# SCR switch

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#### slingsrat

##### New Member
I need a very simple circuit diagram for a SCR switch. I need it so when a circuit is broken power flows through a secondary circuit.

All the scr switch diagrams I've found work with an already broken circuit and connecting it will trigger the scr.

Basically I want a circuit that will trigger a solenoid when a circuit is broken. I used an scr design in the past but have forgotten it!

Thanks for any help.

#### ericgibbs

##### Well-Known Member
I need a very simple circuit diagram for a SCR switch. I need it so when a circuit is broken power flows through a secondary circuit.

All the scr switch diagrams I've found work with an already broken circuit and connecting it will trigger the scr.

Basically I want a circuit that will trigger a solenoid when a circuit is broken. I used an scr design in the past but have forgotten it!

Thanks for any help.
hi,
Connect the normally closed switch across the SCR gate and Cathode, connect a resistor from the Anode to the gate.

When the switch opens the Gate will be triggered, choose a resistor with of the highest value that will trigger the SCR. Remember resistor wattage.

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#### slingsrat

##### New Member
So this is correct then?

pressing the switch will power the solenoid?

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#### ericgibbs

##### Well-Known Member
So this is correct then?

pressing the switch will power the solenoid?
DONT connect it like that or it will fail!.

Ill post a sketch

#### ericgibbs

##### Well-Known Member
hi,
Look at this image.

Once triggered, the SCR will remain ON until +V is removed.

As you havn't said which type of SCR or what the +V voltage is, you will have to calculate the R value.

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#### slingsrat

##### New Member
Thanks for that. How do i calculate R? I'm using a C106D at 12V.

#### ericgibbs

##### Well-Known Member
Thanks for that. How do i calculate R? I'm using a C106D at 12V.
hi,
Looking at the datasheet, a 1.5K or 2.2K resistor should trigger OK.
0.125W or 0.25Watt..

To switch OFF the scr, place a normally open switch across anode to cathode [ short out the SCR when pressed].

OK.?

#### slingsrat

##### New Member
Thanks for that, I'll give it a go.

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