Design Of A Constant Current LED Driver With Dimming Function

LED has many advantages, so we can see more and more application of it in life.At the same time, the market needs more LED driver chip. Its function also requires more human nature. When using the LED to light, the need of dimming function is more and more important.A constant current LED driver chip has been designed in this paper. Its two basic functions are the constant current to drive LED light and the realization of dimming. It also has a protection module to keep the whole system safe. Errors of over temperature,over current, under voltage with power supply will be avoided. It also has two dimming technology, which are PWM dimming and linear dimming. People can choose appropriate dimming mode according to the actual application, increasing the flexibility of chip. The maximum working current of the chip when driving the LED lamp is80 mA. Dimming range is from 0 to 100%. The nonlinear error amount of dimming function is in the range of 2%, In the working temperature range, the current accuracy of LED must be less than 6%.First some of the LED characteristics are summarized, and then the circuit diagram of the chip is determined. This paper focus on the design of error amplifier,under-voltage lockout circuit, over temperature protection circuit, linear dimming circuit and logic control circuit. The task of the error amplifier is to drive power MOS,to achieve the purpose of constant current on LED. When the value of power supply voltage drops for some reason, in order to prevent the logical error, under-voltage lockout circuit starts to work. When the chips are over-temperature, overcurrent or under-voltage, the whole chip will stop working. The task of the linear dimming circuit is to change the current linearly. Eventually the brightness of LED lights will change.Mostly, the structure of every circuit, circuit parameter and circuit simulation of five circuit modules have been detailed analyzed. And through the overall circuit simulation of the chip, conclusion is that function of the chip and design index have reached the design requirements.