Saturday, September 19, 2015

Current Limiter Project Wrap-Up

Four years ago I made my first printed circuit board using EagleCAD and purchased a few units using BatchPCB. It was a version of this current limiting circuit with R5 as a potentiometer, which lets me modify the cutoff current. By the time the boards arrived I probably had exams or something, and so the project was forgotten.

Today I was trying to clean my desk, but I found the boards and got distracted. I scavenged around Sector67 for parts (making backwards progress on the desk-cleaning situation) and populated the board.

When the output draws under some current limit (can be modified by the potentiometer), the green LED is on. When the output would draw more than that limit, the red light turns on, and the output current is limited to what flows through the red LED and resistor in series with it. The concept and operation is described in detail at the Instructables page of the source for this project:

I made the traces thinner than I would have liked. It was my first time getting a PCB made and I didn't realize that I had forgotten to set the trace width until it was too late. The default trace width is probably fine here anyway. It feels good to finally wrap up this project. I could go further with it (compute some values, measure some values, stress test the board, refine the design) but there are hundreds of other projects that will probably take priority.