Other Parts Discussed in Thread: TL431, UCC256302
Hi , I modified PMP21683 48V 500W design to 24V version ; LLC Xformer turns ration from original 29:3:7:7:2 to 32:3:4:4:2 ,
Primary inductance stay 230uH without change , additional leakage inductor stay no change too, 10uH ;
of course I also adjust R128 383K lower to get 25.5V output. But strange thing to me , pls see photo shown below.
Pls not even though I switch components each other ( UCC256302, TL431, photo coupler , and LLC transformer and Lk inductor) ,
the abnormal one is always on PCB #B . and both pcb own the same R138 , R133/R136 , and every chip R chip C components.
samples build at same lot. seems every thing the same , but PCBA # A is normal , but PCB #B not. so confused, can you guide me some
possible reasons ? thanks!
