Research And Design Of A High Power LED Boost Driver Chip

High Power LED (Light Emitting Diode) is a new generation of high-power light source, also known as the"green light", and it is gradually replacing incandescent and fluorescent lighting due to its unique attributes such as high efficiency, low energy consumption, low pollution, long life and high reliability. Considering characteristics of High Power LED, they need to be drive by special circuits. So, it has the very vital significance to research and design the driving circuit of High Power LED.The thesis researched the principle of generating, the characteristics of luminous flux curve and I-V curve of High Power LED. The series-connected resistor circuit, series linear regulator circuit, parallel linear regulator circuit and switching power supply circuit are analyzed. Then, the Switching Power Supply's basic knowledge is researched,including four types'topology structure, PWM voltage control mode and PWM current control mode. Next, describe the designed boost converter's system structure, operation principle and pins'function. Analysis the problems such as instability of open loop when the peak-current-mode converter's working in continued conduction mode (CCM) and the duty cycle is more than 50%. According to the defect of traditional slope compensation, a self-adaptable slop compensation circuit is proposed, whose compensation amount varies with input and output voltage automatically. The small signal model of their main circuits in CCM is derived by Basic Modeling Method and transfer function is established. Finally, the frequency compensation circuit was introduced to guarantee the enough phase margin and improve the stability of the system.A chip which is used in the Boost application to drive High-power LED with a constant current is proposed and designed in this paper. The chip adopts PWM peak -current-mode control. Compensation circuit is designed in order to overcome the disadvantages of current mode control such as instability of open-loop. A soft start circuit which could avoid the large current in course of starting is built-in chip. Beside, lots of protection circuits are integrated in the chip, such as under voltage lockout, over voltage protection, thermal shutdown, and so on. System shutdown was also integrated into the chip. It is designed with HHNEC 0.35μm BCD process with input voltage ranged from 8V to 30V, maximum output load current up to 1A. The chip can drive several 1W~3W High Power LEDs in series with a constant driving current. Spectre simulations are done on each cell and the whole system in cadence, simulation results show that the function and performance of the whole circuit have met all the requirements.