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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 1Overview / 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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Anyhow, thanks for a great post!
I have since chosen a 36v DC supply ( so that I can connect more LED's in each series and maximise efficiency) and found that it once again alters the formula slightly. With the 12v supply I had a steady 302ma current, but with the same circuit and 36v input I am showing a steady 326ma. I am currently using a breadboard, so I'm not sure if the higher voltage is proving more efficient at driving the current through the connecting points... maybe, but I'm rusty as hell with electronics!
The good thing is that the Vgs on the MOSFET is sitting around 3.6v, so no danger there!
Anyway, thanks again for this fab cicuit, and I hope my findings help some others with their experiments!
So, Thank You!!
anyone know.
And if you would 'use this with a microcontroller' (though I do not understand how a microcontroller would deliver such high currents) the Voltage would most likely be 5 V to begin with. Or am I missing something?
I am building a constant power source driver for UV LEDs (4 nos) (High power 11W UV LEDs). The data sheets are as below.
http://www.ledengin.com/files/products/LZ4/LZ4-00U600.pdf
Could you please let me know if I can use your circuit for this.
Thanks in advance
First of all, I couldn't understand why did you insert the R2... Since I needed more input power, I just verified my NFET datasheet (IRF260) and Q1 (BC548) components and I noticed Q2 supports until 200V. So, I connected all the circuit at 180V, (an local 110V plus half-wave retific and filtered voltage). This power in drives a string of 40 5mm white leds (40x3.1=124V).
I know I could put more leds until reach near 180V, but I preferred put 3 paralel strings of 40 LEDs (a resistor was added in series on each LED string in order to fit all the strings to the same current). Of course, NFET will waste the extra voltage, but it doesn't matter to me, the important is to sustain the same 60mA constant current (3 strings of 20mA LEDS) and for this, the circuit is perfect.
So far, so good but, I have questions to ask for the group: what would happen with my 120 LEDs if Q1 openned its base or other else problems with this component ? There is a way to introduce a protection for them?
and more: How this circuit would behave if I strobe the LEDs feed with any flip-flop? it seems that the voltage delay a bit to fall when I just insert the leds... so, in a pulsed condition I belive the leds power will rise a bit.
Thanks
I found that anything above 500mA and I needed a heatsink on the fets, so I bulked them up. I then found that the current actually drops after 900mA.. wasn't the driver, it was my tester diodes needing a fan on the tester heatsink. :p Now it runs steady at 1000mA, and can be dimmed to as low as 100mA. I modified with a 10ohm 1/2w trimpot, and a 10ohm 1/2w resistor paralleled with the trimpot.. making a 5ohm 1w variable resistor. Results.. an "adjustable" constant current driver. :)
Works out to about $8 a driver.
I also found that splurging for 24v sources is actually cheaper than using 12v from an atx psu... less drivers needed in the long run.
I have been watching the progress of your project with interest, I am constructing something very similar myself and you are a couple of steps ahead of me which has been quite useful. I'm interested in how you have incorporated the PWM signal into the constant current driver. How are you generating the PWM signal? I have made some analogue, adjustable PWM generators using 555 chips, I read in an earlier post that you were outputting the PWM signal through 2N2222's, so it sounds like a similar output to mine.
Any advice appreciated, Thanks.
I went back to using 3 10ohm 1/2w resistors in parallel with the 10ohm 1/2w trimpot. This gives a 2.5ohm 2w variable resistor. And with a 24v power supply.. it starts at 250mA and goes to 1200mA or so. I've only gone as high as 1100mA.. then dropped right back down to 1000mA.
Thanks for the info, I will look into it.
In the batch of pictures you recently posted, there was a circuit layout diagram. Could you explain the route the pwm signal takes please. It looks as though you have it coming into the base of a transistor. Sorry to be a pain, just need this small point clearing up.
Many thanks :)
It's taken from a schematic that used to be posted here.. I just swapped the 2m2222 transistor with another FQP50N06 in it's place.
