Electronics > Projects, Designs, and Technical Stuff
"over current" use of a Pulse transformer - ( or an alternative )
mrpackethead:
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.
T3sl4co1l:
Hrm, MnZn ferrite would perform better, that's interesting.
Tim
mrpackethead:
--- Quote from: ogden on December 27, 2018, 10:58:11 pm ---Note that main source of DC bias current is TP (pair) DC resistance umbalance which is allowed by 802.3 to be <= 3%.
--- End quote ---
As 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.
--- Quote --- You shall measure inductance loss @100 KHz using LCR meter/w bias option.
--- End quote ---
I'll read this as a language difference thing, but using the word "shall" really does make you look like some kind of dictator
--- Quote --- It would be good idea to measure inductance loss at max temp as well. Temperature derating table (70oC @ 600mA and 85oC @ 500mA) does not look promising regarding "over current".
--- End quote ---
The 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.
--- Quote ---Those TDK Transformers are indeed nice, small and low profile, but if you ask me - I would not exceed specified 600mA.
--- End quote ---
I'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 ).
--- Quote ---Did TDK FAE answer your questions?
--- End quote ---
One of the things that you really need to do is read forum posts carefully, refer post #41
mrpackethead:
Inductance vs temp and temp vs current
mrpackethead:
Anybody know why the inductance goes up as temp goes up.. ( and then drops of dramatically ). What is in play
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