Gate drive transformers simply don't exist? - Page 1
Forum section: electronics / projects

author: ocset
author_rank: Super Contributor
timestamp: November 27, 2017, 08:07:57 pm
content: Hello,We are seeking an offtheshelf gate drive transformer for our 100khz, 30w Buck converter (400V to 270V).We need it to be……………….1:1LPRI = anywhere from 600uH to 2mHLeakage inductance = <1uHV.us = at least 50At least 1500v pri/sec isolationWe have searched high and low…would you believe no such thing exists!..or may you contrarily tell the tale of deliverance?

author: fourtytwo42
author_rank: Super Contributor
timestamp: November 27, 2017, 08:13:01 pm
content: Hi Treez as I know you still cannot afford an engineerI suggest you look at network interface transformers, for example Ethernet or DSL. Or wind your own on small ring cores ?Of course I realize I have not done engineers salaries any good by replying to you hahaha

author: chris_leyson
author_rank: Super Contributor
timestamp: November 27, 2017, 09:10:38 pm
content: Try Farnell and type pulse transformer into the search box, there's about 400 to choose from, 1:1, 2:1, 1:1:1, 2:1:1 etc through hole or surface mount.

author: BNElecEng
author_rank: Regular Contributor
timestamp: November 27, 2017, 09:12:11 pm
content: Seconded on the pulse transformers. Lots of flavours to choose from.

author: David Hess
author_rank: Super Contributor
timestamp: November 28, 2017, 05:14:27 am
content: You must be looking in the wrong place. Coilcraft sells them as standard parts. Low power inverter transformers are also suitable to be used as gate drive transformers and the reverse.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 28, 2017, 05:48:34 am
content: Gate drive transformers don't work well with extreme duty cycles. I would recommend a high voltage MOSFET driver instead.

author: Berni
author_rank: Super Contributor
timestamp: November 28, 2017, 06:11:14 am
content: Quote from: NiHaoMike on November 28, 2017, 05:48:34 amWell he did mention that it is for a buck converter and those don't tend to use very narrow duty cycles anyway unless you are trying to get out output close to the input. Tho at these sort of voltages and powers you could move to a flyback topology if you needed that.

author: ocset
author_rank: Super Contributor
timestamp: November 28, 2017, 06:28:30 am
content: QuoteThanks, but they all have too high leakage or too low V.uswe wish to extend it to just 500v isolation, and 200uH to 2mH for Lpri, and k>0.99....even then we cant find anythingThis one,http://www.farnell.com/datasheets/2333110.pdf?_ga=2.62201067.675725240.1511812287-287702491.1506211291..seemed good, but only quotes "minimum" leakage, not "maximum" leakage

author: tautech
author_rank: Super Contributor
timestamp: November 28, 2017, 06:38:07 am
content: Quote from: treez on November 28, 2017, 06:28:30 amDespite not finding what you want/need initially, think 'pulse transformer' NOT gate drive.You'll find what you need and if you can't do the calcs and wind your own using appropriate toroids and insulated wire. Some checks with a scope and current probe and hey presto you'll have something tuned up in no time flat.

author: floobydust
author_rank: Super Contributor
timestamp: November 28, 2017, 07:15:56 am
content: EPCOS B82804A Series Gate Drive TransformersWurth Electronics WE-GDT Series Gate Drive Transformers

author: ocset
author_rank: Super Contributor
timestamp: November 28, 2017, 11:40:22 am
content: Thanks,The EP5..........http://katalog.we-online.de/pbs/datasheet/760301106.pdf..is the best that is available, but it has a max V.us of just 30.....this is too low, i mean, our max duty cycle at our 100khz switching frequency is 0.2, and the gate drive voltage is 12V, so we would normally be ok with 30V.us, but for those times when eg the led load is not attached, and the error amplifier therefore rails high, then it will be on max duty cycle, and if the led load is suddenly re-applied, then the gate drive transformer will saturate.----------------------------------I must admit the 786 series of Pulse transformers look ok but the V.us column is said to be the “minimum” V.us product...surely it should be the maximum?786 Series Pulse transformers:https://www.murata-ps.com/data/magnetics/kmp_786.pdf

author: cat87
author_rank: Regular Contributor
timestamp: November 28, 2017, 12:05:49 pm
content: QuoteIt might very well be the case. I've had a rummage for some GDTs a few weeks ago, for frequencies of about 35-50 kHz, which is really low. Most commercial ones cater to the higher frequencies, starting at 100kHz and up to the MHz region.Something to match you specifications, looks more like something you'd make yourself. You can easily get those parameters, but you have to get your own core and make your own winding, That's what I did, at least.I know this is not helpful in any way, but I'm just trying to tell you my recent experience with these things.It's either high Vus - High leakage or low Vus - low leakage.

author: David Hess
author_rank: Super Contributor
timestamp: November 28, 2017, 01:35:39 pm
content: There are secondary side circuits you can use to reduce the volt*second requirements of the gate drive transformer. For example:https://www.infineon.com/dgdl/an-950.pdf?fileId=5546d462533600a40153559ee46511c2

author: james_s
author_rank: Super Contributor
timestamp: November 30, 2017, 12:08:41 am
content: I wind my own, I built several ~500-1kW Tesla coils that way. Somewhere I had a spreadsheet that made calculating the turns pretty straightforward. Transformer drive has the advantage that a MOSFET failure generally won't cause a catastrophic cascading failure.