| 摘要 |
PROBLEM TO BE SOLVED: To reduce the power loss generated in a changeover circuit, by using a transistor instead of a reverse current preventing diode. SOLUTION: When the positive voltage of a DC power supply 1 is higher than the positive voltage of a DC power supply 2, a P-type power transistor 13 is turned off, and the output voltage of a power-supply changeover circuit 4 becomes equal to the one obtained through the subtraction of the forward voltage drop of a diode 11 from the positive voltage of the DC power supply 1. On the other hand, when the positive voltage of the DC power supply 2 is higher than the positive voltage of the DC power supply 1, the P-type power transistor 13 is turned on to make the output voltage of a power-supply changeover circuit 4 equal to the one obtained through the subtraction of the voltage drop caused by the ON-resistance of the P type power transistor 13 from the positive voltage of the DC power supply 2. Since the voltage drop caused by the ON-resistance of the P-type power transistor 13 is smaller than the forward voltage drop of the diode 11, the power loss in the case of feeding a power from the DC power supply 2 to a load 3 can be reduced. |
