| 摘要 |
PROBLEM TO BE SOLVED: To suppress such erroneous operation as switching to a backup power supply by connecting a capacitor between the detection signal output terminal of an impedance element and a power supply, connecting another capacitor between the output terminal and another power supply, and judging whether output terminal potential is higher than a constant value or not by a level judgment means. SOLUTION: When an AC signal is applied to an input terminal, transistors(Tr) Q11 and Q12 alternately become intermittent, electric charge being charged from a resistor R11 to capacitors C12 and C13 moves to a capacitor C11 through the TrQ12 and further to a power supply voltage Vss at a low-potential side through the TrQ11, thus setting the input and output of the inverter B13 to L and H levels, respectively. When no AC signal is applied to the input terminal, either of the TrQ11 and Q12 is turned off and the capacitors C12 and C13 are charged, thus setting the input and output of the inverter B13 to H and L levels, respectively. The retention potential of the capacitors C12 and C13 and the judgment potential of the inverter B13 fluctuate while being linked, thus eliminating the influence of a power supply fluctuation noise.
|
