CFLs and dimmers

AFAIK the dimmable CFL has a PFC (power factor correction) front end to the switcher circuit.

A normal rectifier/reservoir takes only blips of current from the peaks of the AC waveform so the triac in the dimmer gets confused.

The PFC front end is basically a flyback step-up converter, but as it's rectifier has no reservoir capacitor it draws narrow pulses of current during the whole AC cycle.

Instead of a reservoir capacitor, the rectifier has a relatively small non-electrolytic - mainly for filtering, but I expect it also maintains triac holding current between PFC pulses.

You're late to the party. CFL's have always been crap and soon to be replaced by LED's. ...Jim Thompson

[On the Road, in New York]

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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I love to cook with wine.     Sometimes I even put it in the food.

El 31-07-11 17:52, Ian Field escribió:

Hello,

In addition to the PFC to avoid transient currents in the dimmer, there is a circuitry present that detects the dimming action and a circuit that keeps the filaments at a convenient temperature to optimize its lifetime.

The filaments in CFL and tubular fluorescent tubes have so called "hot cathodes" and they use thermionic emission to generate free electrons. It results in low cathode fall and long life of the fragile emissive coating on the filaments.

When the temperature reduces, the number of thermionically generated electrons will be too low to support the lamp current and a sputtering process starts that will very soon breakdown the emissive coating on the filament (resulting in lamp failure).

As the lamp current (the discharge current) goes down, the filament temperature drops, reducing the protective electron cloud around the filaments. To avoid this, the controller will supply additional current through the filaments to maintain the optimum temperature when dimmed.

Wim PA3DJS

Please remove abc first in case of PM

Wimpie wrote in news:af6cc$4e358e01$5355cc82$ snipped-for-privacy@cache120.multikabel.net:

the filaments in FLs are only for starting; once the mercury is ionized,the arc maintains itself without the filament needing to be hot.

--
Jim Yanik
jyanik
at
localnet
dot com

El 31-07-11 22:55, Jim Yanik escribió:

The hot cathode lamps are so designed that when operated at their nominal current, the filaments remain at the best operating temperature (so you don't have to apply additional filament current). You can reduce the lamp current to some extend (to reduce the light output), but reducing to much will reduce the useful life significantly.

You are correct that preheating reduces the ignition voltage, but linear fluorescent lamps and CFL are of the hot cathode type, so they need a hot cathode to rely on thermionic emission.

Wim PA3DJS

Please remove abc first in case of PM

"ps56k"

** Drivel written by some sales dude.

For some real info see:

See reference #10 at the end of the article.

** Nonsense.

** Never come across a CFL that could not be dimmed with a Variac - one 7 watt type from Osram could be brought down to the level of candlelight. ** The electronics is modified, different makers do different things ** Probably "leading edge" v "trailing edge" types - ie triac based and non triac. ** Try reading the pack.

.... Phil

"Ian Field"

** Not the ones I've seen.

.... Phil

On a sunny day (Sun, 31 Jul 2011 15:55:31 -0500) it happened Jim Yanik wrote in :

No, Wimpie is right, in TL tube dimmers the filament is kept hot.

In what way?

"Richard Henry" Jim Thompson

In what way?

** Too many to list really, but a few of them are:

Slow to produce full light, very slow in cold weather.

Ridiculously fragile to handle.

Unsafe in circuits that have a wall dimmer.

Not dimmable by normal wall dimmers.

Inrush surges prevent use of groups on same circuit.

Light output fades significantly over time.

End of life failure modes include smoke and fire.

Easily damaged by moisture - ie rain, condensation and steam.

Will flash slowly in circuits with tiny amounts of leakage ( or a cap) across the switch.

Mercury hazard when disposed of or broken.

Advertised life spans are a blatant scam.

.... Phil

Advertised light output is a blatant scam as well.

.... John

** Not really.

The omnidirectional testing method is to blame, the lumens figure areOK.

Less light goes downwards from most ceiling mounted CFLs ( spirals and tube types) than is the case with normal incandescents.

.... Phil