More Boost With Less Stress: The SEPIC-Multiplied Boost Converter

by Bob Zwicker, Analog Devices, Olympia, Wash., How2Power Today, May 24 2012

Focus:
The SEPIC-multiplied boost converter is a novel but tested topology for applications with moderately high boost ratios in the range of 10:1 to 50:1 and with voltages as low as about 1.8 V on the input and as high as about 500 V on the output. The SEPIC-multiplied boost overcomes many disadvantages of other topologies. This topology reduces voltage stress on the main and rectifier switches without increasing current stress, which widens and improves the choices in MOSFETs and Schottky rectifiers for which high voltage is often a problem. This topology also operates with moderate (as opposed to very high) PWM duty cycles, which allows continuous-conduction mode operation and makes feedback loop compensation easier. Other benefits include higher efficiency and lower noise than other boost topologies. This article describes the origins and operation of the SEPIC-multiplied boost converter, compares this topology with other boost topologies for obtaining high boost ratios, and presents test results for an actual design example--a 50-W 200-V output pentupler based on the ADP1621 dc-dc converter IC. It also provides information on design variations and component considerations.

What you’ll learn:

• How to design a boost converter with high boost ratios (10:1 to 50:1), moderate PWM duty cycles, high efficiency, and low noise
• How to understand the tradeoffs of different boost converter topologies when designing for high boost ratios

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