Help:1200VDC switching through SCR

[abicash]

Hello

I am about to design a trigger circuit for an SCR.
The i/p voltage is 1200Vdc @500mA

The SCR is triggered for a few microseconds, and a current flows from 1200Vdc to a coupling transformer and through the SCR.

My question is regarding optical triggering of the SCR (or pulse transformer if it works)
Any learned member wish to help me understand how this is done?

I saw a few optoisolators but none have a voltage rating of above 600vdc.

Regards

 

[k7elp60]

I think you may be looking for the wrong term. Some manufacters call it the in/out isolation voltage. I have some that list this value at 5300VAC(rms).
Are you sure you want to use a SCR?, as once you turn it on the only way to turn it off is by removing the DC voltage.

 

[abicash]

Thanks for replying.

Yes you are right. I want isolation voltage to be that much.
The scr decays the charge across a capacitor so it commutates on its own.
Can u recommend any optos having higher isolation voltage?

 

[ronsimpson]

go to digikey.com
type "optoisolator" in the search window
I picked "**broken link removed**"
Now you can pick perimeters like 5000 volts.

 

[ronv]

Doesn't the transformer give you isolation?

 

[abicash]

Its used to sink a 1200v,500mA DC current through the primary of the transformer through the scr.
The secondary is used to switch another device.
Now the primary voltage needs to be fed back to my MCU, hence the need of isolation.
Thanks to Ronsimpson . 4n35 sounds good

 

[ronsimpson]

1200v is large.
Is the supply 1200 or more likely the kick back from the transformer is 1200V?

 

[abicash]

Yes its a 1200v supply.
Eventually to trigger an ignitron

 

[moffy]

Use a pulse transformer and have a gate degenerating resistor, I use 47 ohm to guard against false triggering.

 

[abicash]

Hi
After going through a lot of research papers and documents, i replaced the SCR with IGBTs and drew this attached schematic.
The idea is to trigger 2 nos ignitrons.
Do i need to create another thread for this or can someone comment on the scheme?

 

[moffy]

With the 10k/5.1k resistors R6/R1 driving the gate, turn on and off will be pretty slow. Is that deliberate? Why not just drive them directly from a +15v supply?
That is some deadly circuit, 1uF at 3000V!