| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a small and high-efficient switching power supply unit using a metal base substrate, which can suppress a switching noise current to be leaked to an input power supply side. Ž<P>SOLUTION: The switching power supply unit has a serial circuit consisting of a high-side switch element Q1 connected to an input power supply E, a primary winding T1p of an output transformer T1 and a low-side switch element Q2. The unit is provided with a control section CONT2 for outputting a predetermined pulsewidth modulation signal based on an output voltage and for driving to turn on/off both the switch elements Q1, Q2. The control section CONT2 is set at a value in which the maximum value of on-duty of the pulsewidth modulation signal to be outputted exceeds 50%. A pair of potential variation patterns 44a, 44b on which terminals having potential varying due to switching are each mounted among the terminals of both the switch elements Q1, Q2 are provided on a metal base substrate 42. Wiring capacitances CQ1, CQ2 formed between the potential variation patterns 44a, 44b and a metal base 42a of the metal base substrate 42 are the same as each other. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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