An interesting question as to why need electrolytic capacitors. A portion of the problem is indeed avoiding flicker, although I am not convinced that a small PP capacitor right behind the line rectifier would not be adequate. Of course one other challenge is the emphasis on absolute minimum BOM cost, notwithstanding the quality problems that result. One dollar more to assure the 50K hour lifetime would be quite reasonable to me.
What I think to be very interesting would be a cost breakdown on the various devices, since I doubt that any of them has over $5 in electronic parts, and I am talking Digikey prices. Knowing just where the cost lies would be a very good start.
I have also wondered about why nobody markets an LED device that uses the rectified line voltage and a current limiting resistor, and perhaps 80 or a hundred "fairly bright" surface mount, or even through hole, LEDs. No filtering, just leds on the full wave rectified line, with 120HZ flicker, which I don't think we could see. Does anyone see a fundamental problem with that?
I bought a LED desk lamp recently which runs off a switching "wall wart" type 20W supply. The separate PSU is probably good for 50000 hours. The way forward with LED lamps is probably to decouple the bulb from the power supply - the low voltage DC supply should be part of the lamp socket, not the lamp itself.
I don't see why the electronics needs electrolytics. If you full wave rectify the AC, it should be possible to operate the LEDs only during each half-cycle - at 100 HZ the flicker should not be visible? You could still have a switch mode inverter running to power a string of LEDs at several tens or '00s of Kc during each half-cycle? Tony41, or any other hot shot designers, could you comment?
I have been disappointed in both the cost and the working usefulness of the LED bulbs. Another thing that bothered me was (at least one brand) the lamp base was hot...seems to me if a light is generating heat it is wasting energy. I am amazed at the current cost for these bulbs and not at all happy with CFLs! The "working usefulness" issue for me is the directional-ness of these bulbs. They may work great in a reading lamp fixture or an overhead can (ignoring the heat concern) but for general lamp fixture use such as ceiling dome lights, floor/table lamps they do not shine the light in the right direction!! I am not yet going to use these and currently must suffer with CFLs to keep my electric costs down. At least with CFLs they are cheap.
Great article! I also deeply agree with Tony41.
These new LED bulbs are the same kind of trash as currently available CFL. They are intended (supposedly) to replace standard incandescent bulbs. As most bulbs are installed hanging from the ceiling, usually inside a recess, you have your fragile electrolytic cap and other components subjected to the higher possible temp! Very smart engineering!!!
And c'mom, 3 to 4 hours a day? I have a couple of lamps around my house installed for safety reasons that stays on from sunset to sunrise (~7 PM to ~6 AM). You can imagine how will be the lifespan of these electronics, staying hot for 10+ hours in a row everyday...
I have been developing LED lights for many years. I was the first to put them behind a LCD large flat screen for outdoor advertising in direct sunlight.
I would not purchase any of the LED light bulbs on the market today. The LED's may last a long time but the plastics and power supply components will not.
I designed and developed my own LED lights for my home because I could not find one I would purchase. I use long life components as well as RGB LED's to give me the color spectrum needed for proper lighting. I have also been able to get a bright light that is brighter than an equivalent 100 watt light bulb. I have experimented with quantum dots but it dimes the light too much to get a color shift.
I can dim them just by turning off a few LED’s at a time with a switch. I have an LED module that is 2” X 2” X 1/4” thick plugs directly into 120VAC as well.
I can also power them from batteries charged by a solar panel. During a power outage I have lights when all around me are black.
I can see why LED lighting is failing to gain traction in the US. I have been unemployed for over two years and cannot get a job, however just working at home I seem to be well ahead of all of you.
NASA's Orion Flight Software Production Systems Manager Darrel G. Raines joins Planet Analog Editor Steve Taranovich and Embedded.com Editor Max Maxfield to talk about embedded flight software used in Orion Spacecraft, part of NASA's Mars mission. Live radio show and live chat. Get your questions ready.
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