| 摘要 |
PURPOSE: To use a power supply of high priority (for instance, external power supply), even when a power supply of high voltage such as a lithium-ion secondary cell is used as a power supply of low priority (for instance, internal power supply). CONSTITUTION: A device has external/internal power supply input terminals ϕ1, ϕ2 respectively connected external/internal power supplies P1, P2, a comparator circuit 3 for comparing the voltage of the input terminal ϕ1 with reference voltage Vref and a connection switching means for selectively connecting the external/internal power supplies P1, P2 to a load based on the comparison result sent from this comparator circuit 3. The connection switch means can be constituted of the first switch circuit 1 connected between the input terminal ϕ1 and the load and performing on-action by a high level output from the comparator circuit 3 and the second switch circuit 2 connected between the input terminal ϕ2 and the load and performing on-action by a low level output from the comparator circuit 3. |
