Calculate the power in the load

[tommoturbo]

Homework Statement

for the thyristor circuit calculate the power in the load as a percentage of max power for a firing angle of 45^

Homework Equations

Va=Vm/2pi (1+cos theta)

The Attempt at a Solution

theta=arcos 0.707
45^=arcos 0.707

but as there is no value for VS or Vl i don't know what the ratio between them is to calculate power any advice apreciated


Regards

 

[CEL]

Since what is asked is the relationship of output to input powers, you don't need the voltages.
Remember that the mean power of a periodic wave is the integral through one period of the amplitude squared, divided by the period.
At the input you have a sinusoid, so you can calculate the integral. At the output you have only part of the sinusoid, since during the rest of the cycle you have zero V.
For the amplitude of the output voltage, it is either equal to that of the input voltage, or is this amplitude minus the drop in the device junction.

 

[tommoturbo]

Man you so know your stuff. Thanks for the reply I am going to re do the lesson and take on board what you have said to see if i can figure it out

thanks ian

 

[zztop1000]

So presumably then expressing as a percentage

% = sin45 x 100
= 70.71%

Or am I way off?

 

[n.karthick]

You must also take into consideration that Power is proportional to square of output voltage.