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Open-source Firmware & Schematics on Github.

The Inspiration

I'm a college student in EE--not the best, not the worst, which meant for me at lot of breadboard plugging at coffee shops and in libraries trying to meet deadlines. As it turns out, combined with Montreal's standard Canadian weather, filled with rainfall and snow, carrying a power supply is not really convenient. I got by for a while with a cut USB cable, stealing power from my laptop. Otherwise, I had a LiPO battery, which got me weird looks...

I got a few of those cheap-o breadboard supplies, and unfortunately they all either A) ran on inefficient linear regulators, or B) were quite large, unpleasant, and incompatible with USB-C stuff I already had. Though I ended up hacking a random PD trigger board for a while, the jumble of cables wasn't really ideal to carry around all day.

In an analog project where I had plugged some opamps, I started measuring some power supply ripple from the PD trigger board that was being amplified. Last straw for me.

The Design, and Engineering Constaints

I set out to design my own. Besides intuitive controls, I just love those projects that include a nice aesthetic display, and I wanted ProtoV to have one of its own, too. I set out to build with a few of my own design constraints in extra:

- Size: Handheld, and the user interface directly inbuilt.

- Connectivity: USB Type-C for power and data, with a possibility for programmatic control, and data logging from a computer.

- Adjustability: Dynamic range for voltage setting, and current limiting options.

- Form Factor: Built for breadboards, but has the options for other connectors via expansion cards.

- Electrical Capabilities: Low noise, high filtering capabilities, and high current handling.

ProtoV MINI connected to a host computer, delivering both 3.3V and 5V rails into a breadboard.

The Power System

I wanted the maximum adjustability, and also current limiting. At the same time, it had to be efficient due to it being a portable device. That ruled out linear regulators. The variable input voltages due to the USB-C PD standard also made it impossible to only use buck or boost converters alone.

While browsing through options for buck-boost converter chips, I found this line from Texas Instruments, where the reference voltage for the boost converter could be adjusted internally via an I2C interface. It's destined to be implemented in modern USB Power Delivery (PD) compliant chargers--my guess, aimed at different manufacturers looking at an easy way to implement this technology. From my perspective, the output regulation of these chips were perfect for a portable supply, with diverse voltage and current adjustments, along with a small general footprint.

I quickly drew up a schematic for the LM51772, a four-switch buck-boost converter with all the above mentioned features, fitted with an INA226 power measurement chip at its output. That was the first test output test PCB for ProtoV.

First hardware tests for buck-boost converter chips. The rectangular board features the LM51772 from TI. I didn't have a power supply at the time, so a poor blue LiPO battery was used to supply power during all those tests.

Voltage adjustment from 0-20V, 10mV steps. Current limiting from 0-5A, 50mA steps... All the features worked amazing! However, having to put four external MOSFETs due to it being a four-switcher was inconvenient in terms of footprint. I switched to the TPS55289, which, in turn, had the switches included within the chip. Two of those on each ProtoV unit makes up both adjustable channels.

The User Interface

First UI demo running on the Embassy embedded framework, written in Rust! 

Side thing: I love programming. Rust had popped up on my radar a while back, and I've been searching for an excuse to use it since. I found...