To provide enough light output for various lighting applications, high-power LED nowadays is commonly driven at 350mA, with this number continuously moving upward. Accompanying this trend comes the need for power-efficient drivers that can deliver and regulate the LED-current, better yet, provide dimming capability. Existing high-power LED drivers rely on a sensing resistor placed in series to the LED to provide a feedback voltage for LED-current regulation. This method is undoubtedly simple and convenient but may limit power efficiency in future when LED-current keeps increasing....[ Read more ]

To provide enough light output for various lighting applications, high-power LED nowadays is commonly driven at 350mA, with this number continuously moving upward. Accompanying this trend comes the need for power-efficient drivers that can deliver and regulate the LED-current, better yet, provide dimming capability. Existing high-power LED drivers rely on a sensing resistor placed in series to the LED to provide a feedback voltage for LED-current regulation. This method is undoubtedly simple and convenient but may limit power efficiency in future when LED-current keeps increasing.

In this thesis, alternative approaches to LED-current sensing are studied, and a power-efficient LED-current sensing circuit that does not require serial sensing resistor is proposed. Instead, LED-current information is extracted from the output capacitor in the driver for LED-current regulation.

An LED driver in Buck-boost topology is used to demonstrate the idea, and has been implemented in AMS 0.35 μm CMOS technology, with chip area 2.4mm by 2.5mm. The driver drives one 350mA high-power LED with input voltage ranging from 2.7V to 4.2V, which is the common output voltage of a Li-ion battery. It also provides PWM dimming options to drive the high-power LED for lower light output. Measurement results indicate a power-conversion efficiency of 92%. Compared to sensing resistor approach, the power reduction in sensing is 1000 times