| 摘要 |
PROBLEM TO BE SOLVED: To prevent variations in overcurrent detecting point for overcurrent protection. SOLUTION: An FFT 34 and a primary winding of a transformer 36 are connected in series with a DC power supply 30. Induced AC voltage of a secondary winding of the transformer 36 is rectified by diodes 33a and 33b, smoothed by a capacitor 40, and fed to positive and negative output terminals 42P and 42N. A diode 44 and a capacitor 46 are connected between one end of the secondary winding of the transformer 36 and the capacitor 40. A voltage across both ends of the capacitor 46 is changed through a Zener diode 50 into a stabilized voltage and fed as an operational voltage for an error amplifier 54. An input terminal of the error amplifier 54 is connected to a path joined with a positive output terminal 52P. A detection resistor 56 is interposed between one input terminal of the error amplifier 54 and the positive output terminal 52P. A resistance serial circuit is connected in series with the detection resistor 56. The resistance serial circuit includes voltage-dividing resistors 58 and 60 connected in series on the output side of the Zener diode 50. The connection point of the resistors 58 and 60 is connected to the other input terminal of the error amplifier 54. The output signal of the error amplifier 54 is fed to an overcurrent protective circuit 62.
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