Patent ID: 8174202

Claim:
A lamp driving circuit for operating a discharge lamp, the lamp driving circuit comprising: input terminals for connection to a supply voltage source, a series arrangement comprising a first switching device and a second switching device, and connecting the input terminals, an inverter resonant circuit shunting one of the switching devices and comprising an inverter inductance, an inverter capacitance, and lamp connection terminals, a control circuit coupled to respective control electrodes of the switching devices to generate a lamp current commutating at a commutation frequency, the control circuit being configured for: during a first interval of a commutation period, for a plurality of alternating first and second time periods rendering the first switching device alternately conducting during each first time period and non-conducting during each second time period at a high frequency being higher than the commutation frequency, during a second interval of the commutation period, for a plurality of alternating third and fourth time periods rendering the second switching device alternately conducting during each third time period and non-conducting during each fourth time period at a high frequency being higher than the commutation frequency, and extending one of the first time periods at the start of the first interval of the commutation period to have a longer duration than the other first time periods, and extending one of the third time periods at the start of the second interval of the commutation period to have a longer duration than the other third time periods.