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October 3, 2012
News - The Race to the Bottom: L…
about 2 months ago
I did a teardown of a couple of the cheap Cree bulbs when they first came out. https://flic.kr/p/egvUYK this is the 40W equivalent version. I don’t have a picture of the 60 watt equivalent but it just added a second row of LEDs (2x the LEDs), the remainder of the thermal solution was the same! By spreading the increased power over more LEDs (i.e. each LED is driven at lower power) they can still keep the Junction temperature down despite a hotter case.
That model used the Cree XT-E HV (24V model in the 40W and 12V model in the 60W) all hooked in series. The power supplies actually boost the voltage (as all the LEDs are hooked in series)! The only difference in the supplies was a couple component values (inductor and some resistors).
Also it is cheaper to take apart these bulbs and scavenge the LEDs than it is to just buy the LEDs (until you start ordering reel quantities)
about 2 years ago
Yes, that is correct, I get a periodic blink (and a serially transmitted 0 or 1) every 750ms (and about 20-30 additional, but non-periodic events a minute). I do get counts from radioactive sources (ye olde school anti static brush) but there is presumably the approximately 80 cpm offset. I’ll scope in as far as I can and get back to you, but I don’t have a 50x or 100x probe.
Mine has the same 750 ms tick as well, however mine registers a count with each faint tick. Adding capacitance to (pinching) C4 seems to decrease the frequency. Adding a bypass resistance (light finger touch) across R14 seems to decrease the sensitivity enough to eliminate the 750ms periodic trigger (despite the audible noise remaining). Thoughts? Am I seeing a non radiation induced (ie over voltage) dielectric breakdown in the tube? Is that tick the capacitors' dielectrics talking or a breakdown occurring? I guess I will add an adjustable R14 bypass and adjust the sensitivity just below it picking up the tick (not my favorite fix though).
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