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EMC of non switch mode power supply equipment?

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According to the previous posts, the device failing conducted EMC tests in the 100 kHz to MHz range. It's impossible to guess the MHz interference level from the current waveform.

Consider that the limit values are below 60 dBµV (1 mV), respectively 20 µA into a 50 ohm load.

The spectrum measurement suggests that you want > 30 dB attenuation in the 100 kHz to 5 MHz range, in case of doubt both common and differential mode. A 33 mH choke might have too little effect in the MHz range.
 

you speak of interwinding capacitance i believe?
Exactly. Check the attenuation curve in datasheet.
 
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This is a related post to my above, please my i place it here...?

Hello,
We went for conducted EMC testing of our 150W offline led lighting product. (at an EMC Test House)
We told them there is 6 metres of cable running up the post to the lamp.
When we asked if we could include the 6 metres of cable up to the product, whilst the conducted EMC test was being done, (ie from the LISN to the product), they told us they would have to bind the 6 metres of cable up in a certain way.
We do not understand this, it’s a balanced pair cable, you cannot reduce or enhance the line inductance by binding up the 6 metres of mains cable in any way.
So why do they say they will use cable ties to bind up the 6 metres of cable? (binding it up by kind of folding it together in one foot lengths , so its a kind of small pile)

Why do they have to do this?

When we asked, they said it was "so everyone is singing from the same hymnsheet", but couldnt explain further.
 

Please may I put this here, it is related to the above?....
Hello,
We have a 45W, non-isolated , offline product which has failed conducted differential mode EMC as per the following scan (attached). The product actually has no AC mains filter whatsoever, or even any capacitors on its DC bus.
We have thereby designed the attached AC filter which we wish to use to address this.
The problem is that I have just noticed that the 470uH inductor (DR0608-474L) has a SRF of 2.8MHz.
Can you confirm that this almost certainly means that we will still fail due to the >2.8MHz noise frequencies getting through the interwinding capacitance of this inductor?
Can you state any good ferrite beads that we can use in series with this 470uH inductor to be able to mitigate this?

(LTspice AC simulation, schematic and EMC scan attached)

Also, do you know of any good little "potting boxes" that we can mount this filter in? (it will be on a little piece of stripboard)..And also do you know of any potting compound that we can use to cover this filter PCB in the potting box?...we will just have the 4 wires coming out of the potting box then we will pour the potting compound in there. (we need to pot it otherwise the live mains connections will be open to touch.

DR0608-474L 470uH inductor datasheet
https://www.farnell.com/datasheets/...9.2079023285.1495515712-1679746183.1489787856

PR03 resistor datasheet
https://www.vishay.com/docs/28729/pr010203.pdf

(the filter has more attenuation than needed because it was originally designed for our 150W product which needed the greater attenuation...(however, we downsized the current rating of the 470uH inductor to make this 45W version cheaper and smaller)
 

Attachments

  • AC Filter_.jpg
    AC Filter_.jpg
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  • AC input filter.TXT
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  • EMC conducted scan_.jpg
    EMC conducted scan_.jpg
    82.3 KB · Views: 49
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I highly doubt the SRF of the choke is the issue. The 220 ohms of resistance shunting the choke will be a much lower impedance path, even at >10MHz.
 
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Woops yes , of course you are right, and we are wanting some help from the slight bit of internal inductance of the resistor, in attenuating high frequencies, we now use the EP3W resistor type.

- - - Updated - - -

Any answers to post #24 above?, which postulates that the inductance of 6 metres of cable cannot be increased by coiling it up (since it comprises close running "go" and "return" conductors, live and neutral). Do you agree?
 
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