Designing small, USB-C bench power supply

Don’t get me wrong, nothing beats a full-sized bench power supply when you need a good source of clean power (especially at a higher voltage), and you can find a good one pretty cheap these days. But, from a weekend warrior hobbyist perspective, those are still pretty bulky and do not fit in a drawer when weekend is over. They also require a mains connection which is not that big of an ask for a power supply (I admit) but plugging a USB-C cable into a charger you already have is much simpler.

Core idea

USB Power Delivery specifies how to provide (and request) up to 20V @ 100W over a USB-C cable. To access this (almost unlimited) power some communication with the charger/USB host is required but there are ready-made modules available that can do this part of the job for us.

I’ve seen those modules in two flavors: with a fixed output voltage and step-adjustable ones. While the second type would allow quick access to several voltages without any additional parts - I don’t like it. They use a tactile switch for selecting the voltage and I see myself accidentally putting 20V through my precious microcontroller after a week of use or so.

I opted for fixed 20V output USB-C PD trigger module. There is a tradeoff here: if the USB-C charger is not capable of providing the full 20V it will fall back on the standard 5V. This means that it will not be able to use the 12V that some PD-enabled power banks are able to provide.

The next element of the puzzle is a configurable, step-down module RD DPS3005.

This version accepts voltages up to 32V with an output power range of 160W, with a USB-C charger capped at 100W it should be more than enough.

These are the core elements. No let’s make it nice.

The build

To make it feel like a bench power supply it needs a nice-looking box, some banana plug connectors, and some protection of a USB-C socket (it cannot be flapping around on the desk with exposed pads.

Enclosure

I designed a two-part, “almost no supports” enclosure with some vents at the top, holes for the banana connectors, screws, and USB-C cable. The last one can be fitted without cutting off the USB-C plug :)

The whole thing is fixed together with two screws that screw directly into the plastic.

Parts

To summarise, the parts needed are:

• RD DPS3005 (or any of similar-sized modules from RD)
• 2 x banana jack binding post
• USB-C charger (I used Baseus GaN3 Pro)
• USB-C Power Delivery trigger board
• USB-C to USB-c extension cable
• 3D printed enclosure
• 2x M3 screws
• Some cables for internal connections
• (optionally) crimped connectors

Tools

• Soldering iron & solder
• (optionally) 3D printed tool for installing the posts
• (optionally) crimped connectors crimper

Assembly

Putting it all together was a little fiddly. Especially screwing the posts to the panel has proven to be difficult. I printed a dedicated tool to reach the posts inside the box.

Final thoughts

The next step will be to test it under load and with multiple chargers and power banks but this will be the topic of a different post.

There is also some space for improvement here. A right USB-C PD trigger module could try several voltages before falling back on the 5V max. Also, having a screw hole or two on it would allow me to mount it to the enclosure and get rid of the USB-C extension cable.