# SCR Calculations

Discussion in 'Homework Help' started by jlacharite, Dec 1, 2007.

1. ### jlacharite Thread Starter New Member

Dec 1, 2007
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Hey everyone, I'm new here so bear with me .... I've got some calculations to do on an SCR firing circuit, I need to determine V_in based on the criteria given in the attachement. I don't know how to solve this circuit, any help is always greatly appreciated. Thanks

J

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Nov 24, 2007
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3. ### jlacharite Thread Starter New Member

Dec 1, 2007
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hmmmm, i read your posts but I didn't see any calculations, Im trying to solve for V_in based on the two resistor values and Vcc @ 15v. How do you apply V_gt, I_gt and I_h to solve for V_in. Thanks again.

4. ### Nara Shikamaru Active Member

Nov 24, 2007
92
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if you have a R680ohms and you need minimum Ig =9mA so
Vin = 9mA* 680ohms = 6.12V

Thats the voltage you need across the gate and the cathode.to activate the scr....i already prove it in my protoboard...and it works....i triggered a 12VDC Fan motor...so i hope its what you nedd....if not then dont hesitate to post again...see ya

5. ### Nara Shikamaru Active Member

Nov 24, 2007
92
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heres an schematic of what i did with your circuit....

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6. ### jlacharite Thread Starter New Member

Dec 1, 2007
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Hey thanks a lot, I wasnt sure.... but that was the value I calculated too (without knowing it ) That really helps, what would the value of Vcc (15v) have to be to turn the SCR off? thanks again!

Jesse