Starting unit for heated gas discharge tubes

Claim 1

Starting unit for heated gas discharge tubes, in particular fluorescent gas tubes, comprising a heating circuit which includes the tube electrodes, a controlled electronic switch, and the secondary winding (8) of an auto-transformer (8,9) arranged in a series connection; the electrode switch (3) has in parallel with it a series connection which consists of the primary winding (9) of the auto-transformer and a capacitor (23) and in which, with the switch switched on, the capacitor is discharged through the primary winding (9) of the auto-transformer, giving rise to trigger voltage impulses stepped up by the auto-transformer; the tube electrodes (4,5) have connected to them a control circuit (26 to 38) whose output is connected to the control electrode of the electronic switch, the control circuit including a bridge component having a timing component (30, 31) connected across it for the purpose of developing a time-dependent quantity corresponding to the temperature change in the tube electrodes caused by the heating, with the result that the switch-on moment of the electronic switch is displaced approximately proportionally to the temperature of the tube electrodes from small phase angles of the tube voltage up to a phase angle associatEd with a voltage limit value located in the range of the peak value of the tube voltage, while, once that limit value is exceeded, the electronic switch is blocked; and the timing component is provided with means (36) which, with the switch blocked, vary the time-dependent quantity at a quicker rate than would correspond to the temperature behavior of the non-loaded tube electrodes, so that, after several mains voltage cycled, the switch is repeatedly switched on and occasional trigger voltage impulses arise.