Questions about uA741 op amp

Discussion in 'General Electronics Chat' started by worldHello, Dec 1, 2014.

  1. worldHello

    Thread Starter New Member

    Oct 15, 2014
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    I use uA741 to build a Wien bridge oscillator. If you don't know what that is, it is a circuit that can convert DC into AC.

    I am able to get a 60 Hz 5 V sine wave, and this is with a load (R: 2 ohms, C: 100nF). The current should be approximately Irms = 5/2 = 2.5 A since the capacitance is so small.

    However, according to the datasheet uA741 does not output very much current (something like 5mA, I can't remember). Given that, how do I reason it ? Why can the op amp provide > 2 A ?
     
  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    A nice and simple trick is to show the schematics.

    Believe me. It works marvels.
     
  3. worldHello

    Thread Starter New Member

    Oct 15, 2014
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  4. MrChips

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    Oct 2, 2009
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    The last time I checked the data sheet of uA741 the max output current was 25mA.
     
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It looks like you can use ohms law but have not figured out how to calculate reactive capacitance.
    Google what that is at 60Hz for a 100nF capacitor (reactive capacitance calculator). You will see that 2A is not possible and a fuller view of Ohm's law really works.
     
  6. worldHello

    Thread Starter New Member

    Oct 15, 2014
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    Yes. Something like that, but how come I could get 2A?
     
  7. worldHello

    Thread Starter New Member

    Oct 15, 2014
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    Well, the impedance Xc is really big (Since C is so small )which makes Vrms/Xc really small. So one can just ignore it because it is so small.
     
  8. MrChips

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    Oct 2, 2009
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    Simple. You are seeing 60Hz AC noise pickup.
     
  9. GopherT

    AAC Fanatic!

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    Please post your circuit, is the capacitor in series or parallel with your resistor load?
     
  10. atferrari

    AAC Fanatic!

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    Please delete.
     
  11. #12

    Expert

    Nov 30, 2010
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    You can't. Not from that chip. You couldn't possibly be talking about how you measured 2 amps coming through the output pin. You would have mentioned the smoke if that was true. You must be talking about theory, and that leaves us to help with your mistake in either math or understanding. Only a drawing of your circuit can help us now.
     
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