# Find the average voltage for a phase angle circuit

Discussion in 'Homework Help' started by cts_casemod, Nov 16, 2014.

1. ### cts_casemod Thread Starter Member

May 14, 2013
35
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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: Nov 16, 2014
2. ### WBahn Moderator

Mar 31, 2012
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4,701
The same what that the Vpeak/sqrt(2) formula was found -- by applying the definition of RMS voltage.

3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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Pedantry on terminology. Probably unwise to interchange RMS with average.

4. ### WBahn Moderator

Mar 31, 2012
17,458
4,701
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.

5. ### cts_casemod Thread Starter Member

May 14, 2013
35
0
And that will be...?

6. ### cts_casemod Thread Starter Member

May 14, 2013
35
0
For the purpose I'm quite happy with any of the two, if someone is willing to make the effort explaining.

Oct 9, 2007
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8. ### WBahn Moderator

Mar 31, 2012
17,458
4,701
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.

9. ### WBahn Moderator

Mar 31, 2012
17,458
4,701
What is the definition of RMS voltage?