USB 3.3V adapter

USB to 3.3V adaptor for evaluation modules

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 Unported License.
Current Status:   Complete
7th February 2010
Creative Commons Attribution 3.0 Unported License


Presented here is a very simple circuit to convert +5V from a USB port to +3.3V, useful for powering lower voltage micro-controllers and other peripheral devices. It was designed to allow development work on a microcontroller board, whilst plugged into the PC, thus saving an extra power adaptor.

Design information

The maximum current is around 400mA, taking into account the power dissipation in the linear regulator and keeping within the 500mA current limit of a USB port.

The design uses an LM1117-3.3, which is a low dropout (1.2V @ 500mA) Linear regulator. A small heatsink is used to dissipate excess heat at higher loads.

The power input is a standard USB B plug, output is via 2 x PCB pads with wires to suit the end application.

A single sided PCB layout has been provided.
Schematic Diagram

Click the thumbnail to enlarge

PCB Layout

PCB and schematic download
Available here from Github,



Updated 27 September 2020