Voltage Supply

This is not my Variable Voltage Supply project but some notes on voltage supplies.

Confusion

My main point of confusion is the use of transformers. 110VAC can be rectified and switched down to common DC voltages efficiently, so why use a transformer?

5V

This is the most commonly needed voltage, and it can be stepped down to 3.3V with little loss.

5V Micro USB adapter are both common and cheap, the micro USB adapters are about $0.30. Good option for low-power projects.

The LM7805 can step and smooth voltage down to 5V, it's about $0.10 but still only 1.5A.

Switching Costs

Part	Cost
LM25xx	$0.30
LM25xx	$0.30