Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!sdd.hp.com!hp-pcd!hplsla!tomb
From: tomb@hplsla.HP.COM (Tom Bruhns)
Newsgroups: sci.electronics
Subject: Re: How to light a UV tube
Message-ID: <5170120@hplsla.HP.COM>
Date: 13 Mar 91 21:01:32 GMT
References: <1991Mar12.214815.11808@amd.com>
Organization: HP Lake Stevens, WA
Lines: 31

lpdjb@brahms.amd.com (Jerry Bemis) writes:

>I get a bargin price on a UV tube.  In measures .3" x 2.5" with a 2.5" base.
>It has a 6" zip cord coming out the end of the base.
>
>    glase tube
>    |       ______________
>/-----------  base        |====== cord 
>\-----------______________|
>
>
>Now I need to know how to light it.    120 volt AC doesn't light it up.
>----------

You're lucky the 120VAC didn't light it!  At least, I assume this is like
the ones I used in a  project a number of years ago.  Once you get it
turned on, the voltage will drop significantly, and the dynamic impedance
will be vveeeerry low.  So if 120V had lit it, it would have drawn enough
current to destroy itself (assuming you didn't have any current limiting).
As I recall with the ones I was using--very nearly the same size-- it 
took 500 to 1000 volts to get them started, then a couple hundred to keep
them going.  I believe the standard power supplies for them are built like
a scaled-down neon tube transformer.  It's possible to accomplish about
the same thing at the expense of some power dissipation by putting a
reactance (inductor or capacitor) or even resistance in series with a
high-voltage AC supply.

(The application I worked on required modulating the light intensity,
so we used a DC bias current with superimposed AC at the desired
amplitude/phase/frequency; was used to cause electron emission from
a metallic surface, to check for surface cleanliness...)