Problem with flyback transformer design

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saurav_sdpl

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i have designed a flyback smps for 4.2V/2A.using TNY268.

Under no-load condition its working fine between 100V ac to 250V ac.

but when i am giving .5A load the voltage dips to 2.9V, ie i am not able to achieve load regulation. Now if i vary this voltage between 100v to 250V , its again regulated at 2.9V.

Is this the problem of transformer or feedback loop.

I have used 3.3V /.5W zener. biasing resistance for zener is 270r, and opto used is SFH6186.

Wat could be the possible causes for this.

its urgent
 

flyback transformer polarity


You should post the schematic of your smps.
Do you have read the application notes AN-16, AN-17 and AN-18 about flyback transformer design and AN-23 about Tiny Switch of Power Integration?

regards
Stefano
 

Re: flyback transformer

One cause could be core saturation in the flyback transformer. How did you select your transformer? If you wound it yourself, how did you select the core material and size?
 

Re: flyback transformer

check the OCP set value.
 

Re: flyback transformer

i thing polarity of zener might may reversed. or zener value will not be proper



 

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