Why the lack of dimmable CFL and LED mains voltage lamps? - Page 1
Forum section: electronics / projects

author: e100
author_rank: Frequent Contributor
timestamp: June 21, 2012, 10:17:33 am
content: I was in Bunnings today looking for a CFL lamp that would work with a triac dimmer and there were only 2 out of about 50 different types that were specifically labelled for use with a dimmer, and both of those were physically too large for my light fitting.Somewhat dissolusioned I purchased a 4W Osram LED light just to see how it compared to a no-name LED light I bought on Ebay earlier this year. Looks good but is not dimmable just like all the other mains powered LED lights I saw in Bunnings. The brighness stays the same as the phase angle goes down then it starts to flicker and finally goes out.I would of though that adding phase detection and PWMing the LED in sympathy would have mimal impact on the cost given that these LED lights aren't exactly cheap. Then again, perhaps it has something to do with achieving the claimed 25 year lifespan.Mike

author: Psi
author_rank: Super Contributor
timestamp: June 21, 2012, 12:17:30 pm
content: The dimmer devices haven't really caught up with leds yet. Using a triac dimmer for leds is a bit silly.The LED modules should really be supplied with PWM DC directly from a dimmer intended for LED modules, but so far i don't think they exist in the retail market.

author: mukymuk
author_rank: Contributor
timestamp: June 21, 2012, 02:30:42 pm
content: The issue of triac dimming LED's has to do with the LED power supply, not the LED itself. Power Integration is one manufacturer that's addressing this emerging market. They have a lot of design kits that demonstrate triac dimmable LED power supplies.The problem with powering an LED module from a dimmable DC supply is that it represents a paradigm shift in light dimming--millions of triac dimmers are already in place and it's just not cost effective to replace them.

author: free_electron
author_rank: Super Contributor
timestamp: June 21, 2012, 05:24:19 pm
content: the power supplie sof these things need to look at the average incoming voltage and control the led or ccfl. dimming an led is easy. dimming a ccfl very hard. under a certain voltage the ionisation stops and the lamp will stop conducting..as for lack of dimmable led's.. a quick look a the local store here shows at least 80% dimmables.. samsung , osram , ge , sylvania and some other brands.

author: johnnyfp
author_rank: Frequent Contributor
timestamp: June 21, 2012, 08:28:00 pm
content: Mitre10 and Bunnings do a 4w Marexim Dimmable LED. But they cost $100 compared to the $20-$30 for the non-dimable version.Problem is that these lights are still young. I've been through 22 of these things, 14 are those cheap Chinese 100LED mains types that are wired in Series with a cap and when one LED dies the whole lot stops.Then I've blown 6 where the cheap Chinese power LED ones with build in switchmode and three power LED, and 2 where Mitre10 and Bunnings bought name brand power led with switchmode. The issue is that they over heat and the switchmode die because for example they use cheap cap's that are only rated to 85c.There just not quite there yet.

author: T4P
author_rank: Super Contributor
timestamp: June 22, 2012, 12:31:59 am
content: Yeah they are putting a big markup aren't theyFor example a CREE XML-T6 XMLAWT-00-0000-0000T6053 only costs 8.44$ in one-off quantities ... and that's a very efficient diode ...143lm/W ... So why are they charging massive bucks for a 10W LED ?A 3C/W natural cooled heatsink costs 2$ from OhmiteAnd i'm pretty certain the smps+CC circuit doesn't cost a lot does it?(ALL USD PRICES FROM DIGIKEY)

author: e100
author_rank: Frequent Contributor
timestamp: June 22, 2012, 10:12:19 am
content: I did some more research and found this useful page that explains different techniques for dimming including trailing edge dimmers used for capacitive loads which I didn't know about.http://sound.westhost.com/lamps/dimmers.html

author: codeboy2k
author_rank: Super Contributor
timestamp: June 26, 2012, 12:48:52 am
content: just saw this today. TI released it in May this year.LM3447 - Phase Dimmable, Primary Side Power Regulated, PFC Flyback Controller for LED Lightinghttp://www.ti.com/product/lm3447?DCMP=hpa_pmp_lm3447_kr&HQS=lm3447-bti-krIt monitors the phase angle of the incoming AC waveform (after rectification) and dims accordingly, regulating the DC power point (VxA) to the primary side of the isolation transformer feeding the LEDs.Datasheet here:http://www.ti.com/lit/ds/snosc65a/snosc65a.pdf