My apologies that is a typo in the schematic it should read L6385E. I must change that

Heres a link to it's data sheet if anyone wants to look.
http://www.st.com/web/en/resource/technical/document/datasheet/CD00169717.pdf

By body diodes you mean the body diodes on the Mosfets? The though had crossed my mind allright. I probably have a few MUR460 diodes so I might just add them to the circuit. I think that should be OK then?
Thanks for your help.

 

Yes, the body diodes.

 

Hi, So I got the first part of this circuit working which was 30V DC into S1 and S2 which work as a two switch forward convertor and depending on the duty ratio of those two switches roughly 7V across a 40 ohm resistor in place of Vb in the diagram below, S3 and S4 were off in that mode and the MUR460 diodes rectified the output of the transformer.

Now for the second part, S1 and S2 are off and S3 and S4 work in complementary mode as a boost convertor, when I connect up the circuit and turn on the power supply, Chip 1 (STL6385E) heats up straight away and and the magic smoke appears.
The power supply ground and the chip grounds are connected together. Any ideas? I'll add more details later..I have to head out the door now!