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Subject: Re: 20ma current loop with opamps

Date: 01/19/02 at 2:00 AM
Posted by: Russ Kincaid
E-mail: russlk@yahoo.com
Message Posted:

In Reply to: 20ma current loop with opamps posted by roy on 01/18/02 at 7:36 AM:

If you want to operate from a 5 volt supply with a +10 volt input signal, you will need two op amps and a PNP transistor (at least). Attenuatie the input signal to 0 to 2 volts, set the first op amp to unity gain with the + input tied to + 2 volts. The first stage output will then be +4 to +2. Feed this into a unity gain, non-inverting 2nd stage which is driving the base of the PNP. Take the feedback from the PNP emitter so the Vbe is inside the loop. Set the emitter supply voltage and resistor such that +4 volts gives 4 mA (or zero, if that is what you want) and +2 volts gives 20 mA. R=2v/16mA = 125 ohms. Supply v = 4v + 4mA*125 = 4.5v

thankyou roy   Posted at: 01/22/02 (0)

thankyou roy   Posted at: 01/22/02 (0)

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