5V Switching power supply

I came up with the idea for this project because I am sick of the more common 5V USB chargers that can prove dangerous due to miniaturisation and making the parts dangerously close together. There have been numerous reports of cheap phone chargers causing damages. Yes, I could just get a charger from a reputable source but there is no fun in that. I have decided to make my own because, why not? This uses the common SMPS topology. This is wicked efficient but has the downside that it can block radios, complex and isn't isolated but it, however, is light and efficient.

How these SMPS converters work is that there is a small transformer that gets switched at a high frequency then rectified to the 5V output. There is a lot more to it than that but that's the main principle. First, the mains gets rectified, the rectified mains enters the IC through a starting resistor and also goes to the primary. When power is applied a capacitor charges up and the IC soon starts oscillating. The primary is energised until saturation and then is de-energised releasing the energy into the auxiliary winding that supplies the IC and the output windings. On the output, there is a reference and that feeds into the IC through an optocoupler for isolation, it helps regulate the power but changing the drive of it to match the 5V output, or whatever it is set to.

Schematic

PCB Layout

Scale to 41*69mm

2020 OZFix