Circuit arrangement and method for operating semiconductor light sources

1. A circuit arrangement for operating a load, comprising:

an input for inputting a mains input AC voltage,

a power converter circuit,

a converter circuit which converts the mains input AC voltage rectified by the power converter circuit into an output voltage,

a control circuit for controlling the converter circuit, and

a linear regulating circuit which sets a predetermined load current at the load,

the load current being a direct current with a uniform current intensity,

wherein the output voltage is regulated such that a voltage in a ripple minimum is not enough to drive the load with the load current; and

wherein the control circuit controls the converter circuit in such a manner that the current intensity of the load current is reduced when the output voltage is at a minimum.

2. The circuit arrangement as claimed in claim 1 , wherein the load consists of light-emitting diodes.

3. The circuit arrangement as claimed in claim 1 , wherein the converter circuit is a SEPIC converter.

4. The circuit arrangement as claimed in claim 1 , wherein the converter circuit is a boost converter.

5. The circuit arrangement as claimed in claim 1 , wherein the potential at a node between the load and the linear regulating circuit is used to regulate the converter circuit.

6. The circuit arrangement as claimed in claim 5 , wherein a storage capacitor is coupled to the node in such a manner that it has its potential, the potential of the storage capacitor being input to the control circuit for the purpose of regulating the output voltage of the converter circuit.

7. The circuit arrangement as claimed in claim 6 , wherein the storage capacitor is charged via a charging resistor and is discharged to the potential of the node via a discharge diode.

8. The circuit arrangement as claimed in claim 5 , wherein a storage capacitor is coupled to the node via a voltage divider comprising a first resistor and a second resistor in such a manner that it has a potential correlating to the node, the potential of the storage capacitor being input to the control circuit for the purpose of regulating the output voltage of the converter circuit.

9. The circuit arrangement as claimed in claim 8 , wherein the storage capacitor is charged via a charging resistor and is discharged to a potential defined by the voltage divider and the potential of the node via a discharge diode and the first resistor.

10. The circuit arrangement as claimed in claim 9 , wherein a PTC thermistor is arranged in series with the discharge diode.

11. The circuit arrangement as claimed in claim 10 , wherein a resistor is arranged in parallel with the PTC thermistor.

12. The circuit arrangement as claimed in claim 8 , wherein the second resistor consists of a series circuit comprising a third resistor and a temperature-dependent resistor.

13. The circuit arrangement as claimed in claim 12 , wherein the temperature-dependent resistor is a PTC thermistor.

14. The circuit arrangement as claimed in claim 1 , wherein a Zener diode is connected between the output of the converter circuit and the control circuit for the purpose of limiting the output voltage of the converter circuit.

15. A method for operating a load using a circuit arrangement to which a mains input AC voltage is input and which converts the latter into an output voltage, the circuit arrangement having a current limiting circuit which converts the output voltage into a load current for operating the load, characterized in that the circuit arrangement is operated in such a manner that the current intensity of the load current is reduced when the output voltage is at a minimum; and

regulating the output voltage such that a voltage in a ripple minimum is not enough to drive the load with the load current.