Thanks for the help.
Last edited:
How would I cause the transistor to go out of conduction in this circuit? I'm interested in what i can do to cause this. Thanks.If the output falls to 0, the transistor comes out of conduction and the loop current goes to 0. In a 4 - 20 ma loop, that is a failure indication.
Hmmm .... so the OpAmp plays no role in supplying any current? So what is the "real" controlling element?The source of the current is the supply on the right with the battery symbol, labeled "External Loop Supply 7V-36V"
I see what your saying. But what ADC? Do you mean the DAC?The drive to the base of the transistor controls the current in the loop from the external battery, through RS.
The feedback voltage across the sense resistor, along with the output of the ADC are inputs to the amplifier which varies the drive to the transistor, using Rs as feedback for the correct amount as the ADC needs.
My Bad, Typo. The keys are like, right next to each other.I see what your saying. But what ADC? Do you mean the DAC?
I knew it was an ADC and I've read the application note quite a few times but was not understanding how this circuit was doing this regulation of current.
I'm actually interested in changing this circuit from a 4-20 mA circuit to a 0-20 mA circuit. Any ideas? I'm thinking of just adjusting the resistor values but would that be enough to get me 0 mA, i.e. no transmission whatsoever?
How would I go about turning this thing off?
I thought that's what I was doing already?The LPF notwithstanding can you help me in determining the proper feedback connection to get this circuit working like the original.
Try experimenting with the TI filter designer. It can do lots of good things.The reason the LPF is there is because I can have some AC riding on the DC that I want to feedback. I can design a LPF and I probably should have not put that in there but lets just assume I dealing only in DC at the moment.
Thank you for replying though.