Issues with an Ideal Diode

[machinehum]

I'm having some issues with this ideal diode circuit.



When powering from Vin, there is a small voltage drop across Q7 0.01V or so. So Q7 is turning on with no problem. I can draw load from 12V, 1A, and Q7 isn't breaking a sweat. This mode is working.

However when I power the circuit from the 12V, strangely I'm seeing ~3.3V at the Vin pin. I'm not sure how this is possible, but when I draw load Q3 will get hot. So I think it might be flowing out of Q3B.4? But this is a PN junction, so unless I've exceeded the reverse breakdown of the junction this shouldn't be possible. Does anyone know this value on the datasheet? Any other help would be much appreciated!

[Conrad Hoffman]

Base-emitter breakdown is often 5V or so. This isn't a bi-directional circuit and is probably doing just as you suggest. Nothing "ideal" about it compared to what a real diode does.

[PCB.Wiz]

I happened to have this open
https://www.diodes.com/assets/Datasheets/AP74700Q.pdf
that's a better ideal diode controller, charge pump for N-FET

or, there is a simpler version that I think is a fixed version of your SCH, without VBE reverse effect, P-FET.
https://www.diodes.com/assets/Datasheets/DZDH0401DW.pdf

[machinehum]

I happened to have this open
https://www.diodes.com/assets/Datasheets/AP74700Q.pdf
that's a better ideal diode controller, charge pump for N-FET

or, there is a simpler version that I think is a fixed version of your SCH, without VBE reverse effect, P-FET.
https://www.diodes.com/assets/Datasheets/DZDH0401DW.pdf

Thanks for the parts. I'm going to axe what I have and go for one of these guys. I like the first one.

[stowwest]

I happened to have this open
https://www.diodes.com/assets/Datasheets/AP74700Q.pdf
that's a better ideal diode controller, charge pump for N-FET

breakout game

or, there is a simpler version that I think is a fixed version of your SCH, without VBE reverse effect, P-FET.
https://www.diodes.com/assets/Datasheets/DZDH0401DW.pdf

Thanks for your extremely detailed and helpful feedback.

[Smokey]

I've been using the lm5050 recently for some stuff.  Been working great. 
https://www.ti.com/lit/ds/symlink/lm5050-1-q1.pdf

[Peabody]

Could someone explain what the original circuit is supposed to do and how it works?  What do the bipolars do?

[Zero999]

Use another pair of matched transistors, as diodes, to block the reverse voltage. The circuit below shows how it can work at voltages higher than the gate-source rating of the MOSFET. If the voltage never exceeds the gate source voltage rating, or the MOSFET's have built-in clamps, D1 and D2 are unnecessary.

LTSpice Simulation