Research On Multi-channel LED Constant Current Driver

With the increasing of people's awareness of energy saving,contries around the world start focuse on the development of green efficient lighting.With its long life,high efficiency,reliability and environmental friendly,Light-emitting diode(LED)lighting has developed rapidly in recent years and become a new generation illuminant.As a key part of LED lighting,high efficient high power LED driver has become a research hotspot.Based on this background,a two-stage resonant high power LED driver is proposed.And current balancing technique for multi-output LED driver is also discussed.The LED driver proposed in this paper uses Boost converter with L6562 control chip to achieve power factor correction(PFC).This paper makes a detailed analysis on the working principle of PFC based on L6562 which operates in Critical Current Mode(CRM)firstly.The design method of the main parameters is discussed in detail at the same time.The small signal model of the Boost PFC based on L6562 is established,and the design process of feedback loop is shown.On the basis of the simulation of the preceding PFC stage,a prototype of 180 W PFC converter is built up and tested.The theoretical analysis and control strategy are verified.The second satge of the LED driver in this paper is multi-output circuit with CLL resonant.A CLL resonant converter is used in the primary side of the transformer to drive LEDs.With CLL resonant converter,zero voltage switching(ZVS)turning-on of the switches on the primary side and zero current switching(ZCS)turning-off of the diodes on the secondary side are simultaneously achieved.On the secondary side of the transformer,current balance is realized with the balance capacitors,based on the charge balance principle.The capacitor is used to balance the current of the two strings in one module.And an extra balance capacitor is used to balance the current of two different modules.Thus the current in each LED string is balanced.The circuit operation principle of the CLL resonant converter and current sharing principle are analyzed.This paper merges four outputs into one and obtains the equivalent circuit of CLL resonant converter.This paper also adopts the fundamental harmonic approximation analysis method to obtain the voltage and current characteristic of the converter.The key parameters of the CLL resonant converter is also presented.Finally,a four-outpt LED driver prototype is built up and tested.The LED driver has a wide range input with 100~264V/50 Hz and output with 80~120V/0.35 A.The experiment results prove that the circuit can efficiently drive the LED strings.The total efficiency is larger than 0.9 and the PF value is larger than 0.96.Meanwhile,each LED string has a good performance of current balancing.