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Measuring AC current with an oscilloscope.

  1. Feb 5, 2017 #1
    I have a technical question, for research purposes.

    I have LED that we probe in AC mode. To measure the applied voltage in AC and the light-response in AC is no problem.

    However I would like to measure the current going through the device as well and I would like to link it to an oscilloscope. Now OSC usually measure potential (and have limited range) and I'd like to know how to have a signal directly related to the current on the OSC.

    If you know of any particular instrumentation please let me know.
     
  2. jcsd
  3. Feb 5, 2017 #2

    Paul Colby

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    Put a resistor in series with the LED and measure the voltage across it with a scope. That's how I've done it in the past. Ohms law rocks.
     
  4. Feb 5, 2017 #3
    Yes, that's basically trivial.

    I was looking for a more detailed and reliable solution. Currents will be in the range from nano to micro ampere (or even pico-ampere for some other devices) and frequencies above 100 kHz.

    I think that, amplifier aside, I need a bit more than that.
     
  5. Feb 6, 2017 #4

    Paul Colby

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    By AC mode I assume you are using a time dependent driver for the LED. Why are the currents you expect so small?
     
  6. Feb 6, 2017 #5
    Because I am working at low voltages and new materials.
     
  7. Feb 6, 2017 #6

    Svein

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    The standard current-to-voltage converter for very low current is the classic Op-Amp circuit:
    upload_2017-2-6_7-44-41.png
    Depending on your requirements, the circuit can be tweaked to compensate for temperature and bias current variations. Google "current voltage converter".
     
  8. Feb 6, 2017 #7
    Check for some 'current sense amplifier' with programmable gain. Pretty reliable stuff, and usually there is a ton of AppNote too.
     
  9. Feb 7, 2017 #8
    Thank you Svein and Rive.
     
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