| 摘要 |
PURPOSE: To accurately detect small loading with no erroneous action even if there exists distortion in AC power supply voltage by comparing the voltage level of power supply voltage with the voltage level of an input capacitor voltage at the vicinity of a zero-cross point. CONSTITUTION: Voltage Vo to be detected by a power supply voltage detection circuit 8 is inputted to one input terminal of a comparator 11, and voltage Vc from an input capacitor voltage detection circuit 10 is inputted to the other terminal. The output signal of the comparator 11 and the detected signal of a zero-cross detection circuit 7 are inputted into a judging unit 11. In the case where loading is normal, voltage Vc is lower than voltage Vo at all times, however, in the case of small loading, voltage Vc is higher than voltage Vo at the vicinity of a zero-cross point, a signal from the judging unit 11 is outputted to a control circuit 6, and a suspension signal is thereby outputted to an inverted circuit 4. By this constitution, small loading is accurately detected, and heating caused by small loading can thereby be prevented. |
