EMC tutorials - Passive CM-DM separator

#131 In this video I continue talking about a subject I started working on a long time ago... how Common Mode and Differential noise can be separated. I look at the some available documentation on circuits to do this and then build a simple yet effective implementation using passive components. Finally I test out the circuit to see what sort of performance it has.
Previous related videos:
CM-DM separation principles: • Electronics tutorial -...
LISN series EP1: • EMC tutorials - [1/3] ...
LISN series EP2: • EMC tutorials - [2/3] ...
LISN series EP3: • EMC tutorials - [3/3] ...
Further reading:
www.researchgate.net/publicat...
publik.tuwien.ac.at/files/Pub...
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[@zhitailiu3876]

Very inspiring! Thanks FresZ! I love to see that every time you demonstrate something complicated by means of simple ideas, and simple un-expensive stuff.

[@Graham_Wideman]

Another well-done video taking us step-by-step through some theory and practice on an important topic. Thanks!

[@mikemarachov3230]

The best channel on youtube!

[@Chris_Grossman]

I had not seen the simultaneous use of two different cores before. That is an interesting way extend transformer bandwidth.

[@rjordans]

Great one, I'll add building one of these to my to-do list

[@pa4tim]

Very interesting, thanks

[@mayankgupta460]

Great video!!

[@Jeroen74]

If you have one of those fancy split core wideband current transformers like a Fischer F61, you can choose between DM or CM by from which side you let the wires enter the coil. If both enter at the same side the output is the CM current, if one wire enters from the opposite side the output is the DM current, times two.

[@Gengh13]

Awesome.

[@Boehoehuahoei]

If you look at the 150ohm DC-AN's (DC LISN for PV) ... they also use the 2x first winding, 1x secundary winding principles to seperate Common mode from differential mode noise.

[@FesZElectronics]

Are you referring to something like this?: schwarzbeck.de/Datenblatt/k8300.pdf

[@Boehoehuahoei]

@@FesZElectronics Yes. This is listed in the EN55011. The 150ohm termination is a reference to the Load termination (C2 & R8). When using it as a voltage probe (Just the output in parallel with the DUT).. Compliance with common mode has to be met. (Pos 3). Although I don't know if the industry uses this.. or a 50uH/50 ohm LISN (rated for DC), since this is not referenced in the 61000 series. In the datasheet is see that the secondary winding is only used for DM mode.

[@GunnerJoe93]

Is there any nuance to transformer selection in real-world applications to emulate this discriminator circuit? Specifically related to the frequency of the CM or DM noise?

[@marcelosilva9686]

Excellent job!! Thanks a lot. Just one comment when you show the 2 transformers with their secondaries connected in series (8:28) you say that the secondary current of both transformer are building up or cancelling each other depending on the polarity m I believe that you are referring to the voltages and not the currents since they are in series both transformer have the same current. Indeed in the LISN the current noise the converted to a voltage noise using a resistor so the 2 signals output can be added or subtracted using transformers in series connection

[@FesZElectronics]

I find it quite odd referring to transformers as sources of voltage - since they work with magnetic fields, the fields generate currents in the windings; these currents end up translating into a voltage eventually but I just find it a strange way of expressing things.

[@marcelosilva9686]

@@lotecque yes I understand that you can use super position ( turn off one an then the other and sum up the results) to find out what it the net current but in reality the two batteries will have the same current since both are in series. Super position is a excellent tool to work with this linear circuits. What I wanted to point out is although the main principle of then circuit is on (separate the cm and the DM) the explanation might be incorrect since what is really happening is the cancelation of the voltages and the the currents.

[@R2AUK]

Thanks for the video. I think I noticed a little mistake. 8:20 the current on the secondary winding is actually flowing in the opposite direction comparing to the direction of the current in the primary winding. In other words, the arrows on the right part of the schematic should be reversed.

[@FesZElectronics]

I have to be honest, I did not put too much thought into this when creating the drawing; but in the meantime I did do a quick LTspice simulation - a sinewave going into a 1:1 trafo and a resistive load on the secondary. At least with that setup, the secondary current is approximately 90deg phase shifted in reference to the input. So when the primary reaches a maximum or minimum, the secondary passes trough 0. In other words, for a primary current going one way, you can get secondary current going both ways, depending on the time of measurement. I'm not sure what method would be most appropriate to do such a drawing (from the video) without creating confusion...

[@manoA98A]

Really awesome Just for my curiosity, are you an electronic engineer? Where did you learn all of that? I am an electronic engeneering but in italy we lose al lot of time in formula's proof and useless demonstration, so we don't even use ltspice seriously until the last year of study

[@FesZElectronics]

Hello Mano, I can't say any nice words about the universities here either... I guess my main recommendation is practice, regardless of what is being thought at school, try building and experimenting for yourself. You can start with any circuit, build it, get it to work, and then try improving on it - you can only improve something if you understand it. You can start this in the simulator, but practical circuit building will also help.

[@lambda7652]

is there no problem with the core saturating in DM measurement mode?

[@FesZElectronics]

The core can saturate of course, I did not test it though to see what the exact threshold is.

[@peterbrowner4687]

wideband transformer using two cores! Interesting! Do you know any application note about this?

[@FesZElectronics]

Unfortunately no.. But if I find anything I will let you know. I have only seen this applied once in such a commercial CM/DM separator.

[@peterbrowner4687]

@@FesZElectronics Thank you!!