| 摘要 |
PROBLEM TO BE SOLVED: To restrain power loss at the time of turning off without increasing power loss at the time of turning on a switching power supply unit operated in a current discontinuity mode. SOLUTION: This switching power supply unit comprises a transformer 2 which has a primary winding and a secondary winding on it, a switching device 5 which is connected with the primary winding of the transformer in series, a control circuit 7 which turns on/off the switching device, a diode in which the anode is connected with one end of the secondary side winding of the transformer, and a smoothing capacitor in which the cathode of the diode is connected with the other end of the secondary winding of the transformer. In the switching power supply device operated in the current discontinuity mode, a magnetic bias is applied to a core of the transformer by a permanent magnet so as to form a flux in opposite direction to the direction of the flux formed by the current of the primary winding.
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