EMC tutorials - CM/DM filters

#133 In this video I start looking and some of the special characteristics that filters need to have when talking about common mode and differential mode noise. Based on the type of noise you want to filter you will need to take into consideration specific characteristics and you will also need to be aware of the noise circuit and the impedances present.
Related previous videos:
CM-DM separator: • EMC tutorials - Passiv...
LISN series EP1: • EMC tutorials - [1/3] ...
LISN series EP2: • EMC tutorials - [2/3] ...
LISN series EP3: • EMC tutorials - [3/3] ...
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[@littleboot_]

I really like these type of practical videos with free/affordable tools on EMC stuff. Thank you for your effort creating these type of videos!

[@joydeeppal6252]

It is what I was searching for......CM and DM filters......too good

[@ango5421]

I always learn a lot from your videos!

[@nargizatoboeva1287]

Thank you for this practical and useful video! It would be interesting to see consideration of active CM/DM filters as well

[@maksymkloka7819]

Sweet!

[@EliteHEAD]

loved to video, would be interested in some practical filter design example, in other words, this is my circuit, i.e. power supply and these are the steps i will do to design the input filter :)

[@FesZElectronics]

I guess it makes sense to cover some basic principles in more detail separately, and then do a final episode in which everything is applied on a "real" circuit. Thanks for the suggestions!

[@anildhanraj5778]

Hiii Sir, Can you please make an detail video regarding Spectrum Analyser all parameters setting for checking EMI and EMC test.

[@pa4tim]

One thing to take in consideration. The ground of the SA out and input and signal generator are all connected. I got strange results, while measuring with a VNA, compared to what I calculated, designing a balanced dipole/open line tuner The VNA ground from the output and the ground of the input shorted one half of the tuner to ground.

[@FesZElectronics]

Indeed, this common ground will cause a lot of fun... The grounds of the Signal Generator (SG) and the Spectrum Analyzer (SA) are interconnected in 2 different ways - at least in my setup; one path is trough the mains supply cable trough the PE line - this is a long high impedance interconnection; the second way is trough the coax cables and the test setup - usually this will prove to be of lower impedance; in case the second connection is slightly off, the first one will kick in and cause small variations in the measurement, but not always large enough to be obvious...

[@grosserkuchen]

@@FesZElectronics isolation transformer at source signals helps...

[@alientehnologi]

👍

[@paulperano9236]

So what happens if you use a Common Mode Choke, which has dual inductors that work together, one inductor for each power rail. Then you add a series choke in each line after with a shared LARGE value capacitor between + and - rails ? Shouldn't that reduce both CM & DM while keeping the filter balanced ?

[@FesZElectronics]

This is commonly used, having the CM transformer, and then the individual uncoupled inductors together with a set of capacitors between the lines (depending on the filter you can have up to 3 - 1 before the CM choke, one after the CM and before the series inductors, and the third after the series inductors). The exact filter and the component values will highly depend on how much noise you really need to filter. However the larger the component values the more expensive the filter becomes and the more losses you will start to get..

[@paulperano9236]

Since its only one power supply the cost is not that important. A 30mH CM choke and 6800uF caps along with a couple of series 500uH toroid inductors should cut most rubbish down. Hopefully make it usable for OpAmp and small signal work. :-) @@FesZElectronics

[@bobby9568]

I think he's lying.. xD