| 摘要 |
PROBLEM TO BE SOLVED: To elevate switching frequency in a switching power supply, which performs overcurrent protective operation by shortening the switching pulse width. SOLUTION: A switching power supply is so designed, that according to the difference between a divided voltage value Vadj of an output voltage Vo by resistors R1 and R2 and a reference voltage Vref1, a comparator 15 slices triangular waves from an oscillator 16 and a drive circuit 19 controls a transistor Tr1. In the switching power supply, when an overcurrent is detected through an overcurrent detection circuit 11, a first oscillation frequency changing circuit 17 reduces the oscillation frequency of the oscillator 16, and further a RS flip- flop circuit 12 performs overcurrent protective operation. In addition, if an output voltage Vo drops due to output short-circuiting or the like, a second oscillation frequency changing circuit 18 reduces the oscillation frequency of the oscillator 16. Therefore, a switching pulse width for which delay in response in overcurrent protective operation can always be taken into account is obtained, and the frequency under steady-state load can be increased.
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