Research Of White LED Driver IC With Ambient Temperature Compensation Technology

The white LED(Light Emitting Diode) is a welcome choice for illumination and backlighting in consumer electronics, but its allowable forward current is greatly affected by temperature. In traditional white LED driver design, its output current is determined by the maximum working temperature,comparatively small.In this thesis, a novel white LED driver IC is proposed which can dynamically adjust the driver's output current corresponding to the white LED's current-temperature curve. Therefore the highest output current can be safely set over the entire operating temperature range, thereby allowing fewer LEDs to be used for normal display brightness which reduce the cost of application. Moreover, this circuit can protect LEDs from over-driving during high ambient temperatures, so it enhancing the chip's reliability.In the main part of this thesis, firstly, the whole chip's structure is constructed. Using inductor step-up converter to drive White LED is a major method for portable applications. In the process of chip design, the current mode PWM control and ambient temperature compensation technology for increasing the chip's speed, reliability, economic and applicability. And then, the key interrelated technique for Boost DC/DC is studied and the whole chip structure is constructed. The main sub-circuits such as Ambient Temperature Compensation, 170mV Comparator and Under-Voltage Lockout Circuit are designed and implemented with UMC 0.6μm BCD process, and the simulation results are also presented.Finally, HSPICE simulation results of the whole Chip are given: 1 MHz switching frequency. Up to 7 LEDs at 25 mA and the highest conversion efficiency of 86% can all be achieved. The chip can be timely protected by the under voltage protection function. Analog Direct-PWM and brightness adjustment functions can also be achieved. Simulation results show that the chip has achieved the expected demand.