| 摘要 |
PROBLEM TO BE SOLVED: To eliminate malfunctions of a protective circuit. SOLUTION: In this switching power source circuit provided with a microcomputer 11, a DC voltage is applied to a primary winding 7a of a converter transformer 7, a switching element 8 is connected in series to the primary winding 7a of the transformer 7, a switching signal obtained in a PWM control circuit 10 is supplied to the switching element 8, the DC voltage is subjected to switching, and an output DC voltage is obtained by rectifying an AC voltage obtained in a secondary winding 7b of the transformer 7. The pulse width of the switching signal of the PWM control circuit 10 is modulated according to the output DC voltage. The microcomputer 11 makes the output DC voltage constant, detects abnormality of the voltage, and protects the power source circuit. The clock signal of the microcomputer 11 is made synchronous with the switching signal of the PWM control circuit 10.
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