Tolerance design of ballast resistance for multi-string LED driver

This paper investigates a novel tolerance design method for a resistive light-emitting-diode (LED) driver with multi-string configuration in mass production. Considering a trade-off among the current uniformity, the current accuracy in LEDs, and the loss dissipation in the driver circuit, a bus voltage and a series resistor are identified as two design parameters regardless of production spreads both in the LED string voltage and in the ballast resistance. By combining discrete optimization technique with Monte-Carlo method, this paper proposes an effective algorithm to design the circuit parameters. Comparison with the conventional design by simulation and hardware tests shows that the suggested scheme provides more reliability and flexibility in practical situation. Moreover, utilizing only datasheet values eliminates the need for I-V curve extraction in the design process.