Patent ID: 8143814

Claim:
Driver ( 1 ) for driving a gas discharge lamp ( 2 ), comprising: a current source ( 3 ) for generating lamp current, having a setpoint input ( 4 ) for receiving a setpoint signal; a controller ( 10 ) having an output ( 12 ) for generating a current setpoint signal (S M ); a controllable noise signal source ( 20 ) controlled by the controller ( 10 ), designed for-generating a pseudo random noise signal (S PRNS ); an adder ( 22 ) connected to receive the current setpoint signal (S M ) from the controller ( 10 ) and the pseudo random noise signal (S PRNS ) from the noise signal source ( 20 ), and having an output coupled to the setpoint input ( 4 ) of the current source ( 3 ); measuring means ( 40 ) for measuring a characteristic lamp response of the lamp ( 2 ) in response to the pseudo random noise signal (S PRNS ), coupled to a sense input ( 14 ) of the controller ( 10 ) for providing to the controller ( 10 ) a sense signal representing the characteristic lamp response; a memory ( 30 ) associated with the controller ( 10 ), having stored therein at least one reference signal; wherein the controller ( 10 ) is designed to compare the characteristic lamp response as measured by the measuring means ( 40 ) with said predetermined reference signal in the memory ( 30 ).