Low-pressure discharge lamp, particularly fluorescent lamp high-frequency operating system with low inductance power network circuit

Claim 1

In combination with a fluorescent lamp (LP1, LP2), a low inductance power network circuit, adapted to be connected to a power line circuit (U) at power line voltage and frequency, including a power rectifier (2) having output terminals (P1, P2) which form positive (P1) and negative (P2) lamp circuit input terminals, respectively; an input capacitor (C2) connected across said lamp circuit input terminals (P1, P2); a push-pull transistor frequency generator (3) having two alternately conducting transistors (T1, T2) and having a common junction (M1); and an operating circuit for the transistors, including said lamp, an oscillator transformer (RK), including first (RK1), second (RK2) and third (RK3) windings, the second and third windings being, respectively, connected to the base of a respective transistor (T1, T2) and the first winding being connected between said common junction (M1) and a first electrode (E1, E3) of the lamp electrodes, and a series resonance circuit (4) having a series inductance (L1, L1') defining two terminals and having a first terminal connected to the common junction (M1) of the transistors (T1, T2) and a second terminal (M3, M3') connected through a series coupling capacitor (C5, C5') and through lamp filaments of the lamp electrodes (E1, E2, E3, E4) to a resonance capacitor (C6, C6') in the preheating circuit of the lamp (LP1, LP2), and comprising a harmonic filter including a first and a second diode (D8, D9), serially connected in forward current passing direction and defining a first diode junction (M2) between said first and second diodes; a first coupling capacitor (C7) coupling said first diode junction to said common junction (M1) between said transistors (T1, T2); a second coupling capacitor (C8, C8') coupling said first diode junction (M2) to said second terminal (M3, M3') of the series inductance (L1, L1'); third and fourth diodes (D10, D11), serially connected in forward current passing direction and defining a second diode junction (M4) between said third and fourth diodes, said third and fourth diodes being connected in parallel to said first and second diodes (D8, D9); a third coupling capacitor (C9) coupling said second diode junction (M4) to the common junction (M1) between said transistors (T1, T2) of said push-pull transistor frequency generator (3); and wherein said first and second serially connected diodes, and said third and fourth serially connected diodes (D8, D9; D10, D11) are connected between one (P1) of said lamp circuit input terminals (P1, P2) and a second electrode (E2, E4) of the lamp electrodes.