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Spontaneous LED bulb teardown — IKEA ledare 400lm

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I bought this LED bulb about 21 months ago for €11.99.

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I liked it!

Now, you’ve certainly noticed that I used the past tense in the previous sentence. It failed a couple of days ago. Today I tried to have it replaced at IKEA, but they refused. Yes, there is a 24 month ‘warranty’ in the EU, but the WEASELS have ways to wriggle out of that. At least if you don’t want to involve a lawyer over just 12 bucks.

How long did it last? Well, less than 24 months, duh. If I use a conservative estimate of about 1-2 hours of operation a day, that translates into somewhere around 1000 hours. A surprise, maybe not. Very far from the numbers usually claimed, which are in the 10’000s of hours.

This bulb was marketed as a 60W equivalent. With a kWh price of about €0.26, the bulb has payed for itself, barely.

Symptoms: excessive heat, shuts down on its own (presumably over-T protection), very bad smell emanating from the bulb.

I didn’t manage to remove the LED carrier, too much epoxy.

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Texas Instruments TPS-92070-based. Interesting thing, using isolated current sense feedback using a small transformer.

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It looks like there might be a crack in the capacitor, but it’s OK.

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The large transformer is used for DC/DC conversion, the small one provides isolated LED-current feedback. See the datasheet for some details.

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I suspected a blown capacitor, but I didn’t find any of that! Except for the bad smell, I didn’t find anything obvious. Fortunately the LEDs are still OK (350mA-ish @ 16V-ish). The lamp should take 8.1W. The power-supply has an efficiency of about 80% (see datasheet), the LEDs should take about 6.5W (about 400mA). The current-sense resistor of 240mOhm + the current-sense threshold voltage of 100mV give about 417mA, looks OK to me.

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I’ve removed the E27 connector, just to be on the safe side. The hole at the bottom will come in handy for adding a barrel connector.

I think I will convert this bulb to a low-voltage lamp at some point in the future – using my favourite PT4115 constant-current LED driver with an external power supply. After removing the old power-supply, there is enough room for adding a small circuit board with that driver, a micro and maybe 2 buttons for brightness control.


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