Method for actuating a discharge lamp and circuit arrangement for operating such a lamp
A method for actuating a discharge lamp (LP), wherein in order to ignite the lamp a resonant circuit (L, C 1 ) is brought into resonance or near resonance by the action of alternating current and as a result adjustment to give a predetermined amperage is performed by varying the frequency of the alternating current. For this purpose a measuring device transmits measured values of the amperage to means for controlling the frequency, and these means establish the frequency in dependence on the measured values. Before the ignition voltage is applied the electrodes of the lamp are pre-heated by the action on the resonant circuit of alternating current of a different frequency than when the lamp is ignited. During pre-heating a predetermined amperage is set by adjustment in that the means for controlling the frequency are already activated and the procedure is such that the measuring device obtains measured values of the amperage and transmits them to the means for controlling, these measurement values corresponding to an amperage which deviates in a predetermined manner from the amperage specified by measured values during ignition.
1. A circuit arrangement for operating a discharge lamp comprising:
a capacitive element which is connected in parallel with the discharge lamp and an inductive element which is in series upstream of the discharge lamp and the capacitive element, such that a resonant circuit is formed;
a plurality of switches for applying current to the resonant circuit;
means for closing each of the plurality of switches in a mutually alternating sequence at a switching frequency;
means for measuring an amperage of a current flowing through one switch of the plurality of switches;
means for establishing the switching frequency as a function of the measured amperage;
control means for influencing the measured values obtained by the means for measuring, said control means including a source for providing a fixed potential across a switching point of thc circuit arrangement; and
an application-specific integrated circuit operatively coupled to the plurality of switches, said application-specific integrated circuit including a plurality of potential outputs for respectively triggering each of the plurality of switches, a potential input of the means for measuring and a third potential output for providing the source.
2. The circuit arrangement according to claim 1 , wherein the means for measuring include a voltage divider having a plurality of resistor elements, and wherein said switching point being between each of the plurality of resistor elements and being connected via a further resistor element to the source.
3. The circuit arrangement according to claim 2 , wherein the further resistor element has a resistance which is at least five times as large as the largest resistance of the plurality of resistor elements.
4. The circuit arrangement according to claim 1 , wherein the third potential output is connected to ground via a resistor, a Zener diode.
5. The circuit arrangement according to claim 4 , wherein the third potential output is further connected to ground via a capacitive element connected in parallel with the Zener diode.