| 摘要 |
PROBLEM TO BE SOLVED: To obtain a switching power supply unit for PWM control having a soft start function excellent in line regulation, and a soft start function suppressed in a rise of cost. SOLUTION: Two phase compensating circuits are prepared. A switch circuit 121 chooses either phase compensating circuit to phase-compensate an error signal Vea. A first phase compensating circuit 101 has a frequency characteristic shifted relatively to the low-band side as compared with a second phase compensating circuit 102. By selecting and using the phase compensating circuit suitable for the operating state of the switching power supply unit, a soft start operation in start-up operation is realized, and good line regulation in stationary operation is realized simultaneously. Moreover, since the soft start operation is realized by the phase compensating circuit, and the required circuit elements can be shared among the two phase compensating circuits, the rise of cost is suppressed. COPYRIGHT: (C)2010,JPO&INPIT
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