Hi ledtester,
Thank you for your reply,
"Does Z3 need a resistor to protect it from excessive current draw when T1 conducts?" Oepsie yes I forgot.
I was aware of the AN-1533 app-note and used it as reference for the first circuit I build, however I used different parts and that is why this circuit did not work for me.
I was not aware the low voltage of the 431 and I incorrectly assumed it was close to 0V at the time.
The low voltage Vka(low) of the 431 (I used a AZ431 - diodes inc) was around ~1.8V when measured.
In this first circuit I re-used a AP2302B N-mos with a Vgs(th) of just 0.55V, so it was allways on.
I think I will change it to an other fet with a higher Vgs(th) limit to so simplify the circuit and make it work properly.
AN-1533 uses the ZVN4106FTA NMOS with a Vgs(th min) of 1.3V in combination with the:
LMV431AIMF uses a 1.24V reference so the output Vka low ~1V. This will work
SNVA681A uses the TL431 in combination with IRF840 which has a Vgs(th min) of 2V, and is a very big THT part.
the TL431 has a low voltage of ~2V.
It seems this is not a very good part choice, and might not work.
This appnote was a good read and helped me alot
Using the TL431 for Undervoltage and Overvoltage Detection
https://www.ti.com/lit/an/slva987a/slva987a.pdf?ts=1666614347749