# AC driver dimming solution?!?!



## Kandela (Sep 9, 2010)

I'm somewhat new to the high power LED world, but not that new to electronics in general; currently a student in the field..

I want to power 4 cree's for a nice counter top light, I want it to be dimmable, and I want it to run off the wall, and be COST FRIENDLY while having major brand parts for reliability.. My problem is thus; I can't find a suitable dimming solution... I could use a buck puck to make it simple, this is around 20$ to get one that I can easily dim 5-95% or so, and can input up to I think 24v DC or AC... They do not make one that supports line voltage 120VAC.. This seems like a OK solution, but then I'm going to use a wall-wart to power the buckpuck, this seems wrong and counter-intuition; using a AC/DC converter to power a DC/DC converter, especially when the specs of the AC/DC converter are not really known other than 12vDC, 750mA output... I can just see the wall-wart NOT agreeing with the driver's demand and fluctuations in demand and causing issues... Does anyone agree?

My second option was to try a MagTech driver (17$) that would work off line voltage, and use a regular wall dimmer to chop up the wave going into the driver for dimming... I'm not sure if this would work, their website has alot of info on dimming, but nothing that clearly states if a regular driver can be used with a regular wall dimmer on the input. It mostly focuses on their more expensive drivers with 0-10v or PWM dimming.. I'm afraid if I try it, the driver is going to suffer massively from trying to render a chopped wave into the DC output if it's not designed to do so...

HELP! Does anyone know of a suitable driver that can take 120V dc, output 350-1000ma, and is dimmable or can be dimmed via regular wall dimmer, and is around 20$ or less, PLEASE LET ME KNOW! I'm a broke college student, not trying to blow 25$ on a driver to have it melt into a scarring blob on my counter! :duh2:

Also, please give input on using a wall wart to power a buckpuck! Is this safe/acceptable?

(PS- dealextreme's stuff scares me... it screams cheap components)
lovecpf THANKS! new poster, long time troll


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## qwertyydude (Sep 10, 2010)

60 hz ac flicker on led's can be annoying, you'll see it whenever you move under the light because it ends up being half wave rectified if you try a standard dimming solution. Stick with dc.

Would you be willing to settle for 3 led's? I say so because this is exactly enough to make it 12v compatible. All you'll need is a low value dropping resistor of about .5-1 ohm, 1 watt resistors inline with the output of this fabulously cheap regulator/dimmer with a nice aluminum knob to boot.

http://www.dealextreme.com/details.dx/sku.5986

If you can find a 16v power supply, ebay is full of them for about $10 delivered, you could do 4 leds on the dimmer, the controller can handle the extra voltage as long as you make sure current at max is limited to less than 2 amps, which would blow the led's anyway. So match the resistor. On second thought you may want to spend a little more since on closer inspection it's just a rheostat. You can get a heavier duty fan controller, with fan too so you can cool your leds too lol, you can't seem to buy the controller individually. 

http://www.newegg.com/Product/Product.aspx?Item=N82E16835200027

This would be the simplest build. Just wire the power supply to the regulator input, the output is connected in series with the resistor and 3-4 series connected leds. Turn the knob to low so you don't blow the led when you turn it on and measure to make sure max doesn't overload the led. If so add more resistance in series. This ought to keep the whole build under $20, unless you also have to buy the led's with the $20 in which case you may be screwed because 4 cree led's cost about $20.


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## Kandela (Sep 10, 2010)

Yes, I *could* settle for 3 leds but would perfer 4.

Your route is pretty cheap quick and dirty, it's not my preference. You're basically telling me to rely ENTIRELY on resistance for all power control. Firstly the resistors and pots needed in that situation would need to be around 2W to be on the safe side, thats alittle harder to find and more expensive, but my main concern is how LOSSY this would be. It would be making alot of heat, and kinda negating the real reasons for me to convert to leds, the efficiency. Also I'm not sure, but I think power control in this form is really, really abusive to leds, would shorten the life and brightness, and lossy again in general. Wave shaping or PWM is definitely much easier on the led, more efficient, and helps keep colors stable.

