Re: Fastest AC Electronic Fuse
- From: Fred Bartoli <fred._canxxxel_this_bartoli@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 15 May 2007 17:27:19 +0200
MooseFET a écrit :
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 LarkinHow about an AC current limiter?
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Mon, 14 May 2007 16:22:01 GMT, D from BC <myrealaddr...@xxxxxxxxx>To break a DC circuit, a pass transistor can be used.. Easy...
wrote:
This is probably an oldie question on here...One of our customers recently asked us to do that. He needs,
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
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
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..
.--------------------------------.
| |
| |
| .---+---. |
| | | | |
.---+ | .-. .-. |
| | | | | | | |
| +-|| .----+ | | | | |
- ->|| | | '-' '-' -
^ +-||--' >| | | ^
| | |-+ +-|<-+---. |
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.
Under normal working conditions (no tripping/limiting) the supply has no current to provide (just biasing the gate), so the average (or even peak) current can be made 1mA without any pb.
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.
Ok, but it doesn't trip, so you'll need some very serious heat sinking under fault conditions.
--
Thanks,
Fred.
.
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