Operating circuit for low-power low-pressure discharge lamps,

Abstract

To meet IEC regulations in accordance with IEC publication 555-2 class D, r harmonic content of feedback into power networks upon use of low-power fluorescent lamps, an operating circuit for a lamp, or serially connected lamps is provided which includes a rectifier (2), rectifying a-c input energy, and having a smoothing capacitor (C3) connected across its output (J1, J2), the output of which is inverted in a half-bridge inverter using alternately conductive transistors (T1, T2), a passive filter circuit (5) is connected between an electrode of the lamp, or the last electrode of the lamps and a return connection to the rectifier (2). The passive filter circuit (5) has two serially connected diodes (D1, D2) defining a common junction (M2), connected in d-c blocking direction in a connection line between the second electrode (E2, E4') of a lamp (LP1) or the last of a group of serially connected lamps (LP1', LP2') and one (J1) output terminal of the rectifier (2). A first capacitor (C1) is connected to the common junction (M2) between the two diodes (D1, D2), and coupled to the other (J2) of the output terminals of the rectifier (2); and a second capacitor (C2) is connected in parallel across the serially connected two diodes (D1, D2).