Patent ID: 7279844

Claim:
Ballast for low-pressure discharge lamps, comprising a controllable inverter circuit for the generation of a high-frequency supply voltage for a discharge lamp ( 1 ), a lamp inductance (L 1 ) connected to the inverter circuit and serially connected to the discharge lamp ( 1 ), a lamp parallel capacitor (C 1 ) which is serially connected to the lamp inductance (L 1 ) and connected in parallel to the discharge lamp ( 1 ), and a preheating circuit supplying heating current to the electrodes ( 2 , 3 ) of the discharge lamp ( 1 ), wherein said preheating circuit comprises a heating transformer ( 4 ) whose secondary windings ( 5 , 6 ) are connected to electrodes ( 2 , 3 ) of the discharge lamp ( 1 ), wherein the current is supplied to the preheating circuit via an auxiliary winding ( 7 ) arranged on the lamp inductance (L 1 ), said auxiliary winding ( 7 ) being connected to the primary winding ( 8 ) of said heating transformer ( 4 ) via a parallel resonant circuit ( 9 ).