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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I use a SCR for my electric fence. A capacitor is charged to 400-600v and discharged into a coil using the SCR as a switch. I don't have this resistor across the gate/cathode and I don't have any problems. Is it that the stray current manifests itself only with certain SCRs; or, is it a problem if the SCR isn't robust enough? Mine can handle about 50 amps continuous and 500 peak.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
"Probably yes to both". Some SCRs will leak more than others. Some circuits will put more dV/dt across the SCR and hence make false triggering more likely.
It doesn't matter if there's no actual resistor, as long as your gate drive circuit holds the gate down somehow.
Also, the SCR will still work without its gate held down: it just becomes more susceptible to false triggering. If your circuit doesn't do anything to provoke the false triggering, then you'd get away with it.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I just looked at my schematics and I can see that I am using a transitor to drop V+ through a resistor/transistor circuit. When the transistor is off, V+ triggers the gate. This is why I don't have the problem since I am keeping it down as you suggested. Thanks.
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SCR problem
