Patent ID: 7245114

Claim:
A DC-to-DC step-up converter comprising: a step-up circuit stepping up a source voltage to generate a DC output voltage; a ring oscillator generating an oscillator output signal, the ring oscillator comprising a first capacitor determining a low-level period of the oscillator output signal, a second capacitor determining a high-level period of the oscillator output signal, and a switch unit receiving a trigger signal to control the ring oscillator to output the oscillator output signal; a divider circuit receiving the DC output voltage to generate a feedback voltage; a pulse frequency modulation (PFM) comparator comparing the feedback voltage with a reference voltage to generate a comparator output signal for controlling outputting of the oscillator output signal; and a logic control unit reducing ripples of the DC output voltage, the logic control unit comprising a signal hold unit providing the trigger signal to control the switch unit, and an auto-reset unit controlling the operation of the PFM comparator to reset the comparator output signal automatically.