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4-20mA current loop

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David Hess:
You have the right idea but the dual supply TL072 is not suitable because an input common mode range down to the negative supply is required.  Your simulation must not have taken this into account.

IC1B in your circuit is not doing anything useful.  Both functions should be combined into the same operational amplifier.

Typically precision low power single supply operational amplifiers like the LT1006 or OP90 are used.

http://www.circuitdiagramworld.com/transmitter_circuit_diagram/OP90_4_mA_to_20_mA_Current_Loop_Transmitter_16249.html

rs20:

--- Quote from: OM222O on May 07, 2019, 02:19:38 am ---regardless of how much you search, there is nothing about "Powering ICs (or op amps for that matter) from a current source" ... they require voltage sources! simple as that! op amps specifically have voltage rails!

--- End quote ---

Wow, you are obsessed with word matching, and the supreme confidence with which you make completely false statements is remarkable. Even if you have a power supply named "a current source", it will still produce a voltage across its load while pushing current through it. If that resulting voltage is within the acceptable limits for the supply of an op-amp, then the op-amp will run just fine. At no point does the op-amp shout out "hey, wait, that thing that's powering me is CALLED a current source and my pins are CALLED voltage inputs! OMG i die now :-(". If your approach to deciding if a op-amp will be powered correctly is comparing words rather than calculating voltages, then you're just taking a completely flawed approach. I don't know what else to say. V=IR. They are intimately interrelated.

Also, if you have a real world current source, it will have a compliance voltage. If the current source has a compliance voltage of 24V, you can use it to power an op-amp just fine. Even ignoring the compliance voltage, send the current through a 24V zener and power your op-amp off the resulting voltage drop. These are just two of the things you would have found if googling was a viable strategy for designing circuits, let alone confidently asserting what's imposssible.

OM222O:
you can't just use ohms law for a complex IC  :-DD they will not magically create their own "voltage drop" and just work. The "viable design" which you speak of, is making sure at least the basics are right  :-// even if once circuit works under specific conditions, it's still a terrible practice to just assume the exception is the rule.
Even dave showed in one of his videos that you can power an IC from it's IO pins using the protection diodes ... obviously it is not a good design, but it works under certain conditions  :-/O

Please prove me wrong by setting up a circuit that powers op amps or some other ICs using a current sink / source and is stable with all the operating conditions of the ICs (i.e: different temperatures and different input / output conditions).

EEVblog:

--- Quote from: OM222O on May 06, 2019, 09:19:22 pm ---regardless of how much you search, there is nothing about "Powering ICs (or op amps for that matter) from a current source" ... they require voltage sources! simple as that! op amps specifically have voltage rails!

--- End quote ---

Funny how there are chips powered from 4-20mA current sources
https://www.analog.com/media/en/technical-documentation/data-sheets/3255f.pdf


soldar:
I am not sure if the OP is trying to build the remote sensor (to sense what?) or the receiving part. The receiving part is extremely simple, as has already been shown. Basically a resistor will do.

The sensor can be relatively simple depending on what we want to measure. You are looking for a current source which sets a current regardless of voltage. Have a look at the attached circuits.

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