Author Topic: Which injection transformer for feedback loop measurements?  (Read 1046 times)

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Offline jmwTopic starter

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Which injection transformer for feedback loop measurements?
« on: April 23, 2020, 05:57:52 am »
I'm trying to follow the procedure in AN-1889 for measuring the feedback loop gain in a power converter. A transformer is used to couple a function generator signal across a small resistor without passing DC, but I'm not sure what kind of transformer to use. The note says "There are special transformers for such measurements available, which offer a very flat voltage transmission over a wide frequency band." What kinds of commercially available transformers specifically fit this bill? I was browsing Digikey and thought maybe things under current-sense transformers or pulse transformers seem like they could work. Has anyone done this and have recommendations?
 

Offline uer166

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Re: Which injection transformer for feedback loop measurements?
« Reply #1 on: April 23, 2020, 06:09:45 am »
Got this guy at work not long ago, can't comment on how good it is, but it's designed for your application: https://www.picotest.com/products_J2101A.html
 

Offline jmwTopic starter

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Re: Which injection transformer for feedback loop measurements?
« Reply #2 on: April 23, 2020, 07:12:51 am »
Did some searching, looks like this topic has come up before. Seems the options are that Pico-test unit or similarly priced, or homebrew it. Guess that's another project to put on the board  :-DD
 

Offline Mechatrommer

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Re: Which injection transformer for feedback loop measurements?
« Reply #3 on: April 23, 2020, 10:15:28 am »
Got this guy at work not long ago, can't comment on how good it is, but it's designed for your application: https://www.picotest.com/products_J2101A.html
$525 can buy a lot of stuff... did the OP created this thread due to this thread? https://www.eevblog.com/forum/testgear/injection-transformers-bode-plots-application/?topicseen Jay_Diddy_B uses much cheaper Wurth 744 229 Common Mode choke. ($2.46 USD Qty 1 Digikey) maybe testing and try and error with much cheaper transformer first can give us much lesson before we can spend anything near $500 bucks. if i want to do real life testing on this, i will start first with my function generator and/or if necessary wind my own HF transformer with available ferrite core in my stock. ymmv.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 


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