Controller, a driver circuit and a method for controlling a dimmable LED lighting circuit, and a dimmable LED lighting circuit
A controller for a dimmable LED lighting circuit is disclosed, the controller comprising: an LED current controller configured to set a current of a constant current source in dependence on a conduction angle of the phase-cut dimmer; a first feedback circuit configured to control the circuit's power converter in dependence on the constant current source by adjusting an output of the power converter; and a second feedback circuit configured to control a supplementary output load arranged in parallel with the series arrangement of the constant current source and plurality of LEDs, wherein the second feedback circuit is operable to adjust the supplementary output load faster than the first feedback circuit adjusts the output of the power convertor. A driver and lighting circuit also disclosed, as is a method for controlling a dimmable lighting circuit.
1. A controller for a dimmable LED lighting circuit operable with a phase-cut dimmer and having a power converter for providing power to a series arrangement of a plurality of LEDs and a controllable current source, the controllable current source being for providing a current through the plurality of LEDs,
the controller comprising:
an LED current controller configured to set the current of the current source in dependence on a conduction angle of the phase-cut dimmer;
a first feedback circuit configured to control the power converter in dependence on the current source by adjusting an output power of the power converter; and
a second feedback circuit configured to control a supplementary output load arranged in parallel with the series arrangement of the current source and plurality of LEDs.
2. A controller according to claim 1 , wherein the second feedback circuit is configured to adjust the supplementary output load with a time constant which is shorter than a response time of the first feedback circuit.
3. A controller according to claim 1 , wherein the first feedback circuit has an input, the input being in communication, in use, with a node between the current source and the plurality of LEDs.
4. A controller according to claim 1 , wherein the second feedback circuit has an input, the input being in communication, in use, with a node between the current source and the plurality of LEDs.
5. A controller according to claim 1 , configured for use with a supplementary output load which comprises a controllable resistance.
6. A controller according to claim 5 , wherein the second feedback circuit is configured to set the controllable resistance, in a steady state, to a value which varies in proportion to the secant of the conduction angle of the phase-cut dimmer, over at least 170° of conduction angle.
7. A controller according to claim 1 , configured for use with a supplementary output load which comprises a controllable current source.
8. A driver for a dimmable LED lighting circuit and comprising a controller as claimed in claim 1 , a current source for providing a current through the plurality of LEDs, a power converter in communication with and for being controlled by the first feedback circuit, and a supplementary output load in communication with and for being controlled by the second feedback circuit.
9. A dimmable LED lighting circuit comprising a driver as claimed in claim 8 , and a plurality of LEDs in series arrangement with the current source.
10. A method of controlling a dimmable LED lighting circuit operable with a phase-cut dimmer and having a power converter for providing power to a series arrangement of a plurality of LEDs and controllable current source, the controllable current source being for providing a current through the plurality of LEDs,
the method comprising:
setting the current of the current source in dependence on a conduction angle of the phase-cut dimmer;
controlling the power converter in dependence on the current source by adjusting an output power of the power converter and
controlling a supplementary output load arranged in parallel with the series arrangement of the current source and plurality of LEDs,
wherein adjusting the supplementary output load is faster than adjusting the output of the power convertor.