Introduction: How to Make a USB-C Based 1-25V, 0-2A Lab Power Supply

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A small variable voltage and current lab power supply add on for USB-C power bricks

Supplies

The lab power supply needs three electronic modules

  1. A USB-C decoy board that pulls the required voltage (5V, 9V, 12V, 15V, or 20V) from a USB-C power supply
  2. A buck-boost voltage up-converter module to convert the USB-C 20V to >25V
  3. A Constant Current and Voltage Power supply module with built in meters to monitor current and voltage.

Plus two potentiometers to replace the variable resistors on the PS module

4-way banana plug sockets

Power switch, wires, nuts and bolts, wire, etc.

3D printed enclosure

Step 1: Tapping USB-C Power With Decoy Boards

USB C power supply for a laptop can provide 65 W of power at up to 20V. By connecting these power supplies to a USB-C decoy board you can get the USB-C power supply to deliver any voltage from 5V, 9V, 12V, 15V or 20V depending on the specific USB-C power supply.

The USB-C decoy boards I purchased had 3 selector switches that could be used to select a specific voltage as shown in the pictures.

I set the board to 20V by setting the last two switches on ON.

Step 2: Up-converting the USB-C 20V to 27V

These very handy up-converter buck-boost modules were used to convert the 20V from the USB-C decoy to ~ 27V that would be fed to the variable power supply module. I connected the USB decoy to the up converter, plugged in a USB-C power supply and adjusted the variable resistor on the converter to give about 27V.

Step 3: 3D Printing of an Enclosure for the Power Supply

I used FreeCad to design the top and a base for the power supply enclosure. A shoutout to MangoJelly Solutions and others for producing great tutorials on freecad.

Then printed the box on an Ender 2 Pro with black PLA. The dimensions are 3 inches square and 2 inches deep.

The top holds the switch, the terminals, the potentiometers, and the variable PSU board.

The base holds the USB C decoy and the upconverter.

Step 4: Connecting the Modules Together

I had an adjustable PSU module with built in digital meters for voltage and current with a constant voltage and current feature. The module provided from 1-25V with up to 2A of current. This module is a few years old and not as nice as the new LCD power modules but it was what I had.

A quick test fit of the components and some of the wiring indicated that the wires going to the input and output screw terminals of the variable PSU board did not let the board fit into its case. So decided to solder the input and outputs directly to the board rather than using the screw terminals (not shown).

The modules were attached to the top as shown in the photos. The two potentiometers are under the PSU module. A small piece of acrylic was glued in as a light pipe to show the status of the LEDs on the PSU module.

I used a scrap piece of aluminum as a jury rigged heatsink for the PSU IC. The heat sink was glued with thermal epoxy plus some sponge pads that you can just see.

The USB-C decoy board was attached to the base and the output of this board was wired to the input of the upconverter. The positive output of the upconverter was wired to the power switch and the negative output of the upconverter was wired directly to the adjustable PSU module.

Step 5: Wiring Diagram

The diagram summarizes the wiring. USB-C decoy connects to the upconverter. The up-converter connects to the variable power supply module through the power switch for the positive lead and directly for the negative lead.

The outputs of the PS module are connected to the 3-way sockets.

Step 6: Testing

I connected the outputs to a multimeter to check voltage accuracy. The readouts were within 1-2 percent with most of the variation seen at the low end, below about 2.5V.

A 12V incandescent bulb was connected to check the constant current mode. The LED changes from green to red when in constant current.

The small variable power supply is turning out to be extremely useful due to its small size, clear readouts and the ability to use the USB-C laptop power source that is already plugged in at my bench.