Charging for Ultracapacitors

by Mariangela de Martino, Product Application Engineer, and Kamal Najmi, Power Design Engineer, Europe, National Semiconductor, Power Electronics Europe, Feb 24 2009

Focus:
In automotive applications with start-stop operation, the addition of ultracapacitors to the electrical system can improve the transient response of the battery and prevents voltage sag on the vehicle's power bus. Ultracaps can also extend the operating life of the battery. However, use of ultracapacitors requires the addition of a charging circuit. This article describes a dual-phase dc-dc converter that delivers 50 A for charging a single 650-F, 2.7-V ultracapacitor. The dc-dc converter employs National Semiconductor's LM5116 synchronous buck controller, which uses the company's emulated current-mode (ECM) control technique. The article discusses why ECM control is beneficial in this application, describes circuit operation, and explains how to select key components such as the ramp capacitor, current-sense resistor, and power MOSFETs.

What you’ll learn:

• How to design an ultracapacitor charging circuit for automotive and industrial applications

Notes:
Article is found on pages 18-22 of Jan/Feb 2009 issue. Since the charger is designed to charge a single ultracapacitor cell, the issue of cell balancing is not addressed in this article.

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