Electronics > Beginners
Which Op-Amp for a VCCS ?
doublec4:
Hi All,
I have a few sensors here that output 0-5V analog. I have a SCADA modem that has analog inputs but requires 0-20mA input.
I have been searching how to properly do this and came across this here:
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/voltage-to-current-signal-conversion/
Explanation is great and makes sense to me, but since I've never played with an op-amp I'm a little lost as to what characteristics I'm looking for to perform this function in this "transconductance amplifier" circuit. I'm having some trouble finding info to guide me through this process.
Any help would be appreciated!
Thank you
ogden:
You may start with typical 4-20mA circuit, like this one (search result)
doublec4:
Thanks ogden,
I checked out the datasheet and the part on Digikey.
I guess what I'm looking for is more of a "why" this part number? This circuit is for 0-3V input, but if I want to adapt for 0-5V reading I'm not sure what I'm looking for in the parameters on Digikey to do so, or what else to modify in the circuit based on my conditions.
I will have a 24VDC supply for the SCADA modem and a 5VDC supply available for the sensors.
Also, the complexity of this circuit is greater than the original one I posted. Is this for greater precision? I should mention that my application is not for precision instrumentation, so I'm not sure if that changes anything. I am fine with some reasonable amount of error.
I will keep searching for an explanation in the meantime, but if anyone knows of a good link to understand how to go about choosing the components to do something like this it would really help further my understanding.
Thanks!
schmitt trigger:
Go to the Analog devices website.
They have a whole table of 4 - 20 mA loop interface ICs. There are app notes that explain the underlying concepts.
ogden:
--- Quote from: doublec4 on May 31, 2019, 06:01:51 pm ---I guess what I'm looking for is more of a "why" this part number?
--- End quote ---
Dunno. As I said - it did pop-up in the search. If it were another part number - would you wonder less? :)
That seems to be old circuit/appnote referring to old opamp. Most likely you can use any generic opamp.
--- Quote ---This circuit is for 0-3V input, but if I want to adapt for 0-5V reading I'm not sure what I'm looking for in the parameters on Digikey to do so
--- End quote ---
For 0-5V input you need to 1) increase supply voltage from 5V to ~7V and 2) change voltage divider.
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