raschemmel:
so frequency and magnitude
of the current and the area of any loop in the circuit all contribute.What loop ? I think you are talking about an inductor.
Wires carrying current generate magnetic fields which is why they are kept separate from signal wires but I never heard of any one
talking about a power switching device like a mosfet generating magnetic fields. I'm sure there is some magnetic field but it isn't anything to be worried about and certainly nothing to be talking about. Power devices are separated from other devices on pcbs because the traces carrying their current could affect small signal traces and also because there is some heat involved but location of power switching devices like mosfets is not chosen because of any concern about magnetic fields. All of those concerns are reserved for inductors, solenoids, and motors. If you have evidence to the contrary I would be interested in seeing it because this is the first time I have heard this issue brought up in 30 yrs of working with electronics.
Please re-read what I said:
All high-current circuitry generates magnetic fields, but its the rate of change
of magnetic field that induces interference, note - so frequency and magnitude
of the current and the area of any loop in the circuit all contribute. This is the
impact of Maxwell's equations.The MOSFETs switch the current fast, so the rate of change of current is due
to them.
And yes frequency, magnitude of current and the area of any current-carrying loop
all contribute to the amount and range of interference generated. If you can build a
circuit that isn't a current-carrying loop I'd be very surprised.
I specifically did not say that MOSFETs generate magnetic fields, I said currents
generate fields and that the rate of change of current is what's important and that
the switching devices are responsible for that rate of change.
Take a standard 'scope probe, fix the ground clip to the probe tip, then dangle it
near an H-bridge carrying 60A and you'll see what I mean. Also if the battery
wires aren't run together that forms a big loop which will radiate big-time if
there isn't substantial decoupling at the bridge.