A ring diode-capacitor network for current-balancing multiple LED strings

A ring diode-capacitor network for current-balancing multiple LED strings will be presented. The concept is based on utilizing the charge-balance property of capacitors to balance the currents through two adjacently-connected LED strings in one cycle. Such relationship propagates through all the strings in the ring. The architecture has several merits, including 1) simple structure, 2) modular and scalable, 3) current-balancing property independent of the string voltages and the capacitor values, 4) provision of galvanic isolation between driver and strings, and 5) currents through healthy LED(s) unaffected by failed LED(s). The capacitors in the network can also form a part of the resonant component for resonant-type LED drivers. Detailed mathematical model will be formulated. An 80W prototype with 10 strings has been built. Each string has eight 1W LEDs connected in series. Experimental results reveal that the string current variation is less than ±0.5% at any conditions.