From: "Da Man"
Subject: Re: fluorescent lamp inverter problem
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
Date: Fri, 03 Jan 2003 10:14:34 GMT
NNTP-Posting-Date: Fri, 03 Jan 2003 06:14:34 AST
"Eric Y. Chang" wrote in message
> Da Man (firstname.lastname@example.org) wrote:
> : Often the base only contains a magnetic ballast, and the starter is part
> : the tube socket, since the starters wear out. 4 pins are usually needed
> : fire up a tube without a high voltage kick.
> Hi Jeff. The socket is pretty abbreviated. This lamp is designed only
> for use with an electronic ballast which does provide such a kick. I
> looked at some app notes, and they usually consist of some smart IC which
> does this, in addition to running a PFC boost converter and a small
> : > There are just two pins. One going into
> : > each end of the tube. They usually do not have a starter.
> : There is very likely a perminant starter bult into the plug of that tube
> : it only has 2 pins (usally in between the pins in a little protruding
> : (the starter is simular in size to a NE2 neon indicator bulb)). At least
> : every 2 pin tube I saw had one built in. The 4 pin ones had the starter
> : built in the base, or had an elecronic ballast instead of an magnetic
> : Check with a normal tube to be sure. That really does sound like it has
> : starter in it, with the blue flash and then the tube going out. Besides,
> : what else would make a blue flash?
> That is a great idea. I'll have to dig up a regular tube (with filaments)
> Meanwhile, I found an interesting www site which said something about the
> folly of using a non-square loop ferrite (such as the ones found in PC
> power supplies) in a Royer type fluorescent inverter transformer. The
> main point is that these kinds of topologies work best with a square loop
> material. Since the author did not have such a core, he improvised by
> changing the geometry of a PC power supply core so that the region of
> saturation is limited in volume. From the basis of power dissipation,
> this has a similar effect to squaring up the hysteresis loop. He goes
> on to say that this is even better than using a salvaged TV flyback
> transformer core. This does not completely answer my question, but it
> does go a long way.
> Thanks for all the suggestions.
When you were talking about that, I was trying to remember where I put the
link to the site in which you posted ;_). Excellent site. The author really
seems to know his magnetics.
On a manual start magnetic ballast system, 120V is applied through the
ballast (basically an large inductor), to one terminal on each side of the
tube, but the voltage is not high enough for the tube to ignite. The system
would have a button that you press for a second or two. This shorts the two
remaining terminals on the tube together. This causes 2 things to happen, 1)
the heaters at either end of the tube heat up and start to glow (heating the
electrodes makes the tubes much easier to ignite)(sometimes the voltage to
them is high enough to ionize the mercury vapor around them, and the ends
will glow the color of the tube instead of a dull orange), and 2), when the
button is realeased, the current stops flowing through the inductor, causing
a high voltage kick (as long as it's not at (or close to) a zero crossing
(actually just past!) when no current flows, causing no kick, and the button
needcing a second press) which ignites the lamp. Once the lamp is going,
only a current linited supply(the inductor) is needed to keep it going at a
fairly low voltage. The button on these systems can be replaced with a
electric one, the starter. What they do is: When a voltage of say 100 or
more volts peak to is present across it's terminals, it starts to ionize,
which causes a current to flow. this gererates heat, which heats a
bimetallic strip, which closes a set of contacts, thus shorting it out. This
causes the same effect as the button would. When the bimetallic strip cools
enough to open the contacts a second later, a high voltage is produced from
the inductor and hopefully the lamp starts.
Electronic ballasts basically generate a high voltage through a current
limited supply. This directly ignites the tube, and then reduces to a low
voltage higher current supply. They usually connect a capacitor across the
remaining pins to create a current in the heaters for easy igniting, and to
A few things bother me with the tube you have: 1) It's quite odd to have a
florecent tube with only 1 wire per electrode, 2) no heater, 3) Most newer
electronic ballasts don't have replaceable tubes(a real 10,000 hours later,
the plastic, the electronics (HV breakdown), and the caps won't be in the
greatest shape + the companys want you to buy a new one) 4) every 2 pin
replacement tube I saw had a built in starter. Look for places between the
pins and the tube where they could hide a small tube about 1/4" by 3/8".
So to me it really looks like what is happining is that: you have circuity
that ignites and drives the tube with a very differnt voltage waveform then
what would be used for 120V (or 220V if your far away from here!) operation.
So, turning it on, the tube ignites due to a high voltage produced from the
current limited "driver". Since the voltage is higher then when driving it
the standard way, the starter keeps ionizing, thus kicking in, effectively
shorting out the electrodes (there may not be enough current to make them
glow), and shutting the lamp down. When the starter cools enough to open,
the contacts are so close together that the hot ionizing gas rapidly ionizes
again, sucking all the avalible current from the highly current limited
supply (no low frequency 60 Hz and no large inductor for a big kick), and
not allowing the tube to ignite. The contacts in the starter would likely
oscillate at a few times a second.
This can be checked quite easily now that I think about it - if the voltage
across the tube is significantly lower then when it was lit, this would be
confirmed. NOTE: High Voltage! Another method would be to put a 1 ohm
resistor in series with the tube, and use it to measure the current through
the tube. If you have any significant current flowing when the tube is not
lit, you have a starter!
I hope this makes sense, I'm up way too early here!
Good Luck and keep us posted on what the problem was!