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CFL dissection

-October 14, 2013

There was this table lamp in our living room into which I'd put a compact fluorescent lamp (CFL) some while ago and it worked quite nicely for several years until one day, it went dark. Just like that, it was inoperative. I replaced it with a new one and then I decided to dissect the old one to see what I'd find out.

 

I couldn't identify the MOSFETs by type number and the part number for D7 is an enigma to me, but this much is was what I got:

 

 

It looks like diode D2, a 1N4005, blew out shorted and caused resistor R1, the 0.47Ω on the Hot side of the input line to burn up. My guess is that D2 suffered a PIV failure when it shorted out. The ensuing line voltage across R1 would surely have fried that good and proper. Perhaps if the 1N4005 diodes had been 1N4007, the CFL might still be working.

 

To my chagrin, I've somehow misplaced the toroidal core that was used for transformer T1. However, I still have coils L1 and L2 at hand which are photographed as follows:

 

 

I tested the various coil and transfomer windings using the dual resonance method.

 

That test fixture just keeps coming in handy.

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