Patent ID: 7884665

Claim:
A charge pump circuit comprising: a step-up capacitor to be charged and discharged in repeated cycles; a charger that, when charging the step-up capacitor, makes a first end of the step-up capacitor conduct to an input voltage application terminal and makes a second end of the step-up capacitor conduct to a ground terminal; a discharger that, when a negative voltage is provided as an output, makes the first end of the step-up capacitor conduct to the ground terminal and makes the second end of the step-up capacitor conduct to a negative voltage output terminal; and an output capacitor connected to the negative voltage output terminal, the charge pump circuit providing a negative voltage as an output from the negative voltage output terminal, wherein the charge pump circuit includes, as a component of the charger, a field effect transistor to allow/interrupt conduction between the second end of the step-up capacitor and the ground terminal, wherein a first switch is connected between a backgate of the field effect transistor and the ground terminal, the first switch being turned on to allow conduction between the backgate of the field effect transistor and the ground terminal when the step-up capacitor is charged, and the first switch being otherwise turned off to interrupt conduction between the backgate of the field effect transistor and the ground terminal, and wherein a second switch is connected to one of a source terminal and a drain terminal of the field effect transistor that is located on the step-up capacitor side, the second switch being turned off to interrupt conduction between the field effect transistor and the step-up capacitor when a negative voltage is provided from the negative voltage output terminal, and the second switch being otherwise turned on to allow conduction between the field effect transistor and the step-up capacitor.