One of the main functions of the power supply is to convert our 120V mains AC electricity into usable DC electricity. This is done using a transformer and a bridge rectifier circuit.
A step-down transformer is used to convert the dangerous 120V AC electricity into a more manageable 25V. In order to get the 2A output from my power supply, I needed a beefy transformer. The Radio Shack 25.2V center tap 2A heavy duty transformer was a perfect choice (Model #273-1512). This transformer has 3 output leads. In order to get the full 25V, I used the outer leads and safely taped the middle lead out of the way.
I added a 3A fast acting fuse immediately after the transformer in order to protect the circuit in the event of an accidental direct connection to the 120V mains power. The fuse holder is a Schurter 5 X 20mm (part # 0031.8211).
The Bridge Rectifier
The bridge rectifier is a very simple circuit that essentially uses 4 diodes to convert the negative portion of the AC wave into a positive wave.
This video does a great job explaining the whole transformation:
In my project, I used 4 1N5822 Schottky diodes. With normal diodes, you get around a 1.4V voltage drop in a bridge rectifier, while Schottky diodes only have a voltage drop of around 0.6V.
I could have simplified this quite a bit by using an all-in-one bridge rectifier IC but I really wanted to build a traditional version using the 4 diodes. After some positioning and repositioning, I ended up with the following configuration on my circuit board: