| 摘要 |
PURPOSE:To improve the power factor for a light load and reduce the lowering of the power factor for a heavy load, by changing the intermission frequency of a switching element in accordance with the load in an AC-side power factor improving circit consisting of the switching element and a reactor. CONSTITUTION:The voltage from an AC power source 1 is applied to a rectifying circuit 3 through a reactor Ls, and the DC output voltage from the circuit 3 is smoothed by a smoothing circit 4 and is supplied to a load 5, and a load current is detected by a shunt SH2. A power factor improving circuit 2 consists of the reactor Ls, diodes D3-D6, and a switching transistor TR T1, and an overcurrent of the AC current is detected by a shunt SH1. An average DC current is detected by the shunt SH1, and the chopping frequency of a control signal applied to the base of the TR T1 is controlled to be higher for a light load and is controlled to be lower for a heavy load. Thus, the power factor for a light load is improved considerably, and the lowering of the power factor for a heavy load is reduced. |
