to control an electric charge of the capacitor, whereby such that the frequency of the triangular wave is changed so as to be synchronized with the pulse voltage signal; wherein the capacitor and the resistor are arranged outside the control IC and are connected to terminals of the control IC, the capacitor having a predetermined capacitance and the resistor having a predetermined resistance which define a frequency of the triangular wave.