Electronics > Beginners

ADC - Shunt resistor spikes

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max_torque:
Also: Be careful with your Oscope ground clip!  You may be introducing unwanted current paths, depending on how your motor is driven and the power supply arranged! (and where the current shunt sits in the circuit).  The high frequency common mode rejection ratio of your Oscope won't be all that great, and by attaching your probing, you could be providing a nice AC (or DC...) path for high frequency currents from your motor and motor drive.

nixie84:
I put all circuits in post #7.
Oscillogram with and without spikes is in #4 post.
All others oscillograms looked similar, that's why i wrote it works or not.


I try to be careful. I have already seen:







I would like to go back to this circuit:


If there is only a resistor without a capacitor, how is the RC filter formed here?
I know that the probe has some capacity but very small.
With 1k resistor spikes appearing. With 10k or more all looks good. Why?

perieanuo:
Probes have their own capacity.rtfm first and work after, especially with things you can damage,like the scope...


Envoyé de mon iPad en utilisant Tapatalk

StillTrying:

--- Quote from: nixie84 on July 16, 2019, 08:18:10 pm ---If there is only a resistor without a capacitor, how is the RC filter formed here?
I know that the probe has some capacity but very small.
With 1k resistor spikes appearing. With 10k or more all looks good. Why?
--- End quote ---

The ringing in your scope shot is about 70MHz, the scope probe's ~17pF is only about 200R at that frequency so the 10k in series with the probe gives about 50 times less amplitude to the ringing.

nixie84:
Thanks all for help!
I think I understand how it works now.

I will put together bellow circuit on PCB and i will check how its work with Atmega and scope.

PS. Diode on right is schottky.

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