Low-Cost Small-Size Multi-String LED Driver Circuit Architecture

Background: The University of Texas at Dallas is seeking companies interested in commercializing a novel LED driver circuit architecture which promises to provide a low-cost small-footprint Light Emitting Diode (LED) driver solution for a large variety of applications including backlighting for portable devices electronic displays street lighting traffic lights and automotive lighting. LED lighting systems comprised of LED drivers and LED display modules have become very attractive due to numerous advantages such as low power consumption high optical efficiency low cost long lifetime and environmentally friendly operation 1) CMOS Process: Low Cost / Large Microchip SizeUsing the low-cost CMOS fabrication process each power switch in this type of LED driver is composed of numerous low-power transistors thereby dividing the voltage load equally across many CMOS transistors. This results in a physically large LED driver chip that is inexpensive to fabricate. 2) DMOS Process: High Cost / Small Microchip SizeUsing the high-cost DMOS fabrication process each power switch in this type of LED driver is composed of a single (or a few) high-power transistors. This results in a physically small LED driver chip that is very expensive to fabricate. Applications: (1) One LED driver per string: Moderate Efficiency / High Cost / Large PackagingMost commonly a dedicated LED driver is used for each separate string. This allows for simplified implementation particularly when driving RGB LEDs but requires numerous driver components resulting in bulky packaging high total component cost and only moderate efficiency for the overall system. (2) One LED driver for all strings: Low Efficiency / Low Cost / Small Packaging Multi-string LED driver are capable of driving multiple strings using one driver. As mentioned previously fabrication material and aging variations affect the power requirements of each string with some requiring a higher voltage than others. However because conventional multi-string LED driver architecture is limited to providing the same voltage to all power outputs the output voltage of a multi-string LED driver is defined by the string which requires the highest voltage. For strings which require a lower voltage the excess power is sent to ground (wasted) thus resulting in multi-string LED drivers being very low in power efficiency.