Study On Resonant Single-Switch Multi-output Boost LED Driver

In many high-luminance applications,such as large-scale LCD backlighting and street lighting,current sharing of multiple-string LED driver is required to obtain a uniform luminous flux.Compared with active current-sharing technology,passive current-sharing technology has the characteristics of simple circuit structure,small volume,low cost and high efficiency.In view of the fact that the capacitor-diode passive multi-channel current sharing scheme also has the advantages of simple circuit control and high current sharing precision,the operational regularity of the capacitor-diode multi-output current sharing topology is studied.The research result presents that the different diode conduction sequences of capacitor-diode 2n-1 and 2n outputs current sharing topologies due to the circuit structure discrepancies in the two circuits.Assuming that isolated and non-isolated resonant converters are utilized to provide high-frequency AC bus current to the capacitor-diode multi-output current-sharing topology,seven isolated and non-isolated resonant capacitor-diode multi-output current sharing topologies are deduced.As a result of the same current sharing principle of seven isolated and non-isolated resonant capacitor-diode multi-output current sharing topologies,resonant single-switch multi-output boost LED driver converter is taken as an example.Moreover,the operational principles and circuit characteristics of resonant single switch 2n-1 and 2n boost LED driver converter operating in continuous conduction mode(CCM)are analyzed.It can achieve automatically current balancing among 2n-1 or 2n LED strings by using only one active switch,one resonant inductor,2n-1 or 2n resonant capacitors,thus it benefits from simple circuit structure and control,small volume,high efficiency,low cost and regulating all of the outputs with high precision.By controlling only one output current,the other output currents of this LED driver can be controlled via the charge balance principle of resonant capacitors,which makes its control simple.Since the short circuit of one output branch will not affect current balancing among the other output currents in the steady state,it features a natural short-circuit protection.Finally,the theoretical analysis in this paper is verified by a 36W three-output prototype and a 48W four-output prototype.