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Issue with starting VIPer35 flyback

DKotl
Associate

I'm facing a strange situation with VIPer35. First, I bought STEVAL-ISA183V1 evaluation board to got an idea how VIPer35 works. Then I made my first prototype PCB using custom made transformer that also works fine. But when I use the same schematic (but not the same PCB layout) on the PCB that should be the final one and include other circuits, VIPer35 cannot start for completely unknown reason. Yes, it looks like obvious answer that latest PCB layout is not optimal or even has some errors. I tried to even to move components from old PCB to new one but without any success. Finally I've decided to make the same circuit on the breadboard (see below) when wiring is everything the optimal and even that surprisingly to me works!

0690X000006Bw4RQAS.jpg

VIPer35 DRAIN output on problematic PCB is shown below (cyan trace). Yellow trace is output from AUX secondary.

0690X000006Bw4WQAS.png

The circuit schematic is shown below and the same is on the old and new PCB:

0690X000006Bw4bQAC.png

I'm wondering if anyone have any idea why VIPer35 doesn't want to start (it seems to me that he is detecting some fault condition and initiate continuously start up sequence).

Many thanks in advance for any type of answer.

EDIT: I forgot to say that input voltage (DC_BUS) is 100 Vdc, the same is used in all cases (old PCB, "faulty" PCB and breadboard). Also, I'd like to add that for me is the easiest way to simply make another PCB incorporating PCB layout from old working prototype, but in that case I cannot learn what is a source of my problem and it looks more like a pure luck.

1 REPLY 1
DKotl
Associate

After extra few hours and checking all PCB traces related to flyback I found that main secondary line what connected to ground! How embarrassing, that is a short circuit that VIPer35 detected and due to that fault initiate new start up sequence.