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Published 20 hours ago • verified publisher icon LibreSolar

What dose this P-MOSFET do?

Open shivanshumahim opened this issue 3 years ago • 2 comments

Hi, I am trying to understand the significance of this P channel MOSFET (Q9) in the Power section of the BMS. libre_solar_issue

I want to understand it's significance in both charging and discharging condition. I made a Falstad simulation with 1 discharge N MOSFET (Q5) and the P MOSFET. Relevant switches can be used to put the simulation in Charging/Discharging mode. Simulation is in this link.

Also, in case of charging, current flows through Q5 (disabled body diode) , but I am unable to understand how that N MOSFET is turned on. The Vgs and Vds doesn't make sense to me. Screenshot 2022-03-10 131408

shivanshumahim avatar Mar 10 '22 07:03 shivanshumahim

That FET is used to increase the turn-off speed of the discharge MOSFETs (e.g. in case of a short circuit). It is also used in the TI reference design and explained further in this App Note, Fig. 5-2. In the App Note they use a PNP instead of a PMOS, though.

martinjaeger avatar Mar 10 '22 16:03 martinjaeger

How was the 47 Ohm and 100 Ohm series resistor decided for driving the gate? Wouldn't the 47 Ohm resistor decrease the switch off time for the MOSFET?

EarthLord avatar Apr 11 '22 15:04 EarthLord