CREE MTG based LED MR16 - Page 1
Forum section: electronics / projects

author: awabill
author_rank: Newbie
timestamp: June 16, 2011, 12:44:42 am
content: Dear EEV Blog Forum Members,I'm not very well versed in electronics but enjoy following the blog, working on arduino projects and trying to learn more about the field. Recently CREE put out a reference design for a new chip aimed at the MR-16 market. I am in the process of following this design and trying to build a mock up LED MR-16 based lamp. This chip should finally enable lamp makers to have enough lumens to replace 35 and 50 watt halogen lamps.The low voltage power source I have is 12V AC. The LED driver can work off this source just fine. The issue I am having difficulty with is that I decided to try to use a actively cooled Nuventix MR-16 heatsink. This heatsink requires a constant voltage of either 5V DC or 12V DC. I would like to build a small perf board or small PCB that could rectify the 12V AC and supply my Nuventix cooler. However designing such a circuit is a bit over my head. Could anyone provide any suggestions or advice about how I can power my cooler?Bill

author: Psi
author_rank: Super Contributor
timestamp: June 16, 2011, 02:10:22 am
content: HiIs the cooler peltier based or fan based?and what current does it require at 5v / 12v ?If it's a fan then the current will likely be small enough for you to use a linear regulator.ie, Rectify the AC into DC (you'd get around 17V DC) and then use a LM7812 or LM317 to regulated the voltage down to exactly 12V DCAnother option maybe to look at the LED driver, if this can run of 12V AC then it may have regulated 5v or 12V DC available on it somewhere.You'd have to insure it can handle the extra current that you want to draw from it, so this method maybe a little too tricky for a beginner.Can you post some pics of the led driver and this actively cooled heatsink ?

author: awabill
author_rank: Newbie
timestamp: June 16, 2011, 03:00:47 am
content: Thanks for the reply. It's not a fan and I don't believe it's a peltier either. I know that it works like a speaker to puff small jets of air. Since the cooler is wired for 5V operation I think I will try to set it up to run on that voltage. The spec sheet says max current is 310 mA.I plugged these values into the National Semiconductor web bench tool. I plugged in all the parameters but I didn't have an option to indicate AC input voltage. The web bench tool has got me using an LM22674. They called out resistors and caps I would need but no rectifier. They must assume I have DC coming in?I will get some picture posted very soon.

author: Psi
author_rank: Super Contributor
timestamp: June 16, 2011, 06:19:20 am
content: You have to rectify the AC into DC first using 4 diodes and 1 capacitor.Google "bridge rectifier"Yeah, that LM22674 is a switchmode regulator.To get 5V from 17v @ 310mA you really do need it to be switchmode. Otherwise you'd need to burn off 4W of heat, which is exactly what do you don't want when trying to get rid of LED heat.If you don't want to build a regulator there are some really small prebuilt switchmode regulators available that could do that sort of output current/voltage from your input voltage. (You'd still need a rectifier though).egHere is one i found quickly on digikey, seems to be suitable, 5V output @ max 500mA and 6.5-36V DC input.http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=945-1378-ND

author: Zero999
author_rank: Super Contributor
timestamp: June 16, 2011, 05:43:18 pm
content: Going from the first post, he needs a 5V power supply to run the actively cooled heatsink, not the LED driver which can run directly off 12VAC.Is it really necessary?How much power does the actual LED need? Maybe you need a higher quality driver.Can you run the LED at a lower current so active cooling is not necessary?

author: awabill
author_rank: Newbie
timestamp: June 16, 2011, 06:56:31 pm
content: The MTG needs 1 amp. Passive cooling is a much better approach, I know. The Nuventix cooler is a novelty and might help the LED last longer. It's also the only real commercially available MR16 heatsink I could get my hands on.

author: awabill
author_rank: Newbie
timestamp: June 19, 2011, 06:35:35 pm
content: Here is a pic of the nuventix cooler. I haven't been making much progress on the project these days. Hopefully I can work on it more this week.

author: awabill
author_rank: Newbie
timestamp: June 20, 2011, 02:39:27 am
content: Thanks for all the previous replies.Later today I did accomplish some stuff on this project/experiment. I decided for the time being to power the cooler with a 5v constant voltage cell phone charger. I can hear it quietly operating and feel air movement.I later drilled and tapped the heatsink so the MTG starboard could be mounted. I attached leads to the starboard, applied thermal paste and mounted it.I attached alligator clips to the leads on the LED and ran them to the national eval board (http://www.national.com/rd/RDhtml/RD-188.html). To supply the 12V AC I wall outlet power supply that looks like a cell phone charger. My meter says it's kicking out 14 some odd volts. I searched around on the national literature and didn't find the min and max input voltages for the driver. I decided to wing it and try it anyways.With everything plugged in the MTG lit up pretty dimly and seemed to pulsate in its light output. If anyone has some ideas on why I'm getting such low light output I would appreciate your advice.

author: awabill
author_rank: Newbie
timestamp: November 24, 2011, 10:19:03 pm
content: It's taken me a long time to realize this. The National Eval board gets advertised in the CREE reference design but it turns out National ships a version of the board that is set up to run 3 Osram Golden Dragon chips at 330ma. I tried to swap out resistors on the board to get me to the 1A value I need for my Cree chip. In the process I destroyed my eval board. I think I will have advanced circuits make a couple of boards for me and I will buy the correct parts called out in the CREE reference design and assemble.I'm disappointed that no one is manufacturing an MR16 lamp with this CREE chip. The chip has been out for a while now.

