I would like to build an off-line switcher based on the TinySwitch4 family. It implies f=132kHz. Then, VOUT=15V@0.5A. V_IN_MIN=120V, V_IN_MAX=374V (85-265VAC). I typed these values into the Schmidt's calculator to get a rough estimate:
L_PRI=7.36mH. OK, so now use PI Expert Online, provided by the manufacturer:
Automatic design mode => TNY285DG, an EE13 core with L_PRI=1276uH,
0.25mm air gap. Almost 6 times lower than the previous value, okaaay...Now, I don't like the proposed IC and replace it with a bit stronger TNY287DG => L_PRI=497uH and a warning that the air gap is too long (0.745mm, yeah, right...).
The primary inductances differ just 15 times. What's going on here?
Best regards, Piotr