| 摘要 |
PURPOSE:To obtain a precise timer time set circuit stable for the fluctuation of a power source voltage by comparing the charge potential of a capacitor, which is charged with a constant current, with the potential of a voltage dividing circuit connected to the power source through a PN junction element. CONSTITUTION:For the purpose of causing the current flowed to output-side transistor Tr12 of current mirror circuit 14 with the current flowed to input-side Tr11, Tr13 is inserted to charge capacitor 18 with constant current I3, and its charge potential VC'' is applied to the inversion input of voltage comparator curcuit 19. Power source voltage VCC is connected to a voltage dividing circuit, which is constituted by resistances 22 and 23, through diode-connected Tr20 and 21. Reference voltage V'REF is applied from the connection point of resistances 22 and 23 to the non-inversion input of circuit 19. When switch 24 is opened and charge potential V''C of C18 is higher than reference voltage V'REF, output S of circuit 19 becomes 0, a timer time is set. Since C18 is charged with the constant current, the timer time can be set precisely; and since this time is determined by only C18 and resistances 16, 22 and 23, it is not affected by the fluctuation of the power source voltage. |
