基于LCLC恒流网络的LED自均流电路

A Multi-string LED Driver With Constant-current Output and Automatic Balancing

多路半导体发光二极管(light-emitting-diode,LED)并联会造成导通电流不均衡,而电容均流方案由于其简单可靠得到广泛应用。为输出所需的LED电流,电容均流方案采用变频控制会引入无功环流,提高器件应力,而采用定频占空比控制时,变化的LED负载难以保证零电压开关(zerovoltage switching,ZVS)的实现。针对此问题,文中提出一种基于LCLC谐振网络的恒流源输出LED驱动电路,可有效解耦负载对输出电流的影响,定频控制,且同时实现输入阻抗为纯阻性,避免无功环流。该谐振网络亦结合电容均流方案,采用较少的器件实现多路均流。此外,该电路具有短路自保护功能,易于实现脉宽调制(pulse width modulation,PWM)调光。最后,以4条LED支路为例,搭建实验样机,实验结果证明该电路的有效性。

The capacitive balancing scheme is widely used to mitigate current imbalance in driving multiple light-emitting- diode（LED） strings due to simplicity and reliability. To drive LEDs with the required current, variable frequency control will bring the high reactive power and increase VA ratings of the main switches. Fixed frequency control does not permit zero-voltage switching（ZVS） under load variations. To solve it, this paper proposed a multi-string LED driver with constant-current output and automatic balancing. The driver based on an LCLC resonant tank decouples the effect of load variation to output current, and has the resistive input impedance. So fixed frequency control can be implemented to avoid the reactive power. Also, it combines the existing capacitive balancing scheme to realize multi-string current balance with the smallest additional components. Moreover, it has short-circuit protection and the pulse-width modulation（PWM） dimming can be incorporated easily. The analysis, implementation and verification were detailed in this paper.