Please see the attached file to review my design for a 5V, 2A and 12V, 0.3A dual output offline converter
based on the TNY280PN. I am using the PIExpert software to generate the design.
There are two 2MegaOhm resistors from the DC bus to the EN/UV pin shown in the PIExpert design.
Keeping these resistors (as shown in the PIExpert design) causes the TNY280PN to do something
un-understandable. There is no proper switching seen at the Drain pin. Only some damped oscillations that
repeat with a 56KHz frequency.
On removing these resistors, the drain shows switching and the output voltage also builds-up correctly.
Obviously, I like the second result (the one without the resistor). However, I am now confused if the
line sense resistors should be modified in value or should they just be disconnected (as they are now).
Also, keeping the the line resistors disconnected will mean the undervoltage lockout feature cannot