Feedthrough Filter Identification - Page 1
Forum section: electronics / projects

author: fx991ex
author_rank: Contributor
timestamp: September 02, 2018, 11:00:25 pm
content: I would like to identify feedthrough filters that I removed from a circuit. The circuit's supply voltage is between 4.8V and 7.4V. There are three of these same filters on the circuit and I measured their capacitance at 100kHz. The package is 2012 (metric) or 0805 (imperial).FL1 = 601pFFL2 = 657pFFL3 = 668pfIs any characteristic other than capacitance that would help me with the identification?I attached the picture.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 02, 2018, 11:24:22 pm
content: It's a filter if there's inductance (usually ferrite materials), otherwise just a capacitor. Eh, I suppose it'd still be a good enough filter-as-such for high RF.If they're the same part, the cluster of values suggests 680pF nominal value. Kind of oddball I guess, but 620pF would be odder.If there's no significant inductance, then it's just a standard X2Y style cap.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: September 02, 2018, 11:50:18 pm
content: x2y is trademarked. there are feedthrough caps and x2y caps I think that behave differently.that looks like an actual filter (you can buy them from digikey to have like a someorder lpf in a single block like that

author: coppercone2
author_rank: Super Contributor
timestamp: September 02, 2018, 11:59:46 pm
content: http://datasheets.avx.com/L2FL3F.pdfA model of the feedthrough. I wonder how it compares to a x2y. is it the same?They dont advertize it as a CM filter though. Is it different? This one has a model of a ICI filter.here w egohttp://www.x2y.com/appnotes/emi/2002.pdfdifference between feedthrough and x2y

author: coppercone2
author_rank: Super Contributor
timestamp: September 03, 2018, 12:12:28 am
content: ok, i get it. the feedthrough is a DC short, the X2Y is not. duhBut, what would happen if you rotate the feedthrough 90 degrees. Does it become a x2y? Or is it not matched well enough?so the x2y is a super matched feedthrough thats rotated 90 degrees? or is it a electronic conspiracy?if you can market a component by rotating it 90 degrees and calling it superior thats the scam of a century. I am guessing there is some kind of difference that is discernable.

author: fx991ex
author_rank: Contributor
timestamp: September 03, 2018, 12:42:50 am
content: Thank you for quick response!I measured the inductance at 100kHz.FL1 = 250nHFL2 = 260nHFL3 = 260nHThe component appears to be Murata NFL21SP106X1C3D. At what frequency is inductance 680nH as stated in the datasheet?Link to the datasheet for NFL21SP106X1C3D:https://www.murata.com/en-eu/products/productdata/8796731277342/ENFD0006.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 03, 2018, 01:47:36 am
content: Quote from: fx991ex on September 03, 2018, 12:42:50 amInteresting, close, very plausible.The 10MHz cutoff part is measured at 1MHz, and the others at 10MHz.What signal level and/or bias current is that measured at, as well?0.1MHz is probably low enough that the capacitors aren't impacting the measurement, and should be low enough that the ferrite bead part is behaving (usually, in the >MHz range, the inductance goes as sqrt(f), but it should be stable down here).It may be another manufacturer or part, but that's probably a good guess if you needed a replacement part.Tim

author: fx991ex
author_rank: Contributor
timestamp: September 04, 2018, 05:12:09 pm
content: It was measured with DE-5000 LCR meter.Signal level is 0.5 Vrms. I can't find what's the bias current.

author: fx991ex
author_rank: Contributor
timestamp: September 05, 2018, 12:22:51 pm
content: I got Murata NFL21SP106X1C3D filters and I tested one under the same specs.At 100kHz inductance of a filter I tested was 612nH. So inductnce doesn't match with the ones I removed from a PCB.I will have to check out other manufacturers. Is it possible that these are custom made filters?