Design Of A Digital Constant-current Controller For LED Driver

As the essential topic of industrial production and daily life, LED lighting is a new type of environmentally friendly lighting, more and more popular. LED have a high requirement for power, and is different with the incandescent lamps of labor frequency power directly, it need a LED driver circuit to control the current flowing lights. Main functions circuit of most LED driver chip are designed with analog circuits, which have an error amplifier basically for each driver chip. Compared with digital circuits, analog circuits have higher requirement for production process, which will bring some uncertain risks for manufacturers and designers.In this paper, there is a digital LED constant current driver be designed. With maintaining constant output accuracy, the main function block of the chip make use of the digital circuits, so that the chip is to get rid of the process requirements that the analog circuits needed. The regulator supplying power for the chip and constant current control loop is all digital circuit, that is to say, the novel chip sampling algorithm in constant current control loop is used. Constant current control circuit is composed of comparator, digital integrator, state machine and other digital circuit. Through the comparison between the feedback voltage and internal reference voltage of chip, get a square wave signal with the information of the output current. After processed by digital integrator, and transmitted to the state machine, the feedback information adjust the output state of the state machine to control power MOSFET driving signal duty cycle. With PWM and PFM control modes, the chip make use of voltage feedback mode to modulate the driver signal of MOSFET, so that the driver signal have the appropriate duty cycle, and the output current keep constant.Working in non-dimming condition, the chip is designed have a 350 mA output constant current, and based on simulation with TSMC 0.5 μ m BCD process, the current precision resulting error is less than 5% in this article. In the condition of input voltage is 220 VAC, 50 Hz, the lower, the output current precision can meet the requirements for the TRIAC dimming or non-dimming.