How can I get rid of the PWM output noise in my circuit?

SamR

Joined Mar 19, 2019
3,399
You mean, the oscilloscope itself has a low pass filter function?
Well, mine does but it is a newer Digital scope. I don't think that LG model you are using has one. Try building a quick RC lo pass filter to feed the signal into. Or just ignore it... Is it causing a problem?
 

Thread Starter

laco22

Joined Oct 31, 2017
18
Well, mine does but it is a newer Digital scope. I don't think that LG model you are using has one. Try building a quick RC lo pass filter to feed the signal into. Or just ignore it... Is it causing a problem?
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Thanks for any help. Most of the noise seems to be reduced. My Mosfet no longer malfunctions.

Thanks!
 

crutschow

Joined Mar 14, 2008
27,170
A plug-in breadboard is a poor way to build such a circuit.
All the long flying leads are prone to generating and pickup of noise.
If you built it on a vector board with a ground plane, you likely would see a lot less noise.
 

Thread Starter

laco22

Joined Oct 31, 2017
18
A plug-in breadboard is a poor way to build such a circuit.
All the long flying leads are prone to generating and pickup of noise.
If you built it on a vector board with a ground plane, you likely would see a lot less noise.
I thought similar to yours.
Thank you for telling us about that possibility as well.
As you said, I used to think that there could be noise coming from many pins of the breadboard.
 

MisterBill2

Joined Jan 23, 2018
8,711
The PWM circuit is quite similar to a switching-mode power supply, and so certainly filtering will be required. If this is intended to serve as a PWM audio power amplifier then yes, you need a low pass filter able to handle the power level that IC provides.The low pass filter cutoff frequency should be a bit above the top audio output frequency you require.
 
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