| 摘要 |
PROBLEM TO BE SOLVED: To provide a power-factor improving circuit for switching power source with simple structure and capable of making voltage of an input capacitor constant without being affected by load current. SOLUTION: Inputted voltage from a commercial AC power source is detected and an on/off signal to be supplied to a switching element SW1 is controlled so that terminal voltage Vc of the input capacitor C1 is proportionated to a peak value Vp of the inputted voltage based on a detected result by this power- factor improving circuit. When the switching element SW1 is on, the terminal voltage Vc of the input capacitor C1 is applied a winding n1 of a transformer T2 and voltage of Vc×n2/n1 is generated on a winding n2 of the transformer T2. Relation between voltage at a point A and voltage at a point B at both ends of the winding n2 beoomes point A < point B and current IL to flow in an inductor L1 for boosting increases. Therefore, when the inputted voltage of the commercial AC power source is higher than Vc×(1-n2/n1), inputted power flows in, a power-factor improvement effect is obtained and the voltage to be generated in the input capacitor C1 is made to be constant without being affected by the load current of a DC/DC converter 1. |
