Yes that is a big concern as well to pass the emission test
for CE mark and FCC mark. Bulk capacitors and small
value resistors are used to form RC networks to filter
out the pulse current. It seems we have never used
FETs for switching yet. We normally need to drive only
one LED emitter. Transistors are cheaper and easier to 
drive by logic ICs or MCUs using simple constant pulse
current driving circuit.

Regards,
Xiaofan

-----Original Message-----
From: piclist-bounces@mit.edu 
Sent: Friday, October 21, 2005 1:51 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Pulsing LEDs

There are many archives covering this subject in PICLIST.

Be careful however, as the action of switching generates RFI effects. My 
hardest FCC
projects have been those having multiplexed LEDs, especially if the LED 
arrays are
driven by FETs (very sharp, fast rise- and falltimes). Transistors 
switch slower and seem
to reduce this effect.

--Bob

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