| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To improve the conversion efficiency of electric power at light load. <P>SOLUTION: A main side power transistor P1 and a rectification-side power transistor N1 are provided in series in between a power source VDD and the ground GND for converting a DC voltage of a potential difference between the power source VDD and the ground GND into an AC voltage. A reverse current preventing circuit 10a includes a comparator, which compares the AC voltage with a threshold voltage in a period, when the rectification-side power transistor N1 should be turned on. The transistors are controlled, in such a manner that at least immediately prior to the period the rectification-side power transistor N1 should be turned on, a predetermined voltage which is lower than the threshold voltage is given to the comparison input of the comparator instead of the AC voltage; and that when the comparator decides that the AC voltage exceeds the threshold voltage, in a period when the rectification-side power transistor N1 should be turned on, the rectification-side power transistor N1 is turned off. <P>COPYRIGHT: (C)2009,JPO&INPIT</p> |
