loading
Picture of High Power LED Driver Circuits
DSCF4210.JPG
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.


 
Remove these adsRemove these ads by Signing Up

Step 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.

Step 2: Power LED performance data - handy reference chart

Below are some basic parameters of the Luxeon LED's which you will use for many circuits. I use the figures from this table in several projects, so here i'm just putting them all in one place that i can reference easily.

Luxeon 1 and 3 with no current (turn-off-point):
white/blue/green/cyan: 2.4V drop (= "LED forward voltage")
red/orange/amber: 1.8V drop

Luxeon-1 with 300mA current:
white/blue/green/cyan: 3.3V drop (= "LED forward voltage")
red/orange/amber: 2.7V drop

Luxeon-1 with 800mA current (over spec):
all colors: 3.8V drop

Luxeon-3 with 300mA current:
white/blue/green/cyan: 3.3V drop
red/orange/amber: 2.5V drop

Luxeon-3 with 800mA current:
white/blue/green/cyan: 3.8V drop
red/orange/amber: 3.0V drop (note: my tests disagree with spec sheet)

Luxeon-3 with 1200mA current:
red/orange/amber: 3.3V drop (note: my tests disagree with spec sheet)

Typical values for regular "small" LED's with 20mA are:
red/orange/yellow: 2.0 V drop
green/cyan/blue/purple/white: 3.5V drop

Step 3: Direct Power!

Why not just connect your battery straight to the LED? It seems so simple! What's the problem? Can I ever do it?

The problem is reliability, consistency & robustness. As mentioned, the current through an LED is very sensitive to small changes in the voltage across the LED, and also to the ambient temperature of the LED, and also to the manufacturing variances of the LED. So when you just connect your LED to a battery you have little idea how much current is going through it. "but so what, it lit up, didn't it?". ok sure. depending on the battery, you might have way too much current (led gets very hot and burns out fast), or too little (led is dim). the other problem is that even if the led is just right when you first connect it, if you take it to a new environment which is hotter or colder, it will either get dim or too bright and burn out, because the led is very temperature sensitive. manufacturing variations can also cause variability.

So maybe you read all that, and you're thinking: "so what!". if so, plow ahead and connect right to the battery. for some applications it can be the way to go.

- Summary: only use this for hacks, don't expect it to be reliable or consistent, and expect to burn out some LED's along the way.

- One famous hack that puts this method to outstandingly good use is the LED Throwie.

Notes:

- if you are using a battery, this method will work best using *small* batteries, because a small battery acts like it has an internal resistor in it. this is one of the reasons the LED Throwie works so well.

- if you actually want to do this with a power-LED rather than a 3-cent LED, choose your battery voltage so that the LED will not be at full power. this is the other reason the LED Throwie works so well.

Step 4: The humble resistor

This is by far the most widely used method to power LED's. Just connect a resistor in series with your LED(s).

pros:
- this is the simplest method that works reliably
- only has one part
- costs pennies (actually, less than a penny in quantity)

cons:
- not very efficient. you must tradeoff wasted power against consistent & reliable LED brightness. if you waste less power in the resistor, you get less consistent LED performance.
- must change resistor to change LED brightness
- if you change power supply or battery voltage significantly, you need to change the resistor again.



How to do it:

There are a lot of great web pages out there already explaining this method. Typically you want to figure out:
- what value of resistor to use
- how to connect your led's in series or parallel

There's two good "LED Calculators" I found that will let you just enter the specs on your LED's and power supply, and they will design the complete series/parallel circuit and resistors for you!

http://led.linear1.org/led.wiz
http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

When using these web calculators, use the Power LED Data Handy Reference Chart for the current and voltage numbers the calculator asks you for.



if you are using the resistor method with power LED's, you'll quickly want to get a lot of cheap power resistors! here's some cheap ones from digikey: "Yageo SQP500JB" are a 5-watt resistor series.

Step 5: $witching regulators

Switching regulators, aka "DC-to-DC", "buck" or "boost" converters, are the fancy way to power an LED. they do it all, but they are pricey. what is it they "do" exactly? the switching regulator can either step-down ("buck") or step-up ("boost") the power supply input voltage to the exact voltage needed to power the LED's. unlike a resistor it constantly monitors the LED current and adapts to keep it constant. It does all this with 80-95% power efficiency, no matter how much the step-down or step-up is.

