Patent ID: 8395333

Claim:
An electro magnetic ballast ( 110 ) for a gas discharge lamp ( 2 ), comprising: input terminals ( 3 ), for receiving a mains voltage; lamp connector terminals ( 4 ), for receiving a lamp; a controllable semiconductor switch ( 26 ) coupled in parallel to the lamp connector terminals; a current sensor ( 127 ) connected in series with the controllable switch ( 26 ); and a control circuit ( 28 ) for controlling the controllable switch ( 26 ) and responsive to the current sensor ( 127 ); wherein, if the controllable switch is OFF due to ( 1 ) a signal from the control circuit, ( 2 ) mains voltage is not received or ( 3 ) when in an operating mode the lamp fails, and the control circuit ( 28 ) receives a current sense signal from the current sensor indicating current is still flowing to the controllable switch, the control circuit ( 28 ) switches the controllable switch ( 26 ) ON and switches the controllable switch ( 26 ) OFF if said current sense signal indicates that no current is flowing in the controllable switch ( 26 ).