There is a big a difference between knowing something, and really understanding it. That thought occurred to me a few days ago when I made a bad decision on a project I’ve been tinkering with. To explain what I mean, let me describe a bit about my experience as an engineer.
I graduated about 15 years ago with an electrical engineering degree, and I’ve spent my entire career with a desk covered in random bits of electronics. Despite that, it’s rare for me to build a circuit or pick up a soldering iron. Right from the beginning I’ve always been more fascinated with software and what it could make hardware do rather than building the hardware itself. Software was just so much fun that I never seemed to get around to building much.
Recently, however, I’ve started teaching my kids about electronics and I’ve had to dust off the old skills. It has been incredibly fun to build things with them. Last Christmas we built the excellent electronic dice kit from SpikenzieLabs. This year we built Jimmie Rodger’s LoL shield, Adafruit’s MiniPOV3, and SparcFun’s Mr. Roboto, all Arduino-like devices so that they could try their hand at microcontroller programming. The kits are wonderful, and I heartily recommend them for anyone wanting to learn how to solder. My 8 year old rocked the soldering iron! Now we want to try something a little bit more ambitious and build something from scratch.
Building from scratch requires thinking about circuits that I usually take for granted. In this case, we’re building a project which will draw more current than can be supplied by the Arduino’s on board regulator. I needed to get or build a 5V, 2A regulator. This turns out to be new territory for me. Pretty much everything I’ve used so far either didn’t need a regulator or already had one on board. So, I did some research and settled on the well know L78S05CV linear regulator. I picked one up at the local electronics supply, wired it up on a breadboard and turned on the power. Low and behold it worked beautifully, with one exception.
Now, I learned in school that a switching regulator is far more efficient than a linear regulator. I know that the L78xx regulators require a heat sink, and I understand why they generate a lot of heat. However, it wasn’t until I built the circuit and accidentally touched the very hot L2805 that I came to a full and complete understanding of what that means. Ouch!
Should I have known better and chosen a switching regulator at the start? Yes, probably, but now I really know better!