I have built the attached Li-On Battery charger based on MCP 73831 chip and it works well. However I would like to add a reverse polarity protection to it since I've burned 2 chips while putting the battery to be charged the wrong way. Is there a reliable way to do this and sorry for my poor english language.


enter image description here

  • \$\begingroup\$ Schottky diode in series! You do however need to move the voltage feedback point to behind the diode which in many cases is not possible. \$\endgroup\$
    – winny
    Jan 9, 2017 at 22:37
  • 3
    \$\begingroup\$ Use a polarized connector so that this does not continue to happen. Also, I connect batteries to power supplies all the time. I don't think I have ever done it backwards. It seems a bit surprising that you have done it twice. \$\endgroup\$
    – user57037
    Jan 10, 2017 at 4:32

2 Answers 2


I have not seen electronic polarity protection on lithium batteries. Normally a polarized connector is used so that it is not possible to connect the battery with reverse polarity. Barring that, I would think that red/black color coding would be enough to prevent reverse polarity connections.

But if you REALLY want a circuit solution, here it is.


Q1 should be a PMOS FET with low Rds(on) at 2.7V. One possibility is alpha and omega p/n AO3401A. Q2 can be a 2n3904 or any typical logic BJT.

Note that this circuit will prevent a totally dead battery from charging. The battery must be at least 0.6V or so to turn on Q2.

  • \$\begingroup\$ Q2 could also be an NMOS FET such as a BSS138, but then the turn-on voltage would be even higher. \$\endgroup\$
    – user57037
    Jan 10, 2017 at 7:21
  • \$\begingroup\$ "Note that this circuit will prevent a totally dead battery from charging" - Good. If a Lithium-ion cell reads less than 2.5V then it is permanently damaged and not safe to recharge. \$\endgroup\$ Jan 10, 2017 at 8:43
  • \$\begingroup\$ Thanks a lot guys. I'll put the mofdification suggested by mkeith and let you know how it goes. \$\endgroup\$
    – Eddy
    Jan 10, 2017 at 9:08
  • \$\begingroup\$ @BruceAbbott, yeah but a protected cell may present itself as "dead" even though the internal cell voltage is above 2.5V. \$\endgroup\$
    – user57037
    Jan 10, 2017 at 22:52
  • \$\begingroup\$ Li-Ion cells are NOT damaged by going below 2.5v, though they may loose some capacity. But they should be trickle-charged back up to 2.5v before applying a regular charge current. This is to prevent lithium plating on the anode. That is also a danger when charging any Li-Ion cell while cold. Cells should also be monitored for heat buildup when charging at any rate over 0.5A. \$\endgroup\$
    – Guy Gordon
    Oct 23, 2020 at 3:33

The "ideal" solution would be adding an ideal diode circuit. You could also use mechanical reverse polarity protection by using connectors that can't be reversed.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.