Patent ID: 7864553

Claim:
A power supply circuit for boosting a voltage of an input power supply at a predetermined step-up ratio and outputting to a boosted output terminal, comprising: a plurality of switching transistors for selection connected between another-side terminal and a one-side terminal of the input power supply with a connection relationship predetermined according to a step-up ratio; a plurality of shift switching transistors connected between the one-side terminal of the input power supply and a boosted output terminal with a connection relationship predetermined according to the step-up ratio; a shift capacitor connected between one of a plurality of connection points between respective pairs of switching transistors for selection and one of a plurality of connection points between respective pairs of shift switching transistors with a connection relationship predetermined according to the step-up ratio; a holding capacitor connected to the boosted output terminal; and a control circuit for turning the respective switching transistors on and off at a time predetermined according to the step-up ratio to hold the voltage of the input power supply in the shift capacitor, and using the voltage held in the shift capacitor, and then making a voltage at both ends of the holding capacitor be a voltage coefficient multiple of the voltage of the input power supply, wherein the respective transistors are formed on a semiconductor chip, and the power supply circuit has a switching circuit for switching a voltage to be applied to a back gate of at least one transistor, in which the voltage to be applied to the back gate is switched between a common isolation voltage determined in accordance with polarity of the transistor and a source voltage of the transistor, according to a time at which to turn the transistor on or off.