700V nom in 15V and 3.3V out dc-dc converter design

DC-DC Power Converters
1

Hi,

I’m looking for an IC that will enable me to produce a dc-dc converter.
Input <= 700V
output 1 = 15V
output 2 = 3.3V
1.5W total output.
I would prefer isolated outputs but not necessary as the load is common to the 700V bus.

Does anyone have any ideas?

2

buy a module? Otherwise that is a big step down, a flyback would require a 1500V switch give or take. So a 700 to 400 ish step down (buck) followed by a flyback, use the MP power integrations knock offs.

3

SO an MP173A buck to 300 followed by an MP173A flyback to 15 and maybe a 15 to 3.3

4

I’ve done this before with a Texas chip, external FET and transformer about 10 or so years ago and have since left the company and forgotten what chip it was. All I can remember was a resistor provided a kickstart supply of a few uA via a FET and when the auxiliary winding started producing and the supply became self supporting the FET was turned off. The main switching transistor was 1200V and only saw about 100V above rail. A snubber diode and resistor saw to that.