Circuit arrangement to operate gas discharge lamp; has full bridge circuit supplied by direct current and has four controllable switches and circuit to control switches in normal and starting phases

摘要

The circuit arrangement has a full bridge circuit, which is supplied by direct current and has four controllable switches. A gas discharge lamp (LA) is connected between nodes between the first and second and the third and fourth switches. In a start phase, the switches are controlled, so that the fourth switch is closed, the third switch is open and the first and second switches are alternately opened and closed at a given frequency. The circuit arrangement has a full bridge circuit, which is supplied by direct current and has four controllable switches. First (S1) and second (S2) switches are connected in series and third (S3) and fourth (S4) switches are connected in series, the first and third switches are connected together and the second and fourth switches are connected together. A gas discharge lamp (LA) is connected between a node between the first and second switches and a node between the third and fourth switches. A control circuit controls the switches during normal operation of the gas discharge lamp, so that they are alternately switched between first and second states at a first frequency. In the first state, the second and third switch are open, the first switch is closed and the fourth switch is alternately opened and closed at a second frequency, which is higher than the first frequency. In the second state, the first and fourth switches are open, the third switch is closed and the second switch is alternately opened and closed at the second frequency. In a start phase, the switches are controlled, so that the fourth switch is closed, the third switch is open and the first and second switches are alternately opened and closed at a third frequency. An Independent claim is included for a method for operating a gas discharge lamp.