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Old 05-07-2013, 08:13 PM   #8
NN5I
Carl, nn5i
 
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Join Date: Sep 2011
Location: Tallahassee, FL
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Quote:
Originally Posted by Radio View Post
Really? I always thought RMS = pp x .707 or if you wish, pp/1.417 or there abouts.
But you did read the scope right.



And here's where I got all this stuff:

http://en.wikipedia.org/wiki/Operational_amplifier

Refreshing the ol' brain for a test I will need to take to get a promotion at work.
RMS for a sinusoid is 0.707 times the peak-to-peak, which in this case is .707 times 2v, not 1v, so the RMS for this sinusoid is about 1.414 volts, and I was off by a factor of two. Oops, I used the peak value instead of the peak-to-peak.

This square wave, which is not a sinusoid, is always either 12.5v positive or 12.5v negative; so it has the same heating effect on a resistor as 12.5v dc. Its RMS value is 12.5v because it's a square wave and not a sinusoid.

Back when I made my living as a circuit design engineer, I must have designed hundreds of circuits using 741 op-amps and their predecessor the Fairchild 709 -- both created by my personal hero of the time, Robert J Widlar, and his sidekick James N Giles. Your Wiki link brought back memories. Widlar left Fairchild for National Semiconductor, demanded a piece of the action, and got stinkin' rich when NSC took the market away from Fairchild.
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