Hi Sebi,
You are quite right, 2 ohms was a mistake.
I was thinking 2 volts (at 10 Amps)
and put it wrong without noticing,
so i should have put 0.2 ohms.
As to the dissapation, yes a short limited
to ten amps would give 180 watts,
unless you made the cicuit cut the supply for
an interval, then retry.
I see you have recommended two 3055s to cope
with that presumably.
I reckoned that one would do as the supply
probably would drop from 18v to about 10v in
the event of a short.
Thats ok, two is probably better than one.
I see you have a 0.2 ohms in each leg, which
should give a volt at 5 amps each, by putting two
further stages of gain to the feedback, you have
made quite a sharp step or cut-off to the point
on the 'knee' where the current limit occurs.
However the emitter-base voltage at the point
where the small transistor starts to conduct,
is probably around half a volt (dunno exactly)
So maybe the resistors for that, the 0.2 ohms
could be a bit lower value.
Just by the way, i would have joined the emitters
also on the 2N3055's and used a single resistor
as a current sensor. Making low value resistors
is a pain, making two the same would be awkward.
I usually cut up an old food tin
using household scissors and make a long thin
strip by cutting in a spiral. I find they accept
copper wire soldered on quite readily.
Thats how i make very low values.
For ultra-low values i use Mig Welding wire,
and put ceramic beads on it, and use crimping
to mount it.
Unfortunately at higher currents the heat affects
the resistance, so if its for an indicator it has
to be large so as it doesnt get too hot.
Thank you for the modification to my circuit,
it looks fine to me.
Maybe a small preset could be included as the
small transistor would take very little current
in the base lead?
Maybe as shown here?
What do you think ?
I think it gives a degree of control to the maker,
so the 10 amp point could be set without changing
the low value resisistor too many times.
Regards, John