A parallel LED string driver using capacitors for source and string ground separation

A parallel LED string driver using capacitors for source and string ground separation is proposed. The methodology is based on connecting multiple transformers in a daisy chain and using capacitor network in every LED strings to balance the string currents. The grounds of the input source and the output strings are also separated by the capacitor network. A 21W prototype with 7 strings has been built. Each string consists of three 1W LEDs connected in series. Experimental results show that the variation of LED string current can still be less than ±1% even if the string voltages have significant differences. The current level and variation of healthy LED strings will not be affected by any failed LEDs. The string current can be dimmed from 100% to 10%. Modeling, analysis, and design of the proposed driver will be given.