Many times while traveling, I have had the need to debug my firmware on a circuit board. Unfortunately, I was not carrying a power supply. So in turn, I had to wait until I reached my lab before I could power my circuit board to test the new firmware. This new innovative project, the USB Based Variable Power Supply, will solve this issue effectively, affordably, and reliably.
A quality power supply is crucial for anyone who is into computer engineering but most variable power supplies are AC/DC, which are large and very inconvenient to carry while traveling.
VariPower-USB-500A is open source hardware. All hardware design files
and firmware source code are released under the GPL v2 license. It's a
great way to get started with electronics!
Download file: http://www.etonnet.com/download.aspx
Originally I used an LM317T 3 terminal regulator to build the first
prototype. It works, but I found the voltage drop under a load is too high.
Obviously, this is not a good solution for the USB based variable power supply,
since the max voltage for USB power is around 5V. If the output voltage drop is
too high, it doesn’t meet the developer’s requirements. After I compared a bunch
of different regulators performance and cost, finally, I chose MP1401 as the
voltage regulator chip. This chip has a very low voltage drop (around 0.17v)
under a load, plus it supports high current output; although the max current for
USB is 500mA, using an external AC/DC USB adapter it allows higher current power
output (up to 2A). MP1401 also supports a wide input voltage. With the same PCB
board, we built one universal battery charging station with a 12V input. The
output voltage is adjustable so It can charge a single cell li-ion battery or
multiple serialized li-ion batteries. To help the user easily find the output
voltage, I provided a “3-digit” segment LED to instantly display the real time
voltage. An R8C 16 bit Renesas microcontroller is used to monitor the voltage
with 10mV accuracy.
For most circuits, 1.2v to 5V voltage and low current is enough. In case a
user needs higher voltage or higher current output power, then an additional USB
based AC/DC power adapter is required.
Now, I carry this portable power supply in my laptop bag all the time . I can
use it to power most of my circuit boards. I can use it to quickly check LEDs
and find any that are malfunctioning. I am also considering the addition of a new feature in
the firmware to turn this unit in to a USB based voltage meter as well. I find
this is a very useful device and I hope you will too.
Please support this project and get power for your Arduino, BeagleBoard,
Uno32, chipKIT Max32, hacks, and any other circuitry projects you may
By the way, the T-Shirts look great, here's a peek: