High-power LED's: the future of lighting!
but... how do you use them? where do you get them?
1-watt and 3-watt Power LED's are now widely available in the $3 to $5 range, so i've been working on a bunch of projects lately that use them. in the process it was bugging me that the only options anyone talks about for driving the LED's are: (1) a resistor, or (2) a really expensive electronic gizmo. now that the LED's cost $3, it feels wrong to be paying $20 for the device to drive them!
So I went back to my "Analog Circuits 101" book, and figured out a couple of simple circuits for driving power LED's that only cost $1 or $2.
This instructable will give you a blow-by-blow of all the different types of circuits for powering Big LED's, everything from resistors to switching supplies, with some tips on all of them, and of course will give much detail on my new simple Power LED driver circuits and when/how to use them (and i've got 3 other instructables so far that use these circuits). Some of this information ends up being pretty useful for small LED's too
here's my other power-LED instructables, check those out for other notes & ideas
This article is brought to you by MonkeyLectric and the Monkey Light bike light.
but... how do you use them? where do you get them?
1-watt and 3-watt Power LED's are now widely available in the $3 to $5 range, so i've been working on a bunch of projects lately that use them. in the process it was bugging me that the only options anyone talks about for driving the LED's are: (1) a resistor, or (2) a really expensive electronic gizmo. now that the LED's cost $3, it feels wrong to be paying $20 for the device to drive them!
So I went back to my "Analog Circuits 101" book, and figured out a couple of simple circuits for driving power LED's that only cost $1 or $2.
This instructable will give you a blow-by-blow of all the different types of circuits for powering Big LED's, everything from resistors to switching supplies, with some tips on all of them, and of course will give much detail on my new simple Power LED driver circuits and when/how to use them (and i've got 3 other instructables so far that use these circuits). Some of this information ends up being pretty useful for small LED's too
here's my other power-LED instructables, check those out for other notes & ideas
This article is brought to you by MonkeyLectric and the Monkey Light bike light.
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Signing UpStep 1: Overview / Parts
There are several common methods out there for powering LED's. Why all the fuss? It boils down to this:
1) LED's are very sensitive to the voltage used to power them (ie, the current changes a lot with a small change in voltage)
2) The required voltage changes a bit when the LED is put in hot or cold air, and also depending on the color of the LED, and manufacturing details.
so there's several common ways that LED's are usually powered, and i'll go over each one in the following steps.
Parts
This project shows several circuits for driving power LED's. for each of the circuits i've noted at the relevant step the parts that are needed including part numbers that you can find at www.digikey.com . in order to avoid much duplicated content this project only discusses specific circuits and their pros and cons. to learn more about assembly techniques and to find out LED part numbers and where you can get them (and other topics), please refer to one of my other power LED projects.
1) LED's are very sensitive to the voltage used to power them (ie, the current changes a lot with a small change in voltage)
2) The required voltage changes a bit when the LED is put in hot or cold air, and also depending on the color of the LED, and manufacturing details.
so there's several common ways that LED's are usually powered, and i'll go over each one in the following steps.
Parts
This project shows several circuits for driving power LED's. for each of the circuits i've noted at the relevant step the parts that are needed including part numbers that you can find at www.digikey.com . in order to avoid much duplicated content this project only discusses specific circuits and their pros and cons. to learn more about assembly techniques and to find out LED part numbers and where you can get them (and other topics), please refer to one of my other power LED projects.
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Loving this design! It's working really well for me so far, but I'm curious about component selection.
I'm using a (purchased) high powered buck regulator to get the voltage down to as low as I can, and still have this circuit operate. (~0.6V above the LED Vfwd) I'm building 36 of these circuits, to individually power and PWM twelve RGB LEDs (with 3 of the buck regulators, one for each colour), at 700ma per channel, so these serve as excellent low part-count CCRs. However, I'm not sure how various characteristics of Q1 and Q2 relate to the efficiency of the design. At 700ma x 36 any efficiency gains I can get by choosing the correct components will help reduce the amount of heat I have to deal with.
What kind of things should one look for in Q1 and Q2 to help with efficiency, either to allow input and output voltages to be closer, or anything else?
