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Current amplification

  1. Mar 6, 2014 #1
    1. The problem statement, all variables and given/known data
    I had a circuit in lab using an ICL8038 function generator IC, and was using the sine wave output from the chip. I am being asked to add components to increase available current to 1A. The chip pulls a steady 13mA, but I derped and didn't check output current. The spec sheet for the chip says that they had 5mA output for an impedance of 200 ohms.

    So, I figure I'm looking for a current gain around 1A/5mA=200. I grabbed a op-amp current-to-current amplification circuit out of a book in the lab that is as such:

    opamp_problem.png
    Where gain=1+Rf/Rs

    So I choose something like Rf=200kΩ and Rs=1kΩ or some such configuration with the same ratio. Is this correct?

    If it is correct, this only works in the case that the op-amp can push that much current. If I'm running something that I can find in lab, like an LM741 at 12V, how do I know how much current gain I can get? I checked the spec sheet on it, but it doesn't have anything about current limitations. If 1 op-amp won't do it, can I just stick another identical circuit into the spot where the load resistor is?

    Thanks.

    2. Relevant equations
    Given above.


    3. The attempt at a solution
    Given above.
     
  2. jcsd
  3. Mar 6, 2014 #2

    berkeman

    User Avatar

    Staff: Mentor

    Sounds like a good lab. :smile:

    A couple hints... You probably will not find an opamp that can output 1A. Opamps are for lower current signal processing chores. To get higher current output, you will usually use either discrete transistors, or something like an audio amp IC. Try doing some Google searching on those two options (use Google Images to speed up your searching), and see what you find. Post your follow-up questions here in this thread with your search results...
     
  4. Mar 7, 2014 #3
    But I can find transistors that'll handle >1A, so I can just use a Darlington pair, right? ...but, if I'm running on a 12V power supply, then to get my 1A, my load impedance can only be 12 ohms max. This answers the question for my lab, but out of curiosity, if I wanted to run a higher impedance load, could I chain together more Darlington pairs? Could I increase the current through the load by setting the voltage across the collector and emitter to +12V -> -12V instead of +12V -> ground?
     
    Last edited: Mar 7, 2014
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