| 摘要 |
An error voltage Verr, being a difference between DC output voltage Vout and output reference voltage Vref, and an input voltage Vin are multiplied to produce first threshold voltage signal Vth1 in phase with and similar to input voltage Vin and proportional to Verr. Second threshold voltage signal Vth2 is produced from first threshold voltage signal Vth1. The input current is detected as a current detection signal Vi across a resistor 12, whether it is between the threshold value signals is detected by a current range detecting circuit, and accordingly, the timing of turning on or off switching device is controlled so that at least one of an duration on and an off duration of the switching device is limited to enhance a power factor. Unfixed off duration disperses a noise spectrum to prevent an increase in switching frequency, to reduce noise. |
