"over current" use of a Pulse transformer -  ( or an alternative ) - Page 1
Forum section: electronics / projects

author: mrpackethead
author_rank: Super Contributor
timestamp: December 21, 2018, 10:22:45 am
content: https://product.tdk.com/info/en/catalog/datasheets/090007/trans_alt4532p_en.pdfTDK have these small pulse transformers which look really useful, as they have a very small footprint which makes them useful for tight packs. they are rated for POE+ or 600mA. I want to run run at 900mA, which is what the 802.3bt standard for POE can go to.Other than thermal considerations, ( the device would potentially be disipitating approximately twice the power from 600 to 900mA ) would there be any other issues.In this use case, i am confident that i can provide considerable heat releif and cooling, so it might just be possible to get past this issue.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 21, 2018, 06:08:43 pm
content: If you're okay with qualifying for the application then yeah, there's no one else stopping you from doing so, and it is at your own risk.Those could also be paralleled, without much impact on frequency response.Tim

author: 2N3055
author_rank: Super Contributor
timestamp: December 21, 2018, 06:20:31 pm
content: Tim is right on the money.Put two in parallel.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 21, 2018, 06:50:55 pm
content: In my applicaiton, i'm just running 100M ethernet. It's worth considering using them in parallel, however part of the attraction is the size. For this application i can design cooling in from the start.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 21, 2018, 08:26:54 pm
content: Is the cure worse than the poison? -- how much are you spending on high-k thermal goop / potting / resin / thermal pads keeping those wires cool, and how much space is taken up by that plus the heatsinking, versus just using two, or using a higher rated part?Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: December 21, 2018, 08:31:44 pm
content: Quote from: T3sl4co1l on December 21, 2018, 08:26:54 pmYes, this is the balacing act of engineering is'nt it. Constantly having to make compromises and balacing acts.A higher rated part would be great. Right now, that means a much much bigger torrodial transformer pair.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 21, 2018, 08:48:00 pm
content: Can you get individual toroids (single Ethernet lane coupler) and use both sides, same as this part?I would think a pack (2 or 4 transformers plus CMCs) is much larger, but this should be similar. In any case, it can't be much smaller due to signal and thermal limitations, and that hard-limits your device.Tim

author: floobydust
author_rank: Super Contributor
timestamp: December 21, 2018, 08:52:02 pm
content: Why is there no isolation (voltage) rating for the transformer?

author: eb4fbz
author_rank: Regular Contributor
timestamp: December 21, 2018, 10:39:32 pm
content: Quote from: mrpackethead on December 21, 2018, 10:22:45 amYes, there is another issue: core saturation due to excesive current imbalance between the primary halves. So inductance could drop below Ethernet requirements (350uH OCL).

author: mrpackethead
author_rank: Super Contributor
timestamp: December 22, 2018, 08:24:13 am
content: Quote from: eb4fbz on December 21, 2018, 10:39:32 pmThats an issue irrispective of it being one of these devices or just a 'normal' transformer surely? In this case it shoudtn be too much of an issue, as the current will be largely balanced.

author: 2N3055
author_rank: Super Contributor
timestamp: December 22, 2018, 09:35:59 am
content: Quote from: floobydust on December 21, 2018, 08:52:02 pmWithstanding Voltage: Compliant with IEEE 802.3, Impulse 2400V 1.2/50μsIf you look into datasheet, you will see that current curve is flat 600mA from 0°C to 70°C at which point temp derating starts.600mA is probably not thermal bound but defined by core saturation. It will have a security factor, but how much, you will have to characterize yourself.But I will speculate it won't be 60% more...

author: mrpackethead
author_rank: Super Contributor
timestamp: December 22, 2018, 12:19:29 pm
content: Quote from: 2N3055 on December 22, 2018, 09:35:59 amI did see that somehwere but then it went missing on me.Quotei've only got little knowledge of transformers. Since the current flow in each side of the primary is towards the center tap ( opposite to each other ), won't the magnetic field cancel the other side out?

