Minimum voltage level required or Powering CFL's 1

[Fluorescence]

Hello,

I am writing concerning powering CFLs (Compact Fluorescent Lamps) from the mains.

The following App Note from IRF.com shows a fluorescent lamp being powered from the UK mains (240V) ....
...but uses a "valley filler" passive power factor corrector, so the DC bus actually varies from 160V to 330V

http://www.irf.com/technical-info/appnotes/an-1074.pdf

This App Note shows that the fluorescent lamp keeps re-striking at the 160V level, which will damage it by pitting the electrodes and reducing its life.

Please could readers advise, United States mains is 170V peak. Is this high enough to power Compact Fluorescent Lamps? Or will it need a boost converter?

Secondly, if a "valley filler" is used with United States mains, then the DC Bus will vary from 170V to 85V.

Do you believe 85V is too low for a CFL? , and therefore, is it true that "Valley Fillers" cannot be used for CFL's in the United States?

I'd be very grateful for any thoughts.

 

[VEBill]

That App Note is from 2004. I believe that there has been a lot of change in CFLs since then.

 

[Fluorescence]

Thanks VE1BLL,

i am now searching for latest literature on the lowest possible working voltage of a CFL though it does not seem to be available on the web.

 

[marginal]

Figure 2 , page 2 of the following ...

http://pdfserv.maxim-ic.com/en/an/AN3528.pdf

gives you ccfl strike voltages versus temperature.


you can see that at 4 deg Centigrade the strike voltage is some 135V.

So in the United States at low line, (120V peak) you are not going to strike. (unless you use say boost PFC front end)

At USA high line (197V peak) at 4 degrees Centigrade, and using a valley filler input , your CCFL is going to splutter and struggle to strike, -meaning it will be slightly damaged every time it is switched on.

 

[VEBill]

Aren't "99.44%" of all *modern* CFLs now using high frequency switching power supplies using little tiny high frequency magnetic components? And doesn't this imply that they could easily be designed to run off an AA battery if that's was desired?

I live in Canada, and I see more and more people using CFLs in outdoor fixtures - even in the depths of winter. And +4C in Canada is called 'a balmy spring day'.

So what's the disconnect here?

$10 at Costco will get you an 8-pack of modern, nearly fault-free CFLs. That's $1.25 each LOL. It might be worth taking one apart to see what's what.

 

[marginal]

VE1BLL,


I see your point, i thought they could manage any voltage ..

..maybe that app note that i posted is out of date from 2005?

But to be honest, i reckon a CFL will strike on almost any voltage above say 40V....but it will not strike cleanly, and will be slightly damaged meaning its life is slightly shortened.

I think fluorescent type things need high voltage....it's like xrays and other stuff where stuff has to be ionised it needs high voltage.

it would be interesting to see how long the cheapo's last.

I've taken apart UK 15W CFL's....all i see is two T0-92 transistors and an inductor and some caps.

In UK, the FWB output is then something like 330V to 200V as there's only 3.3uF electrlolytic bus capacitance

 

[VEBill]

"...it would be interesting to see how long the cheapo's last."

Price is not a good indicator. The older CFLs were $10 each and failed all the time. More recently they're not really much more expensive than an ordinary incandescent light bulb, and the recent batches are working out just fine.

But even if an occasional CFL bulb fails, at $1.25 it's not really worth getting all worked-up about. They'll have probably earned back their trifling price delta over an incandescent light bulb in a couple of weeks.

One of my coworkers was recently resistant to CFLs because "...they're $15 each." I told him he needs to get out more.


I believe that many of the newer versions are running at several MHz. One wag even converted a CFL bulb into a ham radio transmitter in the 80m band (3.5MHz).

 

[OperaHouse]

I've been buying repair lots of 12V to 120 inverters off ebay for my camp. Many of the new CFL lights have inverters and will run off DC as well as AC. I just run the lights off 140V DC of the inverters since these almost always have the H bridge FETs shorted out. A no cost mod that gives me cheap lighting.

 

[marginal]

VE1BLL

"I believe that many of the newer versions are running at several MHz"

I am fairly sure that none of the cheap mains CFL's run at several MHz. They may produce switching harmonics in the MHz range, but would switch at around 100KHz or so.

At several MHz, Switching losses would be too high when powered from the rectified mains.

Operahouse:
"Many of the new CFL lights have inverters"

...An inverter uses four transistors in a H bridge topology, that would be a very expensive way to design a CFL.

Even the Commercial fluorescent tubes don't tend to use an inverter, -most use a half bridge.

 

[VEBill]

Thanks for the correction on the switching frequency being 100kHz range (not MHz).

 

[OperaHouse]

"newer versions are running at several MHz"

I was working at one of the major corporate R&D centers in the early 80's and saw a CFL running at several MHZ. The toroid was inside the glass envelope to excite the gas. So, there is nothing new. That product still has not reached the market.

Perhaps I should have said electronic ballast instead of inverter. Switching a transformer at khz is still an inverter to me. A 60hz transformer still found in some CFL.

 

[marginal]

hello,

according to this

http://ludens.cl/Electron/Fluolamp/fluolamp.html

the lowest voltage to strike is anywhere between 100 and 1000v