EMI Filter Design - Page 1
Forum section: electronics / beginners

author: Nikos A.
author_rank: Regular Contributor
timestamp: June 20, 2019, 08:14:26 am
content: Hi everyone,Is there any tool/guide/simulator to proper calculate the EMI filters? More specifically I want to design the EMI filter for a DC 12V converter and I am facing difficulties..Thanks is advance!!

author: tszaboo
author_rank: Super Contributor
timestamp: June 20, 2019, 10:09:44 am
content: Würth has a tool for it's parthttps://www.we-online.com/redexpert/#/home/article/emc-design-toolsAnd this is worth looking at, to figure out what you might need in the first place, depending on the frequency.https://www.we-online.com/web/en/index.php/show/media/07_electronic_components/toolbox_1/Poster_Filter-Storage-Applikation.pdfIn the end it can be very difficult, or very easy, depending on what you want to do.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2019, 02:26:15 pm
content: Not really. So much depends on the noise source, what the load is connected to, the layout, the enclosure -- that a general solution will be too general to be useful.In short, guess a reasonable starting value, and allow room for testing of different parts and values. Try all permutations of Y capacitors.With a great amount of experience, you can anticipate which configurations are likely to be the most effective, but it's still guesswork.There are enterprise-grade simulators that can include circuit, layout and enclosure and cabling in a full EM simulation, and produce representative EMI results without building a prototype; but the software suite to do this costs way more than a few protos and a few weeks of lab time, for most users.Tim

author: tszaboo
author_rank: Super Contributor
timestamp: June 20, 2019, 03:07:07 pm
content: Quote from: T3sl4co1l on June 20, 2019, 02:26:15 pmIt could be a simple DC-DC converter for all we know...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2019, 03:17:40 pm
content: What's "simple" about it?There are perhaps fewer variations of "DC-DC converter" than of other kinds, but all of them have to fit inside that generalization; it's still a broad net to cast.Tim

author: Nikos A.
author_rank: Regular Contributor
timestamp: June 20, 2019, 05:04:03 pm
content: Thank you for your answers!!Well this is the dc converter that I am intending to use:https://eu.mouser.com/datasheet/2/687/tel5-519367.pdfand unfortunately the manufacturer does not provide any filtering circuit..I do not have any experience with EMI protection and I do not know how to start..

author: awallin
author_rank: Frequent Contributor
timestamp: June 20, 2019, 07:23:10 pm
content: murata has good application notes, e.g.https://www.murata.com/en-global/products/emc/emifil/knowhow/basicas for components, murata BNX025 has been working OK for me after AC/DC brick-supply, before LDO.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2019, 07:39:02 pm
content: The datasheet claims it does not need a filter, or contains it internally, to meet CISPR 22. As usual, it does not document how it was tested (example, with a load resistor and no other secondary side connection, you can get away with a lot; if it's common ground and both inputs are tested through a LISN, there is much less you can get away with).Do you need to meet a more stringent level? Do you know yet whether you have any EMI problems at all?Tim

author: pinkman
author_rank: Regular Contributor
timestamp: June 21, 2019, 04:40:50 am
content: This really depends heavily on your application and what standard you must achieve. There are varying levels of requirement even within a standard, take CISPR 25 for example. Will you be required to test your design and achieve a specific EMC/EMI certification? If so, which one?Some have commented above that designing EMI filters this can be perceived as "guesswork", that is partially true simply because our minds cannot comprehend what is going on beyond the time domain and empirical data vs your modifications to the circuit may not make sense to you without simulation. If you are not required to test, and have no access to some standardized test setup, you can certainly get an idea of radiated emissions with a relatively simple near field probe setup; you have probably seen these sets of 4 near-field probes that come with a small wideband amplifier. This could be used with a spectrum analyzer to get a semi-reasonable idea of relative emission over frequency but expecting absolute accuracy would be unreasonable. This is more useful for A-B comparison when making modifications. For measurement of conducted emissions you would want a wide bandwidth current probe to start with and those can get a bit pricey.To start with, placing PCB lands for a series ferrite of appropriate size for the output current (consider derating!) on the input and output along with associated capacitors would be a good start; If you end up with conducted emissions problems you may want a spot for a common mode choke on the input.

author: Nikos A.
author_rank: Regular Contributor
timestamp: June 22, 2019, 07:36:11 pm
content: Thank you for your answers!!Quote from: T3sl4co1l on June 20, 2019, 07:39:02 pmYou are right, this specific converter is internally complied with CISPR 22 class A. What I've read is that class A is designated for industrial applications while class B for residential applications. This project is not intended to be used for residential application and thus I won't proceed with any further filter designing..However, I would like to know what the limits are for each class and after searching I found this article by digikey that cites those limits.https://www.digikey.com/en/articles/techzone/2012/jun/understanding-electromagnetic-compatibility-standards-for-switch-mode-power-suppliesWell, in case that I need in the future to comply the product with class B requirements it should be designed a filter to prevent conducted emissions above class B limits isn't?Why the frequency of emissions in the table has a limit of 30MHz?