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I am driving passive LEDs (24 V, 1 A) through two transistors activated by a ~10 kHz PWM signal. The power goes through a shielded cable from the PCB to the LED module. My wider setup should be CE-certified (and international equivalents). I was wondering, what are the best practices in order to avoid EMI issues? I have added two decoupling capacitors and a ferrite bead in series on the 24 V line (see image below).

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  1. Should I add a ferrite bead on the ground line?

  2. I read about "chokes", would they be useful in my case?

  3. Should I worry about transient voltages on this part of the PCB specifically? This part of the setup will not be accessible by humans.

  4. Are there any other components or considerations I should have?

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  • \$\begingroup\$ Look into "slope control" of whatever generates the PWM, before anything else. Also you don't need 10kHz for LEDs to be viewed by slow humans. \$\endgroup\$ Commented Nov 10 at 12:32

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EMI emission problems are mainly caused by fast changing currents in big current loops. So one thing you can do is to control the rise/fall time of the mosfets. For example by adding a RC time constant at the gates. Or you can identify and minimize the loop area of the fast changing current. For example by proper layout technique (e.g. minimize C16/C18 connection length).

Above techniques will avoid potential problems. Ferrite beads can help limiting the problem spreading out to different parts of the circuit, but do not avoid them.

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