An LED current sharing circuit with high luminous efficacy and individual dimming

Soc. for Elec. Eng. The light-emitting diode (LED) VI characteristics of temperature dependence and devices variation make LED be current imbalanced when parallel-connected LEDs are powered by the common voltage source. Current imbalance will cause fast degradation or even failure in some LEDs that should be avoided in LED applications. This paper proposes a current sharing circuit based on the pulse width modulation (PWM) of a common bus voltage to realize the required averaged current. If it is in balance, a small duty cycle will necessitate a large LED on-time current, which may cause temporal overheat and low luminous efficacy of LEDs. The minimum on-time current amplitude control scheme is then proposed to maximize the duty cycles and improve the LED luminous performance. Moreover, the individual dimming control in each LED string can readily be incorporated into the current sharing circuit without additional circuit and cost. The analysis, implementation and verification are detailed in this paper.