Electronics > Projects, Designs, and Technical Stuff
Using SCR's as diode's - reverse blocking voltage
wraper:
--- Quote from: T3sl4co1l on February 12, 2020, 04:40:53 pm ---G-K has a low reverse breakdown voltage
--- End quote ---
Around 0V to be exact, it's simply conductive both ways.
Zero999:
--- Quote from: wraper on February 12, 2020, 04:55:20 pm ---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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It depends on the SCR. K-G is a diode connection. In small, sensitive gate SCRs it should measure the same as a diode, using a multimeter. Larger non-sensitive gate SCRs have a gate-cathode resistor built-in.
wraper:
--- Quote from: Zero999 on February 12, 2020, 06:16:35 pm ---Larger non-sensitive gate SCRs have a gate-cathode resistor built-in.
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It's not a built-in resistor, it's an intrinsic feature of SCR. Small SCR may have this resistance on higher side but it's still there. And this resistance may easily vary 5+ times times within single part number (and so does gate sensitivity).
NiHaoMike:
--- Quote from: Zero999 on February 12, 2020, 04:39:59 pm ---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.
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I'm assuming he has the SCR lying around but not any large diodes and that it's for a temporary application. In that case, add a series diode and resistor combination from anode to gate to trigger it.
Circlotron:
--- Quote from: NiHaoMike on February 13, 2020, 12:16:31 am ---I'm assuming he has the SCR lying around but not any large diodes and that it's for a temporary application. In that case, add a series diode and resistor combination from anode to gate to trigger it.
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That resistor in series with the diode should be something like 10-50 ohms . The value is not critical, just that this lower value makes sure the SCR turns on before the forward voltage gets too high, and the on-stage voltage drop does not give too high a continuous gate current like it would if there was no resistor at all.
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