[R-390] Ballastubes (was inrush current limiters)

[Jim Shorney]

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On Tue, 24 Dec 2002 19:43:32 -0600, Cecil Acuff wrote:

>        I agree with you Drew.....a half wave rectified sine wave has the
>same peak value as a the original sine wave....but not the same peak to peak
>value.  The peak value of a sine wave is half it's peak to peak value.  You
>ended up with the peak value by stripping off the top half of the wave form
>with the half wave rectifier.  So you have satisfied the first part of the
>formula...you divided by 2. Now you multiply by .707 and you have RMS.


The output of a half-wave rectifier is not a sine wave - it is a pulse
waveform with a peak-to-peak value of .5 (one half) the peak-to-peak
value of the input sine wave.  The .707 formula does not apply to pulse
waveforms, or any harmonically distorted sine wave for that matter. 
See:

http://www.wodonga.tafe.edu.au/eemo/ne178/tut2_3.htm

About the middle of the page you will see the graphic for half-wave. 
RMS of a half-wave pulse is .5, average is .318, of peak.


>The formula in my books say to arrive at the RMS value of a sine wave you
>divide it's Peak to Peak value by 2 to arrive at Peak value then multiply
>that Peak value by .707 and you have RMS.


This is only true if you are talking about a pure sine wave with no
harmonic distortion or modulation.  It does not apply to square,
triangle, pulse, audio, modulated RF or baseband, or any combination of
the above.  When thinking of the output of a half-wave rectifier, we
are definitely not thinking of anything close to a pure sine wave.  I'm
with Drew on this one.



- --
Jim Shorney      -->.<--Put complaints in this box
jshorney@inebraska.com
nu0c@amsat.org
Ham Radio NU0C
Lincoln, NE, USA
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http://incolor.inetnebr.com/jshorney/
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