Find the average voltage for a phase angle circuit

Thread Starter


Joined May 14, 2013
Hi all,

Assume I have a triac and I wish to make a light dimmer as below:

Now, assuming I trigger the triac at a given angle my RMS voltage will not equal Vpeak/sqroot(2) anymore. How can I calculate both the average and RMS output voltage in this case?

Last edited:


Joined Mar 31, 2012
Very true. I caught the discrepancy between the title and the description in the post but then looked past the last use of average. Good catch.


Joined Mar 31, 2012
For the purpose I'm quite happy with any of the two, if someone is willing to make the effort explaining.
Okay, if you are quite happy with finding the average, then I'll give that one to you for free. The average is 0 V. Look at your graph. Is it not that case that for every time the voltage is at some positive value that it is later at a negative voltage of the same magnitude? Well, that averages out to zero.