| 摘要 |
PURPOSE:To simplify circuit constitution by installing a winding exclusive for backup having proper winding voltage in a transformer and conducting charging to a battery and feeding from said battery through the winding. CONSTITUTION:Pulses induced in a winding 4d for backup at a time when a switching transistor(STr) 5 is turned ON are applied to a voltage control circuit 22. The voltage control circuit 22 outputs pulses of constant voltage lower than the voltage of pulses applied at that time, and constant-voltage pulse charging is performed. An interruption detection circuit 28 monitors the voltage of an input commercial AC power supply 1, and a changeover switch 27 is changed over to the (b) side when service interruption is detected. A PWM modulation circuit 26 forms switching driving pulses accord to the detecting voltage of a voltage detection circuit 25, and drives the base of the STr5 normally and drives the base of an STr20 upon service interruption. |
