#99 Custom WiFi Mosfet PCB with battery backup

Version 1.0 of the protoboard not as appetizing as the schematic…
Reverse side with thicker black wires for the MosFets.

Creating a a custom 4ch Mosfet switch PCB with a built in backup 12v battery changeover circuit takes some careful planning. Since I had experience working with mechanical relay versions the task was not too difficult however it did come with a few extra challenges.
Mosfets require more parts to work reliably they also have significantly different ratings when compared to relays. In this case I was using an esp8266 with 3.3v logic. I had to create an amplifying circuit out of two transistors in order to get around 6.6V to allow the Mosfets to turn on completely thus allowing me to utilize their max current ratings.

The beginning of prototyping always looks so clean…
Bread Board prototyping is always a good idea before soldering.

On my 4ch PCB I used 3x IRL520N and 1x IRLZ44N N channel Mosfets. The IRLZ44N is the best rated for logic level and also the most expensive and rare here at least at this time. I also needed a large amount of amps for the LED strips it was going to switch on and off. The other three IRL520N Mosfets will be used with applications using under 5A of current. Technically I could have just used TIP120 NPN transistors but I wanted to keep the entire PCB Mosfet compatible in case I wanted to swap out any chips.

Drawing block diagrams by hand help the though process.
Creating a clean schematic in KiCad makes building the board easy.

For more info on the project check it out on Github