Patent ID: 6677716
Filing Date: 2004-01-13
Classification: H05B,Y10S

Abstract:
An operating device for operating gas discharge lamps, having the following features:a free-running half-bridge inverter (HB) which contains two half-bridge transistors (T1,T2) connected in series, a load circuit which is connected to the connection point between the half-bridge transistors (4) and which contains a primary winding (L2) of a current transformer through which a load current flows which is drawn from the half-bridge inverter (HB), in each case one drive circuit (1, 2) for each half-bridge transistor (T1, T2), which in each case contains the following components: a secondary winding (L3) of the current transformer, an integration element (R1, C4) which essentially integrates the voltage across the secondary winding (L3) of the current transformer and switches off the relevant half-bridge transistor on reaching a predetermined integration value, a first voltage threshold value switch (D3), which reduces an integration constant of the integration element on reaching a given first voltage threshold, characterized in thatthe half-bridge transistors (T1, T2) are essentially voltage controlled transistors, and at least one drive circuit (1, 2) has a second voltage threshold value switch (D2, R2) with a second voltage threshold which is lower than the first voltage threshold, with the second voltage threshold value switch (D2, R2) being connected in parallel with the secondary winding (L3).