| 摘要 |
PROBLEM TO BE SOLVED: To provide a low-cost switching power supply, by making the structure of a flyback transformer simple and by detecting an output voltage at the primary side. SOLUTION: A first switching element, which is self-oscillated by a voltage impressed from a drive coil of the flyback transformer to excite an exciting coil, is inserted between an exciting coil and a DC power supply. The drive coil is directly connected to one end of the exciting coil, and an output voltage detecting portion is provided for detecting a voltage corresponding to an output voltage of the exciting coil. An error detecting portion that compares a detected voltage with a reference voltage is provided in the output voltage detecting portion. A switching control device is connected to this error detecting portion. Based on the magnitude of a voltage difference detected by the error detecting circuit, a time constant circuit of the switching control device is made variable to control the ON time of a first switching element in such a way that the output voltage becomes constant by controlling the on-off of a second switching element. COPYRIGHT: (C)2004,JPO&NCIPI
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