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Can somebody help me figure out what the circuit in the red box does?

What is the purpose of the six FETs and how do they behave once P- is connected to the negative supply voltage?

What is the purpose of Q7 and Q8 and what function does it serve?

What is the purpose of Q9 as well and what purpose does it serve?

In addition, what is the overall functionality of these components as a whole?

The image is taken from this website.

enter image description here

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  • \$\begingroup\$ To that, the answer is yes. The question is, what help you need to figure out the circuit in the red box, and at what level you need to figure it out? \$\endgroup\$
    – Justme
    Commented Mar 23 at 9:30
  • \$\begingroup\$ @Justme I have edited the post \$\endgroup\$
    – JoeyB
    Commented Mar 23 at 9:37
  • \$\begingroup\$ @JoeyB are we done here with this question or do you still need clarification in my answer? \$\endgroup\$
    – Andy aka
    Commented Mar 24 at 9:15

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There are two groups of paralleled MOSFETs; the left group and, the right group. Together they form (in effect) a bidirectional switch so that: -

  • the associated battery can be disconnected from a charge circuit (when full)
  • the associated battery can be disconnected from a load when deemed out of charge

Here's an example of back-to back MOSFETs that are basically doing the same thing as your circuit: -

enter image description here

The image comes from How to Design a Battery Management System (BMS).

As for other circuit components, this would likely require a complete simulation to determine what they do in all circumstances. And, the trouble with the circuit in question is that it doesn't appear to have any provenance because it comes from a site that appears to have acquired the schematic through reverse engineering. So, I suggest you simulate the circuit.

  • However, Q7, Q8 and Q9 do appear to be controlling the on-off state of the MOSFETs mentioned earlier.
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