I'm looking at a similar project to drive 3 MCE cree LED's via a LM317 and 555 giving the PWM option for a bike light
can you advise what sort of circuit schematic and values I'd be looking at? I remember seeing a PWM circuit diagram you had on the instructible, but couldnt find it
I want to build this project http://blog.makezine.com/2012/01/02/luminch-one-offers-lumens-by-the-inch/ using RGB high power LEDS, forward current of 350mA. I will be using the Arduino Uno and I want to supply a constant current to the LEDS. Can this be done using LM317, if so how can I do it?
I have built the circuit #5. I am using a microcontroller to control the switching on and off of the LED. However, i have a problem. The LED does not turn off immediately when the signal at the Gate terminal is terminated. It takes quite sometime for it to turn off...With this, i am not able to dim the LED..Could you help me?
But as far as I understood from the text, it limits current by "turning on and off" Q2 and LEDs. So the question is will it interfere with my PWMing rate? I need to have exactly 36kHz and if transistor will also turn LED back and forth it may cause problems...?
Solar powered version:
i know a little about transistors, maybe could use a NPN for turning on the power and PNP for turning off and draining? i really dont know..
My knowledge is limited, but i wish to learn.
I do not really understand your worries why wld you need to drain anything
Wether you can connect the amount of drivers to 1 pin depends on a few things:
Please tell me the following:
what is your value of R1?
What current do your LED's draw?
Do you just want to switch them on and off or do you actually send a PWM signal to the LED's?
If your circuit is now working perfectly, it would seem the easiest to either increase the voltage so you can feed more LED's in series or drive 2 led's in series, so you need 15 drivers and then drive those via 15 diodes connected to the UNO
However, there are two concerns: will the voltage drop over the diode affect opening the FET (but you can try this with one diode), and will the 15 drivers not draw too much current from yr UNO (that is why I was asking about R1)
How much current do your LED's draw. Are they just regular LED's? or power LED's
i would like power around 50-100 high powered LED's...
i have and would like to use:
12vdc 10A power supply (maybe 24vdc and just hookup more LED's in series to makeup the difference and use less drivers in the future)
IRF540N 33A/ 100V/ 0.040 Ohm/ N-Channel Power MOSFET with heatsinks
2N3904 transistor
0R75 ohm 2w resistor
100K ohm resistor 1/4W (i could use different values if specified)
3x 3w epistar white 3.2-3.8v 700mA LED (per built driver) and i can adjust the voltage on dc power supply(11vdc/3 = 3.66vdc each LED)
a fan for the breadboards
and an Arduino uno to control the PWM with one or two pins
now i would love to build this in a way that can PWM control these drivers with one or two pins on the Arduino. i starting building the driver in circuit #5 (and 3x 3w LED's) with great success but when i hooked up TWO drivers to one pin that is when driver #1 LED's would flicker and driver #2 LED's fade out and work like it was suposed to...(programmed the arduino to fade in and out slowly for testing purposes)
so that is when i needed help. i got to thinking.... i suppied circuit #5 with 12vdc to the LED's but i controlled the N-Channel Power MOSFET with my ARDUINO SO what if i suppied the MOSFET or transistor with 5-9vdc or 12vdc and made it supply ALL the drivers somehow. but if i do that, when the power is ON everything will work(i hope) and when the power is OFF, everything might flicker because there is no "DRAIN" hooked up to that circuit.(just like my experiment showed hooking up the drivers directly to the Arduino UNO) i dont know circuitry too well to accomplish this task so i needed some help.
any feedback would be greatly appreciated.
Thank you.
I replied to that message. didn't you get that reply?
Well there might be various reasons for the flickering
I asked about the value of R1 (the resistor connected to the Uno pin). It seems most likely that the two drivers are influencing eachother. diodes maight be the answer but I need to know the value of your resistor R1 is that the 100k Ohm you refer to?
Although theer might be different solutions to your problem (e.g. separating the circuits with diodes or transistors, your thinking of switching all the drivers on and off with another FET is good.
I do not really foresee the problems you mention (and are guessing about).
One of the problems you may have is that you are using an IRF540N FET. As I understand that is designed to work with about 10 Volts as a trigger and though it is odd there would be a difference in how the two circuits you built react, it is well possible that one of the circuit sjust does not get enough trigger voltage from the Arduino.
