**Part Number:**UCC28063

Hello,

I'm working with the demo board UCC28063EVM-723, where I havee replaced the inductors form factor, from toroid to PQ26/20 core, with step-gap to emulate the L Vs. I curve, therefore the indutor has 430uH @0A and 350uH @6A, the Np/Ns=7.8.

When the AC input voltage rise above 260V, so the rectified peak voltage is next to the VDC, and therefore the positive voltage across the inductor become the lowest, even the voltage on Ns become too low the assure the proper zero current detecting and the mosfet is turned on even the current does not reached zero.

I have changed the ZCD resistor down to 10k but the problem still remain.

How I can solve this problem? it is possible to pull-up the ZCD pins to the ref voltage by a few hundred kilo ohm resistor?

The schematic I'm using is exactly the same of the demoboard.

Using i nuovi induttori e mosfet STF18N60M2 the efficiency now is changed from 91% to 95% at 90VAC, the inductor temperature are lower by 20-30°C comparing to the original inductors and the mosfet pratically can works without heatsink.

I'm looking forward for your response.

BR/Roberto Volpini