I am trying to use a PFET to protect my circuit against reverse polarity like such:

Reverse polarity protection schematic

Now I would like to add a LiPo charger to this circuit. Can I just add it after the PFET (@+Vbatprotected)? Will the charge current be able to flow "backwards" through the PFET?


No you can't just attach the charger to +Vbatprotected. The whole point of that PFET (with it's gate hooked to GND) is to effectively operate as a diode, but without the pesky downside of a 0.7V drop (i.e. because it has a low drain-source resistance when it's in saturation).

Even if that wasn't the case, I wouldn't count on a PFET to handle charging current which can be quite high. Just hook your charger to +VBAT directly.

  • \$\begingroup\$ Thanks for the quick and clear answer. In this case, the charger also should be reverse polarity protected somehow, or it would be damaged in case of wrong polarity, right? (i'm looking at MCP73830 for example) \$\endgroup\$ – pixbroker Jul 12 '15 at 19:41
  • \$\begingroup\$ Sure... you might want to consider keyed connectors as an alternative. \$\endgroup\$ – vicatcu Jul 12 '15 at 20:03

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