sheilding pwm from audio

[harps]

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*shielding audio from PWM.

hello : )

i have a pwm signal that runs quite near an audio circuit board. the emi noise from the pwm jumps across to the audio circuit, which isn't great at times.

i am routing the pwm cable as far away as possible, but I need more shielding. Would it be worth purchasing a roll of copper tape to wrap up the pwm cable and then heat shrink over that again? Or would it be best to use a twisted pair and perhaps wrap copper tape over that too? The pwm signal is from a h bridge , so the polarity flips back and forth. I wonder, would i need to attach ground/earth to the copper tape/foil that surrounds the pwm wires ,to help with the shielding? or does it not really matter as long as there is metal between the wires and circuits?

thanks for any suggestions. : )

 

[harps]

hi: ) update.

i think my problem is that my pwm cable is single core with a shield, so i really need two core with a shield to ground for my h bridge output. Maybe also some copper tape for wrapping up my plastic molex connectors and the copper tape also soldered to ground. As without the shields connected to the ground there is no route to drain the interference away.

Am i on the right path, do you think?

peace : )

 

[ronv]

There are lots of possibilities for noise and ways to reduce it. For example if the bridge is from FETs you could perhaps slow them down a bit by adding some gate resistance. Need to watch power dissipation when you do this.
Twisting both the supply and motor wires will also help. Good bypassing of the power supply to the H may also help.
Shielded twisted pair might be a step as well as some small caps (.01 - .1) across the motor leads and the leads to the motor frame for brush noise. Might also consider putting the audio circuit in a metal box. I am assuming you are driving a motor, but most apply to other loads.