I'm encountering a design issue with my switch-mode power supply  that utilizes the InnoSwitch3-EP (INN3678C). The SMPS powers up and outputs the required V when the input voltage is  133VAC or higher, under full load conditions (drawing 3A), but I'm facing problems when trying to achieve reliable operation within a lower input voltage range of 85VAC to 110VAC at full load. 



When I change the input to a lower voltage e.g 100VAC it does not power up.  Note: The input type was selected as Universal in the PI Expert. 

 

Things I have tried.

• Tried different combination of undervoltage sense resistor, still no result the minimum stayed around 130VAC.
• Shorted the undervoltage pin to source so it disables it. The minimum input AC at full load 3A was 150VAC.
• Measured across C8 on the primary bias and I can see it was fluctuating until the input AC reached ~130VAC. Then It was 15V
  
   

Any insights, suggestions, or advice related to this  would be greatly appreciated.