Final Project
Power Electronics

The first thing I did for my final project was make a power supply to power my amp. Unlike my other projects, audio amplifiers draw a lot of current, and can't be powered by USB or a battery. This means that I had to draw power directly from the wall. Additionally, audio signals are dual ended, which means that they're centered around ground, and can be either above or below ground.

In order to work with a dual ended signal, my power supply too had to be dual ended. This is something I had never worked with before. While looking around for advice on making an audio amplifier, I came accross this website, specifically the circuit at the bottom. The basic idea is to use a torroidal transformer to step down the 120V 60Hz out of the wall to 30V 60Hz. Then this AC signal is rectified and regulated, outputting ~30V DC. If you make two boards, each of which have isolated supplies, and connect them in series, you have a dual ended 30V power supply.
First, I tore apart an old power coard and soldered it to my torroidal transformer so that I could plug directly to into the wall. Something important to know here is that the black wire is power in the US, which I learned at the price of shocking myself. I made sure to use a lot of heat shrink insulation to avoid any future electrocution.

I also soldered connectors to the output of the transformer, so plugging into my power boards would be easy.

Then I designed the power boards in EAGLE. This was fairly straightfoward. The one important point when designing boards that carry a lot of current is to make power carrying traces to be as thick as possible to minimize output resistance.

Many of the components are through hole components, but by trimming and bending the leads they can be easily turned into surface mount components. Many also have heat sinks, and it's important that these do not touch since they're usually connected directly to one of the pins, so touching heatsinks will result in a tough to diagnose short.

Finally, I bought two very large capacitors from digikey. These serve two purposes, they help filter out any AC from the power supply, and they can be discharged quickly to provide big "kicks" for the subwoofer. Since these can store so much energy, they take a while to discharge when disconnected, so it's important that you discharge them every time. It also means that the the amplifier can continue to play music after being unplugged.

Eagle files