DC-to-DC Power Converter (600V to 5V, 5W)

I'm looking to have a small switchmode 5W DC to DC power converter designed. This power converter needs to take DC inputs in the 400-600V range and output 5V at 1AMP. Size, cost, and reliability are important considerations. Barry Davis' book "DC Power Supplies" indicates that the simplest design is a Transistor Converter that is "Transformer coupled, single transistor" on P. 115 (1981 edition). Basically it uses a single transistor connected to a basic transformer. The base of the transistor Q1 is forward biased by resistors R1 and R2 allowing a small emitter-collector current to flow. This small current through L1 induces a potential in L2, which increases the forward bias on transistor Q1, causing further increase in collector current. This action continues until saturation point is reached and Q1 collector voltage is minimum. At this point the magnetic field collapses, reversing the polarity which turns the transistor off and cuts off the collector current. Once the energy from the collapsing field is spent, R1 and R2 forward bias Q1 and the process repeats itself. If this design was to be selected, the transistor, resistors, transformer and rest of the rectification/filtering circuit would have to be show. An acceptable solution was one that did switch-mode down to <12V and then used a linear regulator to get a smooth 5V. The unit must have input polarity protection and output protection for voltage and current. Material cost of the components should be well under $50. Deliverables: Schematic, Component List, Spice data model (including relevant output PDFs). Open to your feedback on this specification. I'm a computer guy that is a hack EE. ## Deliverables [login to view URL] requirements notice: As originally posted, this bid request does not have complete details. Should a dispute arise and this project go into arbitration "as is", the contract's vagueness might cause it to be interpreted against you, even though you were acting in good-faith. So for your protection, if you are interested in this project, please work-out and document the requirements onsite.