Solution Finder

TNY290 Design - SMPS Resets above 200 Vac

Posted by: kd on Fri, 12/03/2021


Please Find my schematic. I have designed SMPS based on TNY290 Ic. I have populated 2 boards. Now one board (BOARD - A) is working fine but another board (BOARD - B) keeps resetting after I increase the input voltage above 200 Vac. On Board-B I have checked all the components & also replaced IC and transformer but it only works in the range of (70 - 200 Vac) after that it automatically resets itself!


From where should I debug the board? should I change the values of the resistors of overvoltage protection? (But it still works on the BOARD - A ) 


Note: Test condition - SMPS Output power consumption is  6 watts. (Cant change the load settings as this board is part of (power supply) larger circuit. 



Submitted by PI-Wrench on Mon, 12/06/2021

What do you mean by reset? Do the outputs simply shut down when 200V is reached? You might want to check the values for R4 and R5 on the board that is malfunctioning to make sure they are correct.

Submitted by PI-Wrench on Wed, 12/08/2021

Another thought - please check and see if the transformer output polarities are correct on the defective board. All the outputs appear to be positive, so the anodes of the output rectifiers should go negative during the TinySwitch "on" time. A backwards polarity on one of the outputs could cause the power supply to go into overcurrent protection.