| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To prevent a current from flowing from a backup power supply to a load, even if a main power supply is selected, when the voltage of the main power supply drops to a value lower than the voltage of the backup power supply, in a power supply switching circuit so constructed that either of the main power supply and the backup power supply is selected and connected to the load, based on the result of comparison of the voltage of the main power supply with a reference voltage. <P>SOLUTION: The power supply switching circuit includes a first detection circuit that compares a first supply voltage with a second supply voltage and outputs a logic signal, indicating the result of the comparison; a second detection circuit that compares the first supply voltage with the reference voltage and outputs a logic signal, indicating the result of the comparison; a selection circuit that selects either the first supply voltage or the second supply voltage, whichever is higher, based on the logic signal outputted from the first detection circuit and supplies it to at least the first and second detection circuits; and a switching circuit that selects either the first supply voltage or the second supply voltage, based on the logic signal outputted from the second detection circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT</p> |
