Patent ID: 7248030

Claim:
A step-up/step-down DC-DC converter for generating an output voltage from an input voltage, the step-up/step-down DC-DC converter comprising: a choke coil; a pair of step-down transistors and a pair of step-up transistors connected to the choke coil; and a control circuit for controlling the pair of step-down transistors and the pair of step-up transistors based on the output voltage of the DC-DC converter, the control circuit including: an error amplifier for comparing the output voltage with a reference voltage and generating an error signal that is in accordance with voltage difference between the output voltage and the reference voltage; a pulse width modulation comparator, connected to the error amplifier, for comparing the error signal with a triangular wave signal and generating a control pulse signal having a pulse width that is in accordance with the voltage difference between the output voltage and the reference voltage; a pulse detector, connected to the pulse width modulation comparator, for receiving the control pulse signal and generating a mode switch signal for switching an operation mode of the DC-DC converter in accordance with the state of the control pulse signal; and an offset voltage adding unit, connected to the pulse detector, for adding an offset voltage to the triangular wave signal or to the error signal in response to the mode switch signal.