| 摘要 |
An objective of the present invention relates to a switching power supply, capable of fabricating a capacitor having a small capacity to supply power supply voltage without operating failure. The switching power supply includes a control circuit (3a) for controlling an on/off state of a switching device (Q10), a second rectifying smoothing circuit (diode (D10)) for smoothing voltage generated from a third winding (P2) of a transformer (T) to supply the smoothed voltage to the control circuit (3a) as the power supply voltage (Vcc), and a capacitor (C10). A starting circuit (1a) is provided to the control circuit (3a) as starting current (ls) if the power supply voltage (Vcc) is equal to or less than a first threshold voltage (V1) lower than starting voltage (Von) (stop voltage (Voff)) of the control circuit (a), or exceeds the starting voltage (Von), and supplies second constant current (lb) greater than the first constant current (la) if the power supply voltage (Vcc) exceeds the first threshold voltage (V1) so that the power supply voltage (Vcc) is equal to or less than the starting voltage (Von). |
