why output of op amps is finite to +dc and -dc supplies

Discussion in 'General Electronics Chat' started by sabbi, Feb 4, 2010.

  1. sabbi

    Thread Starter New Member

    Feb 2, 2010
    why output of op amps is finite to +dc and -dc supplies?
    i mean why ouput of op amps ca have any value between +Vcc and -Vcc?
  2. Mike33

    AAC Fanatic!

    Feb 4, 2005
    An opamp needs a little power to operate, so most of them never get quite out to the V+ and V-. Those are the "power rails". SOME can operate very close to the rails, however!
    An amplifying device can only give out as much as is put in - by the input signal and the power supply. You are using the input signal to control how much of the power supply becomes the output. You can't get more out than there is to offer from the power supply! That would violate the laws of conservation of matter, LOL.

    Check out the E-books on here, and use Google to look up "amplifying device tutorial", "opamp tutorial" and the like. There is much information about this out there, for free! :eek:)
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008

    Yep that's the universal "No Free Lunch" law. :)
  4. russ_hensel

    Distinguished Member

    Jan 11, 2009
    But you could build an op amp with a few hidden charge pumps inside and get more than rail to rail output. Conservation of energy applies to energy, not to voltage. I do not know of any such device, but a max232 sort of does it.