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Car rear indicators mean radiated emissions failure?

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Advanced Member level 5
Jun 13, 2021
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Our contractor tells us we will fail radiated emissions because our rear indicators are ON/OFF, as you'd expect...meaning pulsed currents with steep di/dt edges, and this in the wiring all the way to the rear....antenna!
We dont want big filter inductors though, due to the LC is he right?...will we fail it?
Can we use ferrite ebads instead of actual inductors.

I mean , there are loads of switching loads. Surely they dont all fail radiated EMC?

The last thing we want is an inrush limiter for every time the indicator gets flashed on. He also reckons it will interfere with the radio.?

Thanks, also, is our new 12A switching load going to give us any problems with radiated or conducted EMC?
LTspice and jpg attached.


  • 12A switching
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  • 12A switching loads.jpg
    12A switching loads.jpg
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I guess you have a tool to measure, even approximately, the radiated electromagnetic waves. Otherwise, how will you know that a proposed solution is good?

As a simple solution may be to use a shielded TV cable from the controller output to the indicators. I think the voltage drop on the cable for 12A won't be high, but a real test has the last word.
Last edited:
Thanks, i believe crucial for us will be common mode chokes either end of the 2 metre cable of the "Mouse scarer"?

A car turn signal is Hz-range and any ringing EMI will be
tone-bursts on that "heartbeat". A spectrum analyzer might
"average it away" and pass the frequency mask. Figuring
that a wireball "ring note" is probably overwith in a microsecond
or ten, you'd see any spurs averaged down by a factor of
1E5 - 1E6? Unlike (say) the same line banged at 100kHz and
the ringing never quite getting done, before next edge.
EN radiation specs.
Also, the duty is 50% with period 10ms to 4sec repeatedly sweeping up and down. Willw e get flicker problems.?

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