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I have a circuit that was made for me some time ago by an electrical engineer. But looking at many other TP4056 circuits I see that my circuit has a few parts that no one else has.

So my question is, what are these parts purpose?

My circuit: enter image description here

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So my question is, what are these parts purpose?

It looks pretty much like a reverse voltage protection circuit. In other words, if the incoming supply to VIN were incorrectly connected regards polarity, the MOSFET inside your red/orange box would turn off and prevent your battery getting reverse polarized.

Here's a link to a site that explains how it works. It uses a slightly different gate bias circuit but, in essence, it does the same thing.

Here's a link to a Q and A on this site that might help.

However, I notice that VIN also connects to pin 4 of the TP4056 so, maybe your circuit designer started off with good intentions but missed a trick later on.

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    \$\begingroup\$ Thank you! I guess this is a good protection to have then so I’ll leave it in there. Appreciate you taking the time! :) \$\endgroup\$
    – Dogbone06
    Commented Feb 3, 2022 at 16:35
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    \$\begingroup\$ @user2965339 it's not a 100% protection due to the late amendment in my answer so be aware that it will only protect the battery and not the TP4056 chip. Please take the 2 minute tour to understand how to give proper thanks. \$\endgroup\$
    – Andy aka
    Commented Feb 3, 2022 at 16:40
  • \$\begingroup\$ I see your edit there. Yes indeed. From what I understand power should be drawn directly from the battery. My designer made it so that power is drawn from pin 4 which also charges the battery. No other schematic has this. Seems to be quite a few problems on this one. \$\endgroup\$
    – Dogbone06
    Commented Feb 3, 2022 at 16:41
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    \$\begingroup\$ Yeah, I'm not all that sure on the design myself - the chip will certainly blow if it gets a reversed VIN but, quite possibly the battery will be safe. However, if the chip blows then what might it cause the VBAT pin to do and, where is the battery connected? \$\endgroup\$
    – Andy aka
    Commented Feb 3, 2022 at 16:44
  • \$\begingroup\$ I will for sure switch this circuit out for the common ones I’ve found online. They’re all very much the same for this chip so it should work just fine. \$\endgroup\$
    – Dogbone06
    Commented Feb 3, 2022 at 16:52

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