Patent ID: 8796941

Claim:
A method for operating at least one discharge lamp in a circuit arrangement having an input with a first and a second input connection for connecting a DC supply voltage; an output with at least a first and a second output connection for connecting the at least one discharge lamp; an inverter with at least a first and a second electronic switch that are coupled in series between the first and the second input connection, wherein a midpoint of the inverter is formed between the first and the second switch; an ignition device that comprises a lamp inductor and a resonant capacitor; a preheating device that comprises the series connection of a primary inductor, a third electronic switch and a current measurement resistor that is coupled between the midpoint of the inverter and the second input connection, and a first secondary inductor and a second secondary inductor coupled to the primary inductor, wherein the first secondary inductor is coupled to the first output connection and the second secondary inductor is coupled to the second output connection; a control device that is coupled to the current measurement resistor in which at least two sets of operating parameters assigned to different types of discharge lamps are stored, wherein one set of operating parameters constitutes a current set of operating parameters, wherein the control device is designed to actuate at least the first, the second and the third electronic switch in accordance with the current set of operating parameters; wherein in the preheating phase a first value of the voltage drop correlated with the reciprocal of the electrical resistance of at least one coil of the at least one discharge lamp is determined across the current measurement resistor at a first instant, and a second value of the voltage drop correlated with the reciprocal of the electrical resistance of the at least one coil of the at least one discharge lamp is determined across the current measurement resistor at a second instant, wherein the second instant is after the first instant; the method comprising: a) determining the difference between the first value of the voltage drop and the second value of the voltage drop; b) b1) if the difference is greater than a first threshold value: determining lamp-type; b2) if the difference is not greater than the first threshold value: c1) if the difference is greater than a second threshold value, wherein the second threshold value is less than the first threshold value: d1) determining a coil short circuit is present if the second value is greater than a third threshold value of the voltage drop: d2) operating the lamp with the current set of operating parameters if the second value is not greater than the third threshold value of the voltage drop.