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
When looking for affordable and commonly available MOSFETs in SA I came across a few candidates. Now there are mostly big tradeoffs with N-channel logic level MOSFETs however, I find that most of the time I use them instead of relays for slow switching applications. Most of my projects have not been using PWM so I have not had any issues using the logic MOSFETs . And I find that I use the N-channel MOSFETs almost all the time.
“real fet” characteristics
“fake fet” characteristics
Finding MOSFETs with decent specs for a decent price was quite tricky but I found a sweet spot with the IRL520N now there’s always the chance of getting fake chips and I might have fallen victim to this but the “fake chip” had specs that were quite close to the “real chip” in a comparison I did between two chips. The fake one also had a slightly larger and glossier form factor.
“real fet” left and the “fake fet” right
These are my top 3 N-channel MOSFETs which are common
IRL520N
IRLZ44N
IRFZ44N
I would like to add some honorable mentions as well. These N-channel MOSFETs are either not common stock with the online stores I use or are way to expensive for a hobbyist however sometimes they are mandatory requirements for specific projects.
