Hi,
I have to deliver 5V-400V out of 21V-30V, max. 200W, but load covers a very wide range from no load to 750mA (not at 400V). I also have to use standard parts, no custom transformers!!
After lot of investigation, discussion and simulation cycles I came up with a modular design. 4 identical moduls, each of them produce 1.5V to 100V, 50W. The outputs were connected in series to get the sum.
And I used a 4-phase switching schema to get lower ripple at the input.
Now I start working with the real thing, but:
Switching frequency is about 1.8Mhz instead on 150kHz?? In the first step I used only one module free running to test the basic functionality of a module.
The first module dies within minutes, but the second module I have produced let make me some measurements, I included togethet with the schematics. The Res pin told me, that the module enters some Kind of protection mode. Ok.
My questions: Any idea to get the switching frequency down to the value I calculated with? Yes, the RT is correct and the Connection is correct, so no Problem during PCB design or manufacturing (broken wire).
How can I find out, why the chip enters protection mode? But maybe this is a result of the wrong switching frequency.
Thanks a lot for helping.
With best regrads
Gerhard