Patent ID: 7872426
Filing Date: 2011-01-18
Classification: H05B,Y02B

Abstract:
1. A ballast protecting device, comprising: a voltage sensing circuit adapted to receive an AC input voltage across first and second voltage input terminals; a current sensing circuit having an input connected to the first voltage input terminal and a first output connected to one output terminal of the device; a pulse forming circuit having an input connected between an output terminal of the voltage sensing block and a second output of the current sensing circuit, wherein the output terminal of the voltage sensing block provides a reference signal in phase with the AC input voltage, and the second output of the current sensing circuit provides a signal representing a phase of a current through the device relative to the reference signal; a switch unit arranged between the second voltage input terminal and another output terminal of the device, and controller means operatively connected to the pulse forming circuit and the switch unit for determining a phase angle difference between the reference signal and the current through the device and for controlling the switch unit in response to the determined phase angle difference, wherein the switch unit electrically disconnects the second voltage input terminal from said another output terminal of the device when the controller means determines an undesired phase angle trend.