On Fri, 14 May 1999 20:15:18 -0700, you wrote:

>At 02:28 PM 5/14/99 -0400, you wrote:
>>Anybody know of a SMT regulator which can handle 45V input, 5V/50mA output?
>> 40V * 50mA = 2W - an awful lot for a tiny PCB to handle.
>>
>>I'm finding very few options in the datasheets.
>>
>>PCB size is a premium. Reliability is SUPER important, component
>>cost/complexity is secondary.
If reliability is important, you don't want to be dissipating 2 watts,
especially in a small space. Use a switcher, e.g. nat. semi. LM2574HV
which takes up to 60V input and comes in a 14 pin SO or 8 pin DIP.
Although it will take more board space for components, you'll save the
space you'd otherwise use on the heatsinking you'd need for a linear
reg, as well as drastically reducing the power draw from the 40V
supply.
At 50mA o/p you should be able to use a pretty small inductor, diode
and caps.