Measuring AC current with an oscilloscope.

In summary, the person is looking for a way to measure current through an LED and is considering an Op-Amp circuit.
  • #1
FM79
4
0
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.
 
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  • #2
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.
 
  • #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.
 
  • #4
By AC mode I assume you are using a time dependent driver for the LED. Why are the currents you expect so small?
 
  • #5
Because I am working at low voltages and new materials.
 
  • #6
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".
 
  • Like
Likes FM79 and jim hardy
  • #7
FM79 said:
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.
Check for some 'current sense amplifier' with programmable gain. Pretty reliable stuff, and usually there is a ton of AppNote too.
 
  • #8
Thank you Svein and Rive.
 

Related to Measuring AC current with an oscilloscope.

What is an oscilloscope and how does it measure AC current?

An oscilloscope is a scientific instrument used to measure electrical signals. It works by displaying a graph of voltage over time, allowing the user to visualize the shape and characteristics of the signal. To measure AC current, the oscilloscope uses a probe to capture the voltage signal and then converts it to a time-varying graph.

Why is it important to measure AC current?

AC (alternating current) is the type of electricity used in most household and industrial applications. It is important to measure AC current to ensure that electrical devices are functioning properly and safely, and to troubleshoot any issues that may arise.

What factors should be considered when measuring AC current with an oscilloscope?

When measuring AC current with an oscilloscope, it is important to consider the voltage range, frequency range, and bandwidth of the oscilloscope. It is also important to ensure that the probe is properly connected and calibrated for accurate measurements.

How is AC current displayed on an oscilloscope?

AC current is displayed on an oscilloscope as a sine wave, with the amplitude representing the voltage and the period representing the frequency. The shape and characteristics of the wave can provide information about the AC current, such as its magnitude, frequency, and any distortions or abnormalities.

What are some common challenges when measuring AC current with an oscilloscope?

Some common challenges when measuring AC current with an oscilloscope include noise interference, incorrect probe placement or calibration, and limitations in the oscilloscope's voltage or frequency range. It is important to carefully follow instructions and troubleshoot any issues that may arise to ensure accurate measurements.

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