author: Zero999
author_rank: Super Contributor
timestamp: December 22, 2018, 02:36:49 pm
content: Quote from: mrpackethead on December 22, 2018, 12:19:29 pmNo, because the current doesn't flow from both sides of the tap simultaneously. It alternately flows from each side to the tap.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 22, 2018, 07:16:25 pm
content: Quote from: Hero999 on December 22, 2018, 02:36:49 pmSorry but there's not really much I can add... it's a linear circuit, currents don't simply stop and start, it's a superposition of continuous, variable currents where that continuity includes values of zero and negative.Also, the only nonlinearity we expect in the circuit, results in greater current flow, not lesser, nothing to make it discontinuous.Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: December 23, 2018, 08:31:28 am
content: Quote from: T3sl4co1l on December 21, 2018, 08:48:00 pmI have not found any if they in fact exisit.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 23, 2018, 08:35:28 am
content: Quote from: Zero999 on December 22, 2018, 02:36:49 pmThe 'power' component is nominally 52V DC ( or GND ) , and its applied at the same time to to both sides, and it flows out the CT. Its DC?? The signal component is of course is effectively AC, but the magntitude of that is very small in comparision to the power.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 23, 2018, 08:40:56 am
content: Quote from: ogden on December 22, 2018, 07:55:29 pmWhy would it not pass?The real question is what the limiting factor of this part is. Its it thermal, or is it something else. ( core saturation ). I will have to find out.

author: Zero999
author_rank: Super Contributor
timestamp: December 23, 2018, 10:17:17 am
content: Quote from: mrpackethead on December 23, 2018, 08:35:28 amIf you're talking about the power flowing through both sides of the CT simultaneously, then of course you're right: the flux will cancel, not no net magnetic field induced in the core, both it sounds like a strange, non-standard setup, rather than how the transformer is supposed to be used.Post a schematic.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 23, 2018, 11:52:39 am
content: Mrpackethead has been deeply involved in PoE applications (I don't know how obvious this is from the OP or his posting history), and as far as I know this is a standard application, for which there are such transformers as linked above, as standard off-the-shelf components.Yeah, differential data passes by, common mode power is drawn through the CT. Everything is transformer-isolated so there should be no balance issues outside of insulation/conductor failures.Nice name change..?Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: December 24, 2018, 03:26:35 pm
content: Quote from: Zero999 on December 23, 2018, 10:17:17 amThis is a very standard Power over ethernet set up. I'd suggest 10's if not 100's of millions of ports of POE has been done. Generic schematic is set up.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 24, 2018, 03:32:38 pm
content: Quote from: T3sl4co1l on December 23, 2018, 11:52:39 amThe difference between current flowing in each side of the transformer should only be minimal. The cable connecting each side is the same guage, and it will be the same length, ( with a few mm ). This is no differnet from any transformer that is being used for this application.My gut feeling says that the limitations here, are thermal, and that the device was only ever tested to 600mA because thats what was requried for POE+.

author: cdev
author_rank: Super Contributor
timestamp: December 24, 2018, 06:48:17 pm
content: You're probably right about them never needing to carry more so likely being able to handle it.But suppose it did get too hot, would there be any technical reason you could not usetwowith their windings simply *in parallel* with one another? - I suppose then you would lose the size advantage, though, so not worth it.Are all of these POE-ready pulse transformers all rated at the same 600 ma because of the rating being that?Quote from: mrpackethead on December 21, 2018, 10:22:45 am

author: mrpackethead
author_rank: Super Contributor
timestamp: December 24, 2018, 07:55:55 pm
content: Quote from: cdev on December 24, 2018, 06:48:17 pm

