Research On A High Power Factor And Primary Side Controlled LLC Resonant LED Driver

LED is fourth generation lighting source after incandescent lamp,fluorescent lamp and HID lamp,which has the advantages of high luminous efficiency,long service life and environmentally friendly.These advantages are meeting the basic national policy of "energy-saving and emission reduction",which is enabling LED to be promoted quickly and facilitating the development of LED driver industry.In order to improve the power grid quality,a series limits of input current harmonic with lighting electrical appliance which more than 25 watts has been established by many authoritative organizations to decrease harmonic pollution of the grid.Therefore,it is necessary to design PFC scheme specialized to meet the harmonic demand.The PFC scheme of LED driver can be divided into passive power factor correction(PPFC)and active power factor correction PFC(APFC).The PPFC has the advantages of simpler design,lower cost and higher efficiency,it is suitable for medium and small power supply which cost pressure is greater.However,there are defects ofworse power factor(PF)and narrow range with existed PPFC.Consequently,research on more cost-effective PPFC and higher efficiency resonant converter are need to be carried out to the small and medium power LED driver in brutal market competition.A compensating charge pump PFC circuit to improve the drawback of existed charge pump PFC that the input and load range to realize PFC is narrow was proposed in this paper.The main circuit consists of charge pump power factor correction circuit and LLC resonant converter to realize PFC and single stage AC/DC conversion,the PFC range of charge pump circuit was expanded by compensating circuit.The working principle of the proposed circuit,the condition of PFC and the design method of key parameters was analyzed in this paper.The veracity of circuit was verified with the result of experiment and simulation.Base on higher cost performance and stability,a primary side control scheme with LLC resonant converter to regulate the output current constantly was proposed in this paper.The second-side control chips and optocoupler was eliminated by primary side control,it can not only reduce cost,but also increase power density and stability.The principle and performance characteristic of LLC converter with constant output current was analyzed,and the key parameters of proposed circuit combined the characteristic of charge pump was designedin this paper.A prototype of 90W and 2A constant-current and primary side controlled single stage LED driver was built in this paper.When input voltage range is from 175Vac-rms to 265Vac-rms,PF is greater than 0.96,THD are less than 15%,which is meet the criteria of IEC1000-3-2 Class C.The experimental results are shown as follows:the highest PF is 0.996,the lowest THD is 4%,the highest efficiency is 91.16%,thesmallest output current ripple is 6%.The feasibility of theoretical analysis is verified with experimental results.