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

[David Wise]

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.

The optimum 317 design requires a ground,
not for the regulator but for the filter cap.
Half-wave rectify, filter, and current-regulate
the resulting DC.  A series resistor softens
the inrush and takes on some of the 317's heat
burden.  This is the minimum parts-count
regulated solution and it's an excellent, quiet
regulator, but it puts out a heck of a lot of heat,
more in fact than the 3TF7.

73,
Dave Wise

> -----Original Message-----
> From: Jim Shorney [mailto:jshorney@inebraska.com]
> Sent: Monday, December 23, 2002 6:31 PM
> To: R-390@mailman.qth.net; Drew Papanek
> Subject: Re: [R-390] Ballastubes (was inrush current limiters)
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> On Mon, 23 Dec 2002 17:37:02 -0500, Drew Papanek wrote:
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> >RMS voltage and current are what define heating power in a=20
> waveform (DC=20
> >"waveform" included).
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> That's what I thought, but all the references I could find searching
> last night only talked about average.
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> >One of my references lists RMS value of a half wave=20
> rectified sinewave to be=20
> >half the PEAK value.
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> I finally found a reference that agrees with this.
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> >The half=20
> >wave rectified RMS value:  ( 35.6)(.5)=3D17.8 VRMS.
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> I knew there was a reason this idea still bothered me....
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> >A 12AU7 will not work as it=20
> >draws 150 mA when configured for 12 volts.
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> Thought so, but I was focused in on the other area.
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> >Replacing the BallasTube with solid state current regulator=20
> has also been=20
> >discussed.   A while back Dr. Jerry designed an AC current=20
> regulator using a=20
> >full wave bridge wrapped around an LM317 configured as a DC current=20
> >regulator, providing a clipped sine wave
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> This is exactly one of the ideas I was kicking around, since I have a
> drawer full of 317Ts.
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> >As far as regulator-induced noise is concerned, filtering=20
> would help but I=20
> >am not sure that this is necessary.
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> Manufacturer's recommended filter/bypass caps are always necessary,
> IMHO.  I remember the time a CBer brought me a home-built 12v power
> supply that would spike to >18 volts when he unkeyed his radio.  The
> solution was to get out the data book and install the caps=20
> for the 317T
> that National Semi said shouldbe there for stability and transient
> response.  There was also the blurb in QST years ago from the ham who
> tossed a bunch of bypass caps at the regulators and zeners in, IIRC, a
> TR7 and IC551 and saw a noticable improvement in the noise floor.
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> >Another solid state regulator approach is to half wave=20
> rectify the 25.2VAC,=20
> >filter and apply to a 3 terminal regulator configured as a 300 mA DC=20
> >regulator.
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> The same without filtering should give a clipped half-sine wave as
> above.  Since we start out with an RMS of 17.8 volts, there should be
> enough headroom.  Another variation I've been thinking about.
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> >I believe that the imbalance is small compared to the total=20
> transformer load=20
> >and probably wouldn't make much difference.
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> I tend to agree.
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> >Have a happy holiday and may Santa bring each of you a=20
> sleighload of 3TF7's!
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> Maybe I should shut up until I actually get my radio up and running.=20
> Or at least find out if my 3TF7 is good...
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> God rest ye merry, gentlemen.
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> - --
> Jim Shorney      -->.<--Put complaints in this box
> jshorney@inebraska.com
> nu0c@amsat.org
> Ham Radio NU0C
> Lincoln, NE, USA
> EN10PT
> http://incolor.inetnebr.com/jshorney/
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