Method for operating at least one fluorescent lamp, and electronic ballast therefor

Abstract

An integrated control and regulating circuit (IC) controls, via a half-bridge circuit (V,V,), a load circuit (,) having the at least one fluorescent lamp (FL) by means of a drive circuit (CCO, SEL, HSD, LSD) regulated in a high-frequency manner. In the control and regulating circuit, each time the lamp is started and/or when there is a disturbance, a timer (PST, IT, CT) is started, which thus defines a sequence predetermined periods of time (&Dgr;pt, &Dgr;it, &Dgr;st, &Dgr;ot), inter alia preheating period (&Dgr;pt) and ignition period (&Dgr;it). In a monitoring circuit (MON), the pulsed load current of the load circuit is cyclically monitored in comparison with reference levels (Mp, Mi, Mdo and Mo) which are respectively predetermined for the periods of time, in order to detect a normal state or a disturbance in the load circuit, to control the current regulation of the drive circuit (CCO, ISC, SEL, HSD, LSD) in the normal state, or to trigger an automatic disconnection of the electronic ballast in the event of a disturbance. During the ignition period (&Dgr;it), a current signal which is derived from the load current and is fed to the monitoring circuit (MON) has superposed on it an internally generated DC signal (DC) having a defined level. The value thereof is dimensioned in accordance with the types and/or circuits of the fluorescent lamp(s) which are used in the load circuit, with the result that the signal that is superposed in this way is adapted to the predetermined, fixed reference levels (e.g. Mp, Mi) of the monitoring circuit (MON) independently of the lamp selection in the load circuit.