| 摘要 |
PURPOSE:To eliminate malfunction due to noise and momentary power failure, by setting a variable resistor to set an optional power failure detection time without the influence of the voltage variance of an AC input while the output of a regulator is normal after power failure by a simple CR charging circuit. CONSTITUTION:In the normal state, a transistor TR 5 is turned off only for a short time near the zero-crossing point of an input power source 1 to charge a capacitor C4, but the TR 5 is turned off immediately to discharge the electric charge of the capacitor C4. If a short-time power failure occurs, the TR 5 is turned off to charge the capacitor C4, but the capacitor C4 is discharged before a comparator 4 reaches a reference voltage V4 for power failure detection signal, and the power failure detection signalis not generated. If a long- time power failure occurs, an output V3 of a regulator 3 generates a certain DC voltage till a certain time because of capacitors C1 and and C2. After passing this time, the comparator 4 is charged by the capacitor C4, and the comparator 4 generates the power failure detection signal at the time when it exceeds the reference voltage V4. As the result, power failures are not detected to continue the normal operation when the momentary power failure occurs frequently. |
