A Dual Control, No Sampling Resistor, Fast PWM Dimming LED Driver Circuit Design

With the growth in the living standard of common people, an ever-increasing demand on high-level consuming electronic products impels the miniaturization of portable product, like mobile phone, lap-top, etc. Since idea of energy conservation is wining more and more support, people also pay an increasing attention to environment protection on modern electronic systems. The display module of those devices, LED, owning to its environment-friendly, simply design and true colorful display, has gained a great development on application. For most electronic devices need a backlight voltage higher than battery supply, the boost DC-DC converter has become an essential part of them. Besides, due to the brightness characteristics of LED, the design of constant output current, higher conversion efficiency and integration boost converter has become vital important in the new energy-saving and environmental-friendly electronic systems.This thesis begins with the introduction of the basic DC-DC converter, then some control methods and techniques will be studied and compared. Compared with resistive load, the differences exist in the small-signal analysis and system stability with LED load. Besides, for PWM dimming, LED driver has to work and switch under two extreme conditions of full-or no-load, which asks for stricter design for the system stability and load response. To overcome these difficulties, a dual-path control method is proposed here. And by adopting adaptive current sensing method, it’s able to drive a series of LEDs with a constant current with wide range of output voltage without off-chip compensation. In addition, the optimized current mirror maintains adequate accuracy while transistors work in triode region instead of sensing resistor to uplift system efficiency; and constant off-time control method is adopted to quicken system response.The converter was fabricated in CSMC0.5um25V BCD process. The measurement results demonstrate a conversion range from input voltage of5V to output voltage of6-24V and the overshoot or undershoot are only0.5%of its output voltage at a load current step of200mA. Output current ripple is within+-3%while the recovery time is less than240ns.