Libre Solar Community Forum

Reverse protection FET

Hi everone.

Around two years ago I had my first look into the schematics of the MPPT-1210-HUS, but since then could never understand the functionality of Q2.

Just today when I checked the schematics of the MPPT-2420-HC I saw the note:

“Reverse polarity protection and PV reverse current blocking”, here Q3.

But I still don’t understand why the gate of this FET is conncted to LS_DRV. Could anyone help me out here?


Hi Dan,

yes, the FET is indeed for reverse polarity protection and reverse current flow. It’s connected to LS_DRV to save the parts for an additional MOSFET driver, so it’s always enabled as soon as the DC/DC is enabled, which only happens if a plausible solar voltage is measured. The diode prevents discharging of the (internal) gate capacitance during the off-time of the low-side MOSFET.

See also this GitHub issue where someone asked a similar question.


Thanks for the link. I’ll read up on it.