My question is simple - maybe silly. I've got 2 circuits:

  1. MCU with DAC, ADC and another 3.3V electronics enter image description here
  2. Dummy load (Max 24VDC). enter image description here

Do I need to connect two separate grounds (MCU ground and dummy load ground) into common ground?

I think yes, still not certain about it - i don't know the impact on the accuracy of the measurements taken by ADC.

If no, where should I ground the R's and D's - to the MCU ground or dummy load ground? If you have any remarks on this circuit feel free to criticise me.

  • \$\begingroup\$ What is the purpose of R and Zener in your circuit? \$\endgroup\$ – Unknown123 May 13 at 22:12
  • \$\begingroup\$ When the voltage exceeds the maximum limit eg. 24V the zener makes the short circuit to GND. R's are here because of the voltage divider - 24V could harm 3.3V logic. \$\endgroup\$ – gunnersson May 13 at 22:14

Yes the grounds should be connected together, otherwise you don't know what your Vgs on the MOSFET is. You have a bigger problem, however, because your power resistor is on the wrong side of your MOSFET. You should be doing low-side switching, otherwise you will not be getting your gate voltage high enough over your source voltage.


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