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mohannad100
Joined: 16 Jan 2008
Posts: 67
Location: iraq
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 17 Jun 2008 21:54 4-20ma current source |
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hi every body
can any one tell me how to get a 4-20ma current source
to be used in my circuit.then it converted to 0-5v and then tn mc
but basically i need help in how to get 4-20ma current
thanks.
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TekUT
Joined: 17 Jun 2008
Posts: 413
Helped: 23
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17 Jun 2008 22:10 4 20 ma current source |
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Hi mate,
there is many approach, most simple was use a simple voltage regulator like the LM7805 (look inside the component datasheet, you can found the schematics used to build a very simple constant current generator, but this one can't be useful for low corrent like you need ad this info is just only for completeness), another way is use a simple operational amplifier and a few resistor around it to make the current source (I've often used it to simulate 4-20 mA current loop interface), another approach (best result but with some cost), will be use one of more specific integrated circuits (e.g. MAXIM http://www.maxim-ic.com/appnotes.cfm/an_pk/1064).
Cheers
F.F. a.k.a. Powermos
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17 Jun 2008 22:10 Ads |
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FvM
Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany
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18 Jun 2008 8:00 4-20 ma current source |
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The maximum Rload respectively maximum voltage drop requirements should be known. A voltage drop of 10 V wouldn't be unusual for a 4-20 mA loop, cause it may be used to supply loop powered circuits.
A ground referenced voltage input may be desirable, involving a differential amp circuit with additional resistors. I'm typically using a darlington transistor to reduce current error and a current limiting base resistor.
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Candy8866
Joined: 15 Jan 2008
Posts: 42
Location: shenzhen
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18 Mar 2009 3:32 designing 4-20ma source |
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| by amplifying sensor current/voltage through an OP-Amp
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pauloynski
Joined: 06 Oct 2004
Posts: 277
Helped: 34
Location: Brazil
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19 Mar 2009 3:48 simple current source |
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Here is a simple circuit with adjustable gain and off-set. Itīs output is referenced to an external voltage (current sourced by the receiver), which is a more common approach than the one shown above.
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Candy8866
Joined: 15 Jan 2008
Posts: 42
Location: shenzhen
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26 Mar 2009 8:53 how make circute current source 4-20ma |
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you can check the datasheet.
hope can help you.
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