Quote:
Originally Posted by AndrewJ
In nearly all cases, if you use PWM you will get RFI.
Even new commercial boxes marketed as having low RFI are affected
The main problem is not the box, its the wire going to the strap
as that radiates away like blazes, and PNP vs NPN wont fix it.
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Hi Andrew,
You are right, switching power causes interference. You are also right when you blame the cables for radiating most of it. Another possible path is throught the changing load on the battery depending where you connect your supply.
As far as reducing the radiation from the cable you could use shielded cable and connect the shield to ground - hence my preference for switching the high side and leave the gound connected through.
You could also add some softer switching at a lower frequency and reduce the spectrum you radiate - I guess that alone will take away a good deal of your problems.
If all that doesn't work and RFI is still critical you may have to suffer the loss of a linear regulator design.
I will be aiming to preserve battery power AND keep the design quiet. I am sure it can be done.
Cheers,
Peter