Patent ID: 7528589

Claim:
A step-up DC/DC converter comprising: an output transistor of an N-channel field-effect type; a synchronous-rectification transistor of an N-channel field-effect type; an energy storage element of which a first end is connected to the output transistor and to the synchronous-rectification transistor and of which a second end is connected to a point to which an input voltage is applied; a first driver making a gate voltage of the output transistor pulsate between a ground voltage and the input voltage; a second driver making a gate voltage of the synchronous-rectification transistor pulsate between a switching voltage appearing at the first end of the energy storage element and a bootstrap voltage equal to the switching voltage plus at least an ON threshold voltage of the synchronous-rectification transistor; and an output smoother smoothing the switching voltage to output a desired output voltage; and a control circuit directly fed with the output voltage as an output feedback signal and switching, based on the output voltage only, the output transistor and the synchronous-rectification transistor complimentarily via the first and second drivers.