Investigating Efficiency of AC Direct Drive of LED Lighting

This project explores the rapidly-expanding area of AC direct drive for LED lighting. AC LED driving does not use typical DC-DC converter-based driving but uses semiconductor switches and a linear regulator to activate a number of LEDs proportional to the input voltage at any given time. This allows bulky, expensive magnetics to be eliminated from the system. The goal of this project was to develop a flexible simulation of a common AC LED system to find areas of significant power loss and attempt to improve them. This allows future versions of an AC LED system to start with major loss areas in mind, reducing development time and increasing performance. Systems tested included a three-stack binary switching system, a four-stack step-up switching system, a four-stack binary switching system, and a five-stack binary switching system. Through each simulation, the common theme was that the loss of the linear regulator was the dominant loss of the system. It was found that as the number of switches (and therefore switch states) increased, the loss of the MOSFET could be reduced significantly by reducing the voltage dropped across it. With three stacks using binary switching, MOSFET loss was 22.4W, or 29% of input power. With five switches, the MOSFET loss was reduced to 333mW, or less than 1% of input power

AC Direct Drive LED Lighting Using Low Cost Analog Components

This project explores the rapidly expanding area of AC direct drive for LED lighting. AC LED driving does not use typical DC-DC converter-based driving but uses semiconductor switches and a linear regulator to activate a number of LEDs proportional to the input voltage at any given time. This allows bulky, expensive magnetics to be eliminated from the system. The goal of this project was to design a scaled-down physical AC LED direct drive system to validate the conclusions of methods for improving efficiency from a previous investigation that found minimizing voltage across the linear regulating MOSFET led to higher efficiency at the cost of increased input current THD. This project found that this conclusion is physically realizable, with a final efficiency of 94.46% and an input current THD of 58.9%. This result was achieved by taking the previous investigation’s final design as a starting point and replacing ideal switches and control signals with discrete components. The final version uses a set of comparators and sense resistors to determine when a given LED stack should be on for a simple, analog control solution. Once the system was simulated this way, the assembled version was used to measure efficiency, power factor, current THD, flicker index, and DC supply power. Additional plots of the stack voltages and control signals were collected to verify proper operation and compare to simulation. The final measurements aligned with trends from simulation and result in a simple AC direct drive solution that requires no specialty ICs