[sdiy] circuit protection question

[megaohm]

On Tue, Dec 14, 2010 at 9:02 AM,  <blacet at blacet.com> wrote:
>
> Why don't any other companies use this? Too cheap? I dunno.
>
> People WILL plug things in backwards, it's guaranteed.
>
> John "the Guru" Blacet
>


John and all,

I use your technique on all my modules.
I've come up with a few questions I'm wondering about:

It seems to me that the reverse diodes are doing the protective work
for the module. What are the polyfuses doing? I'm figuring that they
protect the PSU? I wondered if they protected the circuit in different
ways. So I tried an experiment and put an op amp in backwards. It
smoked.
I'm also a bit foggy on the value of the polyfuse and figure it
depends on the current draw of the particular module. Looking at a
Bourns data sheet, generally, the lower the trip point the higher the
resistance of the polyfuse in it's normal operating state. Doesn't
adding resistance in series with the power lines make them less stiff?

Semi related:
How about if someone plugs the power cable in and they are off to the
side one pin?
Say...+15V header is now connected to PSU ground and PSU ground and
-15V are connected to the header ground and the -15V header pin is
unconnected (the power connector is shifted one over where it should
be).

Your article convinced me to use your technique years ago. I'm just a
bit embarrassed that I don't know everything that is going on with
this.

p.