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UCC2803: Flyback isolated AC/DC converter, tina ti

ABHISHEK KUMAR

Prodigy 120 points

Part Number: UCC2803

Hii Everyone..

I am designing a 19 V, 60 W, AC-DC flyback isolated converter using UCC2803 Controller, but I am facing an issue in the voltage divider circuit on the secondary side. As suggested in the Webench design there should be a Schottky diode. As shown in fig:

When I insert the Schottky diode in my simulation, I am getting an output voltage of 5 V approx.

But after removing the Schottky diode, getting the perfect result.

Please suggest, why is it happening? How to get perfect output even after using that Schottky diode?

Thanks

over 3 years ago

0 Jerry Xu over 3 years ago

TI__Expert 3160 points

I will spend some time reviewing your schematic.

0 Jerry Xu over 3 years ago

TI__Expert 3160 points

Diode is used for soft start. You can add the simulation time and watch if the output voltage can be 19V.

0 ABHISHEK KUMAR over 3 years ago in reply to Jerry Xu

Prodigy 120 points

But after adding the diode in simulation, the ripples in the output increase. How to reduce it?

0 ABHISHEK KUMAR over 3 years ago in reply to ABHISHEK KUMAR

Prodigy 120 points

Also, what is the work of both the bipolar transistor in the design?

0 Jerry Xu over 3 years ago in reply to ABHISHEK KUMAR

TI__Expert 3160 points

By adding the simulation time, can the output voltage be regulated correctly?

0 ABHISHEK KUMAR over 3 years ago in reply to Jerry Xu

Prodigy 120 points

yes, but getting high ripples in output

0 Jerry Xu over 3 years ago in reply to ABHISHEK KUMAR

TI__Expert 3160 points

They are for slop compensation and pull-up separately

0 ABHISHEK KUMAR over 3 years ago in reply to Jerry Xu

Prodigy 120 points

Hii

How to reduce ripples in output then?

0 Jerry Xu over 3 years ago in reply to ABHISHEK KUMAR

TI__Expert 3160 points

Can you share your simulation model?

0 ABHISHEK KUMAR over 3 years ago in reply to Jerry Xu

Prodigy 120 points

yes sure....but takes a lot of time to run.

5383.UCC2803.TSC

+1 Jerry Xu over 3 years ago in reply to ABHISHEK KUMAR

TI__Expert 3160 points

When removing diode, your simulation still have issues. The COMP pin shouldn't drop to 0V. I didn't have enough time to help find out the problem.

0 ABHISHEK KUMAR over 3 years ago in reply to Jerry Xu

Prodigy 120 points

I am not getting such a problem after removing the diode but still, the issues are resolved.

Thank you