Pros:
- consistent LED performance for a wide range of LED's and power supply
- high efficiency, usually 80-90% for boost converters and 90-95% for buck converters
- can power LED's from both lower or higher voltage supplies (step-up or step-down)
- some units can adjust LED brightness
- packaged units designed for power-LED's are available & easy to use

Cons:
- complex and expensive: typically about $20 for a packaged unit.
- making your own requires several parts and electrical engineering skillz.



One off-the-shelf device designed specially for power-led's is the Buckpuck from LED Dynamics. I used one of these in my power-led headlamp project and was quite happy with it. these devices are available from most of the LED web stores.

Step 6: The new stuff!! Constant Current Source #1

Picture of The new stuff!!  Constant Current Source #1
lets get to the new stuff!

The first set of circuits are all small variations on a super-simple constant-current source.

Pros:
- consistent LED performance with any power supply and LED's
- costs about $1
- only 4 simple parts to connect
- efficiency can be over 90% (with proper LED and power supply selection)
- can handle LOTS of power, 20 Amps or more no problem.
- low "dropout" - the input voltage can be as little as 0.6 volts higher than the output voltage.
- super-wide operation range: between 3V and 60V input

Cons:
- must change a resistor to change LED brightness
- if poorly configured it may waste as much power as the resistor method
- you have to build it yourself (oh wait, that should be a 'pro').
- current limit changes a bit with ambient temperature (may also be a 'pro').

So to sum it up: this circuit works just as well as the step-down switching regulator, the only difference is that it doesn't guarantee 90% efficiency. on the plus side, it only costs $1.


Simplest version first:

"Low Cost Constant Current Source #1"

This circuit is featured in my simple power-led light project.

How does it work?

- Q2 (a power NFET) is used as a variable resistor. Q2 starts out turned on by R1.

- Q1 (a small NPN) is used as an over-current sensing switch, and R3 is the "sense resistor" or "set resistor" that triggers Q1 when too much current is flowing.

- The main current flow is through the LED's, through Q2, and through R3. When too much current flows through R3, Q1 will start to turn on, which starts turning off Q2. Turning off Q2 reduces the current through the LED's and R3. So we've created a "feedback loop", which continuously monitors the LED current and keeps it exactly at the set point at all times. transistors are clever, huh!

- R1 has high resistance, so that when Q1 starts turning on, it easily overpowers R1.

- The result is that Q2 acts like a resistor, and its resistance is always perfectly set to keep the LED current correct. Any excess power is burned in Q2. Thus for maximum efficiency, we want to configure our LED string so that it is close to the power supply voltage. It will work fine if we don't do this, we'll just waste power. this is really the only downside of this circuit compared to a step-down switching regulator!


setting the current!

the value of R3 determines the set current.

Calculations:
- LED current is approximately equal to: 0.5 / R3
- R3 power: the power dissipated by the resistor is approximately: 0.25 / R3. choose a resistor value at least 2x the power calculated so the resistor does not get burning hot.

so for 700mA LED current:
R3 = 0.5 / 0.7 = 0.71 ohms. closest standard resistor is 0.75 ohms.
R3 power = 0.25 / 0.71 = 0.35 watts. we'll need at least a 1/2 watt rated resistor.


Parts used:

R1: small (1/4 watt) approximately 100k-ohm resistor (such as: Yageo CFR-25JB series)
R3: large (1 watt+) current set resistor. (a good 2-watt choice is: Panasonic ERX-2SJR series)
Q2: large (TO-220 package) N-channel logic-level FET (such as: Fairchild FQP50N06L)
Q1: small (TO-92 package) NPN transistor (such as: Fairchild 2N5088BU)


Maximum limits:

the only real limit to the current source circuit is imposed by NFET Q2. Q2 limits the circuit in two ways:

1) power dissipation. Q2 acts as a variable resistor, stepping down the voltage from the power supply to match the need of the LED's. so Q2 will need a heatsink if there is a high LED current or if the power source voltage is a lot higher than the LED string voltage. (Q2 power = dropped volts * LED current). Q2 can only handle 2/3 watt before you need some kind of heatsink. with a large heatsink, this circuit can handle a LOT of power & current - probably 50 watts and 20 amps with this exact transistor, but you can just put multiple transistors in parallel for more power.

