Hi!
I'm in the middle of reverse engineering a fancy BMS (JK BMS) and I have a few questions about how they are driving back-to-back mosfets at the input. I'm just a hobbyist so extensive answers are appreciated
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
The input circuit is the following:
![Back-to-back N-channel MOSFET Vgs? 1967493-0](https://www.eevblog.com/forum/index.php?action=dlattach;topic=408261.0;attach=1967496;image)
- B0, B1 and B2 are the battery inputs, isolated from the rest of the circuit.
EDIT: B0 is the negative terminal of battery 1. B1 is the positive terminal of battery 1 and negative terminal of battery 2, and so on. The batteries are in series.
- COM_1 and COM_2 are two common buses where the MCU reads the voltage from. COM_1 is connected to all EVEN inputs, COM_2 to ODD inputs.
- UNK_1 is a common bus for all the driving PNP transistors which connects somewhere unknown.
- The GND shown in the schematic is not connected in any way to the batteries. Think of the circuit as being powered by an isolated PSU.
The circuit is double sided but has many components and is a bit hard to trace, plus it does not really answer my question: How can the mosfets (Q1, Q2, Q5, Q6, Q9, Q10) be driven without any clear potential in their source?
My guess is they are doing something with the COM_1, COM_2 buses and UNK_1, such as using COM_1/COM_2 as a ground (from the mosfet point of view) and UNK_1 with a potential.
Regards,
Iscle