Products > Test Equipment
DIY Transformer for use with Bode Plots.
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TopQuark:
I have been down this path of building wide BW transformers before as well.

I tried the Vacuumschmeize cores, while they are good, it likely won't improve things beyond what you have now. My only issue with them is they are quite fragile, I believe my Vacuumschmeize core shattered after living on my bench for a while.

My current build uses a ~ 3 USD high permeability core from Taobao (https://item.taobao.com/item.htm?id=561000102517), works quite well as shown in measurements.
mawyatt:
Thanks, but that link doesn't work! Do you have another in English, or the part number and OEM, and what size is the core, looks large?

Performance looks good, have you done any open-loop measurements with an op-amp in a closed loop amplifier?

The limiting factor maybe not be the core, but the ability of the DSO to "pull out" the response where the overall loop gain is very high a low frequencies. However, the larger core may have a benefit of allowing a larger DC thru current while still remaining somewhat linear.

Thanks for the response.

Best,
mawyatt:

--- Quote from: TopQuark on May 22, 2022, 07:45:04 am ---I tried the Vacuumschmeize cores, while they are good, it likely won't improve things beyond what you have now. My only issue with them is they are quite fragile, I believe my Vacuumschmeize core shattered after living on my bench for a while.

--- End quote ---

Please explain the core shattering, do you mean actually cracking while overheating, or physical stress (dropped)?

Best,
TopQuark:
Yea Taobao is a pain to work with, I've attached a screenshot of the item listing.

It is quoted as a nanocrystalline core with 50mm OD, 32mm ID, 15mm Height. No mention of who "AT&M" makes it or any part number, as per usual for stuff listed on Taobao.

I haven't used it for opamp open loop measurements, but have used it in SMPS loop response measurements and it works well, can't find the screenshot at the moment, might run a test and post the loop measurement later.

TBH as long as enough signal goes through the transformer, the actual response of the transformer does not matter that much to me, as the measurement of the loop response is always done after the injection signal goes through the transformer, not before it.

Cheers
TopQuark:

--- Quote from: mawyatt on May 22, 2022, 02:41:13 pm ---
--- Quote from: TopQuark on May 22, 2022, 07:45:04 am ---I tried the Vacuumschmeize cores, while they are good, it likely won't improve things beyond what you have now. My only issue with them is they are quite fragile, I believe my Vacuumschmeize core shattered after living on my bench for a while.

--- End quote ---

Please explain the core shattering, do you mean actually cracking while overheating, or physical stress (dropped)?

Best,

--- End quote ---

It was working fine when I built the transformer, but measuring the transformer response after a few months yielded very poor results. I could hear something loose shaking the core, but the core looks fine externally, as there's a plastic casing around the core material.

I am not 100% certain it was shattered, but re-winding the transformer did not improve things. Most likely it shattered internally when I bumped it around / dropped it off my shelf etc.  :-\
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