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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

Dogbone06
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1 Answers1

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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.

Andy aka
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    Thank you! I guess this is a good protection to have then so I’ll leave it in there. Appreciate you taking the time! :) – Dogbone06 Feb 03 '22 at 16:35
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    @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](https://electronics.stackexchange.com/tour) to understand how to give proper thanks. – Andy aka Feb 03 '22 at 16:40
  • 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. – Dogbone06 Feb 03 '22 at 16:41
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    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? – Andy aka Feb 03 '22 at 16:44
  • 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. – Dogbone06 Feb 03 '22 at 16:52
  • Isn’t TP4056 reverse polarity protected as is? – winny Feb 03 '22 at 19:07
  • @winny not according to the data sheet unless I'm [reading it wrongly](https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf). Page - under absolute max ratings. *·Input Supply Voltage(VCC)：-0.3V～8V* – Andy aka Feb 03 '22 at 19:10
  • The datasheet isn’t great, that’s for sure but I interpreted “No blocking diode is required due to the internal PMOSFET architecture and have prevent to negative Charge Current Circuit.” as you can flip the battery without issue. – winny Feb 03 '22 at 19:12