D from BC said:
Doh!
Hopefully, I won't need any fuses if I cook up an AC limiter/breaker
based on posts in this thread.
I've cooked up a 2 op amp latchup circuit for inside the bridge.
It has massive positive feedback for latch up.
This allows a cool 0.1ohm current sense resistor.
Thermal stability and precision current trip point are also benefits.
Faster speed can be accomplished with high speed comparators.
I've come up with a single IC circuit with no discrete small signal
transistors.
D from BC
Don't knock the discrete transistor approach.
To turn the Mosfet off fast you need to pull the gate charge out, which
takes
relatively high peak currents. The discretes give you this capability.
Slightly off topic: when I were but a slip 'o a lad, I worked for a summer
in a test lab. One fun bit was helping a Real Engineer test a circuit
breaker - a 1A model was the target. First we checked that it tripped
properly at the nomial current, then came the fun bit.
A circuit breaker has to break the circuit, especially under fault
conditions. That means you have to check that it does so under
not just reasonable conditions, but also unreasonable ones.
The Real Engineer's test area was surrounded by a metal cage,
and in back a door led into a vault which had double walls, and
was filled with a couple of tons of heavy duty batteries, switchgear
and massive bussbars through the walls into the test area.
We spent a morning making sure the batteries were all fully charged,
and connecting up the poor little unsuspecting Consumer Unit
1A circuit breaker in a safety chamber. We then retired to a "shack"
within the test area, and threw the switch. ISTR the current was
4000A, and blew the circuit breaker to pieces. The result was
a "pass" as it broke the circuit ;-)
Regards
Ian
