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Why do the output of the bridge rectifier shoot above 1KV when an inductor is placed as a filter in series with it?

Amal Babu
Associate III

Hi,

I am designing an inverter using ST's application note AN2794.I have customized the application note which was designed for 1KW power to 1.65KW.The problem i am facing now is that when i probe the output of the bridge rectifier placed at the output of the transformer,i am getting square pluses which means rectified output from the transformer which is of peak voltage 400v.But when i place an inductor the peak voltage shoots to about 1400v from 400v.Why is that so?is it that the inductor value is in appropriate for my design?Actually the transformer turns ratio is 18 and having a maximum input voltage of 42v.The output of the transformer is rated at 350v with a 4.72A.How should i go about designing the inductor? In my design i am using LC filter.

I calculated the induct or as per the reference design but it doesn't seem to work.How is the value of inductor related to the peak voltage ringing caused by inductor? I have also attached waveform which i obtained from the output of the rectifier.i have also attached the schematics of the same.

The shown below is the schematics of the design.0690X0000087y7NQAQ.png

0690X0000087y78QAA.pngThe waveform shown below is the output of the bridge rectifier:

0690X0000087y8fQAA.jpg

the waveform shown below is the output with L mounted without C, the waveform changes as below:

0690X0000087y9dQAA.jpg

the waveform shown below is the output of rectifier with both l and c mounted.

0690X0000087yA7QAI.jpg

i happen to probe the primary of the transformer and i found similar waveform at the primary too:The image attached is the drain voltages of both mosfets placed in primary.I happen to see the same ringing there too.Why is that?

0690X0000087yAqQAI.jpg

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