USB Charger Provides Battery Backup And Load Switching With Easy, Low-Cost Design

by Budge Ing, Maxim Integrated, San Jose, Calif., How2Power Today, Feb 15 2014

Focus:
The circuit described here takes power from a USB port and uses it to both power a low-current consumption device and to charge a 1-cell Li-ion battery. When the USB power drops out, the circuit switches the load over to the battery backup. The circuit also disconnects the battery when the terminal voltage drops to a user-determined voltage. Consisting of just a few ICs and some external parts, this design represents a low-cost, easy-to-implement solution that requires no coding (there’s no microcontroller) and has an ultra-small footprint. Although it’s designed to operate from a 4- to 7-V supply, it can withstand inputs up to 28 V. The original application for this circuit was an RF system and any mobile device with low power consumption, such as a device which periodically transmits radio packets, will find this circuit useful.

What you’ll learn:

• How to build a simple, low-cost USB-powered power source with a 1-cell Li-ion battery backup

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