author: cdev
author_rank: Super Contributor
timestamp: December 24, 2018, 08:00:45 pm
content: If you find it runs hot and its potted I guess you could slap a heat sink on it although it might look funny-that would likely help.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 25, 2018, 11:10:35 am
content: Worst case, at 100m, you 12.87ohms vs 12.13.total current = 900mA.. this would result in 463mA in one conductor and 437 in the other 26mA.Its unclear if this difference will be enough to cause saturation of the core. It will need to cope with 18mA unbalance if its going to run at 600mA.The articale you reference while interesting is to do with the inblance between the pairs, this particular problem is related to a single pair.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 25, 2018, 07:22:38 pm
content: One would hope, the transformer is designed with nominal imbalance in mind. This does however limit the average permeability, which means more core size and wire length are more limited (larger).Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: December 25, 2018, 09:25:41 pm
content: Yes, one would hope so.I've contacted TDK and hope they will come back with some more info.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 25, 2018, 09:47:03 pm
content: Quote from: ogden on December 25, 2018, 09:32:22 pmOgden, we'll see what happens. You nor i actually know the characterisistics of this transformer for operating outside the rated limits. ( i assume you hav'nt tested it, in this situation, but if you have, i'd be all ears ). For me, its well worth pursuing this. If it works i'll be very happy. If it does'tn i've not lost a lot.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 25, 2018, 11:27:04 pm
content: Nice thing is because it's intended to be a bias tee, you can intentionally unbalance it in a test, run some current through it, and measure the saturation flux on the free winding(s)!Just gotta order up some parts and put 'em to the function generator and scope.Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: December 26, 2018, 04:13:47 am
content: Quote from: ogden on December 25, 2018, 09:52:48 pmYour not making any sense. You say i fail miserably, with my assumption. ( which was that you dont' know about this specific transformer ), then you go on to say you dont' know this particular transformer in the very next sentence. You need to live outside the datasheets a little, life is much more exciting and interesting there. :-)

author: mrpackethead
author_rank: Super Contributor
timestamp: December 26, 2018, 04:17:34 am
content: Quote from: T3sl4co1l on December 25, 2018, 11:27:04 pmAnd TDK have really conveniently provided a little dev board which makes it really easy. ( is ordered but i'm still 3 weeks away from getting back home ).worse case, its not suitable, best case i have a great solution

author: mrpackethead
author_rank: Super Contributor
timestamp: December 26, 2018, 03:34:14 pm
content: Quote from: ogden on December 26, 2018, 04:42:38 amThanks so much for your valuable contributions. I'll keep it in mind.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 26, 2018, 05:19:21 pm
content: Quote from: ogden on December 26, 2018, 05:04:23 pmOnce again thanks for your contribution. I've just ordered the sample parts, and designed a simple pcb so i can do some base evaluation, and had some intital feedback from TDK, which indicates that this is well worth pursuing.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 26, 2018, 11:17:09 pm
content: Quote from: ogden on December 26, 2018, 05:04:23 pmAs I've noted many times before on this forum... what do you expect, it's only free advice. Just a bunch of hear-say from self-proclaimed experts (not leaving myself out here) until something actually gets made, and someone else actually gets paid.Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: December 27, 2018, 07:56:35 am
content: Quote from: T3sl4co1l on December 26, 2018, 11:17:09 pmOne of the skills you need in life is to determine what 'free advice' you should take and which you should discard. There is the weighting of information based on previous experience. If somones given you good advice in the past, there is a good chance it will be good again. Theres the 'boast' factor. Advice that is prefaced with " i'm a ... with ... years of experience " normally is a good indicator to treat it with caution. " X worked for me, becuase ..... " is a good indicator of something to look at deeper. Advice that comes with a verifiable link... ( I got this from 'ABC' and it cost me $X ) (www.x.com/abc/price.html) is good too.Its also never wise to assume the knowledge or expereince level of anyone asking a question. You have no idea what they know.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 27, 2018, 09:37:54 pm
content: So, this ALT4532 part is rated at 180uH @ 8mA. With modern Phys ( well anything later than about 2004 ) we need > 120uH, to get BER of 10-8. (NB: The 350uH @8mA came from ANSI X3.263: 1995, to mitigate against Base Line Wandering, essentially a DC bias that occurs when you send a Long string of zeros or ones, which effectively set up a DC bias, however the modern phys all employ compensation schemes to get around this. ).The real question, and one that will only be answered by testing, is how much inductance will be lost as well increase the bias. Will we drop below 120uH before we have a bias current >25mA.The cores are based on Ni-Zn ferrite material so they have both high magnetic permeability and saturation flux density. And being machine manufactured, rather than hand wound.. theres a fighting chance here.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 27, 2018, 10:35:29 pm
content: Hrm, MnZn ferrite would perform better, that's interesting.Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: December 28, 2018, 08:14:52 am
content: Quote from: ogden on December 27, 2018, 10:58:11 pmAs you've said several times. Got anything new to add, though if repeating yourself over and over helps you, then i'm pleased to provide this thread as a public service to you.QuoteI'll read this as a language difference thing, but using the word "shall" really does make you look like some kind of dictatorQuoteThe the permability of Ni-Zn is very flat till about 120C. A rise in temp, ( over a sensible range ) is not going to cause a significant reduction in inductance. The derating is likely related to how hot the copper is going to get. how far the inductance drops due to the DC bias is not yet clear.QuoteI'm glad you've made that decision not to exceed 600mA in your design. in 1961 a certain president did not have a datasheet that said they could go to the moon. but in 1969 they did. ( they had a few opps moments on the way though ).Manufacturers give parts ratings so that they relaibly operate across a wide range of conditions, and so they minimise their liability. And that is just fine. Engineers can sometimes push past those things when they understand the constraints, and if you do not need to operate across a wide range of conditions, and can control the environments, you can sometimes do things that are 'outside' of the datasheet. What you cant' do is expect thigns to work outside of the constraints of what are fundementals.. ( you can't just decide that gravity no longer applies or that you can have perpetual motion ).QuoteOne of the things that you really need to do is read forum posts carefully, refer post #41