-I was trying to keep the driver itself in the 20$ range. I would say I have 80$ to spend total. I figure 8$ tops shipped per led=32$,20$ for driver, and 28$ or whatever i need for random hardware like metal heatsinking, thermal grease, wire, switches, screws, etc etc... I'll probably be making a simple enclosure out of aluminum diamond plate because it's so purty and cheap in my area.. plus the polished aluminum backside should make a good mounting surface.

I suppose I could hit the books and make a nice PWM 555/fet circuit, but I doubt it'll be efficient, and I'd rather drop 20-25$ on something reliable and already tested, besides a custom brew PWM power supply, is... well at my level of knowledge, atleast an entire weekend or more of researching, reading and soldering, and probably atleast 15$ in parts and solder... help me peeps!


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## Mkala (Sep 10, 2010)

The best solution I know to use with wall dimmer (triac dimmer ? ) is from National :

http://www.national.com/analog/led/triac_dimming

It is a specialized LED driver, without flickering issues.


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## doctaq (Sep 10, 2010)

for your application if you can live with one or two brightness levels you can build a transistor based led driver

http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/

replace r3 with two resistors in parallel with a switch to have two levels of brightness


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## Steve K (Sep 10, 2010)

doctaq said:


> for your application if you can live with one or two brightness levels you can build a transistor based led driver
> 
> http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/
> 
> replace r3 with two resistors in parallel with a switch to have two levels of brightness




I'm not sure that most triac dimmers can drive an inductive load like a wall-wart. I believe they are usually intended for resistive loads like incandescent bulbs and heating elements.

regards,
Steve K.


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## Kandela (Sep 10, 2010)

*Steve, doctaq's post didn't mention triacs, but you are still right, all ordinary drivers SHOULD NOT or more than likely CANNOT be used with a triac dimmer for that specific reason... Do you know why?? Would this help or fix it? The datasheet for it is lacking.... to say the least...

http://ledsupply.com/9005.php

Sigh.. makes me wonder if I should've gone the engineer route.. :ironic:

doctaq, that's a nice instructable, very clean and minimal parts, could be decently efficient depending on the quality of the fet and wall-wart, the other transistor should'nt matter much, but i'm still trying to stay away from homebrew. Besides, there's some amazing drivers to be had in the 10$ and less range specifically for powering 1 led with some amazing functionality and efficiency at the 10$ price point..

Mkala, that thing is puuuurty *coo* Looking around I see chips for around 4$ and a entire ready to go board for around 100$, so it seems like with this chip you still have to do alot of "homebrew", soldering and designing around the chip yourself, unless you got the fat wallet. However, with how sexy that chip is, it may be worth looking into. If I can't find a suitable driver ready to go out the box for around 20$ This will probably be my route. Awesome find. Do you have any personal experience with it?

-Anyone else reading this, any experience with LM3445?


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## doctaq (Sep 10, 2010)

i'll build you one if you want, what current do you need, i can provide leds and a power supply too. 15v 1A and xp-e q5 cool white. pm me if you want it cuz i gotta find out how much i paid for parts


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## Kandela (Sep 10, 2010)

Or; use these forums and share your knowledge with the world!! :welcome:
:wave:


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## doctaq (Sep 10, 2010)

Kandela said:


> Or; use these forums and share your knowledge with the world!! :welcome:
> :wave:



? me?


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## Kandela (Sep 10, 2010)

Yea, just saying... Not trying to be rude but I was saying multiple times I'm trying to stay away from homebrew, and that if I had to, I could build one from scratch.. Besides, it'd take quite a garage tinkerer to beat the efficiency, size and ease of use of a buckpuck @ twenty bucks shipped in a reasonable amount of time. If you can offer something as reliable and efficient for less, I'd consider it. But really, if I was going to go homebrew i'd still probably go deal extreme over homebrew, they offer drivers I should be able to tinker with and modify at around 5-10$ each.

I guess you could say i'm afraid of this thing failing, I abuse my regular leds, but when i'm paying 8$ for something not as bright as a 30cent incandescents, I take it much more literal, and use store bought parts and drivers to try and make back every cent I spent. I've had a few high power led projects, and i've been "textbook" about each one and have never had a fail or even so much as a minor problem, everything has gone perfectly fine!~ *crosses fingers*


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## Mr_Light (Sep 10, 2010)

I made a lamp with 8 Cree XREs 2 X 4 parallel drive from a surplus 16V laptop AC adapter with a buckpuck with integrated dimmer. This was the cheapest solution I could think of using UL listed components. I am nervous using cheap DX class AC components. Works great.