2) voltage. the "G" pin on Q2 is only rated for 20V, and with this simplest circuit that will limit the input voltage to 20V (lets say 18V to be safe). if you use a different NFET, make sure to check the "Vgs" rating.


thermal sensitivity:

the current set-point is somewhat sensitive to temperature. this is because Q1 is the trigger, and Q1 is thermally sensitive. the part nuber i specified above is one of the least thermally sensitive NPN's i could find. even so, expect perhaps a 30% reduction in current set point as you go from -20C to +100C. that may be a desired effect, it could save your Q2 or LED's from overheating.

Step 7: Constant current source tweaks: #2 and #3

Picture of Constant current source tweaks: #2 and #3
DSCF4172.JPG
these slight modifications on circuit #1 address the voltage limitation of the first circuit. we need to keep the NFET Gate (G pin) below 20V if we want to use a power source greater than 20V. it turns out we also want to do this so we can interface this circuit with a microcontroller or computer.

in circuit #2, i added R2, while in #3 i replaced R2 with Z1, a zener diode.

circuit #3 is the best one, but i included #2 since it's a quick hack if you don't have the right value of zener diode.

we want to set the G-pin voltage to about 5 volts - use a 4.7 or 5.1 volt zener diode (such as: 1N4732A or 1N4733A) - any lower and Q2 won't be able to turn all the way on, any higher and it won't work with most microcontrollers. if your input voltage is below 10V, switch R1 for a 22k-ohm resistor, the zener diode doesn't work unless there is 10uA going through it.

after this modification, the circuit will handle 60V with the parts listed, and you can find a higher-voltage Q2 easily if needed.

Step 8: A little micro makes all the difference

Picture of a little micro makes all the difference
DSCF4230.JPG
Now what? connect to a micro-controller, PWM or a computer!

now you've got a fully digital controlled high-power LED light.

the micro-controller's output pins are only rated for 5.5V usually, that's why the zener diode is important.

if your micro-controller is 3.3V or less, you need to use circuit #4, and set your micro-controller's output pin to be "open collector" - which allows the micro to pull down the pin, but lets the R1 resistor pull it up to 5V which is needed to fully turn on Q2.

if your micro is 5V, then you can use the simpler circuit #5, doing away with Z1, and set the micro's output pin to be normal pull-up/pull-down mode - the 5V micro can turn on Q2 just fine by itself.

now that you've got a PWM or micro connected, how do you make a digital light control? to change the brightness of your light, you "PWM" it: you blink it on and off rapidly (200 Hz is a good speed), and change the ratio of on-time to off-time.

this can be done with just a few lines of code in a micro-controller. to do it using just a '555' chip, try this circuit. to use that circuit get rid of M1, D3 and R2, and their Q1 is our Q2.

Step 9: Another dimming method

Picture of another dimming method
ok, so maybe you don't want to use a microcontroller? here's another simple modification on "circuit #1"

the simplest way to dim the LED's is to change the current set-point. so we'll change R3!

shown below, i added R4 an a switch in parallel with R3. so with the switch open, the current is set by R3, with the switch closed, the current is set by the new value of R3 in parallel with R4 - more current. so now we've got "high power" and "low power" - perfect for a flashlight.

perhaps you'd like to put a variable-resistor dial for R3? unfortunately, they don't make them in such a low resistance value, so we need something a bit more complicated to do that.

(see circuit #1 for how to choose the component values)

Step 10: The analog adjustable driver

Picture of the analog adjustable driver
This circuit lets you have an adjustable-brightness, but without using a microcontroller. It's fully analog! it costs a little more - about $2 or $2.50 total - i hope you won't mind.

The main difference is that the NFET is replaced with a voltage regulator. the voltage regulator steps-down the input voltage much like the NFET did, but it is designed so that its output voltage is set by the ratio between two resistors (R2+R4, and R1).

