designing PWM-motor interface for low EMI 1

[geekEE]

Does anyone have any tips or links to info on designing a PWM interface for a DC motor in order to reduce EMI? I've got a tiny fan (less than 50mA current draw). I plan on driving it with a PWM output using a PNP transistor on the high-side. I figured that I would put a backwards diode across the motor. Anything else that I should consider? A capacitor? An RC snubber? Ferrite beads? Are these things bad sources of EMI or am I being overly cautious?

Thanks in advance.
Glenn

 

[Skogsgurra]

Overly cautious, probably. Is the environment very EMI-sensitive?

A free-wheeling diode should be there also for other reasons (free-wheeling when transistor is off) and a ferrite bead or ring with both armature wires through it is always nice. And, to kill the brush noise, put a small capacitor across them.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[geekEE]

The environment is not partcularly EMI-sensitive, but I would prefer to have component locations that are depopulated rather than having to redo the PCB if problems are found.

Thanks for the info Gunnar!

Glenn