Patent ID: 7285989
Filing Date: 2007-10-23
Classification: G01R,G06F

Abstract:
1. A device for detecting a power-off of external input power from a power supply device, comprising: a detection unit for generating an induced current in response to an AC current provided by the power supply device; a voltage supply unit for converting the induced current generated by the detection unit into a detection voltage; and a voltage comparison unit for comparing the detection voltage provided by the voltage supply unit and a reference voltage, and for providing a power-off detection signal when there is a difference between the detection voltage and the reference voltage; wherein the detection unit comprises a transformer which includes a first coil which forms a magnetic flux in response to the AC current provided by the power supply device, a second coil which is responsive to the magnetic flux formed by the first coil for generating an induced current which is smoothed and rectified so as to provide a DC voltage, via an output circuit, to an electronic appliance, and a third coil which generates the induced current in response to the magnetic flux formed by the first coil; said device further comprising a voltage divider connecting the output circuit to an inverting input of the voltage comparison circuit for providing a divided voltage thereto as the reference voltage; and wherein the voltage comparison circuit provides the power-off detection signal via the output circuit, to the electronic appliance, whereby the electronic appliance is safely prepared for power-off.