author: mrpackethead
author_rank: Super Contributor
timestamp: December 28, 2018, 10:57:08 am
content: Inductance vs temp and temp vs current

author: mrpackethead
author_rank: Super Contributor
timestamp: December 28, 2018, 09:15:33 pm
content: Anybody know why the inductance goes up as temp goes up.. ( and then drops of dramatically ). What is in play

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 29, 2018, 01:32:24 am
content: More temp leads to more activation of more ferromagnets, until it's too much, they get scattered randomly and the house of cards falls over (Curie temp).The activation energy is all over the place, usually a blend is used (the exact mixture of Ni to Zn to Fe, and any dopants) to give some combination of properties for a purpose. Some, you'll see multiple humps in the mu(T) plot, as different energy bands become active.Which might imply, and quite rightly so, it is true -- that, as temperature goes up, Bsat goes down. That is, there is more energy pushing the magnets out of alignment, so there are fewer able to line up with the applied field (if also more readily so -- high mu), even when driven heavily.So it's actually very important to note that Tc is quite low for this material. That means the drop in Bsat is nearby too, and it would be very easy to heat up this part, with DC current, enough to also spoil its DC imbalance handling.Or if not due to DC heating alone at room temperature, then it will severely limit your ambient temp range.I'm rather surprised and perplexed why they went with NiZn here; it certainly makes it harder for your application.Example:Given the axes, this looks like it might be for nickel (it's from ResearchGate, I didn't read the article). The curve is similar for other materials, adjusted for low-temp Bsat (left intercept) and zero-field Tc (bottom intercept).Tim

author: ogden
author_rank: Super Contributor
timestamp: December 29, 2018, 01:38:43 am
content: Quote from: T3sl4co1l on December 29, 2018, 01:32:24 amMaybe they did not design those trafos for his application?

author: mrpackethead
author_rank: Super Contributor
timestamp: December 29, 2018, 08:25:43 am
content: Quote from: ogden on December 29, 2018, 01:38:43 amYou once again seem to have missed the point. We know what they were designed for. We know what the datasheet says. What we dont' know are what the 'real' limits of 'were it will work to. Please stay on topic, or find another thread to pollute. Its not even about is this a good idea. Its about understanding what will happen if you push past the datasheets limit.

