LNK6775K problem/solution

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Hello everyone on the forum.
I have one problem, and it would be good if there was a solution to this.
I did a design where I use the LNK6775K and everything works fine in the 85Vac to 265Vac range.
Specifically, I have now received a request from a customer that they need to go down with an input voltage of up to 40Vac.
Is there a solution for the same chip, or do I have to change the whole design?
Thanks in advance, Aleksandar

Hi Aleksandar,

The output power and voltage was not specified. The minimum voltage required on the drain at start-up is 50V to charge the BP capacitor. You need to re-design the transformer (Lmag) and bias winding turns to deliver the required power at minimum input voltage. Please monitor thermals due to additional loss.

Hi and thanks for your reply.
I don't have any information about the transformer from the manufacturer.
It was specifically designed for this chip and this schematic.
With best regards, Aleksandar.

TitleSize
LN6775K.pdf996.65 KB

Hi,

If you are looking for magnetics design support, use online tool on PI website.
https://ac-dc.power.com/design-support/pi-expert/pi-expert-online/

Regards
csbabu