author: PetrosA
author_rank: Frequent Contributor
timestamp: November 26, 2011, 04:26:56 am
content: Just an electrician's input:Don't forget when calculating input voltages that most existing MR16 lamps will be in fixtures with a dimmer installed. They may either have a magnetic transformer or an electronic one.I am really waiting for the day when MR11, MR16, PAR20, and PAR30 LED lamps can actually output similar lumens to their halogen counterparts for a reasonable amount of money. $100 or more per lamp is not reasonable...

author: Unknown
author_rank: Unknown
timestamp: November 26, 2011, 02:46:24 pm
content: Quote from: PetrosA on November 26, 2011, 04:26:56 amHow much would you, as an electrician, charge to change a few blown PAR lamps? And I wont even touch the area of how much would an electrician (not pointing at you) quote for the bare lamp in the first place....I think they should be $200 each and it would still be good value.

author: kripton2035
author_rank: Super Contributor
timestamp: November 26, 2011, 03:33:45 pm
content: I replaced last year all my mr16 12v 35w halogen bulbs with gu10 3w smd leds lightsI removed the transformers 12vac, directly feeding the gu10 with 220v acthe lamps where available on ebay for some $5 eachI dont see any difference in luminosity, only a small color differencethe lamps payed themselves on a year of electricity...I'm looking now for replacing bigger halogen bulbs (150w) with led lamps (around 15w ?)but I have to take dimming into account, and it's not that simple ...regards

author: PetrosA
author_rank: Frequent Contributor
timestamp: November 27, 2011, 06:34:51 pm
content: Quote from: Alex on November 26, 2011, 02:46:24 pmAbsolutely not. In most residential conditions, where you can reach the lampholder from a 10' ladder or less, or can use a lamp changer, it makes no sense at all to use LEDs. They're not on enough hours a day, they're almost always on dimmers which increases their lifespan up to 15 or more times and I charge $75/hour to change them. I can change a lot of lamps in an hour.In commercial use where lights are on 10-15 hours per day, where lamp changing may require special lifts and where kW/H rates are much higher, then yeah, it might make sense. The problem is, that PAR38 LED lamp that costs over $100 doesn't even have the light output of a 50W halogen lamp and it uses 24W. Even in commercial, it only really starts to make sense to many customers when changing lamps requires special lifts and they can tolerate much lower light levels. Often the better option is not to retrofit LEDs, but to swap out the lights for HID or commercial CFL fixtures.Sorry, forgot to add my lamp pricesI charge from $8-$10 for PAR 20 and 30 lamps (long life) and up to $15 for special PAR38 bulbs. For that LED I'm referring to, I'd have to charge about $125 unless the customer were buying more than 24 of them. My cost is about $115 per lamp. Simple retrofits aren't always possible due to the fact that in commercial settings there are strict guidelines for lighting levels and swapping PARs for LEDs will most likely reduce those levels to below spec without adding more lights, which in turn increases costs considerably.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 27, 2011, 10:03:30 pm
content: As a residential user, all discussions of LED lighting, cost and payback still sound like ravings from a lunatic asylum. Until I can buy a lamp for <$10USD it's a non-starter. Once CFLs came down in price they made sense and I use a lot of them. I still notice that they rarely last as long as the people who figure out payback say they should.My remaining problem area is my electronics room. It presently has 6 65-75 watt reflector floods on a dimmer. I've got another 6 or 8 in the family room, also on a dimmer. There is no cost effective solution for replacement right now, even if the payback is a couple years. $120USD in the hand is far more useful for paying bills in a tough economy than for upgrading lights for some future payback, and any LED solution is way more $$ than that.

author: IanB
author_rank: Super Contributor
timestamp: November 28, 2011, 12:58:32 am
content: I was looking at dimmable LED reflector bulbs in Home Depot just yesterday and I think they were around $20 each. Perhaps prices are coming down to a more accessible level.On the other hand, I hate the color rendition of CFLs and LEDs so I have no desire to use them. I run my lighting at 30-50% dim all the time and like the warm orange glow. When I go into a home with lights on full power I need sunglasses to protect my eyes.

author: kripton2035
author_rank: Super Contributor
timestamp: November 28, 2011, 08:00:57 am
content: there is no problem on dimming leds if you have access to the wiring and are able to rewire it in low voltageyou can dimm with 12v pwm (there are cheap ones) and then high power leds on the outputit's difficult if you want to use the existing wires and dimmers...there are circuits availables from texas, national, maxim also max16841 for examplebut they are still expansive (specially the surrounding circuitery)I wanted to replace the 12v halogen bulbs in my kitchen with led stripesluminosity is ok, but power is notI finally decides to rewire the transformer 220vac to 12vac by transformers with 220vac to 12vdcand then the led stripesit is not really expansive this way, and it gets paid in a year or so of electricity.

author: IanB
author_rank: Super Contributor
timestamp: November 28, 2011, 08:02:52 am
content: The LED lamps I was looking at are direct replacements for mains bulbs and are dimmable by a normal light dimmer. No special modifications required.

author: kripton2035
author_rank: Super Contributor
timestamp: November 28, 2011, 09:19:50 am
content: Quote from: IanB on November 28, 2011, 08:02:52 amyes these are still expensive ...

author: PetrosA
author_rank: Frequent Contributor
timestamp: November 28, 2011, 01:22:00 pm
content: Quote from: kripton2035 on November 28, 2011, 08:00:57 amI think you're right and that ultimately we will likely see a shift towards more low voltage circuits (12-24V) wired in new houses for lighting. The main hurdle will be voltage drop.