Transformer-isolated resonant driver for parallel strings with robust balancing and stabilization of individual LED current

This paper presents a transformer-isolated resonant driver for parallel strings with robust balancing and stabilization of individual LED current. The methodology is based on connecting multiple transformers in a daisy chain to balance the string currents. To ensure service continuity of all LEDs, each LED has a bypass thyristor, which is triggered upon open-circuit failure, so that the healthy LEDs in the string would still be operated. A 21W prototype with 7 strings has been built. Each string has three 1W LEDs connected in series. Experimental results show that the LED current can still be regulated at the reference value within ±1% error even if the whole circuit has only one piece of LED in operation and all other LEDs fail short or open.