Switching power supply controller
In an example embodiment, a controller generates a switch signal for controlling a switch to convert an input signal from a phase cut dimmer into a driving signal for a solid state lighting element. The controller determines a conduction period of the input signal from the phase cut dimmer within a half cycle period of the input signal, determines a burst period within the conduction period is a period of time less than the conduction period, and generates a switch signal comprising a plurality of switching cycles over the burst period. The switch signal has first and second subsets of switching cycles. The controller controls the switching cycles of the second subset such that the average energy transferred per switching cycle to the driving signal is less than the average energy transferred per switching cycle to the driving signal for the switching cycles of the first subset.
1. A switching power supply controller, the switching power supply controller configured to generate a switch signal for controlling a switch to convert an input signal from a phase cut dimmer into a driving signal for a solid state lighting element, wherein the switching power supply controller is configured to;
determine a conduction period of the input signal from the phase cut dimmer within a half cycle period of the input signal;
determine a burst period within said conduction period comprising a period of time less than said conduction period;
generate a switch signal comprising a plurality of switching cycles over the burst period, the switch signal comprising a first subset of switching cycles and a second subset of switching cycles, wherein the switching power supply controller is configured to control the switching cycles of the second subset such that the average energy transferred per switching cycle to the driving signal is less than the average energy transferred per switching cycle to the driving signal for the switching cycles of the first subset.
2. The switching power supply controller according to claim 1 , in which the switching power supply controller is configured to control the switch signal such that the energy transferred per switching cycle to the driving signal is decremented over the switching cycles of the second subset.
3. The switching power supply controller according to claim 1 , in which the second subset includes a plurality of switching cycles, the duration of said switching cycles controlled such that the peak current achieved over subsequent switching cycles in the second subset is reduced over the second subset.
4. The switching power supply controller according to claim 1 , in which the switching power supply controller is configured to control the duration of the switching cycles of the first subset by determining when the current flow during a switching cycle reaches a predetermined maximum peak current.
5. The switching power supply controller according to claim 1 , in which the first subset includes a plurality of switching cycles in which the energy transferred in each switching cycle is maintained substantially constant.
6. The switching power supply controller according to claim 1 , in which the switching power supply controller is configured to position the burst period within the conduction period by a) using a voltage threshold, wherein the burst period is configured to comprise a period of time during the conduction period in which the voltage of the input signal is greater than or equal to the voltage threshold or b) by using timing information of the conduction period and positioning the burst period such that it is temporally spaced from the end of the conduction period for a forward phase cut dimmer or spaced from the beginning of the conduction period for a backward phase cut dimmer.
7. The switching power supply controller according to claim 1 , in which the switching power supply controller is configured to determine an output power level setting by measurement of the input signal, the switching power supply controller configured to generate the switching signal as a function of the output power level setting.
8. The switching power supply controller according to claim 7 , in which the switching power supply controller includes a feedback arrangement configured to receive a measure of the driving signal and compare the output power level setting with the measure of the driving signal and generate an error signal, said error signal used to control the number of switching cycles and/or the duration of each switching cycle.
9. The switching power supply controller according to claim 7 , in which the switching power supply controller is configured to determine the average energy per switching cycle of the second subset using a function of the output power level setting or the error signal.
10. The switching power supply controller according to claim 1 , in which the switching power supply controller has a minimum peak current threshold, the switching power supply controller configured to control the switch signal such that the minimum peak current threshold is reached during each of the switching cycles.
11. The switching power supply controller according to claim 1 , in which the switching power supply controller includes a maximum burst period threshold.
12. The switching power supply controller according to claim 1 , in which the switching power supply controller is configured to start the burst period at the start of a conduction period when the input signal comprises a forward phase cut input signal.
13. The switching power supply controller according to claim 1 , in which the switching power supply controller is configured to temporally align the end of the burst period with the end of the conduction period when the input signal comprises a backward phase cut input signal.
14. A solid state light driver comprising an input terminal for receiving an input signal from a phase cut dimmer, a switching power supply including an inductive element, a switching element, a diode, and a pair of output terminals for connecting to a solid state light, the driver further including the switching power supply controller of claim 1 , for controlling said switch element.
15. A solid state light comprising the solid state light driver as defined in claim 14 and at least one solid state light element, said driver configured to power said solid state light element.