# Find the average voltage for a phase angle circuit

#### cts_casemod

Joined May 14, 2013
35
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?

Regards

Last edited:

#### WBahn

Joined Mar 31, 2012
26,398
The same what that the Vpeak/sqrt(2) formula was found -- by applying the definition of RMS voltage.

#### t_n_k

Joined Mar 6, 2009
5,455
How can I calculate the average output voltage in this case?
Pedantry on terminology. Probably unwise to interchange RMS with average.

#### WBahn

Joined Mar 31, 2012
26,398
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.

#### cts_casemod

Joined May 14, 2013
35
The same what that the Vpeak/sqrt(2) formula was found -- by applying the definition of RMS voltage.
And that will be...?

#### cts_casemod

Joined May 14, 2013
35
Pedantry on terminology. Probably unwise to interchange RMS with average.
For the purpose I'm quite happy with any of the two, if someone is willing to make the effort explaining.

#### WBahn

Joined Mar 31, 2012
26,398
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.

#### WBahn

Joined Mar 31, 2012
26,398