The current-limit circuit works the same way as before, in this case it reduces the resistance across R2, lowering the output of the voltage regulator.

This circuit lets you set the voltage on the LED's to any value using a dial or slider, but it also limits the LED current as before so you can't turn the dial past the safe point.

I used this circuit in my RGB Color Controlled Room/Spot lighting project.

please see the above project for part numbers and resistor value selection.

this circuit can operate with an input voltage from 5V to 28V, and up to 5 amps current (with a heatsink on the regulator)

Step 11: An *even simpler* current source

Picture of an *even simpler* current source
ok, so it turns out there's an even simpler way to make a constant-current source. the reason i didn't put it first is that it has at least one significant drawback too.

This one doesn't use an NFET or NPN transistor, it just has a single Voltage Regulator.

Compared to the previous "simple current source" using two transistors, this circuit has:

- even fewer parts.
- much higher "dropout" of 2.4V, which will significantly reduce efficiency when powering only 1 LED. if you're powering a string of 5 LED's, perhaps not such a big deal.
- no change in current set-point when temperature changes
- less current capacity (5 amps - still enough for a lot of LED's)


how to use it:

resistor R3 sets the current. the formula is: LED current in amps = 1.25 / R3

so for a current of 550mA, set R3 to 2.2 ohms
you'll need a power resistor usually, R3 power in watts = 1.56 / R3

this circuit also has the drawback that the only way to use it with a micro-controller or PWM is to turn the entire thing on and off with a power FET.

and the only way to change the LED brightness is to change R3, so refer to the earlier schematic for "circuit #5" which shows adding a low/high power switch in.

regulator pinout:
ADJ = pin 1
OUT = pin 2
IN = pin 3


parts:
regulator: either LD1585CV or LM1084IT-ADJ
capacitor: 10u to 100u capacitor, 6.3 volt or greater (such as: Panasonic ECA-1VHG470)
resistor: a 2-watt resistor minimum (such as: Panasonic ERX-2J series)

you can build this with pretty much any linear voltage regulator, the two listed have a good general performance and price. the classic "LM317" is cheap, but the dropout is even higher - 3.5 volts total in this mode. there are now a lot of surface mount regulators with ultra-low dropouts for low current use, if you need to power 1 LED from a battery these can be worth looking into.

Step 12: Haha! there's an even easier way!

I'm embarrassed to say i did not think of this method myself, i learned of it when i disassembled a flashlight that had a high brightnesss LED inside it.

--------------
Put a PTC resistor (aka a "PTC resettable fuse") in series with your LED.  wow.  doesn't get easier than that.
--------------

ok.  Although simple, this method has some drawbacks:

- Your driving voltage can only be slightly higher than the LED "on" voltage.  This is because PTC fuses are not designed for getting rid of a lot of heat so you need to keep the dropped voltage across the PTC fairly low.  you can glue your ptc to a metal plate to help a bit.

- You won't be able to drive your LED at its maximum power.  PTC fuses do not have a very accurate "trip" current.  Typically they vary by a factor of 2 from the rated trip point.  So, if you have a LED that needs 500mA, and you get a PTC rated at 500mA, you will end up with anywhere from 500mA to 1000mA - not safe for the LED.  The only safe choice of PTC is a bit under-rated.  Get the 250mA PTC, then your worst case is 500mA which the LED can handle.

-----------------

Example:
For a single LED rated about 3.4V and 500mA.  Connect in series with a PTC rated about 250 mA.  Driving voltage should be about 4.0V.

1-40 of 438Next »

another thought

could I just use an extra 3W 1A bead to forward another 3 volts to the 10w chip

I believe the 10w LED draws 10.5V and if I used another 3.4V LED that would put me at 13.9 V my 100 AMP PSU can be overvolted to 13.65V

would this keep the LED's in a range where they will not try and draw more current?

also if I used 2x 500ma PTC parallel would that then handle 1amp with 2 amp cut off ?

I was thinking instead of using diodes to drop voltage why not just use an LED and an 3w LED bead should have the same current rating as the 10w

I bought 10w LED
I believe they have 3x1w beads in series and 3x parallel runs ( 9 beads )

when combining LED's in series does their running current also increase ?

ie) if they where 1w 3.5v 350ma beads would they cut out at 1050ma ?
or would they still cut-out at 350 current and use 1050ma power ?

