The Design Of Linear Constant LED Driver Chip

LED is regarded as a new green light source. With the advantages of high lighting efficiency, low power dissipation, security, reliability and long lighting life, LED has been widely used in displays, motors, backlight and household lighting. With the wide application of LED lighting, the development of LED driver chips concerned is sparked. The LED driving modes become increasingly diverse and the LED driver chips are getting better in performance and function with increasingly deep research.A linear constant LED driver chip with high performance has been designed in this thesis. Power LDMOS, low power control circuit and protection circuit are integrated in this chip which is all round. If being applied in 220 V AC supply, the output current of a signal chip is adjustable and high up to 80 mA. The variation of its output current is less than 6% over the whole range of temperature.The strong points and weak points of each LED driving ways are analyzed firstly. Then the overall structure of the chip and its operation principle are explained. Parts of function blocks are introduced in detail, including band-gap reference block, voltage regulation block, the error amplifier and the linear dimming block. The band-gap reference block is used to produce a stable and reliable reference voltage. The function of voltage regulation block is to provide some other voltages via making the band-gap voltage reference divided by resistance network. The error amplifier is a key because it adjusts the gate voltage of the power device to make the LED current constant. The linear dimming block regulates the voltage dropped on the sampling resistance linearly by injecting or extracting current, which makes the LED current have linear variation.In this thesis, the parameter analysis, parameter setup, design ideas and simulation results of the four function blocks are provides in detail firstly. Then, all function block are connected and the whole chip is verified through simulating.