SMPS, flyback isolated - 230 V AC to 3,3 V DC 5W problem with output voltage.

[WTK]

Hello everyone!

I am at prototype stage of making power supply like in title. The problem is my output is 10 times smaller than it was expected to be - i have 0,33 V instead of 3,3 V . I have no clue what could be wrong, circut on the board is ok, transformer also seems to be ok. Any suggestions will be checked instantly, thanks for any response.

The circuit




Used transformer




I am thinking about what should I do with second pair of secondary winding. Now both unused pins are disconnected from main circuit, since I need only one output. Maybe they cannot be left on their own ?

 

[mukeshp11]

If transformer is fine, then there may be problem with the feedback circuit. I mean you can check by giving 3.3V from outside to your viper switch and check for 3.3V output if its coming correct and this will verify if everything including transformer and your switching of mosfet, is fine and then compare giving your actual feedback and check switching of the mosfet if fine. This may be a step for trouble shooting.

 

[WTK]

If transformer is fine, then there may be problem with the feedback circuit. I mean you can check by giving 3.3V from outside to your viper switch and check for 3.3V output if its coming correct and this will verify if everything including transformer and your switching of mosfet, is fine and then compare giving your actual feedback and check switching of the mosfet if fine. This may be a step for trouble shooting.

I,ve connected DC power generator directly to FB and GND of the viper switch pins 3,3 V value, with input 230 AC from isolated generetor - I measured 0,8 V value on output.

Thing about transformer - there was no double secondary winding, secondary winding is like double wired so you have to connect end of one coil to begining of second - i think it´s called bifilar winding but I am not sure. After rearranging schematics, the output is 0,8 V - still too low.