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TNY288PG dual output flyback unreliable

Posted by: pwatson on

EDIT 1-19-17: I found the problem. The custom transformer I was using had its output windings wound backwards, in such a way that the winding polarity was reversed. I tested it today with new transformers and it works as intended.

 

Hello all,

 

I am working on a 5V 2A and 20V 0.05A output flyback converter with universal mains input, based off of a design recommended by PI Expert, which I have attached. Note that I substituted the TNY287PG in the design with a TNY288PG, due to availability.

 

The circuit barely works, and is very unreliable. When it has an extremely light load, it works as intended, with a stable 5V and ~20V output. However, when I increase the load, it stops regulating and begins to restart over and over again. It seems to predictably fail at about 0.02A on the 20V output and about 0.4A on the 5V output.

 

Furthermore, sometimes it seems sensitive to the input voltage. When I gradually increase the input voltage from zero, it always starts regulating at about 85 VAC. Sometimes it will continue regulating as I dial the voltage up to 120 VAC and then 260 VAC, but more often it seems that as the voltage approaches 110 VAC, it fails and begins to restart endlessly. I also noticed that if I just start the circuit up in 120 VAC without the gradual ramp-up, it never starts regulating.

 

Since it works at all, even intermittently, it seems to me that the connections must be good, but one or more of the components has an inappropriate value. Please advise. Thank you.

 

Perry

 

Comments

Submitted by PI-Traveler on 01/17/2017

Hi Perry,

Thank you for choosing Power Integrations.

Could you also please send your transformer design so I can help you review. 

Please also check the voltage across your BP pin and capacitor. This voltage should be around 5.8V and should not go down below 4.9V

Submitted by pwatson on 01/19/2017

In reply to by PI-Traveler

Hey, thanks for getting back to me, but I discovered the problem myself. As it turns out, the custom transformer I was using had its output windings wound backwards. I just got new transformers today and my circuit works as intended. We can consider this issue resolved. Thank you.