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

[Drew Papanek]

Hello David,

Thank you for the intriguing synopsis on the operation and iterations of the 
3DW7.  Putting in the microcontroller  and writing the program is certainly 
a labor of love!   My repect goes out to all of those intrepid souls who 
painstakingly unsnarl software.

By his own admission, Dr. Jerry's design (bridge rectumfier wrapped around 
LM317) does not have as good current regulation as its parent regulator chip 
and my computer simulation confirmed this.  My simulation showed a +1.5%, 
-2.5% variation in RMS current output over a +-15% line voltage change.  
This is still better than non-regulated schemes and may be good enough for 
some uses.  It appears that the varying unregulated "shoulders" of the 
clipped current waveform are traversed in a reasonably (it seems) short time 
and contribute only a small portion of the total current.  Under the 
conditions of a nice sinusoidal input voltage confined to the aforementioned 
range, and the constant load of tube heaters, clipping the current peaks 
might be considered a workable approximation of true RMS current regulation.

Dr. Jerry's description of his trials and tribulations mention extensive 
testing using a variety of RMS current measuring methods, some of which 
actually agreed with one another.

Your 3DW7Tubester makes all this seem academic.  How about including an 
orange LED in the 3DW7 to simulate that warm filament glow :-)

Drew

>
>From: "David Wise" <David_Wise@Phoenix.com>
>
>The problem with using a '317 to clip the
>sinewave is that the only part of the wave
>that's regulated is the clipped region.
>The "shoulders" are not regulated.  BTDT.
>If you regulate anything other than DC,
>you must regulate RMS, not average, not peak.
<snip>


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