Flyback Control using UC3844

#1

Hi All,

I am trying to control Flyback Control using UC 3844. I am using app note for the same. However, when simulating the circuit. The sytem only works fine if both the input and output are on same ground. How can we simulate with different grounds since Flyback converter is supposed to give isolated output

#2

Please post your schematic. It is likely that something odd is happening. It could be that you are using the “node to ground” voltage probes instead of the node to node probes when your secondary is isolated. image .

If you are using the node to ground then you will get garbage waveforms when the secondary is isolated.

#3

Schematic
Schematic.png2050×846 16.4 KB

I have attached the schematic. The system is operating fine if both output and input grounds are same. But if i remove ground of output side to make it as an isolated supply , it doesnt work.

#4

image
image.png842×605 39.8 KB
if you remove this ground your voltage feedback is no longer referenced properly and it won’t work. You need to use the isolating voltage sense element. image

Does that make sense?