Patent ID: 7075356

Claim:
A charge pump circuit, comprising: first and second diodes interposed in series between an input portion for receiving a power source input to an object to be stepped up and an output portion for outputting a stepped up voltage such that a forward direction of each diode is directed to a side of the output portion; a capacitor interposed on a connecting path between a connecting portion of the first diode on a side of the output portion and a ground, the first diode being disposed on a side of the input portion with respect to the second diode, the capacitor having two connecting portions; a first switch for conducting and cutting a connecting path between one of the connecting portions of the capacitor and the ground; a second switch for conducting and cutting a connecting path between the one connecting portion of the capacitor and the input portion; and a driver for conducting the first switch and the second switch alternately in phases opposite to each other; wherein: a constant current charging and discharging circuit, using a first follower circuit and a second follower circuit, is arranged to be along a first path, through which a current flows when a connecting path between the one connecting portion of the capacitor and the ground is conducted by the first switch and a current from the input portion charges the capacitor, and along a second path, through which a current flows when the connecting path between the one connecting portion of the capacitor and the input portion is conducted by the second switch and the capacitor is discharged; the first follower circuit comprises: a first transistor interposed at any position on the first path for controlling an amount of a flowing current flowing through the first path and functioning as the first switch; and a first resistor connected in series to the first transistor on a downstream side in a current flowing direction of the first transistor; the second follower circuit comprises: a second transistor interposed at any position on the second path for controlling an amount of a flowing current flowing through the second path and functioning as the second switch; and a second resistor connected in series to the second transistor on an upstream side in a current flowing direction of the second transistor, wherein one end of the second resistor is connected to the first diode and another end of the second resistor is connected to the second transistor; a third resistor; a fourth resistor; and a third diode, wherein the third resistor, the fourth resistor, and the third diode are directly connected to each other by a first connecting point, and the first connecting point is directly connected to a base of the first transistor.