David Duffy (AVD) wrote:
> I have a product that would normally be used with a DC input of 12V -
> 36V.  It uses an LM2575 switching regulator to derive the 5V rail (@
> few 100 mA) for a PIC and other chips.
>
> The lowest of the maximum Vdd ratings on these chips is 6V.

Which is irrelevant since you apparently want the circuit to still work
while powered from this alternate source.  If this circuit includes a PIC,
the maximum *operating* voltage is probably 5.5V.

> There is
> a situation where some customers may need to power the board from 5V.

You didn't say anything about the relative importance of cost, efficiency,
user hassles, etc.

One possibility is to use a different switcher that can take the full range
of 5 (or even less) to 36 volts in and produce the 5V for the circuit.  A
switcher that can go both up and down from its input is a bit more
complicated and usually a little less efficient than a dedicated buck.
However, it would make the whole system simpler for the end user, more idio=
t
proof, possibly simpler to test in production, and fewer field issues.
Depending on the sophistication of the end users, this may be the cheapest
alternative.  Again, these are all tradeoffs for which you haven't given us
any guidance.


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