An average current modulation method for single stage LED drivers with high power factor and zero low frequency current ripple
Conventional single-stage AC-DC LED drivers with a high power factor contain significant LED current ripple at twice the AC line frequency, and require large energy storage capacitors to limit the effect on LED light. Conventional designs and novel control techniques aim to power LED loads with a DC voltage to ensure a limited low frequency current ripple. This paper proposes an average current modulation method that is capable of driving LEDs from a voltage that contains significant AC ripple, while maintaining zero low frequency current ripple. This allows the energy storage capacitance of the PFC stage to be reduced, avoiding the need for electrolytic type capacitors, and prolonging the life of the LED driver. The average current modulation circuit requires a single low voltage MOSFET, a current sense resistor and a simple control circuit. By requiring no additional magnetic components, the cost of the average current modulation circuit is very low, and has minimal impact on the efficiency of the overall LED driver. A 25 W experimental prototype with a Flyback PFC converter has been built to verify the capability and excellent performance of the proposed driving technique.