Research Of High Performance LED Dimming Circuit

Luminance and correlated color temperature dimming technology is the developing direction of lighting industry. According to the current development situation of LED technology, these dimmable LED lamps’ promotions and applications will meet their important stage in the three or five years. High efficiency power supply is the key impetus to the development. In the near future, the power source combined with LED and digital control technology will serve the intelligent world.This paper gives complete theoretical analysis and design of a high-performance power supply of dimming LED lamps from four aspects:Dimming method, power circuit, MCU control circuit and software. Finally, the prototype has been made. The experimental results are analyzed and show consistencies with theoretical results. Several fields have been studied as following in this paper.1. Two kinds of basic theories are introduced in the paper. Firstly, two conventional LED dimming methods and numerical computation methods are presented. Secondly, switching power supply topology, operation mode and control method are introduced.2. Optimization of the conventional two-channel high & low temperature white LED PWM dimming method is realized. A more simple, efficient and reliable control strategy is proposed. Aiming at solving the problems of free duty ratio and independent phase, a PWM control method of dimming lighting based on cold & warm white LEDs in time hybrid color mode is proposed in this paper. The control strategy restrict the relations between the phases of two-channel PWM control signals, which means a 180° phase difference exist. At the same time, the dead time of drive signals is set.3. A novel circuit is proposed, which include a single-stage flyback APFC converter, a linear constant current regulator, a PWM dimming circuit and a digital controller. The single stage flyback APFC converter is the main structure and the linear constant current regulator is link to the APFC’s output terminal, which ensure accurate constant output current. At the same time, micro-controller detect voltage drop on the power transistor of the linear regulator, and feedback to power manage controller and adjust the output voltage. The regulator can eliminate high ripper as well as reduce the loss and achieve high efficiency. The power transistors of linear regular can be used as switchers for PWM dimming control. It reduced driver volume.4. The preemptive parallel multitasking structure is applied to build the MCU control system, which can realize the output voltage regulation, soft dimming, timing dimming and ultra low standby consumption, etc.5. An experimental prototype is made. The experimental results show that the prototype have good performance, such as high power factor, high efficiency, accurate constant current ability, tiny volume and digital control characteristics. Design idea and design method are verified and the design requirements are met.