In Part 1 (and in the LED bulb dimming video) I looked at the basic performance characteristics of this readily available, $16.99 Best Buy 60W-equivalent LED bulb, and found they were excellent. Which just begs the question, what’s inside?
The bulb emits a nice, even glow, and I assumed it had some sort of pedestal in the middle that held the LEDs. But why couldn’t I see anything? The plastic enclosure isn’t that opaque. So I tried illuminating it from behind with a high-power (LED) flashlight – and saw nothing was in the center of the bulb to cause a shadow.
Then it dawned on me – The LEDs must be mounted directly on the heat sinks. Let’s see!
After a great deal of fiddling around it became obvious that the plastic light defuser was going to have to be destroyed (as in, cut off with a Dremel) to get it off. So here’s what it looks like:
There are three Cree LEDs, mounted on a substrate that’s screwed to the aluminum heat sinks. At the bottom is a mirror-like thin sheet of aluminum that helps to reflect the light out of the bulb.
The mirror sits on the bottom of the plastic diffuser/cover; You can see it lying next to the bulb at the top of the picture; The white circle is where it was glued down.
All of the electronics for this bulb lie beneath the mirror in the base of the bulb, in a separate and encapsulated (potted) compartment. The wires carrying the regulated power leave the electronics section and go to the three parallel strings consisting of three LEDs each. At this point the light is still functional, so let’s measure the voltage at each string:
The LEDs turn on at 8.1V, gradually increasing in brightness until the voltage reaches a maximum 9.1V. When dimming down from the 9.1V, they cut off at 7.9V.
Unfortunately, there’s no other way to find out what the power control circuitry looks like than to destroy the bulb. After cutting around the base to pop it off, here’s what you see: What appears to be an inductor poking out from the black potting compound.
First, a word about the white base: It’s of aluminum, and is thermally tied to the the LED heat sinks. There was some nice, creative design here on dispersing heat both from the power electronics as well as the LEDs themselves (which are the main heat producers.)
Back to the electronics: The next step consisted of lots of pulling away/digging out the rubbery potting compound to find that the electronics were mounted on two separate kind-of-roundish pc boards that cleverly nestled together. This is just a brilliant job of packaging. I’ll cut to the chase here and show how they fit together without the potting compound :
To put this into perspective, here’s the drive electronics from an older LED light:
(…and by older I mean about a year ago.)
Not only is the packaging quite different, but there are a lot more electronics. For example, there are three electrolytic capacitors in the older design, one of which is significantly larger. Much is made of the unreliability of e-caps, but when de-rated for temperature, they can be quite reliable. It’s their size which makes them a pain for LED lights.
Here are the two different generations of drivers side-by-side, where you can see that the Best Buy driver has two relatively small e-caps, compared to the older design.
But enough of this packaging and component stuff: What is the driver controller IC?? It must be something brand new I’ve never seen before to enable all this reduction in parts size and count, right? So now for the Big Reveal…
The “SUL B” is the marking for the Texas Instruments LM3445. But wait, this part isn’t brand new – we last saw it in the Home Depot EcoSmart bulb which was introduced in summer of 2010. (I think the LM3445 itself was introduced in early 2009.)
The entire bottom half of the Ecosmart, surrounded by the white aluminum heat sink, is electronics.
So this is verrrry interesting – what’s happened in dimming LED driver design in the past two years that have allowed circuits based on the same controller IC to evolve so elegantly? To be continued… in Part 3.
But right now is an excellent time to whole-heartedly endorse this bulb. At $16.99, this is a price breakthrough for 60W-equivalent LED lights that makes LED consumer lighting technology cost-competitive. (The 40W-equivalent version is $13.99) This is the first LED bulb that I will buy for my own use to save money while enjoying the performance equivalent to the old incandescents. Excellent job, Best Buy.