Part Number: UCC2889
Have several questions on the UCC2889.
Using the UCC2889 as the controller in an offline bias supply in dual flyback configuration, similar to app note u-149. In the application, line voltage range is 600 - 1500V. Setting Ron so that minimum current into Ton is greater than 220 uA, but UCC2889 still goes into line voltage fault mode with .5msec off time pulses.
1st question, what is the minimum current into Ton pin for IC to operate and not be in line voltage fault? Should current be sum of startup current and the minimum i (Ton) current for line fault?
2nd question, if the VCC pin is connected to an external voltage, why does the Ton period change compared to when the VCC pin is only connected to a bypass cap?
3rd question, when the controller is running, why would the measured voltage across the output cap in 1st flyback stage be twice the calculated voltage based on the vout = vin*d/(1-d)? The calculated voltage is 85V and the measured voltage is 130V. Let me know what info on the setup is needed to address these questions.