Re: Fastest AC Electronic Fuse
- From: MooseFET <kensmith@xxxxxxxxx>
- Date: 15 May 2007 07:32:50 -0700
On May 14, 11:54 pm, Fred Bartoli
<fred._canxxxel_this_bartoli@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
D from BC a écrit :
On Mon, 14 May 2007 11:40:08 -0700, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr...@xxxxxxxxx>
wrote:
This is probably an oldie question on here...
I'd like to break the AC "hot" if there's too much AC current.
This would be due to a short or ground fault.
Or....
Shunting the load to burn a fuse on the AC line would be ok too..
I'm afraid that a fuse maybe too slow to protect the electronics from
burn out..
Let's say the electronics I'm protecting cannot withstand 1.5x
overcurrent.
What's faster than a fuse on a AC line?
Details
Load: The load on the line is not a transformer and is not inductive.
Current draw: 2Amps
Line voltage: 240Vrms, 60Hz
Surge rate: guessing 45Amps in 1uS
Rule: 1/4watt current sense resistor.
The load circuit has a power bridge rectifier.
Maybe I could modify the bridge with transistors to interrupt the
surge current?
D from BC
One of our customers recently asked us to do that. He needs,
basically, an SSR that also acts as a programmable circuit breaker
*and* a current limiter. He needs to simulate cable faults and switch
power circuits without exploding anything. We've been scribbling
circuits for days, and it's non-trivial. We just a few minutes ago
finished whiteboarding the design of a breadboard pcb so we can test
the dynamics.
John
To break a DC circuit, a pass transistor can be used.. Easy...
But breaking 240V AC...huhhh.. :(
I might look at using a little transformer to sense a current surge
and have that fire a shunt circuit until a fuse blows..
How about an AC current limiter?
.--------------------------------.
| |
| |
| .---+---. |
| | | | |
.---+ | .-. .-. |
| | | | | | | |
| +-|| .----+ | | | | |
- ->|| | | '-' '-' -
^ +-||--' >| | | ^
| | |-+ +-|<-+---. |
o-----+ +--. /| | | | | +-------o
| .-. | | | | | | |
- | | | ___ | |/ --- --- z -
^ | | '-|___|-+-| --- --- A ^
| '-' |> | | | |
AC in | | | | | | | AC out
'---+--------------+---+----|---+----'
.-.
| |
| |
'-'
|
o---------------------------------+----------------o
I worry a bit about the forward current on the Zener. I guess that
with the values put in, the current will be small enough.
Also if you don't mind a little leakage:
Modified version:
.--------------------------------.
| |
| |
| .---. |
+----------. | | |
.---+ | | .-. |
| | | | | | |
| +-|| .--------+ | | |
- ->|| | | | '-' -
^ +-||--' - | | ^
| | | | | +-|<-+---. |
o-----+ +--. | | | | | | +-------o
| .-. | - | | | | |
- | | | ___ | |/ | | | -
^ | | '-|___|-+-| --- --- z ^
| '-' |> --- --- A |
AC in | | | | | | | AC out
'---+--------------+---+----|---+----'
.-.
| |
| |
'-'
|
o---------------------------------+----------------o
It relies on the device capacitances to hold the NPN on through the
zero crossing.
.
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