Design And Implementation Of Quasi-Resonance Multiplex LED Driver

High Brightness Light Emitting Diode(HB-LED)has been widely used in street lamp,huge screen display,LCD backlight,automobile lighting,etc.With its excellent characteristics of high light efficiency,long life,low energy consumption and fast response,LEDs has gradually entered the field of general lighting.However,due to the low power of single LED(0.5~3W),series-parallel topology is used in most cases.Based on the research of Quasi-resonant Circuit(QRC),a new type of structure is proposed to make up for the shortcomings of the existing LED driver,which aims at high efficiency,long life and low cost.Specific research contents are as follows:The capactive charge balance scheme is widely adopted to eliminate current imbalance in driving multi-channel LEDsdue to the high accuracy of current sharing.In order to get the required LED driving current,variable frequency control directly leads to large reactive circulation and increases the stress of devices,and the EMI circuit is complex.Soft switching can’t be guaranteed by constant frequency operation under load variations.Hence,a multiplex LED dimming circuit based on variable inductance(VI)is proposed in this paper,whichcompletes the constant frequency operation,alleviates the complexity of EMI circuit,and realizes the ZVS to improve the energy conversion efficiency.The proposed circuit with superimposed half-bridge structure will increase the number of outputs and simultaneously share resonant inductor,so that the power density is improved and the LED dimming unit is simplified.The current sharing scheme of capacitive impedance matching has been widely used to eliminate current imbalance duo to simple control versus easy expansion.However,as the number of strings increases,the current sharing effect decreases,and the reactive loss increases.At the same time,traditional topologies using PFM are bound to cause high EMI.In this paper,a novel LED driver with the current sharing is proposed under constant frequency operation.The proposed converter can be derived by upper and lower half-bridge interleaved output,which greatly alleviates the unbalance of multiple LED and loss caused by capacitive mismatch.Meanwhile,LED wide range dimming with the constant frequency is achieved by using the switch-controlled capacitor(SCC)module of the resonant unit.Since the switching circuit adopts PWM and can realize soft-switching,the conversion efficiency of the machine is high.Moreover,in consideration of many new lighting applications,the independent control to achieve different levels of luminance is particularly important.Existing passive and active approaches have their own limitations in both current sharing and independent control,which brings new challenges to the design of LED drivers.In view of this,a multichannel resonant converter based on Switched-Capacitor Control(SCC)is proposed to solve this challenge.In the resonant network of the upper and lower half-bridge,SCC is used instead of fixed capacitance.Then the individual current of the LED array is obtained by regulating the effective capacitance of the SCC under a fixed switching frequency.In this way,the complexity of the control unit of the circuit and the precision of the multichannel outputs are further improved.The bulky electrolytic capacitor is required to compensate the difference of pulsating power,thereby restricting the drivers lifetime,and the conduction loss is increased due to the existence of a full bridge structure.The existing drivers adopting Pulse Frequency Modulation(PFM)is bound to arouse heavy electromagnetic interference(EMI).Therefore,the Series Resonant Converter(SRC)based LED driver is proposed to attenuate the low frequency ripple delivered from the Power Factor Correction(PFC)to LEDs;therefore,the capacitance is reduced for energy storage of off-line LED drivers.On account of the replacement of the fixed capacitor with the Switching Controlled Capacitor(SCC),the constant frequency operation(CFO)is achieved by the regulations of the equivalent capacitance.In addition,the sharing of SCC and half-bridge switching unit not only increases the circuit of the power density,but also eliminates the full-bridge rectifier diode.In this paper,the working principle and related parameters of all the structures are analyzed,and on this basis,the experimental verification is carried out.The results prove the feasibility of the proposed structure and the correctness of the theoretical analysis,as well as the high conversion efficiency of the proposed structure.