[RFI] Noisy LED shop lights

[Steve Kurtzman]

The lighting industry folks call the power supplies "Drivers", usually
constant current type.

Steve
sparkie001 at pobox.com
stevew7sjk at gmail.com
www.facebook.com/imetsteve



On Thu, Jun 14, 2018 at 11:40 AM, Dennis Monticelli <
dennis.monticelli at gmail.com> wrote:

> 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
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