Hi Rajyavardhan,

I am having difficulties to understand the problem.

You are saying : power limiting due to increase on ovp at bias winding.
But.. in 'power limitation' usually the output voltage or output current gets reduced.
OVP however, is triggered by increased output voltage, not reduced one.

Targeting 12V output the bias and output turns have to be roughly the same. If that is the case, to trigger the bias OVP the output must be very high - means no regulation.

I need more information to debug. Please sent you PIExpert design (or link to it ) to piexpert@power.com. Also the actual schematic (if different) and load/mains condition when the problem appears.

Best Regards,

As soon As i increase load the Bias winding voltage gets increased & which tends towards ovp shutdown at no load it is 9 V avg.at 7 W output load.

Thank you Rajyavardhan,

for the schematics and explanation.
Please provide the actual transformer constructruction and the design file .

72 W SMPS
VIN = 230 VAC
VOUT = 12 V ,IOUT = 6 A
VDS = 581 V
BIAS VLTG = 6.75 V (AT NO LOAD) , BIAS VLTG = 16.01 V (AT FULL LOAD)
Lp = 352.24 UH , Npri = 31 TURNS , NBIAS = 2 T , Nsec = 3 T
I SOLVED ISSUE WITH THESE CONFIGURATION, BUT ISSUE IS MY NO LOAD VOLTAGE IS 16 V WHICH IS NOT DESIRABLE. I HAVE ADDED PRELOAD CKT IT IS LIMITING MY NO LOAD TO 12.678 V, BUT IS THERE ANY OTHER WAY TO CONTROLLED IT.
IS I HAVE TO INCREASE BIAS TURNS ?
SO THAT MY NO LOAD VLTG AT BIAS WILL GO ABOVE 9V.

Here are the answers:

https://ac-dc.power.com/forum/low-power-design/topswitch-jx-and-auxiliary-coil-no-load/