| 摘要 |
PROBLEM TO BE SOLVED: To improve the efficiency of a DC power supply by stopping the power factor improving operation of a power factor improving circuit when the output current value of a DC-DC converter is smaller than a preset value. SOLUTION: An AC power supply 1 is connected to the input terminal of a rectifier circuit 2 and the input terminal of an active filter 3 which works as a power factor improving circuit is connected to the positive-and negative-side output terminals (a) and (b) of the rectifier circuit 2. A current detecting circuit 10 usually detects the output current value of a DC-DC converter 4 and compares the detected value with a preset reference value by means of a comparator circuit 11. When the detected value is smaller than the reference value, an on/off circuit 12 stops the operation of the control circuit 5 of the filter 3 by outputting a signal Vo so as to set a switching element Q1 to a nonoperating state while the element Q1 is turned off. In such a way, the power loss of a DC power unit is reduced by stopping the operation of the filter 3 when the output current of the converter 4 is small. |
