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EMC conducted emissions pre-compliance testing with home-made LISN
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uski:
Hi


--- Quote from: T3sl4co1l on October 11, 2015, 12:12:50 am ---So for the present case, I would be more than happy to accept a much more basic problem: does the effective inductance, of the main series inductor, remain within tolerance, at rated current?  And this can sometimes be found in the datasheet already, or calculated from core data.
--- End quote ---

You're right... and I think Jay_Diddy_B answers that above ! :)

uski
EMC:
Well test may be the only way, I will work on that.

Just another unrelated comment, if you update the DSA815TG to firmware 1.12 at the bottom of the span menu you can select log x axis.   Much better for this device under test.
Jay_Diddy_B:
Hi,

Let me try and show why the inductor is absolutely fine for this application.

Test 1 Inductor Saturation Test

I used an Inductor saturation tester, this is described in this thread:

https://www.eevblog.com/forum/projects/inductor-saturation-tester-alternative-route-to-dump-the-excess-energy/msg181720/#msg181720



The scope shows a linear ramp, indicating that the inductance is not changing significantly through 10A.


AC analysis of the LISN circuit



The 0.1uF can be considered to be a short at 800kHz, so the 3dB point on the response is given by:

F = 1/ (2 x PI x L / (Rsource in parallel with Spectrum Analyzer))

If Rsource = 50 Ohm

Spectrum analyzer = 50 Ohms

F = 1 / (2 x Pi x 5uH / 25 Ohms) = 795 kHz (3 dB point)

This is shown in the modelling results:



Stepping the Source Resistance

The source resistance is probably only 50 Ohms if the LISN is being tested with a Network analyzer or a signal generator. The impedance of the noise source is during use is probably much less than 50 Ohms. This is true, because if the noise source had a 50 Ohm impedance it would be very easy to filter.

In this model I am stepping the Source resistance from 1 ohm to 100 Ohm:



The results show how the frequency response changes with the source impedance. The effect is much stronger than a 10% change in inductor value.



The inductors chosen are fine in this application.

Regards,

Jay_Diddy_B










EMC:
Jay_Diddy_B,

With regard to inductor choice.   If you had the data and knowledge you now have after design, build & test would you go with the WE 744 314 110 again?   e.g. would you move up in current range, i.e. WE 744 331 010 0.   I understand the major changes are:

RDC goes down 3.15m to 2.5m
I Sat goes up 13 to 52 amps
Core 'material from 'Superflex' to iron power 
Size increases to 1210 (12.1 x 11.4mm)
and I assume but don't know max freq comes down

Regardless of that option are you confident that WE 744 314 110 is the best choice?

(Implicit in that question you may think I am saying it is the wrong choice; that is not the case; you have proved it is fine no question.  I just wondered if it could be stretched a bit for higher current.)

Thank you,

Steve
Jay_Diddy_B:
Hi,

The choice of the WE 744314110 (HCI series) was originally made because I got 500 pieces very cheap from eBay, but it turned out to work exceptionally well. My thoughts were that any deficiencies in the inductor, versus an air core, would be balanced by the really tightly controlled construction.

I have measured my LISN design with a Network Analyzer and it has been compared against commercially available LISNs all with good results.

If you need higher current, then the Wurth 7443310100 (HCC Series) should work. In fact, I used a similar inductor 744 332 1000 in my line voltage LISN. The line voltage LISN is shown in this thread:

https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/msg641108/#msg641108


So I can't really say that the 744 314 110 is the 'best' choice. It works well for my applications below 10A.

Regards,

Jay_Diddy_B
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