| 摘要 |
<p>PURPOSE:To surely detect a power supply break by setting first and second reference levels to a comparing circuit and providing first and second timers and switching the reference level to the lower reference level at the time of output from the second timer. CONSTITUTION:A power supply break detecting circuit consists of a power input rectifying and smoothing circuit 2, a voltage comparator 3, timers 11 and 12, a power supply relay 5, and a transistor TR 4 which controls this relay 5. In this case, first and second reference voltages to be given to the voltage comparator 3 are provided. The second reference voltage is generated when a TR 6 provided in parallel with a resistance R2 of a series circuit consisting of voltage dividing resistances R1 and R2 is turned on. This TR 6 is turned on to switch the reference voltage of the comparator 3 by the timer 12. Thus, a prescribed turning-off time (about 1sec) is certainly secured when a power supply break is detected, and this circuit copes with even the load variation when the power supply is turned on.</p> |
