MIL-STD-461 grading for input supply - Page 1
Forum section: electronics / projects

author: rakeshm55
author_rank: Regular Contributor
timestamp: January 25, 2019, 04:00:51 pm
content: I was looking for a board mountable solution to achieve MIL-STD-461 grading....looking for a dc to dc converter module to achieve this.Input source voltage range is 24V-34V.output voltage 12V.There is a catch thoughInput source (Battery ) powers two module one works directly from supply other goes to a DC to Dc converter module....In this case what to do??Do I need to fit in an EMI filter?? If so any COTS solution available for EMI to meet standard....Is there standard Dc-to dc modules available to meet standard??Please advice

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 05:14:16 pm
content: There is no emi to meet standard. You have heavy filters which attenuate but depending on your load it might not ben enough and you might need a custom emi filter, two filters in a row (diminishing rreturns, some manufacturers specify series operation) or maybe get away with adding some ferrite.Search military emi filter because if you filter dc rail with a dcdc converter you get some negative resistance stuff and the mil emi filter will have a dampened cap to make it work rightYou need to read the standard carefully to see what the allowed noise levels are inside of your subassembly past the power distriibution point but you dont want to contaminate their systemsCommercially no one would care since its your own black box so long you dont get degraded performance..I cant see why the mil would try to specify noise levels in your circuit unless you have some claus that say ttl logoc at some impedance needs to have noise margin of so and so. Commercially it would just need to pass emissions and suceptance.And its impossoble to tell you on a forum how to pass class b or tighter emi compliance. If you posted full schematics, pcb layout and your notes and the chassis assembly mechanical assembly shop prints and detailed pictures we still could only guide you on what can possibly be improved.Cots look for medical and stuff advertized as low emi etc but you need to test it lol... people dont always claim to have met the sayings of the datasheet.One thing that comes to mind is the expensive ltc umodule (the one advertized as meeting class b), they have a few. Its has minimum extra components needed and small loop area

author: rakeshm55
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:48:48 am
content: Hi,MIL EMI filter available in market Will they work with specific dc to dc converters or are they generic??.One of the dc-dc converters considered for this design is LMZ14203. Data sheet says ""Low Radiated EMI (EN 55022 Class B Tested)""I may have to use multiple modules to meet power requirements (48W) + de-rating.What are the parameters to look for to obtain a matching EMI filter for DC to Dc converter ??

author: coppercone2
author_rank: Super Contributor
timestamp: January 28, 2019, 06:59:45 am
content: look at your noise spectrum and superimpose the filter curve on it to see how much attenuation you can expect.you need a testits a filter. thats all you can do.expect some where around 30% of the theory IMO