Circuit for controlling a fluorescent lamp, method for operating the circuit, and system comprising the circuit

1. A circuit for driving a fluorescent lamp, the circuit comprising:

a half bridge comprising a first switch and a second switch,

a drive unit for driving the first switch and the second switch at a switching frequency,

said drive unit being configured to indicate a fault state of the fluorescent lamp by modulating said switching frequency while providing a driving current for said fluorescent lamp.

2. The circuit as claimed in claim 1 , in which the driving of the first switch and of the second switch can be modulated between a first frequency and a second frequency.

3. The circuit as claimed in claim 2 , in which the driving of the first switch and of the second switch can be modulated between the first frequency and the second frequency at a third frequency.

4. The circuit as claimed in claim 3 , in which the driving of the first switch and of the second switch can be swept between the first and second frequency at the third frequency.

5. The circuit as claimed in claim 1 , wherein an integrated circuit is provided which comprises the drive circuit.

6. The circuit as claimed in claim 5 , wherein the integrated circuit is an ASIC.

7. The circuit as claimed in claim 1 , wherein the circuit is an electronic ballast for the fluorescent lamp.

8. The circuit as claimed in claim 1 , wherein the modulation of said switching frequency takes place during a waiting period prior to shut down of said driving current.

9. The circuit as claimed in claim 1 , wherein said fault state triggers a predetermined waiting period.

10. An arrangement comprising a circuit and a test circuit,

a half bridge comprising a first switch and a second switch,

a drive unit for driving the first switch and the second switch at a switching frequency, said drive unit being configured to indicate a fault state of the fluorescent lamp by modulating said switching frequency while providing a driving current for said fluorescent lamp,

wherein the driving of the first switch and of the second switch can be modulated between a first frequency and a second frequency,

the driving of the first switch and of the second switch can be modulated between the first frequency and the second frequency at a third frequency, and

the test-circuit comprising:

at least one of an output capacitor or a resistor connected to the circuit, and the third frequency can be detected using at least one of the output capacitor or the resistor.

11. The arrangement as claimed in claim 10 , wherein the fault state of the fluorescent lamp can be interrogated using the modulated driving of the first and of the second switch.

12. A method for testing a circuit for operating a fluorescent lamp, the method comprising:

detecting a fault state of the fluorescent lamp;

modulating a drive signal; and

detecting a modulation of the drive signal by a test circuit.

13. The method as claimed in claim 12 , wherein the modulation of the drive signal is altered between a first frequency and a second frequency with a third frequency.

14. The method as claimed in claim 12 , wherein a first switch and a second switch of a half bridge are operated using the drive signal.

15. A light-emitting system comprising a circuit for driving a fluorescent lamp, the circuit comprising:

a half bridge comprising a first switch and a second switch;

a drive unit for driving the first switch and the second switch at a switching frequency,

the drive-unit being configured to indicate a fault state of the fluorescent lamp by modulating said switching frequency while driving said fluorescent lamp.