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Issue with 12V to 230V full bridge 1.5kW converter

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--- Quote from: T3sl4co1l on September 19, 2023, 11:10:51 pm ---Huh, are your probes poor quality? Or is there a high frequency compensation adjustment that's been neglected?  Strange seeing the "droop" artifact at this time scale, and I don't see why it would show up in the circuit otherwise.

You might want to zoom in and investigate the transient (edges and peaks).  Or determine if that's also a probe artifact as well, or what.


--- End quote ---

Q20 Lower right leg of H bridge - non differential RT-ZP03 probe which was a little overcompensated.
Q14 Lower left leg of H bridge - differential 1.4kV probe Cal Test 2593-1 is slightly undercompensated for high frequency and there is no compensation pot.
Other two channels Micsig DP10007 1kV differential probes, also no way to compensate it.

How to do compensate diff probe? I do not want to open it, it might be ultrasonically welded.

Aha, the HF trimmed kind, that would do it.

CT2593-1 says 50...uhhhh, kΩ source impedance and load??  Surely that's a typo and they mean 50Ω?  Well, it's obsolete now I guess, so unless you have a printed manual somewhere, that might be about all there is to know about it anymore, shrug.  Does it have rated gain (is it off by 2x)?  Does it read better with 50Ω termination enabled?  At 25MHz BW, it's never going to read as crisp as the passive probe, of course.

https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/4846/DS_1768_Catalog.pdf p.8


I swapped A and B places of U13 and still nothing good is coming from that.

SCR68 bow give correct MOSFET switch on and off
SCR69 zoomed out start up showing output
SCR71 zoomed in start up showing output

I also tried to drive transformer using signal generator (50Ohm output).
SCR72 generator tried outputting sine.
SCR74 generator was set to output square wave.

Well transformer is working. Can somebody see what have I missed?

Edited: CT2593-1 with 50Ohm termination didn't help at all, just amplitude collapsed. It looks like its output is about 75Ohms.
Edited 2: I must have been blind. From current configuration A and C have to be swapped.

Made it. After carefully checking all connections, I had to swap AB lines as I had done and had soldering error. Cold joint. It is not that easy to heat 12Oz copper (6x2Oz) and solder DFN on top.

I have an update on the issues I had. The datasheet contains three nasty mistakes I had found so far.

The First issue and the reason why I created this thread is obvious: mislabeled pins. Right after I measured them it is clear - A and B needs to be swapped places. Yes, there is a line in the datasheet describing them correctly, but not on a section which describes pins, whats more reference schematic contains the same mistake.

The second issue: Missing information about a resistor necessary to prevent core saturation at light load. This information is published in SLUA275, yet there is not a word about it in the main datasheet.

The third issue: incorrect or even false information about compensation scheme in peak current mode in which I want controller to operate.

Lastly (icing on the cake): I had found a texas instruments forum thread discussing issues with a client which offered to write organized paper describing all the error he had found in UCC2895 datasheet and TI just didn't respond to that. I hope my struggles with help somebody someday.

Anyway, I will attempt to compensate it and try to stick with companies which put more attention to documents (Intersil, Maxim (now AD), Linear Tech (now AD), NXP). This chip was orginally designed by unitrode and its documentation is not upto Ti standards.


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