| 摘要 |
<p>PURPOSE:To detect the time when a backup battery need to be replaced and to replaces the battery without destroying memory contents even when the battery is removed during the battery replacement by providing a voltage monitoring circuit for the backup battery and a charging circuit which prevents a temporary break of power supply during the battery replacement. CONSTITUTION:The voltage monitoring circuit 15 outputs a voltage drop signal 20 and a battery switching signal 21 when the output voltage of the backup battery 13 drops. A battery switching circuit 22 when recognizing this battery switching signal 21 switches the backup power source for the break of a main power source 1 from the backup battery 13 to a spare backup battery 14. Further, electric power is supplied from the spare backup battery 14 even when the battery 13 which decreases in power source capacity is replaced, so the memory contents of a system memory 5 are never destroyed even in case of a voltage drop due to the decrease in the capacity of the backup battery 13.</p> |
