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?
My 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:
Here are some overview shots for the first one:
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:
Here’s a series of closeups of the product markings:
And of the passive airflow vents at both ends:
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:
Subsequently inserting (and twisting) a wide flat-head screwdriver completed the deed:
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:
Here are three straight-on shots of various orientations:
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:
One of the four wires was pretty short, so I left it connected:
The PCB backside is pretty unremarkable, unless solder points and a mix of standard and bidirectional diodes are your thing:
Now let’s look at the second CFL bulb:
Here’s another series of shots of the ballast:
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):
That lead to a clearer straight-on shot of the PCB backside:
So, 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.