Salve Lipn*,

>Edson, something tells me that a resistor is required between each SCR gate
>and its catode, to make sure there will be low voltage (zero) at the gate
>when the photocoupler is off, since right now it seems to be floatting and
>it "can" make the SCR goes crazy, unexpected operation and such.
>
yes, I was already thinking about this. I think I'll try it.

>The residual charge over the photo coupler could be enough to trigger the
>SCR for a very fast and small time, enough to launch the mess.
>
As I want maximum reliability it's worth the effort.

>I understand the 100nF capacitor could transfer something, but now enouth
>to light a 20W bulb, right?
>
The 100nF capacitor IS transfering some energy. Actually, my prototype
have 9 taps so I have 9x100nF capacitors transfering energy. I would
like to avoid using 9 snubbers so I'm thinking if it would be feasible
to take the snubbers off and using some other arrangement to improve gating.

There's a circuit sketch on "Static Voltage Regulator (SVR)   Ride
Through Support For Semiconductor Facilities" (google for it. It's an
interesting reading) with only a snubber across a transformer (no
snubbers across the SCRs) and I'm thinking if it's only a circuit
simplification or if it could work this way.

Maybe a resistor (4K7 is enough?) between each SCR's gate and cathode
would eliminate the necessity for a snubber as the on switching time
doesn't seens to be a very critical thing on this project.

Best regards,

Brusque

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Edson Brusque                 C.I.Tronics Lighting Designers Ltda
Research and Development               Blumenau  -  SC  -  Brazil
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