Drive Multiple LED Strings with SEPIC Converters

by L.K. Wong and T.K. Man, National Semiconductor, Santa Clara, Calif., How2Power Today, Nov 24 2009

Focus:
A common method to drive multiple LED strings is to make use of a power converter together with linear current regulators. Based on the input voltage and the output voltage, which is related to the number of LEDs in a string, a buck or boost topology will normally be used in the power converter. However, if the input voltage is close to the output voltage, buck and boost topologies are not suitable. This article explains why a SEPIC topology offers the best solution to this problem. As a design example, a SEPIC-based LED driver circuit for driving three LED strings is presented. The circuit is based on National's LM3431 controller IC. Circuit operation is explained, equations are presented for calculating key parameters and component values, and performance results are presented.

What you’ll learn:

• How to drive multiple LED strings using SEPIC converters and linear regulators
• How to drive multiple LED strings when the input supply voltage is close to the required drive voltage

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