| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power unit which is equipped with a constant-current drooping characteristics, without being provided with a constant current control circuit at its secondary side. SOLUTION: The switching power unit is equipped with a regulator 2 from a drain and auxiliary winding VCC; a circuit 6 for detecting the drain current of a switching element 1; an oscillation circuit 9; a feedback signal control circuit 11 which controls the drain current by detecting the control signal from the secondary side; a clamp circuit 12 which controls the maximum value of the drain current; a clamp voltage varying circuit 13, which varies the clamp voltage of the clamp circuit 12 and the oscillation frequency of the oscillation circuit 9, according to the voltage of VCC; and a clamp voltage regulating circuit 60. When the output voltage drops at overload, the oscillation frequency and the maximum current value of the switching element become small, due to the clamp voltage varying circuit 13, but the rate of change is adjusted to be optimum from the outside a semiconductor device for switching power control by the clamp voltage regulating circuit 60. COPYRIGHT: (C)2004,JPO&NCIPI
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