Patent ID: 7724551

Claim:
A step-up circuit that steps up an input voltage and outputs an output voltage, the step-up circuit comprising: a constant-current control circuit arranged to produce a first reference current as a reference constant current when a first detection voltage according to the output voltage is lower than a reference voltage, and arranged to stop the reference constant current when the first detection voltage exceeds the reference voltage, wherein the constant-current control circuit is further arranged to produce, as the reference constant current, a second reference current that is smaller than the first reference current when a second detection voltage, according to the output voltage, is lower than the reference voltage, the second detection voltage being higher than the first detection voltage, and arranged to produce the first reference current when the second detection voltage exceeds the reference voltage; and at least one constant-current operated step-up unit arranged such that stepping-up operation is performed by an input constant current according to the reference constant current, wherein the constant-current control circuit comprises: a first differential amplifier circuit to which the first detection voltage and the reference voltage are inputted, the first differential amplifier circuit performing differential amplification on the first detection voltage and the reference voltage inputted thereto; and a second differential amplifier circuit to which the second detection voltage and the reference voltage are inputted, the second differential amplifier circuit performing differential amplification on the second detection voltage and the reference voltage inputted thereto, wherein, based on operation of the first and second differential amplifier circuits, the constant-current control circuit determines whether to produce, as the reference constant current, one of the first and second reference currents or stop the reference constant current.