| 摘要 |
<P>PROBLEM TO BE SOLVED: To reduce a loss by changing a boost voltage, and to simultaneously obtain appropriate output holding time according to a load state. <P>SOLUTION: A power factor improvement circuit 3 is interposed in a pre-stage of a DC-DC converter 4 for supplying a stabilized DC output voltage Vout to a load 18. The power factor improvement circuit 3 switches a switching element 12 to boost a rectified voltage VA, and improves a power factor to output the boost voltage VB to the DC-DC converter 4. Also, the power supply unit includes a voltage detection circuit 26 for detecting the rectified voltage VA, a current detection circuit 27 used as a power detection circuit for detecting load power, and a control circuit 25 for setting the output holding time according to the load current, calculating a command value of the boost voltage VB according to the rectified voltage VA within a range satisfying the setting value of the output holding time, and outputting a pulse drive signal following the command value to the switching element 12. <P>COPYRIGHT: (C)2011,JPO&INPIT |
