Solution Finder

Adding a balance or cancelation winding to a transformer

Posted by: Tony Costa on Wed, 09/29/2021


I designing a 10W SMPS with the TNY286 and would like to add a cancelation winding to my transformer to mitigtate any potential common mode noise problems.  I came across this PI design note,, and am interested in implementing this.  But I don't understand the solution presented in this document.  Can someone please explain and provide details like number of turns calculation for the "cancellation" and balance shield" windings. 




Submitted by PI-Jedidiah on Mon, 10/11/2021

Hi Tony,

There's no specific turns calculation for cancellation and balance shield windings. You have to do several iterations to check the effect of either increasing or decreasing the number of turns of your shield windings. For starting point, you may use 1/2 number of turns in 1st layer of primary winding for cancellation winding. Also, you may start to use same number of turns for 1st secondary winding for balance shield winding.