High power DC - DC converter

[ykurban]

Is there any DC DC converter commercially avaible with this specs

input voltage   : 12vdc
output voltage : minimum 250vdc -or up to 500 vdc
outout power  : >= 250 w

[MagicSmoker]

Are you looking for a self-contained device (ie - in a box with input/output terminals, safety agency approval, EMC certification, etc.), or are you looking to hack something together? If the latter then look inside almost any automotive 12V to 220VAC inverter; at the 250W power level there is usually a two-switch forward stage that boosts and isolates the nominal 12V input to around 310V to 350V before an H-bridge chops it into 220VAC to 240VAC RMS.

[ykurban]

i tried 12vdc to 220vac car invertes but, im more looking something lie self-contained device.

[tszaboo]

I was researching something similar to a one off project. I ended up a with this setup :
Bunch of step up isolated converter, connected in series. Not nice, very expensive, but works. Put a reverse diode on each output, some few Kohm resistor to dump the power when off, and capacitors separetaly. You dont need the capacitor if it is a complete power supply, but I would still put there the diode.