Method for operating at least one low-pressure discharge lamp and operating device for at least one low-pressure discharge lamp

An operating device for at least one low-pressure discharge lamp, comprising:

• a voltage rectifier (GL) having connections (1,2) for receiving a system voltage and operable to provide a supply voltage between a positive DC voltage output (+) and negative DC voltage output (−), wherein the negative DC voltage output (−) is coupled to a circuit ground;
• a half-bridge inverter (T1,T2,TR) coupled to the voltage rectifier and operable to receive the supply voltage from the voltage rectifier, the inverter including a first transistor (T1), a second transistor (T2), and a driver circuit (TR) for alternately switching the first and second transistors, wherein the inverter further includes a disconnecting apparatus that is activated in response to occurrence of a rectifier effect in the at least one low-pressure discharge lamp (FL1,FL2);
• a load circuit (L1,C1,C2,C3) coupled to the inverter and the at least one low-pressure discharge lamp (FL1,FL2), the load circuit comprising a resonant inductor (L1), a resonant capacitor (C1), a first half-bridge capacitor (C2), and a second half-bridge capacitor (C3), the load circuit (L1,C1,C2,C3) being operable to deliver a current to the at least one low-pressure discharge lamp (FL1,FL2), the current including positive half-cycles and negative half-cycles;
• an evaluation unit (MC) coupled to the driver circuit (TR) of the inverter, the microcontroller including first, second, third, and fourth inputs (A6,A7,A8,A11);
• a first sub-circuit (R6,R7,C5) coupled between the positive DC voltage output (+) of the voltage rectifier (GL) and the first input (A6) of the evaluation unit (MC), the first sub-circuit being operable to provide a first voltage signal to the first input (A6) of the evaluation unit (MC), wherein the first voltage signal is proportional to the supply voltage;
• a second sub-circuit (R8,R9,C6) coupled between the second half-bridge capacitor (C3) and the second input (A7) of the evaluation unit (MC), the second sub-circuit being operable to provide a second voltage signal to the second input (A7) of the evaluation unit (MC), wherein the second voltage signal is proportional to a voltage across the second half-bridge capacitor (C3);
• a third sub-circuit (R10,R11,C7) coupled between the first half-bridge capacitor (C2) and the third input (A8) of the evaluation unit (MC), the third sub-circuit being operable to provide a third voltage signal to the third input (A8) of the evaluation unit (MC), wherein the third voltage signal is proportional to a voltage across the first half-bridge capacitor (C2);
• a fourth sub-circuit (D3,D4,R14,R15,C10) coupled between the half-bridge capacitors (C2,C3) and the negative DC voltage output (−) of the voltage rectifier (GL), the fourth sub-circuit being operable to provide a fourth voltage signal to the fourth output (A11) of the evaluation unit (MC), wherein the fourth voltage signal is proportional to an average value of the positive half-cycles of the current through the at least one low-pressure discharge lamp;
• and
• wherein the evaluation unit (MC) is operable:
• (i) to detect, by way of the first, second, third, and fourth voltage signals, occurrence of a rectifier effect in the at least one low-pressure discharge lamp;
• and (ii) in response to occurrence of a rectifier effect in the at least one low-pressure discharge lamp, to activate the disconnecting apparatus of the inverter.