delivered by the constant current sources 54 a 54 b and 54 c respectively the capacitor 53 is discharged in the on period of the semiconductor switch 52 a comparator 55 generates a setting signal u2018 set u2019 for setting the flip flop 43 indicated in fig4 when the charged voltage of the capacitor 53 exceeds a predetermined specified reference voltage vref the control signals qb 1 qb 2 and qb 3 are used for controlling charging of the capacitor 53 by the constant current sources 54 a 54 b and 54 c more specifically the constant current source 54 a 54 b and 54 c are driven by the power supply voltage vdd through switches 56 a 56 b and 56 c to deliver the constant current i 1 i 2 and i 3 the switch 56 a turns on receiving the control signal qb 1 and drives the constant current source 54 a the switch 56 b turns on receiving the control signal qb 1 or the control signal qb 2 through an or circuit 57 to drive the constant current source 54 b the switch 56 c turns on receiving any one of the control signals qb 1 qb 2 and qb 3 through an or circuit 58 to drive the constant current source 54 c consequently the capacitor 53 is charged rapidly when the control signal qb 1 is given with the current i 1 i 2 i 3 delivered by the constant current sources 54 a 54 b and 54 c when the qb 2 is given the capacitor 53 is charged with the current i 2 i 3 delivered by the constant current sources 54 b and 54 c when the qb 3 is given the capacitor.