Quasi-Hysteretic Floating Buck LED Driver with Adaptive Off-Time for Accurate Average Current Control in High Brightness Lighting

摘要

Current accuracy of an LED is vital to its brightness control. Existing hysteretic current control method provides accurate average current, but requires high power dissipation. Peak current control (PCC) method mitigates the power issue, but does not supply accurate average current. A quasi-hysteretic control with adaptive off-time technique is thus proposed in this paper to solve both problems, where low power loss is obtained with discontinuous low-side current sensing, and accurate average current is achieved, regardless of input, output, temperature, and process variations. The design was implemented with 0.35-μm CMOS process. Its average current achieves less than 1% variation, whereas the traditional PCC method with constant off-time control suffers 33.6% current variation with equivalent load conditions.