I'm designing, for a railways application, the power supply circuit on a pcb board that supply 5Vdc starting from a 24Vdc(coming from a not clearly defined source, sure a 24Vdc line).

I'm using the TRACOPOWER TEN 40WIR isolated DC/DC converter(railways compliance): (https://www.tracopower.com/products/ten40wir.pdf)

My questions concern the EMI filter circuit. I'm reading the application note from Tracopower (ten40wir-emc-consideration from Traco website) where I find this figure with suggested filter to comply EN50155 Immunity: enter image description here

Can someone help me, giving me indications on how to design and size an EMI filter that satisfies the en50155?

Maybe there is a commercial solution that is suitable for railways use?

Thanks you

  • \$\begingroup\$ A quick check suggests, that 50155 is about surge and transient immunity. Your average conducted emission EMI filter does not help against that. It is just left in as a block in the TRACO diagram, to suggest that you still need this block, but it plays basically no role in the 50155. \$\endgroup\$
    – tobalt
    Nov 15, 2021 at 13:10

1 Answer 1


Your EMI link includes 3 pdf files which identify how to layout the PCB and select the inductor and size the capacitors.


If you ask for the version with F added to suffix , they can make or find stock to include filter.

Suffix -CMF

  • \$\begingroup\$ So, I can use the suggested filter on page 1 (for example) and put it in the EMI FILTER black box. Unfortunately, it seems that there is no possibility to request the device I chose (TEN 40WIR 2411) with the emi filter inside ( and obviously, the filtered model costs a lot). \$\endgroup\$
    – Cataldo
    Nov 25, 2019 at 9:06
  • \$\begingroup\$ If the factory cannot make the PCB, then demand is too low. So you must ask them or yourself for a make/buy ROI calculation \$\endgroup\$ Nov 25, 2019 at 13:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.