# SCR Triggering Questions

#### Thranton

Joined Jan 7, 2020
5
Hey everyone!

I have a very simple question, with it being more of a reinforcement to my knowledge (hopefully).
In the below circuit let's assume the following:
-120vAC 60Hz Input
-A 90 degree firing angle
What are the SCR ratings and values of the circuitry?

Now the course I am taking we have very simple formulas and may not be exact; however, this is what I have been lead to believe..
PIV/PRV Value = 120*1.414 = 169.68v
Edc = 120 * 0.45 = 54v
iLoad = 1000 / 54 = 18.52A

However, would it not be Edc = 27v and iLoad = 37.04A? Due to the firing angle of 90 degrees and half of your positve AC waveform is cutoff.
Thanks!

#### crutschow

Joined Mar 14, 2008
25,398
What's Edc represent?

Do you want peak current or average current for ILoad?

#### Thranton

Joined Jan 7, 2020
5
What's Edc represent?

Do you want peak current or average current for ILoad?
DC Voltage component that the load will see.

#### crutschow

Joined Mar 14, 2008
25,398
DC Voltage component that the load will see.
So the average or the RMS component?

#### Thranton

Joined Jan 7, 2020
5
So the average or the RMS component?
I'm unsure what you mean exactly. With using just the DC Voltage component can we not obtain the DC Current?

Like I said, we are doing very basic introduction into electronics and don't go to deep into it. However I'm in a stalemate with my Prof and classmates because I believe the answer is 27vDC and 37.04A DC. With them stating 54vDC and 18.52A DC.

#### Jony130

Joined Feb 17, 2009
5,181

#### Thranton

Joined Jan 7, 2020
5
Yes, the average voltage across the load will be equal to 27V.

Are you sure?
If I did my math correctly yes I believe that is correct. As we see 27V DC across the purely resistive 1,000w load we should then see P=IE transpose to I=P/E, 1000w/27v = 37.04A.

#### Danko

Joined Nov 22, 2017
989

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