Hello,

I just want to get your thoughts on why this circuit won't work as intended?

 

How IS it intended to work?
I would guess that 0V out from the DAC should correspond to 4mA and 3.3V should correspond to 20mA

 

How does it not work?

 

Pin 4 on the op amp should be connected to the Emitter of Q1 not ground.

 

VREG will be powered by external thru the Jack. There is no data being received or transmitted by DAC to the MCU.
I am wondering if I should power DAC independently from VREG?

 

Hi Dave,

Why should it be connected to emmiter of Q1? due to current sense?

 

How IS it intended to work?
I would guess that 0V out from the DAC should correspond to 4mA and 3.3V should correspond to 20mA

This is to control the a ventilation system - the end unit will have some sort of a fan.