Overview
A 50W COB LED work light that draws all its power over USB-C Power Delivery — including straight from my eBike powerpack, or any PD adapter capable of delivering 50W. Started on 2 June 2026 with the Arduino circuitry, the goal was less “I need a light” and more “how much can I learn building one”: PD power negotiation, buck-boost conversion, PWM dimming, embedded safety logic, and a fully custom 3D-printed enclosure.
The result is a light that not only dims and displays live stats, but actively protects itself and the power adapter feeding it — throttling output if the LED gets too hot or if the USB-C source can’t keep up with demand.
Key features
- 50W COB LED driven from a USB-C PD trigger board requesting 20V, stepped through a buck-boost converter to a regulated 15V with a 3.3A current limit — needed because the LED’s resistance drops as it heats up, so without a limit it would pull more and more current until it burned out
- Arduino Nano (chosen for its small form factor) controls brightness via a dedicated PWM regulator, adjustable through an onboard potentiometer
- Onboard display shows live stats: output percentage, input voltage, and calculated wattage/amperage draw to the LED
- Input voltage monitoring via a voltage divider — the light won’t power on below 12V, and it detects voltage sag (when the USB-C adapter can’t supply what the LED is demanding), automatically throttling output to bring the voltage back to normal
- Thermal protection: a thermistor mounted directly under the LED die tracks temperature. Output is throttled as it approaches 50°C, and the LED fully shuts off into a cooldown mode above that threshold, only turning back on once it’s dropped below a configured temperature
- Single-button interface to cycle which stat is shown on the display
- Active cooling: heatsink + thermal paste + 12V fan (with its own 12V converter, since nothing else in the system ran on 12V)
- Custom 3D-printed PETG housing (chosen for its heat resistance), split into two hinged halves — electronics base and LED head — so the beam angle can be adjusted and held at any tightness via the hinge
- Housing design details: flush countersunk screw holes and heat-set threaded inserts for mounting the lid and internal components like the buck-boost converter
Challenges
The biggest lessons came from buying the wrong parts before understanding the physics involved:
- First attempt used a fixed 12V buck converter with no current limiting. Turned out the LED needed 15V to hit its full potential — and more importantly, as COB LEDs heat up their resistance drops, so they pull increasing current at a fixed voltage. Without a current limiter, that’s a direct path to burning out the LED.
- For dimming, I originally used a motor PWM driver, which actually worked fine for the LED. But once I decided the Arduino should own dimming (to layer in the safety features), I tried to “hack” into the motor driver’s potentiometer input using optoresistors. It wasn’t reliable enough, so I switched to a dedicated PWM regulator that accepts a direct PWM signal from the Arduino.
- Getting the power output ramp curve right so the USB-C PD adapter doesn’t trip its own overcurrent protection when the LED suddenly demands a lot of current.
What I learned
- USB-C PD triggering and negotiating higher voltages for power-hungry loads
- Buck-boost conversion and current limiting as protection against thermal runaway in high-power LEDs
- Safely reading higher voltages into a microcontroller using a voltage divider
- Building real-time protection logic: voltage-sag detection and thermal throttling/cutoff with cooldown hysteresis
- 3D design techniques for functional enclosures — heat-set insert holes, flush countersunk screws, and adjustable hinge mechanisms
- Iterating on hardware choices quickly when a component doesn’t actually meet the electrical or thermal requirements of the project