🚀 go-pugleaf

In article <1992Nov13.005442.11157@u.washington.edu> whit@carson.u.washington.edu (John Whitmore) writes:
>In article <1992Nov12.083015.16121@bernina.ethz.ch> schaerer@isi.ethz.ch (Thomas Schaerer) writes:
>
>>If you generate a stabilized voltage with a linear-mode- or switched-
>>mode-power-supply you are never shure if the circuit goes damaged in
>>worst case. About this you must think, because a CD-Player is an
>>expensive device. You shold save your CD-Player with an additional
>>power-zener of about 3.6V and a fast-fuse in serie of it.

>	The zener might be a good idea, but the fuse isn't.  The
>LM317 is internally limited, it NEVER will blow that fuse.

Only as long as the LM317 isn't fried.  Then all bets are off.

>The LM317M would be internally limited at circa 750 mA, and
>would be more dependable than most fuses (as well as faster
>acting).  

Ie: the fuse would be a no-op.  That doesn't make it a BAD idea, just
not necessarily useful.

HOWEVER, while the LM317 may be internally limited to some
current draw, what if the 317 dies (due to a voltage spike etc.) and shorts its
input to its output? The Zener *AND* CD player will fry, because the fuse
controlling this circuit is 10A or more.  The zener won't save your buns
because there's no telling how low the drop resistance is going to be -
likely to be very low.  Unless you have a series resister (as others have
suggested) to get some of the wattage out of the regulator.

The circuit should be fused (at around 1A).  Whether the fuse is in the
input to the 317 or the output is largely irrelevant.  Putting fuses in
both places may not be a "good idea", but it wouldn't be a "bad idea"
either.

Radio installers put additional in-line fuses into car radios installations,
even tho they're already 12V and don't need the step-down.  They have a reason
for that.