I used PI expert to design a Link Switch CV design. The results are in the attached file. I laid out a board and have a prototype of this design. The problem I am having after initial testing is that the 3.3V output is not regulating well at all. Under light load (5mA) the output is at 3.2V. The designed load should be 0.4A. As soon the load starts to increase the voltage begins to drop. At 20mA it is 2.93V, 70mA it is 2.54V, 200mA it is 2.20V, and 400mA it is a very wavey 2.23V. The voltages here are the mean, there are spikes of 3.2V when the control chip is pulsing the primary (every 180uS @ 200mA load there are 2 or 3 pulses).
The 12V output is lightly loaded during this test, 10mA. If I load the 12V only, it regulates better. It constantly keeps a mean voltage of basically 12V under all load conditions, with ripple up to 1V depending on load. During the 12V loading the 3.3V output increases to a maximum voltage of 4.15V mean (4.5V peak).
I cannot use this 3.3V supply for its intended purpose as it is. Should I just create a single supply of 12V and use a separate regulator to get 3.3V? I thought I could save some components by building a dual voltage supply. Any advice would be appreciated.