In Reply to: DC/DC Converter posted by Francis LHeureux on 12/17/02 at 11:54 AM:
A buck converter is probably the topology you'll want to use, assuming you don't need galvanic isolation between input and output.
I expect you will need to use an external switching MOSFET given that input voltage range. The 85V input will be much too high for switchmode regulator I.C.s with a built-in switching transistor.
There's a lot of controller I.C.s around that will drive an external MOSFET - try Linear Technology, Maxim, Texas Instruments, National Semiconductor, Micrel . . . Some websites organize the range of controller I.C.s according to the topology you intend to implement (buck, boost, flyback, etc); that helps to narrow down the choice. The datasheets and application notes nearly always have examples of circuits, so you might well find just what you need there - or at least hints on what MOSFET and other components to use with the controller I.C.
Some I.C.s offer extra features such as a logic-level shutdown input, soft-start, or current-limit setting using an external resistor. But one characteristic that you will need to look at is the operating frequency. Controllers offering a higher switching frequency will allow you to choose smaller inductors and capacitors, allowing the regulator to be made physically smaller - but the downside is, the efficiency tends to get lower because the switching losses increase with frequency.
Hope these hints are useful.