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| Using SCR's as diode's - reverse blocking voltage |
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| adamcord:
In a project I'm working on, I'm thinking of using some beefy SCR's as diodes by tying the anode to the gate (a practice which is usually kosher). I want to use these SCR's due to their high blocking voltage and high current ratings. But since the Gate would be shorted to the Anode, I'd eliminate one of the P-N junctions that might otherwise be there to block the reverse voltage, leaving only one P-N junction, right? So my question is: Does shorting gate to anode on an SCR lower it's reverse blocking capability? (I guess similarly, what if my gate driver conducts between gate-anode during the reverse voltage condition? Again, would this pose a risk of reverse breakdown?) |
| schmitt trigger:
I randomly checked the very first power SCR that I found a Vishay VS-111RKI120PBF. This is a 110 amp device. Its data sheet indicates a VDRM/VRRM of 1200 volts, yet its maximum peak gate voltage is only rated between 20 volt and -10 volts. |
| Zero999:
Dumb question: why not use a diode? To answer the original question. SCRs can normally block the same reverse voltage as their off voltage rating. The only issue is the gate typically has a maximum reverse voltage rating of around 5V. Connect a small diode with a high enough reverse voltage rating in series with the gate and a high value resistor (100k to 1M) between the gate and cathode. You should use a diode, if you don't need a switch. It's much cheaper and easier. |
| T3sl4co1l:
G-K has a low reverse breakdown voltage, like BJT B-E (and for the same reasons). IIRC, there are some SCRs made that way, with high breakdown on both terminals; I forget what special application they serve though. Or maybe it's what a TRIAC is internally, of course pasted together with its complement so the device switches AC without much concern over drive magnitude or sign. Tim |
| wraper:
You should first have tried to measure G-K resistance with multimeter and find that it conducts in both directions with tens to hundreds of Ohm resistance. |
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