I'm consider to design power supply with TOP272EN. Since audio amplifier may consume over 400W, most likely it will be optimal to use 2xTOP272EN to power each channel separately.
1) Input, - universal AC 100-240VAC
2) Output (2 x TOP272EN) - 2 x 429V / 459V / 500V / 300mA (selectable by switch), 2 x 6.3V / 8A, 2 x 100V / 50mA
3) Lowest ripple and HF noise possible.
There are some tips and questions which come into my mind when I took a quick look at TOPSwitch datasheet.
1) Transformer construction mentions air gap. Is air gap necessary? Is there any DC current passing through transformer winding(s)?
2) I'm consider to use amorphous or nanocrystalline tape wound toroid core instead of EI ferrite in order to reduce size, leakage inductance and HF noise. Any thoughts?
BTW, is it necessary to ground metal toroid core?
3) Design Example Report 218. There as ia capacitor #2 - 2.2nF 250VAC, connecting transformer primary pin 1 and secondary pin 10/11. What is the purpose of this capacitor?
Additionally, there is a bug in DER-218 schematic - pin 4 of transforer connected to nowhere. This is probably PDF conversion glitch.
4) In order to get 500V output voltage - 2 stacked full bridge rectifiers, reducing voltage requrements to diodes. For example, 250V + selectable 179V / 209V / 250V. Are 600V diodes will be enough for this purpose?
I found this tip on the forum (thread was discussing 400V Output PS):
The diode has to withstand the output voltage plus the additional reverse voltage induced when the primary side MOSFET turns on. If the transformer turns ratio (primary: secondary) is 1:3 then for a 375 V bus voltage (265 x sqrt 2) the addition diode stress is 1125 V giving diode minimum diode rating of 1125+400=1525 V.
Is that correct or misleading statement?
5) What happens if one by mistake reverses polarity of primary or secondary? On prototyping stage, everything is possible. Is TOP272EN design crash proof? I meat reverse start and end of winding, not completely swap connection.
6) Does it makes sense to replace L1 DC choke with common mode choke in order to reduce HF noise?
7) What is the best material for EMI / FRI common mode chokes - ferrite or powdered Fe-based nanocrystalline?
8) 5 - 10 sec. soft startup (gradual increase of output voltage) - is it somehow possible?
Thanks in advance for any suggestion(s).