author: mrpackethead
author_rank: Super Contributor
timestamp: December 29, 2018, 08:39:51 am
content: Quote from: T3sl4co1l on December 29, 2018, 01:32:24 amRight... That I would have never guessed or sumized. RTheres some underlying physics i have never run into before.QuoteAs I did look at some of the various mixes they use for ferrites i did see some graphs like that. ( see the one above for example, it only had one hump ). Interesting stuff.QuoteThe TDK Engineer did'nt have all the lab testing results. ( theres a LOT more data that is not on the datasheet, but hopefuly I will get it soon, being Christmas/New Year its not a great time ). It was suggested its been run up to 1000mA, but the thermal range was reduced. The target market for these thigns are low profile servers, ( yes running on POE ). and i guess they dont' want to spend any energy on cooling. I guess at 1000mA, its 'window' for being useful is greatly reduced and would be problematic for many of their key applications.In several of the applications i'm going to be running, i'm likely to be pushing 20kW of power plus from a single location. Active in rack cooling ( AC ) is not out of the question for those deployments.I'm rather surprised and perplexed why they went with NiZn here; it certainly makes it harder for your application.Example:Given the axes, this looks like it might be for nickel (it's from ResearchGate, I didn't read the article). The curve is similar for other materials, adjusted for low-temp Bsat (left intercept) and zero-field Tc (bottom intercept).Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 29, 2018, 09:34:27 am
content: Quote from: mrpackethead on December 29, 2018, 08:39:51 amYeah, but at least that's not entirely your fault -- magnetism is...weird, even among physicists. Real materials have all sorts of quirks they don't tell you about, that are just not very important in their dominant applications, and that aren't at all worth researching in depth.Example, the traditional sigmoidal B-H curve is a lie for a lot of materials; it's actually a bit pinched in the middle, as reflected by the "initial permeability" parameter often seen. This can be quite dramatic in some, like silicon steel where mu_i might be ~800 while mu_avg (at say Bpk = 1T) is closer to 10k or more.Or the interplay between hysteresis loss, skin depth, Bsat and eddy currents in an induction heating application. I saw one application where a deep case hardening was desired (~6mm deep) on a 6" ball (something like a ball-socket part). Some simulations were attempted, with modest results, but including that many nonlinear material parameters was definitely pushing the capability of the simulator used. The power supply ended up being a 3kHz machine (it was LOUD), uhh I forget if it was 150 or 300kW or what, and the exact profile (power level and duration) was dialed in by hand (run a part, slice it in half, take hardness readings around the edge; repeat..) as usual.With better simulation tools, with better material characterization, with better physics in general -- perhaps the problem could be solvable fairly quickly for any arbitrary part within a class of shapes (since, you can't heat just anything, there are limitations on where fields will go). But that would probably take decades of study, and no one's got time for that. So we're left with a reasonably useful, yet still murky mystery that is magnets.Tim

author: ogden
author_rank: Super Contributor
timestamp: December 29, 2018, 11:08:59 am
content: Quote from: mrpackethead on December 29, 2018, 08:25:43 amWell.. I already tried to bring your attention to thermal derating curve, but seems you were busy profiling me. Youwould want tocalculate heat dissipated by transformers and chokes at target current (1A). Worth to consider slightly bigger magnetics having lower internal DC resistance, rather than spent BOM money and real estate in heat spreaders. Disclaimer: englisch is not my native language, please respect this fact.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 14, 2019, 10:37:48 pm
content: Some good news, at 1A current ( some 100mA over my target current ) the transformer does not overheat. It does get warm. ( around 91C, some 71C over the ambient heat ). I tryed attaching some heatsinks and it makes very little difference. I put this down to that the wire is not well coupled thermally to the ferrite, and the ferrite itself has quite poor thermal conductivity ( roughly 100x less than aluminium ).Some futher testing with forced air ( which is not an issue, as this is going to have fans anyway ), dropped the ferrite temp to just 54C. The physical design of the transformer lends itself to being able to have forced air coming underneath it, via a cut out in the pcb.. This also means it does not require any additional parts.I am about to start testing for DC Bias and inductance versus temp. With 30mA of bias it did not fall over.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 16, 2019, 03:36:58 am
content: This is what i'm going to do to keep these cool. ( it works in a hacked up test, now to more formally test on a designed pcb )Air will be forced up from under the pcb, past the wire which is where the heat is. This is going to be quite simple to implement