Patent ID: 8330382
Filing Date: 2012-12-11
Classification: H05B,Y02B

Abstract:
1. A discharge lamp ballast comprising: an inverter coupled to a DC power source and comprising a plurality of switching elements, the inverter operable to provide an AC output current having positive and negative polarities; an asymmetry determination circuit functional to determine whether the AC output current from the inverter is symmetrical and to provide a corresponding output; a control circuit functional to control the plurality of switching elements to provide lamp power dependent upon an operating mode and on the output from the asymmetry determination circuit; wherein the control circuit controls the switching elements in a normal mode upon receiving a determination of symmetrical current from the asymmetry determination circuit; wherein the control circuit transitions to a delay mode when the polarities are determined to be asymmetrical by the asymmetry determination circuit, the delay mode comprises a delay operation wherein each of the plurality of switching elements are turned off for a predetermined delay period so as to stop power output to the discharge lamp; and wherein the control circuit transitions to a restart mode for a predetermined period of time after the predetermined delay period elapses.