Hi,
Let me add a few things to the discussion.
Reference:
https://www.schaffner.com/fileadmin/media/downloads/application_note/Schaffner_AN_CISPR17_Measurements_E8.pdfThis talks about the issue with filters measured in a 50
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
/ 50
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
environment and then used in a 0.1
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
100
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
environment.
0.1
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
100
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
is correct for Differential Mode emissions. The LISN inputs are in series.
0.1
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
25
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
is correct for Common Mode emissions because the LISNs are in parallel for CM inputs.
Inductor Model
Here is the curve from the datasheet:
![Conducted emissions issue with multiple Mean Well AC/DC converters](https://www.eevblog.com/forum/index.php?action=dlattach;topic=244077.0;attach=1005559;image)
From the datasheet we know:
The nominal inductance is 700uH
The Rdc = 24m
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
From the curve we know that the SRF is around 3MHz
We can calculate parallel capacitance as 10pF
We need to add a parallel resistance to set the maximum attenuation, at resonance, to be 32dB in the 50
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
test circuit:
![Conducted emissions issue with multiple Mean Well AC/DC converters](https://www.eevblog.com/forum/index.php?action=dlattach;topic=244077.0;attach=1005549;image)
If I run the model and plot V(vin)/V(vout) I can get the attenuation of the CM choke per CISPR 17 in a 50
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
50
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
test circuit:
![Conducted emissions issue with multiple Mean Well AC/DC converters](https://www.eevblog.com/forum/index.php?action=dlattach;topic=244077.0;attach=1005551;image)
Given the simplicity of the model, this is pretty close to the datasheet.
Application Circuit
The CM choke forms a filter with the Y caps. The X cap connects the two lines in parallel, so the Y capacitors are considered in parallel.
If we believe Schaffner, and accept that noise source is 0.1
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
and you trust me that a pair of LISNs presents 25
![Ohms \$\Omega\$](https://www.eevblog.com/forum/Smileys/default/omega.gif.pagespeed.ce.G89vbH4KGC.gif)
to CM signals.
Then the application circuit can be modeled:
![Conducted emissions issue with multiple Mean Well AC/DC converters](https://www.eevblog.com/forum/index.php?action=dlattach;topic=244077.0;attach=1005553;image)
The result from running the model shows how the CM choke works with the Y-caps to create an effective filter:
![Conducted emissions issue with multiple Mean Well AC/DC converters](https://www.eevblog.com/forum/index.php?action=dlattach;topic=244077.0;attach=1005555;image)
Y-cap location
The location of the Y-caps depends on if you are stopping emissions or improving immunity.
In a power supply, normally the plan is to reduce emissions, so the Y-caps should be located on the input of the power supply, the mains side of the CM choke.
Here are the modelling results showing the impact of having the Y-caps on the wrong side:
![Conducted emissions issue with multiple Mean Well AC/DC converters](https://www.eevblog.com/forum/index.php?action=dlattach;topic=244077.0;attach=1005557;image)
In the diagram of the DCP405 the Y-caps are on the wrong side of the CM choke.
Regards,
Jay_Diddy_B