A Non-auxiliary-winding LED Constant Current Driver With Frequency Jitter Technology

As low carbon and environmental protection has gradually become a trend in the development of various international industries,China also vigorously promotes Green Lighting Engineering.LED is‘shining’on more and more stages.In April of this year,Apple claimed to adopt Mini LED screens in the latest products,which also reflects the fast upgrade and popular market demand of LED.Since LED has both the characteristics of diode and light-emitting,its brightness is approximately proportional to the forward conduction current.Thus,the stable output current has become one of the hot spots in the current LED driving research.In response to the current market’s requirements for LED drivers,this article proposes a constant current LED driver adopting frequency jitter technology and non-auxiliary-winding topology.The converter adopts primary side regulation without auxiliary winding,and proposes a demagnetization detection scheme based on gate coupled resonant current,which can sample the demagnetization time T_demag on the primary side,effectively saving the cost of peripheral devices.In order to break the limits of least significant bit LSB of the switching cycle adjustment module in traditional digital circuits,the system introduces a dual-threshold comparison module to achieve switching frequency jitter.The module first superimposes two compensations with opposite polarities on T_demag to establish dual thresholds T_TH＿H and T_TH＿L,and then compares the half switching cycle 1/2T_s with them in turn.The module adjusts the switching cycle T_s to T_sH and T_s＿L,making the average value of the switching cycle （?） over 8 consecutive cycles become the weighted superposition of T_sH and T_sL.This method indirectly improves the resolution of the switching cycle adjustment module,thereby reducing the error between （?） and 2T_demag,and then improving the accuracy of the output current I_o.Applying the line voltage compensation technology in the peak current limiting module,high-precision constant current output control is achieved.The LED driver chip has been implemented in HHGRACE 0.35μm BCD process,and a 80V/0.3A constant current controlled prototype has been fabricated.The experimental results show that the deviation of output current is within±0.98%under different inputs and loads,whereas the linear adjustment rate is 0.99%and the load adjustment rate can reach nearly 1.03%.Meanwhile,the conversion efficiencyηis higher than 87%over the entire operating range.Thus,all indicators of the proposed LED driver meet the design requirements.Compared with similar design in literatures,the converter designed in the thesis has better performance in terms of peripheral cost,design difficulty,accuracy of output current,and system conversion efficiencyη.Therefore,the proposed chip has broad application prospects in the field of LED driving.