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## qwertyydude (Sep 10, 2010)

It's rather difficult to satisfy every condition you're asking for. You're asking for pretty much a custom power regulator, off the shelf, power efficient, with complete reliability for extremely cheap.

These kind of things it's better to build yourself. Perhaps you'll learn electronics more along the build. Because if you're gonna ask the forum to do all the searching, research and design for the electronics you're probably not going to be happy with the results. There are a lot of very qualified people here who could easily design these systems perfectly but for $20 you'll get what you pay for. With that in mind this is the only thing I could possibly find that is off the shelf for less than $20.

http://www.amazon.com/dp/B003L4KKF2/?tag=cpf0b6-20

Please don't say now that box is too ugly or PWM flicker is unnaceptable because if you're not willing to go with a lossy resistance either through a varistor design or with hard wired resistors. I really don't see an acceptable solution for you.


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## Kandela (Sep 10, 2010)

Mr_Light, do you know what amperage the p/s was, and does it ever get hot? What kind of % dimming would you say you get?

qwerty, I'm not trying to be like that, just have a budget and needs that I know can be met in that budget off the shelf.. Not really custom, just 120v AC with dimming, as in residential use, at a budget cost. DC drivers are everywhere with dimming in and around twenty bucks, incorporating these into residential is somewhat new and I'm not sure of the avaliability of drivers out there. It's not like i'm asking for the death star. I'm just asking for a off the shelf alternative!

edit* The thing in the link is going the wrong direction, the buck puck is the same price and offers way more input and output options and control.


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## qwertyydude (Sep 10, 2010)

If you're worried about efficiency too forget about using an AC transformer and AC buckpuck. Those things waste as much power if not more than any resistored dimming device for led's. Low power wall wart transformers are usually only 60-80% efficient so the one watt of power dissipated by a dc varistor system is probably eclipsed by the two watts of heat produced by an AC transformer especially the accumulated losses of that transformer plugged in and not being used. In fact European efficiency laws are what really drove the push to eliminate wall warts in houshold devices, which now use digitally regulated power supplies, case in point every plug in phone charger you see uses a digital power supply.


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## Kandela (Sep 10, 2010)

really? Well i can't say I know for sure, but I would def think a buckpuck driver and switching wallwart or what have you would beat a purely resistive regulation anyday. If not in efficiency, surely in led life. Besides, like i said the buckpuck has way more options than a standard rheo design, for the same price.

-I realize the lost power while it's plugged in but not used.. One portion of my design was to include the wall-wart inside the cabinet and have the on/off switch prior to the wall-wart. Tear open an old power cord or something... Yep yep! cheers!


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## Steve K (Sep 10, 2010)

Kandela said:


> *Steve, doctaq's post didn't mention triacs, but you are still right, all ordinary drivers SHOULD NOT or more than likely CANNOT be used with a triac dimmer for that specific reason... Do you know why?? Would this help or fix it? The datasheet for it is lacking.... to say the least...
> 
> http://ledsupply.com/9005.php
> 
> Sigh.. makes me wonder if I should've gone the engineer route.. :ironic:




Triac dimmers just cut out part of the AC voltage sine wave. That works fine with a resistive load, but causes problems with inductive loads because you can't just stop the current in an inductor! 

Only LEDSupply can tell you what is in their gadget. I don't know what's in the Acriche device either, so I really can't help. Maybe the LEDSupply gadget is just a big power resistor??

On Semi has an excellent handbook on triacs and other thyristor devices:
http://www.onsemi.com/pub_link/Collateral/HBD855-D.PDF
240 pages of leisure reading! 

regards,

Steve K.


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## Mr_Light (Sep 11, 2010)

Dimming with the prewired pot goes down to about 20% (visual estimate) before shutting off. The AC adapter is from an IBM Thinkpad 16 volts 3.36 amps. Doesn't get warm at all.



