Hello

I am a newbie in flyback design and have created a TNY275 converter circuit, as attached. The converter is intended to produce 17V at 0.4A and 12V at 0.5A.

The transformer core is E25/13/11, originally without a gap. Two 0.11mm isolators are added under the side ferrite pillars.

Primary winding inductance is approximately 3 mH with 110 turns.

Secondary has 6 turns, with 7 turns total (6 included in 7 turns).

The converter is meant to supply a 12V fan (160mA) and a gate driver (17V).

For circuit design, I used PiExpert Online, but I added a 100-ohm resistor between the TVS and UF4007, as PiExpert draws it without a resistor, contrary to datasheets and application notes.

When connecting the fan to contacts 3 and 4 of terminal block J2, output voltages reaches 4v and converter tries to restart . 17V driver is not connected..

What could be the reason of such behavior ?

Is measuring between contacts 4 and 5 of the TNY275 with a multimeter for short circuit is  the only method for detecting chip failure? i dont think that's the reason.