| 摘要 |
PROBLEM TO BE SOLVED: To stop switching operation, and to prevent an extraordinary temperature rise of a component, if an oscillation frequency becomes extraordinarily high by a malfunction of an oscillation circuit, by providing a frequency abnormality detector for detecting abnormal oscillation of the oscillation circuit which determines the switching frequency of a stabilized power supply. SOLUTION: If a triangle wave oscillation circuit 1 malfunctions, a triangle wave having an extraordinarily high frequency is outputted from the oscillation circuit 1 to an error detector 2. The triangle wave having the extraordinarily high frequency is compared with the voltage of a capacitor 6 by an operational amplifier 13, and the difference is outputted as a duty ratio to a transistor 3 and a frequency abnormality detector 9. A square wave of the extraordinarily high frequency inputted to the duty stabilizing circuit 10 of the abnormality detector 9 is outputted to an integrating circuit 11. If a voltage inputted to an inverse input terminal of a comparator 12 from the integrating circuit 11 becomes equal to or higher than the voltage of the non-inverse input terminal of the comparator 12, the comparator 12 becomes in an on-state, and stops switching operation.
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