Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Op-Amp as a Current Supply

  1. Aug 14, 2008 #1
    guys, i need some help...

    is it possible to construct a variable-output current supply using op-amp(s)?

    if so, can anyone help me about how to construct one?

    thanks :)
     
  2. jcsd
  3. Aug 14, 2008 #2
  4. Aug 14, 2008 #3
    thanks very much!!

    so that's why, i used "supply" for searching... should have used "source"...

    :)
     
  5. Aug 14, 2008 #4
    oh, and one more thing..

    how about a variable op-amp current source?

    when i search the web i only find constant current sources using op-amps...

    or is there any of the kind?

    sorry for the "newbie-ness" of mine...

    :)
     
  6. Aug 15, 2008 #5

    rbj

    User Avatar

    by "variable", do you mean voltage-controlled? if no, your current source is determined by the component values. those can be changed.
     
  7. Aug 15, 2008 #6

    berkeman

    User Avatar

    Staff: Mentor

    As rjb says, you could use a potentiometer for the current setting control. Or, if you want it to be voltage controlled (like from a microcontroller), you could use a "digital potentiometer" device, or use a MOSFET as a voltage controlled resistance (but there are nonlinearities in doing this that need to be accounted for).

    Digital pots and uCs: http://www.maxim-ic.com/appnotes.cfm/an_pk/408


    .
     
  8. Aug 15, 2008 #7

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

  9. Aug 15, 2008 #8

    berkeman

    User Avatar

    Staff: Mentor

    Think the current I is just [tex]I = \frac{ (V_s - V_{in}) }{ R }[/tex]

    Don't see where alpha would enter in...
     
  10. Aug 15, 2008 #9

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    I'm guessing alpha accounts for the difference in collector and emitter currents for the transistor, and is very close to 1. So your equation would work just fine too.
     
  11. Aug 15, 2008 #10

    berkeman

    User Avatar

    Staff: Mentor

    Oh, I see the alpha factor now. Thanks Redbelly.
     
  12. Aug 16, 2008 #11
    thanks guys,

    this forum works like magic... well, strictly-physics speaking, magic don't exist... but not in this case...

    :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Op-Amp as a Current Supply
  1. Op amp supply (Replies: 3)

  2. Op amp current supply (Replies: 7)

  3. OP AMP power supply (Replies: 7)

Loading...