PURPOSE: To eliminate the need of a high resistance and to facilitate the constant design by generating two comparison voltages by dividing a constant-voltage by a resistance, discharging a capacitor by a constant-current of some constant multiple of a current for flowing through its resistance, and executing its constant multiple by a current mirror circuit.

CONSTITUTION: A capacitor C12 is charged and discharged by a constant-current which has brought an input current to some constant multiple, by a constant-current charging/ discharging circuit 10 and a current mirror circuit 11. When the capacitor C12 is charged and a voltage is boosted gradually, and exceeds an (a) point voltage, the output of a comparator 13 is inverted, and a (c) point voltage drops to Low. When it is received, a comparison voltage switching circuit 10 outputs a voltage of an (f) point, a constant-current charging/discharging circuit 11 outputs a discharge use constant-current i4, and the capacitor C12 is discharged. When the capacitor C12 is discharged and its voltage drops from the (a) point voltage, the output of the comparator 13 is inverted again and returns to its original state. Thereafter, it is repeated. When V1 drops, its current i1 also becomes smaller, and charge/discharge use constant- currents i7, i4 also become smaller, therefore, it is compensated that V2 becomes smaller.