duty cycle and sine waves

Jan 23, 2011 11 Replies

I was talking to a guy currently in college who had a lab in which he had to calculate the duty cycle of a sine wave. The professor provided a formula which he didn't remember. What's this about? In a square wave it's proportional to the average voltage, so I thought maybe it's a matter of having a DC component.



Reply in group, but if emailing add one more zero, and remove the last word.

Average voltage in a square wave? I think that would be more appropriate to say average in a sine wave or pulse train.

Avg = 2/Pi; Vp = Peak Voltage; Pk = RMS*1.414;

in any case, Vavg = Vp in a 50% duty square wave (+&-) No difference there.

A pulse train, that is an ON and base line off, no (-)

Vavg = (b/a)*Vp; B = ON Time, A = the time from the start of ON time to the next start of on time.

In a sine wave the average is 2/pi * Vp = 0.636 * Vp

A triangle wave:

Vavg = Vp * .5;

A trapezoid wave

Vavg = A+B / 2* A *Vp

(A) being the base line width and (B) being the Peak width and Vp being the Peak voltage.

Jamie

Sounds meaningless to me. What was the answer?

John

"Duty cycle of a sine wave" works as well as "Blood pressure of a pine tree".

For some specific purpose there may be an _equivalent_ between the duty cycle of a square wave and of a sine wave. Or maybe the prof was thinking 50% (which is oddly obvious). Or something.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html

"Duty cycle of a sine wave" works as well as "Blood pressure of a pine tree".

For some specific purpose there may be an _equivalent_ between the duty cycle of a square wave and of a sine wave. Or maybe the prof was thinking 50% (which is oddly obvious). Or something.

Tim Wescott I usually find it non-productive to guess what the assignment was meant to accomplish. A good deal of the time the assignment was not even perceived correctly by the student. They come here looking for answers but they don't know the question.

Tom

50%, if the DC offset is zero.
You can't fix stupid. You can't even put a band-aid on it, because it's Teflon coated.

"Tom Del Rosso"

** Normally, continuous sine and square waves are bipolar waves with average values of zero - so, unless gated on and off, their duty cycles are both 1 or 100%.

With a rectangular pulse wave that only swings from zero to some value, the duty cycle is proportional to the average value - only becoming 1 when the average and peak values are identical.

If a (continuous) sine wave is offset from zero - it has an average value the same as that offset.

The " duty cycle of a sine wave" is, as my high school maths teacher would have wryly said - " undefined ".

.... Phil

I didn't ask what the answer or the "right" answer were.

Reply in group, but if emailing add one more zero, and remove the last word.

Possibly he got the term mixed up with phase or something. It's even possible the professor did.

Reply in group, but if emailing add one more zero, and remove the last word.

100%. 1-((time@zero)/time(non-zero))x100%

Well, with Maple it can matter. :-)

I am a Druid; I have been washed in the blood of The Tree. ;-)

(That's what you tell people when they comment on the roach clip pendant.)

Cheers! Rich

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