| 摘要 |
PROBLEM TO BE SOLVED: To reduce variations of an upper limit value and a lower limit value in adjustment of an output voltage, and to reduce fluctuation of the output voltage owing to temperature, in setting of a switching power source. SOLUTION: In an overvoltage protecting circuit for power devices having an adjusting means which adjusts the output voltage of a power device, a fixing means which fixes the output voltage to a predetermined limit value, a comparing means 23 which compares a detected value by a detecting means with the predetermined limit value, and a choosing means 26 which chooses between making the adjusting means effective and making the fixing means effective, on the basis of the comparison result by the comparing means 23; the fixing means is provided with an error amplifier 16 and fixed resistors 19, 20 provided in an IC for dividing the output voltage, and the voltage of the voltage-dividing point of the fixed resistors 19, 20 is inputted to the inversion input terminals of the error amplifier 16 through the choosing means 26.
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