Patent ID: 6100647
Filing Date: 2000-08-08
Classification: H05B,Y10S

Abstract:
An electronic ballast for an electron discharge lamp, said ballast comprising an inverter having a resonant output circuit coupled to the lamp to supply high frequency power thereto, and also comprising a drive control circuit for supplying a switching signal to said inverter having a frequency which is variable in order to control the power supplied to the lamp by said inverter and thereby control the lamp intensity; characterized in that said ballast further comprises:voltage sensing means coupled to the lamp for producing a signal representative of lamp voltage;current sensing means coupled to the lamp for producing a signal representative of lamp current; andpower calculating means coupled to said voltage sensing means and to said current sensing means for combining the lamp voltage signal and the lamp current signal so as to derive therefrom a signal representative of power supplied to the lamp, the power signal being applied to said drive control circuit to adjust the frequency of said switching signal in accordance with said power signal;the lamp voltage signal and lamp current signal being combined in such a way that the power signal derived therefrom takes account of any phase difference between lamp voltage and lamp current.