Process Research And Circuit Implementation Of AC Direct LED Driver IC With High Output Power And Low Optical Flicker

Light emitting diode(LED),as an emerging lighting source with small size,high luminous efficiency,long lifespan,safety and environmentally friendly,is gradually replacing traditional lighting sources throughout the world.Unlike those traditional lighting sources,LED cannot be powered by alternating current(AC)directly.Therefore,it is necessary to use LED driver power supply to connect AC source and LED,as well as provide effective energy transfer.To give full play to the advantages of LED,LED driver power supply needs to meet the requirements of low cost,long lifespan and high efficiency.Among all kinds of LED driver power supplys,the AC direct LED driver power supply emerges as a promising solution because of its simple peripheral circuit,electrolytic-capacitors-less and small switching loss.However,there are remaining issues for the AC direct LED driver power supply which is powered by single-phase AC,such as obvious optical flicker and low output power.Therefore,on the basis of maintaining its original advantages,it is of great significance to design an AC direct LED driver power supply with high output power and low optical flicker,mainly for the design of the AC direct LED driver intergrated circuit(IC)in the driver power supply.Based on the consideration of the operating voltage of the low-voltage devices in the driver IC,which is proportional to the output power of the driver IC under the same chip area,the work of this paper is divided into two parts.In the first part,referring to an existing foreign AC direct LED driver IC powered by 100 ~240 V single-phase AC,which includes 500 V high-voltage devices and 15 V low-voltage devices,a new Bipolar-CMOS-DMOS(BCD)process,which is suitable to produce the existing dirver IC,is developed to fill the gap in domestic.Moreover,in the second part,an existing domestic 700 V BCD process,which contains 700 V high-voltage devices and 5 V low-volatge devices,is used to redesign the AC direct LED dirver IC and the redesigned driver IC is expanded to 380 V three-phase applications to overcome the inherent drawbacks of obvious optical flicker and low output power in single-phase working mode.The works and innovations of the paper are as follows:1.A 1 μm 1P2 M BCD process which only uses 14 masks is developed for the existing foreign AC direct LED driver IC to fill the gap in domestic.In the process,500 V high-voltage devices and 15 V low-voltage devices can be achieved.Moreover,the corresponding files for DRC(design rule check),EXT(extraction)and LVS(layout versus schematic)are compiled.Finally,all of them mentioned above are validated by simulation.2.Aiming at the phenomenon of insufficient current capability of NJFET due to the process compatibility between NLDMOS and NJFET,a new structure of NJFET is proposed to meet the current demand of the existing foreign AC direct LED driver IC without adding masks.The simulation results show that the NJFET with conventional structure is almost pinched off in the application where the gate voltage is 0 V and the source voltage is 15 V,while the proposed NJFET can provide a current capability of 3.55×10-5 A/μm to make the chip work normally.3.An AC direct LED driver power supply with high output power and low optical flicker,which is powered by the 380 V three-phase AC is designed and implemented in an existing domestic 1 μm 1P1 M 700 V BCD process by using 700 V high-voltage devices and 5 V low-voltage devices.In addition,the influence of the conduction voltage distribution scheme of LED strings on percent flicker is analyzed in the proposed driver power supply and a good distribution scheme is given.The experimental results show that the output power of the proposed driver power supply is 72.3 W,the frequency of the output power is increased from 100 Hz under single-phase AC input to 300 Hz,and the percent flicker is reduced from 100% under single-phase AC input to 12.77%.4.To solve the problem of insufficient power factor(PF)in the AC direct LED driver power supply,a total harmonic distortion adjustment circuit is proposed.The experimental results show that the PF of the AC direct LED driver power supply with proposed total harmonic distortion adjustment circuit can be improved from 0.945 to 0.993.5.Aiming at the problem that the output power is too low and the flucturation of the output power is too large due to excessive power compensation,negative feedback is introduced to the power compensation circuit.The negative feedback has been added into the driver IC during circuit design,the output power without negative feedback cannot be measured.So,the simulation results are adopted.The simulation results show that when the voltage fluctuates by ±10% at 380 V AC,the output power fluctuates from-6.24% to 8.57% without negative feedback,while the fluctuation range is narrowed from-2.3% to 0.7% with negative feedback.