SMD common mode choke for 150W offline 230VAC LED driver

Hello,
We wish to use the MSD1260T (180uH) common mode choke in our offline 150W linear LED driver.
It has a 1W Buck bias supply which is what is causing the common mode noise.
We cannot use a through hole common mode choke, because our PCB is all surface mount and cannot tolerate any PTH components due to cost pressure.

Do you think the closeness of the coils in the MSD1260T will mean we get emissions coupling from one coil to the other and thus not "seeing" the common mode inductance?

MSD1260T common mode choke:
https://www.coilcraft.com/pdfs/msd1260t.pdf

I would doubt it, the magnetic field is well confined in the core and they also have a shield around them. It probably wouldn't be a good idea to actually touch each other in case it allowed some capacitive coupling but even a tiny gap should prevent that.

You would have to experiment to find actual effectiveness.

Brian.

Thanks, i suspect that the coils (presumably enammelled copper wire) inside that tiny case do actually touch each other. It doesnt bode well for when mains transients come, i pray we will be ok.

I meant the screening around the coil itself shouldn't touch.

Don't lose sleep over mains transients, the voltage will be divided between each turn so from one to the next will be quite small and the insulation should be good to many tens if not hundreds of volts. There are also two layers of insulation to penetrate, one on each adjacent turn. The whole idea of a choke is that the rapid changing current is converted to a magnetic field in a lossy core anyway so the voltage will diminish quickly.

Brian.

treez said:

Hello,
Do you think the closeness of the coils in the MSD1260T will mean we get emissions coupling from one coil to the other and thus not "seeing" the common mode inductance?

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I can't parse what you're trying to ask here. Why would the windings being close together make a CM choke less effective (voltage tolerance aside)?

When analyzing filters like this, you have to be specific about the interference source(s) and and how the filter components are connected to the mains/load. A full schematic should be given.

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betwixt said:

I meant the screening around the coil itself shouldn't touch.

Don't lose sleep over mains transients, the voltage will be divided between each turn so from one to the next will be quite small and the insulation should be good to many tens if not hundreds of volts. There are also two layers of insulation to penetrate, one on each adjacent turn. The whole idea of a choke is that the rapid changing current is converted to a magnetic field in a lossy core anyway so the voltage will diminish quickly.

Click to expand...

I believe treez is more concerned about primary to secondary insulation, not turn-to-turn insulation on each winding. If there aren't any TVS devices between the mains and the CM choke, I would be very concerned about failures.

I believe treez is more concerned about primary to secondary insulation, not turn-to-turn insulation on each winding. If there aren't any TVS devices between the mains and the CM choke, I would be very concerned about failures.

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I'm not sure what he's concerned about. The datasheet specified "500 Vrms isolation" has to be read as test voltage. So my concern would be that the part is not suited for 230 Vrms mains voltage. Common mode chokes for mains voltage have e.g. 1500 Vrms test voltage.

To know the effectivity as mains filter, we would look on as common mode and differential mode attenuation plot. As the part is apparently not intended to be used as filter choke, respective data aren't provided by Coilcraft and have be measured by yourself.

If there aren't any TVS devices between the mains and the CM choke, I would be very concerned about failures.

Click to expand...

Thanks,
We are using a TMOV module upstream of the common mode choke. However, once its MOVs have failed, it switches itself out and we then have no MOVs upstream of the common mode choke.
From your comments I thus now suspect that this common mode choke is no good to us, and we will have to get one custom made with good separation between the coils. Either that or just try and get away with getting common mode emissions down with two inductors, one in live, and one in neutral.

TMOV module:
https://www.littelfuse.com/~/media/...littelfuse_varistor_lsp05gx_datasheet.pdf.pdf

MOVs are pretty rotten with mains transients, as the datasheet below shows, a 275V MOV lets through around 700V when its conducting as little as 10A.

MOV datasheet:
https://www.littelfuse.com/~/media/...telfuse_varistor_tmov_itmov_datasheet.pdf.pdf


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Even though the MSD1260T common mode choke is only tested to 500Vrms, its hard to see it actually going short circuit between the coils from a mains transient...do you agree?

Staff at AGW company told me that "enamelled copper wire is rated to 1000V"...mind you that was several years ago and the staff member no longer works there now.

It might be worth it to give coilcraft a call and ask what the intended application of those CM chokes is, or if they have any thoughts on using it for mains applications.

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treez said:

Staff at AGW company told me that "enamelled copper wire is rated to 1000V"...mind you that was several years ago and the staff member no longer works there now.

Click to expand...

Enamel comes in a wide chemistries and thickness...