What are the constituent components of CFL bulbs?

Article By : Brian Dipert

This teardown aimed to answer two questions: what are the constituent components of CFL bulbs, and what caused the demise of these two?

I recently wondered, after replacing my second one, how the internals of compact fluorescent (CFL) bulbs compare and contrast to an LED light bulb? I anticipated I’d find a plethora of passive analog and power components (along with a comparative dearth of digital components) versus their LCD counterparts but there’s only one way to find out, right?

/wp-content/uploads/sites/3/2021/03/contenteetimes-images-edn-edn-hands-on-project.pngMy various LED bulb teardowns over the past several years have consistently been among my most popular. We’ve covered standard, Zigbee-controlled, Wi-Fi augmented, and Bluetooth-enhanced versions, so we have plenty of information for comparison.

Today’s victims are both 13W (60W incandescent-equivalent) T2 form factor CFL bulbs, with claimed 825 lumen output, “generic” (i.e., not brand-name), and in equally-generic packaging:

photo of CFL bulb package

Here are some overview shots for the first one:

photo of a CFL bulb

photo of the other side of a CFL bulb

And here’s the second of the two CFL bulbs, accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

photo of the second CFL bulb laying on a table

photo of the other side of the second CFL bulb laying on a table with a penny for scale

Here’s a series of closeups of the product markings:

photo of the markings on a CFL bulb base

photo of the markings on a CFL bulb base

photo of the markings on a CFL bulb base

photo of the markings on a CFL bulb base

And of the passive airflow vents at both ends:

photo of a CFL bulb's bottom vents

photo of a CFL bulb's top vents

Time to dive in. Although the two halves of the base are presumably pressed together, judging from the seam, their union is likely augmented by adhesive. The glass tube attached on the end makes twisting them apart even more complicated from a potential-injury perspective; I therefore initiated the process with a shallow hacksaw cut:

photo of a CFL bulb in a vice with a hacksaw for cutting it open

photo of the saw cut made into the CFL bulb base

Subsequently inserting (and twisting) a wide flat-head screwdriver completed the deed:

photo of the CFL bulb cracked open

photo of the CFL bulb's components exposed

photo of the CFL bulb cracked open showing the PCB

In that last image you can see the two wires that connect the PCB to the electrical contacts in the base. They seemed to be sturdily soldered at both ends so I just snipped ‘em leaving the PCB topside (i.e. the “ballast”) inside fully exposed to view:

photo of the empty CFL base

photo of the exposed CFL bulb PCB

Here are three straight-on shots of various orientations:

photo of the top of the CFL bulb PCB

photo of the top of the CFL bulb PCB

photo of the top of the CFL bulb PCB

Obvious constituent components (even to my binary IC-biased eyes) include the toroidal inductor and transformer, along with the discrete transistors and several different-sized capacitors and other inductors (what more/else of note do you notice, my more analog- and power-attuned readers?). Note, too, the two wire pairs, presumably headed to both ends of the coiled fluorescent tube. Let’s find out:

photo of the wiring connecting the CFL bulb and PCB

photo of the wiring cut between the CFL bulb and PCB

One of the four wires was pretty short, so I left it connected:

photo of the PCB pulled away from the CFL bulb

The PCB backside is pretty unremarkable, unless solder points and a mix of standard and bidirectional diodes are your thing:

photo of the bottom of the CFL bulb's PCB

Now let’s look at the second CFL bulb:

photo of the second CFL bulb cracked open

Here’s another series of shots of the ballast:

photo of the top of the second CFL PCB

photo of the top of the second CFL PCB

photo of the top of the second CFL PCB

photo of the top of the second CFL PCB

This time I got all four wires headed to the fluorescent tube snipped off (although I snipped the top off one tube end in the process):

a photo of the bottom of the CFL tubes

That lead to a clearer straight-on shot of the PCB backside:

photo of the bottom of the second CFL's PCB

read more teardownsSo, circling back to this writeup’s title, what caused these CLF bulbs to fail? The potential-cause list is long, and these bulbs have been sitting on my teardown pile for a while now, so my memory’s a bit fuzzy. But I don’t recall a pop, puff of smoke, or other evidence of ballast-component failure, nor do I see any bulging capacitors, singed circuitry, a discolored base, or the like. Instead, take a look back at the overview photos (specifically the blackened segments of the fluorescent tubes in the base’s proximity, and you’ll likely conclude (as I have) that the root cause in both cases is more traditional in nature: degradation of the electrode filaments.

With that, I’ll turn the fluorescent bulb’s illumination in your direction for your thoughts in the comments!

This article was originally published on EDN.

Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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