| 摘要 |
A serial circuit of the primary winding (21) of a transformer (2), a switching device (3) and a current-detecting resistor (4) is connected between a pair of dc terminals (18, 19). A smoothing capacitor (7) is connected to the secondary winding (22) of the transformer (2) via a diode (6). A resonance capacitor (5) is connected in parallel with the serial circuit of the switching device (3) and the current-detecting resistor (4). The current detection signal, the output voltage detection signal, and the switch voltage detection signal are combined to provide control pulses for the switching device (3). A control circuit (13) includes a minimum nonconducting period determination circuit for setting a first and a second minimum nonconducting period with hysteresis. The nonconducting periods of the switching device are placed under the limitation of the minimum nonconducting periods when the load is light. The zero-voltage switching of the switching device (3) is effected upon lapse of the minimum nonconducting periods and upon completion of the release of the stored energy from the transformer (2). <IMAGE> |
