[EE]:: Reversed battery or charger protection

Protecting a battery and charger against a reversed battery (or charger)




A simple and retrospectively obvious answer to an inobvious problem.
The links below relate to the use of a TP4056 charging module and a single
LiIon cell, BUT this method applies for any battery chemistry (that comes
to mind)

Protection of circuitry against a reversed battery using a FET operating in
the 3rd quadrant is very well known.
This works when the load accepts energy from the battery.

When the load IS the battery and is being charged the circuit doesn't work
- magic smoke happens enthusiastically, potentially in charger and battery,
if polarity is correct. .
Instead of the charger seeing a small voltage drop to the load (battery) it
now sees full negative battery voltage as the load.
Stuff happens.

Addition of a jellybean bipolar, 2 resistors and a diode (arguably
optional) makes the 'reversed battery when charging protection' work
correctly.

Discussion here


https://blog.deconinck.info/post/2017/12/22/18650-Battery-charger-reverse-polarity-protection

Obvious latterly circuits here:

Low side NFET

https://blog.deconinck.info/public/Reverse_polarity_protection/battery_protection_low_rdson_mosfet.png

High side PFET

https://blog.deconinck.info/public/Reverse_polarity_protection/.P-mosfet_m.jpg

See text for why you may get away without  using the diode.



        Russell