[RFI] Noisy LED shop lights

[Dennis Monticelli]

My former employer designed and produced the chips that control LED lights.

Yes, there is a "ballast" in each one but a better description is switched
mode power supply.  Like any SMPS there is the potential issue of excessive
conducted mains emission that turns into radiated emission via the power
line (green wire included) acting as an antenna.  CM chokes are the answer.

Unfortunately there is potentially another more insidious source of noise.
Yup, direct radiation.  The SMPS is of the current output type, not the
voltage output type.  Because your eye cannot visualize the optical ripple
that derives from current ripple (the eye sees only the average), it is
common for the circuit designer to cut costs by lightly filtering (or not
filtering at all!) the current ripple.  The LED's are series strung
so.....you guessed it....there is a large current loop involved.  If the
return path is not properly managed for field cancellation, you've got
yourself a healthy direct radiator.

This situation cannot be easily corrected. Trying to add current filtering
is likely to mess up the feedback loop.  Basically, it's a redesign.  If
one goes to the trouble of a redesign then I encouraged ripping out the
SMPS board and using a linear wall adapter along with a series resistor to
set the current.  Yeah, the efficiency would drop but the result would be
absolutely zero noise of any kind because the LED's themselves are dead
quiet.

Dennis AE6C