# Firing SCR Bridge rectifier at 90 degree & beyond

Discussion in 'General Electronics Chat' started by whywhy68, Aug 21, 2008.

1. ### whywhy68 Thread Starter Member

Jun 11, 2008
13
0
as i knw the power factor is defined as

PF = [I(rms, fundmental)/ I rms ] * cos (alpha)

suppose the alpha = 90 degree wouldn't the PF be 0 based on the above formula.

suppose alpha > 90 degree, wouldn't the PF be negative?

can anyone advise me on the calculations of PF for alpha having angle of 90 degree and beyond.

Thanks

2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
I can't say anything about the power factor, but I am curious what that has to do with triggering SCR's at phase angles beyond 90. As far as I am aware, as long as the SCR is forward biased, it will go into conduction with a gate pulse.

3. ### whywhy68 Thread Starter Member

Jun 11, 2008
13
0

yes i understand your pt.. but firing the SCR at high angle gives low voltage.. & i am required to find the power factor at low voltage without changing the amplitude of the input source.. That means by firing the thyristor beyond 90 degree but lesser than 180 degree i will be able to get a low voltage output..

anyway in which i can calculate the power factor for SCR bridge at high angle triggering? Needed on that for my project.