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Design Decisions: Protect Electronic Ballasts in Fluorescent Lamps
10/2/2012

A typical circuit utilizing a PPTC device for protection of IC integrated ballasts.
A typical circuit utilizing a PPTC device for protection of IC integrated ballasts.

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TJ McDermott
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Is this actually used?
TJ McDermott   10/2/2012 11:09:31 AM
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Are compact flourescent lightbulbs protected with this technology?  If they are, why are there so many anecdotes of them overheating, burning, and arcing when they fail?

CFL bulbs have an overall very negative reputation because of this.

naperlou
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Re: Is this actually used?
naperlou   10/2/2012 11:29:21 AM
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TJ, I had not heard that.  My experience with CFLs is that they do not last nearly as long as rated.  I expect that the reason is that they are cycled far more often than they are designed for.  We do that with incandescant bulbs and think nothing of it.  Might this overvoltage protection approach help with that problem?

TJ McDermott
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Re: Is this actually used?
TJ McDermott   10/2/2012 11:59:07 AM
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Naperlou, I would hope so.

Snopes.com reports the fire hazard is a sort of urban legend

http://www.snopes.com/inboxer/household/cflbulb.asp

However, their own refutation text is cause for alarm:

CFLs (compact fluorescent lamps) don't burn out the way incandescent light bulbs do. Instead, as they near the ends of their lives, they grow dimmer. While some CFL bulbs merely stop emitting light when they finally quit working, others kick the bucket with a dramatic "pop"! sound and then vent a distinct odor. A few even release a bit of smoke at their termination. Sometimes the bases of the bulbs turn black. This seemingly cataclysmic reaction has to do with the breakdown of the bulb's ballast, which is contained in the part of the bulb that is screwed into the socket. As the bulb ages and degrades, so does its ballast. Yet as scary as odors, smoke, and even blackening of the base of the bulb might be, these lamps are fireproof and are meant to fail safely at the end of their lives.

 An incandescent lightbulb does not turn black, does not emit smoke or an odor when it fails naturally.

How is this better than an incandescent bulb?  Maybe the technology described in this article prevents the failure symptoms listed above.  I hope so; it might improve the image of the bulbs.

The alleged cost savings aren't there.  The light given isn't as bright.  They fail in a messy and annoying manner.  I forget why they're being forced on us.

 

loadster
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Gold
ahead of ourselves
loadster   10/4/2012 12:31:54 PM
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The ballast referenced is a T5 14W circuit built for the linear tube fluorescents in commercial and shop applications. They have end-of-life issues different from CFLs

Though related, I think this circuit is chasing problem of low population as I understand new fluorescent ballasts have requirements to be more EMI and otherwise future modulation distribution compatible. Hopefully, this problem is addressed by smarter self-protection circuits.

The takeaway should be that as engineers with low wattage circuits we need to understand that PWM and boost power supplies can create fire hazards that need to be anticipated early in design.

No B.S?

Natacha Watson
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Iron
Electronic Ballasts
Natacha Watson   1/17/2014 4:31:08 AM
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Nice tips thanks! I've found some great ballast models in here for more insights: http://www.directindustry.com/cat/power-supplies/electronic-ballasts-C-2039.html

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