Nevertheless, driving all the drivers as a load by another MOSFET should be possible (then ofcourse you would need to change yr circuit accoring to say #2 or 3#)
Nevertheless, you may try something else:
Change your circuit into circuit #2 or #3 (does not matter which one) and put a transistor in parallel with R2 or Z1 and add a 10 k in its baseline. Drive that 10 k with your uno. That should work. (although it will invert the signal: high = off, Low=on)
As I am not building this myself it is a bit of trial and error, but subsequently you could go two or 3 ways. The easiest would be to give each of your drivers their own transistor and connect these all to one Arduino pin (make sure you do not draw more than I think 40 mA) or you could hook up all the circuits to one transistor (but I'd suggest you would use separation diodes then).
I suggest you adapt the two circuits you built in the way i describe and see if you can drive both of them with one pin
I am glad I could have been of help. It took a while before I exactly understood what you wanted, but I am happy you got what you wanted. I hope it all will still be fine with a dozen of them, you may need to trim the value of R3 perhaps.
Go dluck and if you need more help don't hesitate to ask
I want to build a constant current source which has input voltage between 3-311v.
how can i make it with low cost and transistor based circuit?
Thank you very much.
that is kind off a stretch. Do i understand correctly that you want 1 circuit that can drive 1 LED with 311 Volt as well as 80 LED's with 311 Volt?
if the LED is 3,2 Volt you would need a transistor that can take at least 310 Volt as Vce or as much as (311-80x3.2)=55 Volt when you use 80 LED's.
Going by the circuit I just uploaded before (but you are going to need a different transistor) you would need an emmitter resistor of about 30 Ohms (1/4 Watt more than enough). But I would not know a transistor that can take 310 Volts just from the top of my head. Even the BU111 can only take 300 Volt, but even then, that would be overdoing it as it can take 6 amps and u only need 20MA.
The MJ16110 can take 400 Volts, but at 15 amps and tht is looking launching a scud missile to kill an ant. I am really not aware of a 350 Volt 50-100mA low power transistor.
If beforehand you would already know that you will drive 80 LED's then it becomes a whole different ballparc because then a BC546 would be enough.
I am not saying you should do things different from what you plan but as far as I understand your plans you are setting yourself up for trouble and high cost, whereas it could be simple and cheap.
Also, are you really bound to 311 Volt? because even with 80 LED's you still will be turning 55 Volt*20mA=1 Watt into heat.
Perhaps your project will still be possible if you rethink a bit what you are doing
One may want to consider taking circuit 4 and replacing the zener with a transistor that has its base pulled low via 1 M resistor and that receives its PWM signal via a (say 4k7) base resistor
http://www.mouser.com/Search/ProductDetail.aspx?R=1N5334BRLGvirtualkey58410000virtualkey863-1N5334BRLG
I bought a bunch of MC34167's hoping to run some led's with it, only to find that it doesn't have current sensing. So you saved my reer.
To make sure of the Forward voltage drop being close to your input voltage though, the MC34167 is a tremendous choice. It is a single chip step up/down converter with a minimum of external components available that will get you to the correct voltage for super cheap and not have to worry about heat as it is crazy efficient.. I now use this along with most of your circuit for current control for 4ampere's worth of 100lumen/watt led's in an automotive environment....... CRAZY bright. And no heat given off anywhere except for the LED's themself. Best of all, no need for an O-scope and you can get this much efficiency. Lets face it, if you have a $4000 scope you can make your own PWM circuits and not have to worry about any of this. But if you don't it is good to know there is still ways to do things.
When calculating the wattage of resistors in version 1, it would be of great educational value to demonstrate the calculation using the Power=I*I*R formula
Great job.
This will be for a mtn bike light so the heat sink will get plenty of air flow.
biglongurl
Unfortunately, the current doesn't seem too stable. :(
the voltage is 13-14v
my battery runs 12v (car off) and 13.6v (alternator charging)
would this be acceptable to run direct from battery, or should i run a dc-dc converter
the link is what i'm looking at
http://cgi.ebay.com.au/5-PC-BRIGHTEST-25W-WATT-HIGH-POWER-WHITE-LED-1400-Lumen-/390118430163?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5ad4ded5d3