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

Fri, 27 Dec 2002 14:45:57 -0800

Here's IMO the simplest regulator that's also really good.

Parts list:
5ohm 10W resistor.
10ohm 10W resistor.
2.2K 1/4W resistor.
2.7K 1/4W resistor.
1K pot.
3000uF/50V cap.
Silicon rectifier.
LM317 on heat sink.

Vin goes to 5ohm resistor.
5ohm resistor goes to anode of rectifier.
Cathode of rectifier goes to cap and LM317 IN terminal.
Other end of cap goes to ground.
LM317 OUT terminal goes to 10ohm resistor and 2.2K resistor.
2.2K resistor goes to LM317 ADJ terminal and 2.7K resistor.
2.7K resistor goes to 1K variable resistor.
1K variable resistor and 10ohm resistor go to Vout.

This will adjust from 280mA to 335mA.  It has
four big components, three of which are also hot,
and it requires a ground.
This was my first step on the road to the 3DW7.

How's it work?  The rectifier and cap give you DC.
The 5ohm resistor softens the charging peak and
takes on some of the heat load.
The LM317 will do anything in its power to maintain
1.25V from OUT to ADJ.  This puts 1.25V across 2.2K
for 0.57mA, which also flows through the 2.7K
resistor.  (The LM317's current out the ADJ pin
is negligible.)  0.57mA * (2.2K + 2.7K) =3D is 2.78V .
The LM317 will do anything to make that 2.78V happen.
In this case it punches 278mA through the 10ohm resistor.
If you increase the 2.7K resistor to 3.7K, the
voltage is 3.35V instead of 2.78V for 335mA out.
I can't remember what range of AC input voltage this
will work over, but it's at least 25.2 +/- 5% .

73,
Dave Wise

> -----Original Message-----
> From: Jim Shorney [mailto:[email protected]]
> Sent: Tuesday, December 24, 2002 3:57 PM
> To: Bill Smith; [email protected]
> Subject: Re: [R-390] Ballastubes (was inrush current limiters)
>=20
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> -----BEGIN PGP SIGNED MESSAGE-----
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> On Tue, 24 Dec 2002 13:55:22 -0800, Bill Smith wrote:
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> >Why not made a 300ma current source (zenner, two resistors,=20
> transistor, or
> >your improvement) and hook it up to the +/- terminals of a=20
> bridge rectifier.
> >Hook the AC terminals of the bridge rectifier to pins 2 and 7 of the
> >ballast.
>=20
>=20
> That's along the line I was thinking.  As wonderful as Dave's little
> gizmo sounds, and I *do* wish him the best of luck with it, I don't
> plan on buying one.  I'm just brainstorming for ideas that I can brew
> up with parts on hand in the event my ballast tube is bad and my buddy
> Steve doesn't give me a spare for free...  :-)  Yeah, I'm a tightwad,
> and I'm not one of those purists who has to have everything look
> original; I don't mind wiring something in if it is a good solution.
>=20
> I'm sorry if this made anyone irritable, I've enjoyed the discussion
> and learned a thing or two.  So what if it's a dead horse?  At least
> I'm having fun!  I hope the rest of you are, too.
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> God rest ye merry, gentlemen.
>=20
> Jim
>=20
> - --
> Jim Shorney      -->.<--Put complaints in this box
> [email protected]
> [email protected]
> Ham Radio NU0C
> Lincoln, NE, USA
> EN10PT
> http://incolor.inetnebr.com/jshorney/
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