RE: Power Supplies

["Phil Harris" <phil@xxxxxxx>]

> >... it is always OK to use a *REGULATED* PSU in place of an
unregulated
>
> Is that strictly speaking true?

Well given that a question has been asked and an answer requested then much
as I feel it's pointless saying it but "Yes, it is true".

Otherwise I wouldn't have bothered saying it.

> Someone knowing the theory better than I remember it may be able to
> correct the bollox I'm about to come out with here, but...
>
> IIRC, the voltage output from an unregulated supply is actually higher
> than it's rating and varies with load. A device requiring, for
example,
> a 12V regulated supply could use an onboard 12V regulator and an
> external 12V unregulated PSU. The onboard regulator (particularly a
> linear regulator) has a voltage drop of it's own - that's why they get
> hot, so to provide a 12V regulated output, you need at least 12V + the
> regulator drop. With an unregulated supply, that's usually OK because
> the actual voltage is higher. With a regulated supply, the output from
> the device's regulator could well be too low - potentially causing
> problems.

Right ... assuming your circuit *NEEDS* 5v which is generated by an on
board
regulator.

If the on board regulator needs at least 8v to generate 5v and you stuff a
9v unregulated PSU on it or a 9v regulated PSU on it then it'll do the same
job.

Now, the unregulated PSU - if not loaded heavily enough - could have an
output *ABOVE* 9v (considerably perhaps) but if the manufacturer has
specified a 9v unregulated PSU then they should have built in enough
tolerance into the on board regulation that it can cope with the extra
voltage. As long as the manufacturers have actually given the right ratings
then if they say "12v 500mA unregulated" then you can use a 12v
500mA
regulated.

If it needs more than the manufacturer has said then the manufacturer has
fucked up with their ratings.

Phil