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DIY Injection Transformer for Power Supply Control Loop Response Measurements

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MatteoX:
Few references for electronic signal injection:

Galinski  "Use Op-Amp Injection for Bode Analysis"
http://www.edn.com/design/analog/4369185/Use-op-amp-injection-for-Bode-analysis


Keeney "Simple Signal Injection Aids Controol Loop Analysis"   
http://powerelectronics.com/power-electronics-systems/simple-signal-injector-aids-control-loop-analysis

EmmanuelFaure:
What about using a linear optocoupler instead of a transformer?

LeonV:
Any one know what the frequency response from an air core transformer would be?
Or what if you wind a cooper loop into another loop? Like copper wire wound into a toroidal shape, then a winding around that as if it was a toroidal core.

T3sl4co1l:

--- Quote from: LeonV on October 11, 2016, 04:11:41 am ---Any one know what the frequency response from an air core transformer would be?

--- End quote ---

Awful.  I'd be impressed if you got bandwidth more than 10 times the center frequency.

Tim

rx8pilot:
I have been using a Jensen VB-1BB isolation transformer used for analog video. Not perfect, but not bad assuming that 10hz is not a necessity. It does ok down to rather low frequencies though. I paid $20 on eBay. BNC 75 Ohms in/out

http://www.jensen-transformers.com/product/vb-1bb/

I tried to use it with the Keysight power application on my MSOX6000 but was quickly stopped by it's inability to deal with the noise in SMPS. The newer software on the 3k's and 4k's seems to be a lot better at filtering and allowing a LUT for the injection voltage to get a better SNR on a range of frequencies. I was able to get measurements, but manually stepping through the frequencies, injection levels, averaging, and math filtering. A bit slow, but I think I was able to get believable measurements. After getting some pricing on dedicated FRA's, I am determined to figure out how to get what I need on the scope. I will design about 4-5 SMPS's per year so I need this capability for a grand total of maybe a week per year as I work out the supply design.



Having a real VNA would be nice, but certainly not a must.

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