Measuring AC current with an oscilloscope.

AI Thread Summary
To measure AC current through an LED using an oscilloscope, a common method is to place a resistor in series with the LED and measure the voltage across it, applying Ohm's law. However, for very low currents in the nano to pico-ampere range and frequencies above 100 kHz, a more sophisticated solution is needed. Current-to-voltage converters, particularly using operational amplifiers, can be adapted to handle these low currents effectively. Additionally, current sense amplifiers with programmable gain offer reliable options and come with extensive application notes for guidance. This approach ensures accurate measurement of the light-response current in AC mode.
FM79
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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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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.
 
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.
 
By AC mode I assume you are using a time dependent driver for the LED. Why are the currents you expect so small?
 
Because I am working at low voltages and new materials.
 
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".
 
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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.
 
Thank you Svein and Rive.
 
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