Op Amps (how does it work)

Discussion in 'General Electronics Chat' started by activex, Mar 12, 2014.

  1. activex

    Thread Starter New Member

    Mar 5, 2014
    3
    0
    Hi,

    Just wondering..

    Op Amps ... it amplifier the signal...but does it actually amplify the power? I mean, I know op amps has highest efficiency is 100%, that is, it amplify the input signal to have as much power as the input reference power, correct?

    Anyway...so this lead to my question,

    "does op amps give more output power than its input power?"

    my believe is no.

    any help is appriciated.

    I just cannot explain how this works but i have a feeling that is how it works:D
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,395
    497
    Power=I*V

    Check the V and I of the input signal, calculate power.
    Check the V and I of the output signal, calculate power.
    Compare the two calculated values of power.
     
  3. activex

    Thread Starter New Member

    Mar 5, 2014
    3
    0
    i don't have an op am to test too bad. i bet the ouput power is lower than input power
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,237
    If by input power you mean the input signal power, then yes, the op amp output power can be (much) more than the input power.

    If by input power you mean power for the op amp, then no, the op amp power cannot be more than the input power (and the efficiency of output power to power supply power is always less than 100%).
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,447
    3,363
    No, you may be thinking of transformers where the power transfer is less that 100%.

    An amplifier (or op-amp) is like a control valve. A small amount of power in can control a much larger power out.

    The output power is determined by the resistance of the load. If you keep the voltage the same and reduce the load resistance you get more power.

    Power P = (V x V)/ R
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Then you should ask another question, what property of "the signal" does it actually amplify? Does it amplify voltage? Does it amplify current? Or both? Does this depend on how the opamp is configured and what is the load?

    Also, generally speaking when you talk about input and output power, you are talking about the signal path, excluding the power supply wires that feed the opamp. So amplifier can provide more power on output than it gets from the input, and the difference is supplied by taking power from the powersupply.
     
  7. LvW

    Active Member

    Jun 13, 2013
    674
    100
    ...but Pout is derived mainly from the supply (as outlined in crutschow`s contribution).
     
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