I removed C8 from S-D MOS and put it where it was.
I also removed diode from S to GND so all of the attached pictures are now from the board that is not modified. Well... if not described differently below
Pictures explained:
1.) Default board: 3.3V (yellow) and op-amp output (blue).
2.) The same as on the picture 1, just a zoom to ADC (reading) part.
3., 4. and 5.) All pictures was shoot when 100 % power was used and I can see no clear difference if unmodified board was used (3) or with a 1000uF capacitor added at the input of regulator (4) or with 1000uF at the input of regulator and 470uF at the output of regulator (5). I didn't put 1000uF capacitor directly to the 24 V power supply, it is a diode between 3.3 V regulator and 24 V. I just thought of this now
Maybe I should put another (at least) 1000u straight to 24 V line...
6.) AC coupling with full power load: 24 V (yellow) and 3.3 V (blue).
7.) The same as picture 6 just with DC coupling.
I believe that it got a little better than before but not that much.
Again I must point that I have more problems on lower temperatures (270 C) then on higher (360 C).
Does that make any sense? Maybe because of higher voltage to noise ratio?! David?
Thing I should do and didn't have time:
- different power supply
- checking noise, op-amp output and other locations on my daily using Ksger soldering station (I bought just controller and case from Ksger and I used different PSU then what you normally get with Ksger) that is working as it should just to see if there is the same noise
David, thank you for your information, simulation and everything else!