Reverse Polarity protection for 18650 battery charger (tp4056)

Thread Starter

cyberdyne

Joined Jan 29, 2019
3
I need advise on best value components for this Reverse Polarity protection schematic (pictured).

source.

The original author just used what he had laying around,
>2N2907A
>IRL2203N
as i will be buying everything new, that gives me a lot of options.
Requirements:
  • 18650's charge up to 4.2 volts
  • Max continuous 1000mA (1A)
i need to make 20 of these for my charging board,
so i dont want to waste money over engineering it.
Cheapest reliable parts will be fine.

im new to electronics & totally confused on how to select the right transistors?
Also do i need to be worried about the volt drop over the mosfet?
 

crutschow

Joined Mar 14, 2008
23,816
The BJT can be just about any PNP such as the common 2N3906.
The N-MOSFET can be any logic level type (with a Vgs threshold of <2V) that has an ON resistance of ≤10mΩ.

Yes, you need to be concerned about the voltage drop across the MOSFET.
10mΩ On resistance will give a maximum voltage drop of 10mV @ 1A.
 

Thread Starter

cyberdyne

Joined Jan 29, 2019
3
The BJT can be just about any PNP such as the common 2N3906.
The N-MOSFET can be any logic level type (with a Vgs threshold of <2V) that has an ON resistance of ≤10mΩ.

Yes, you need to be concerned about the voltage drop across the MOSFET.
10mΩ On resistance will give a maximum voltage drop of 10mV @ 1A.
Hey Thanks crutschow.
I just placed an order for the 50x 2N3906 fro $1.
After searching on mouser.com to find a MOSFET options that met the specs you listed, i checked eBay for price.
I cant seem to find anything cheaper than what the original guy used "IRL2203N" @ $4.28 for 10pcs.
Good price?

Do you have a formula or rule i can use to work out for myself in the future? or a video guide or something?
I've also been wondering the best way to join them without a pcb...?
 
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