Kandela said:


> Mr_Light, do you know what amperage the p/s was, and does it ever get hot? What kind of % dimming would you say you get?
> 
> qwerty, I'm not trying to be like that, just have a budget and needs that I know can be met in that budget off the shelf.. Not really custom, just 120v AC with dimming, as in residential use, at a budget cost. DC drivers are everywhere with dimming in and around twenty bucks, incorporating these into residential is somewhat new and I'm not sure of the avaliability of drivers out there. It's not like i'm asking for the death star. I'm just asking for a off the shelf alternative!
> 
> edit* The thing in the link is going the wrong direction, the buck puck is the same price and offers way more input and output options and control.


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## Kandela (Sep 11, 2010)

Nice, that's a hefty supply to have sitting around though, the best i've got is 12v @ 750mA, that i'm not using... I'll prob go my original/mr.light's route!


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## doctaq (Sep 11, 2010)

if you use a buckpuck with that youre only going to get 10v which is pushing 3 leds depending on what you use

as for dx drivers ive never seen even a discrete dimming model, they do have a 3 led 900? ma model that was interesting, i wouldnt suggest dimming any ac driver through the ac side or pwm . maybe a meanwell eln 60 48d? although its probably a big larger than youd want


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## SemiMan (Sep 11, 2010)

http://www.roallivingenergy.com/pdf/Tropo Ballast Replacement.pdf


This does pretty much what you want I believe. They work.

Semiman


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## qwertyydude (Sep 12, 2010)

I can't find that even for sale and the closest one I could find like it is $36 plus shipping.


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## SemiMan (Sep 12, 2010)

http://www.futureelectronics.com/en...True,Ns:P_Price1|101|1|,Nea:True,N:4294900296

Lots in stock but yes they are $30+. They work. They take no time to implement. They are off the shelf. They plug directly into AC with no transformers or power supplies. You get what you pay for.

The DIMRIGHT from Luxdrive goes in parallel across the Acriche. It draws a maximum of 1/2Watt. Likely it is an "intelligent" parasitic load which is what dimmers seem to like.

Semiman


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## Kandela (Sep 13, 2010)

doctaq, correct, I realize wallwarts are going to have a different value with a different load..? I havn't had the time to try it yet, but will soon, but I'm assuming that since led's are not very resistive and that there probably won't be a single resistor in the circuit (besides in the driver) that the output will likely be higher than it's rated?? Not sure, kinda a very very broad assumption. I understand that generally you estimate the output LOWER. I'll def meter it once it's all hooked up aswell.

Either way I'm powering 2 strings of 2, so I really only need 8v(MAX 9/10 depending on driver's drop). A 12v wallwart will hopefully give me that. I just found one this morning in my closet with 8v 1.0amp, might use that one aswell... I'm thinking that I'll be pushing either one to their max about though, so I may ended up going with a used dell laptop wallwart, 19.5v, 4.62A, switching, unreg... (under 10$)

*SemiMan, THANKS for chipping in! That's pretty much EXACTLY what i'm looking for I'll check it out in detail later on, but 120v input, C.C. output, dimmable, 30-35$, excellent! Sure there had to be something, nice! Thanks!
^


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## Mkala (Sep 13, 2010)

Kandela said:


> Mkala, that thing is puuuurty *coo* Looking around I see chips for around 4$ and a entire ready to go board for around 100$, so it seems like with this chip you still have to do alot of "homebrew", soldering and designing around the chip yourself, unless you got the fat wallet. However, with how sexy that chip is, it may be worth looking into. If I can't find a suitable driver ready to go out the box for around 20$ This will probably be my route. Awesome find. Do you have any personal experience with it?
> 
> -Anyone else reading this, any experience with LM3445?



Yes, this solution requiere a lot of work, knowledge and equipement... unless you buy the demo board (if it is ok for your application).

No I have not tested this chip. It is relatively new and look promising.

I have found another approach from another chip maker :

http://www.powerint.com/en/applications/led-lighting#design_examples1

Here you can found design reports / ideas.
One more time, this requiere time, serious knowledge (even more than National I think, you have to wire the transformer)

For a ready-to-use solution, SemiMan have found a good thing I think


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