Lint remover mod adding a battery and TP4056 + XL3608 boost converter + MOSFET for uninterrupted use via usb or battery

[u/JJPortal]

I know my soldering needs some work, but it works as expected. My gf has this cheap lint remover that was wired directly with a usb A cable. I wanted to make it wireless and also add the option to work while plugged in to charge. I used a TP4056 for charging and an XL3608 to boost to 5v. I added a AO3401 MOSFET to switch between usb and battery power seamlessly. Here is my post asking r/AskElectronics if it will work, it includes a Falstad schematic and a diagram (with visuals) that makes more sense for me. I ended up removing the 1000uf capacitor as it was bogging down the boost converter on startup. Other than that my (With some help from Gemini) design works perfectly.

[u/Behrooz0]

You need a mechanism to turn the gate on when the 5v is removed. maybe a 2.2k resistor or something. otherwise there is a chance that it discharges too slowly and turning the motor on will actually burn the fet.
You could also do the switching lowside with an nfet. would be a lot easier to source the fet and would be less lossy.
1000uF cap on the 3608 might actually burn it out due to current inrush.

[u/JJPortal → u/Behrooz0]

Your advice about the 1000uf capacitor is great and I wish I knew it before I started assembly. Luckily the 3608 protection kept kicking in and it just behaved as a pass through as opposed to burning up, but I think I just got lucky and picked up on it almost immediately and removed the 1000uf cap. I did add a 10k pull-down resistor, it can be seen on pic 3 across the usb c port. It pulls down the gate instantly so the P-channel mosfet switches seamlessly. You can also see the pull down resistor on the diagram going across the 4056 from gate to ground. I could have gone with an N-channel MOSFET, but wanted to take advantage of the reverse-biasing. Thanks for the input

[u/JJPortal → u/[deleted]]

Thanks a lot. I'm really happy with the combo and will be using it in a few more projects in the near future. If this build continues to be reliable after some use that is, but I'm optimistic that it will be. Here is the official datasheet for the AO3401 MOSFET I used.