If you’ve been wanting to dive into basic electronics but haven’t figured out where to begin or are too intimidated by circuit schematics and Printed Circuit Boards, and want to start with something simple, then this is the project for you! The Solar USB Charger, our latest addition to Weekend Projects, combines the very familiar technologies of a solar cell and a USB cable to convert the sun into USB power. This is made possible with the assistance of just two other components, a rectifier diode and a zener diode. Here’s the design in a nutshell. This solar cell from RadioShack is rated at 6V 50mAh. The maximum voltage of USB is rated at 5V±5%, or 4.75V-5.25V. So how do we get from 6V to 5V? In their forward bias zener diodes operate like normal diodes, allowing electricity to only flow in the forward direction. However their reverse bias is designed to have a controlled breakdown at their “Zener voltage” rating, and this zener diode is rated at 5.1V, within the tolerance range of USB’s power demands. This component ensures that the output power is constant, irrespective of changes in the input voltage from the solar cell. The rectifier diode ensures that any excess voltage from the circuit doesn’t spill back into the solar cell.
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More: See all of the RadioShack Weekend Projects posts (to date)