Simple Adjustable DC-DC Converter

I bought this lab power supply off eBay, with a single 0-30V and 0-3A output. Great! But what if I needed more than one output? I decided to scrap this usefull little guy together.

Two of these simple and adjustable converters sit on a perf-board. If I need 3.3V, 5V, and 12V, I can simply set the power supply to 12V, and use the converter for the other two provided they're low power.

Pictures

Schematic

This schematic is found in the datasheet. I didn't follow this exactly, I forgot the output filter capacitor, which is kinda important, but it works fine. D1 will protect your converter if the output spikes up higher than the input. You can learn more about how it works if you read the LM317 datasheet.

Because the LM317 is a linear regulator, it is primarily limited by thermal limitations. The LM317 can technically handle 1.5A, but that does NOT mean you can run it at that worry-free. It'll handle that only if its heat dissipation is taken care of. I have small snap-on heatsinks, that can probably only handle a few watts of dissipated power. Because it's a linear regulator, the heatsink will need to dissipate all the energy needed to drop the voltage from Vin to Vout linearly. A linear regulator works like a voltage divider that varies based on feedback. The power dissipated as heat is Pout-Pin, or (Vin-Vout)*Iload. So if you need 5V 1A at the output, it's not a good idea to set the input to 30V. 1 or 2 volts above the output would be ideal. Thankfully, the LM317 is smart and won't let you easily burn it up. It will reduce the output to a safe level if it gets too hot.

I used PCB Artist for this. It's a fantastic little program with a very large part repository. It's very intuitive and keeps it down to the basics. There's no need to break out Altium if your circuit only has a dozen parts. Sorry about the silly European symbols, and I'm not quite sure how to change it yet.