All parts, except the boards and standoffs, were ordered from Jameco
- Trans MOSFET N Channel 60 Volt 50A 3-Pin (3+Tab) TO-220 Rail - FAIRCHILD FQP50N06
- 3 LD PLASTIC PKG (APK=AM) - FAIRCHILD 2N5088BU_NL
- RES, CF, 10 OHM, 1/2 WATT, 5%, (100 BAG)
- POT,10 OHM,3299Y-100,25-TURN,.5 WATT,CERMET
- HEASTSINK, 531202B02500, TO-220 POWER W/PINS BK - 7.5°C/W
- Connector Terminal Blocks 3 Position 5mm Solder Straight Thru-Hole 16A
- Connector Terminal Blocks 2 Position 5mm Solder Straight Thru-Hole 16A
The 100K power, and 1K PWM resistors I already had on hand.
I also just did up an Eagle CAD layout.. I may just have to try etching instead of actual wiring.. it looks soooo much easier :p.
You should be able to see what's going on with the PWM signal now.. I labeled the pins. In "my" circuit, the PWM is selectable by the jumper pin just above the input terminal block. Positions 1/2 = normal mode. Positions 2/3 = PWM mode.
Just remember to connect the PWM's ground to the power source's ground.. I did this by twisting the ground wire of the Arduino with the ground wire of the 24v source, then inserted into the terminal block. I plan on having a junction box, with all power supplies and PWM signals, where they get rerouted to their various destinations. This will result in the Arduino being grounded within the junction box, and the 6 PWM signals can then be shared by as many drivers as you want.. within reason. I have 21 drivers in total.. 6 wavelengths, with 1 wavelength spread over 2 drivers per box. So.. 6 wavelengths that can be PWM'd. And seeing as I have 21 drivers, or 18 PWM instances.. I can share each PWM signal with 1 driver/wavelength per box.
Thanks, that's exactly what I was after. Nice diagrams btw ;)
One other small thing, I assume you are running the arduino pwm generator at a fairly low voltage, say 5V or whatever, and the led driver has a 24V supply. So all I need to do is power them from their respective voltages and tie the grounds together like you say?
Many thanks for your help so far, I'm really close to getting this going now.
I made an Arduino for the PWM. It's an Atmel based microcontroller board. The actual script I'm using comes from the coral reef community.. fades up, fades down.. sunrise, sunset. The chip I'm using is the atmega328.. 6 PWM pins. There's bigger atmegas that have something like 14 PWM pins, but that's surface mount.. haven't done that yet :p. You can buy premade.. but where's the fun? :D
Google "Who wants a cheap, simple, Arduino-based LED controller?" at reefcentral.. has the script there, as well as a pcb project for the board. My board was a different design, but they added more things.
Any key component with a set point that may vary by 100% is surely utterly useless.
You will not know untill you receive the PTC exactly what its trip point is.
The example shown raises more Q's than A's:
You may end up driving at the desired 500mA or the unwanted value of 250mA.
The circuit copied by the poster possibly employed this method but I'll bet the PTC 's were carefully sped'd & tested to be sure they were within an acceptable range, not something the hobbyist can easilty do!
In the battery pack of Laptop are Ptc used? You can take them?
Input supply : 12V-13V motorcycle battery
# of LED : 2 LED in series at around 350mA
does this driver be possible to use?please reply
thank you very much
works fine, too cool really
the IRF520 (at 800mA calculated R3) was "cool", no heat at all
so I tested the consumption of the three 3W leds I use... only 540mA with R3= 0,66 ohms
so I changed R3 with a New Voltage Drop value... to get close to 800mA. R3= 0,45 ohms. But Consumtion was only 570mA.
could it be that with IRF520 or any mosfet I would need to use a really low R3?
or should I test another NPN (I'm using MPSA18 which has much more gain than 2N3904)
maybe here is the problem,.... as I read that on BASE from the NPN there should be more than 0.5V for it to work right.
Great instructable! It reignited my desire to custom build drivers over store bought ones, so I can start to really push leds, like the newer XML's to 3amps..
Following this build, I immediately bought some high quality, low dropout, high EFF adjustable voltage regulators with built in buck/boost options all in a T0220 package, got them for around 2$ apiece. I currently use luxdrive's drivers for all my projects, but now I'm going to start playing around again and see if I can come up with something just as rock steady and functional as my beloved buckpuck.