I had ordered 500ma PTC but now thinking I really needed something a lot lower

RamanaR11 month ago
I have 12v, 10w bright led, can u help me to build drive circuit from 220v
RobertK131 month ago

I can confirm that this circuit works, but a couple things to mention. You definitely want to do your math right or your MOSFET will get pretty hot. It wont take much to get this baby hot. Second, if you have a stable power source from your power supply, there really isn't a need to control your current in such a manner. Simply using a resistor in series with your LEDs will work. The MOSFET can and should be used to soft start your LEDS extending there overall lifespan. Also when using a MOSFET, adding some TVS diodes to protect it is a good idea specifically gate to source.

KiSwiSje2 months ago

I really don't think the pptc is regulating the current. It is just protecting the battery from excessive current draw and posibly explosion.

As the pptc needs time to warm up under overcurrent conditions, the led will probably die before it trips. And if it does not trip, the resistance over the pptc is fairly low. Transition from not-tripped to tripped is fairly fast.

This sounds more like the 'throwie' principle where the battery's internal resistance will limit the current, combined with the small margin the driving voltage is over the needed forward voltage of the led.

I wish I had the necessary components to test this out. My 250mA pptc did not play nice with my 20mA leds :(

Clark572 months ago

PLEASE PLEASE HELP!

I have a Constant Current LED driver module that I removed
from a LED grow light, rated 80-100V @ 600ma. It currently runs a 45 LED
string. It says that it’s a HP060 but it doesn’t look like anything I’ve seen
that matches that on the web. I can’t really see any of the part numbers, but
there’s a transformer surrounded by smaller components, including the only
adjustable thing, a little blue potentiometer. (I have no schematic, but I
assume this might be a “typical’ circuit.)

What I want it to do is to run a 23 string @ the same
rating. The PROBLEM is that when I do, the supply kicks the total voltage down
to equal the same voltage across each LED. Basically, I am trying to double the
voltage at the same current, but it won't let me. (The LEDs are rated at over
double their current power so I am not worried about blowing them.)

Real world:

I measure across the LED while 45 of them are on and the
voltage is 2.225VDC @ 600ma. I then short the string to 23 and measure and it
is still 2.225VDC@600ma, but I want 4.45VDC@600ma across each LED. (2.225@1200ma would do but I don’t think this
thing will do it.)

Like I said, there's a micro blue potentiometer on this
module and I don't know what it does (nor do I have a schematic) but I need to
know what to do to adjust this up to 4.45VDC.



I’m assuming there’s some kind of resistance sensing circuit going on, but I’m
looking at it and I see the transformer, a couple of what look to be SCRs on
heatsinks, a choke, three electrolytic caps (and some smaller caps, too), and
the potentiometer. I’m not comfortable randomly adjusting the pot when I don’t
know what it does.



(As well, a miniature supply that could do what I want would be considered,
too.)

I need this, like, 8 years ago so please help!

Will

conquer3 months ago

Hello!

I wish you a nice day!

We are looking for LED drivers and dimmers for project. We
have finished with wiring.

Lighting system in that project have about 450 meters of LED
strips inside aluminum profiles recessed in ceiling, separated in parts
with lenghts 0.75 m, 1 meter, 1.5 meter and 2 meters.. Also, there are parts
with individual lenghts of 5.4 m, 3.2 m.... Type of LED strip is 3014 SMD
14,4 W/m, input voltage DC 12V, 120pcs/m, pure white color. So, that is
450(m)x14,4(W/m)=6480W, around 6,5kW power of whole system at full load. Lighting system
must be dimmable and wireless controlled. I need help with choosing right LED drivers and controllers for system. You can see project in attachment.

Thank you in advance.

For LED drivers.jpg
node-xD3 months ago

Trying to wrap my head around this and I've got a few questions that hopefully somebody can clear up.

1. " LED current is approximately equal to: 0.5 / R3."

Is he using the value of 0.5v because that is the "Vce Saturation (Max)" value for Q1, the 2N5088BU transistor? If not, where does it come from?

2. "The input voltage can be as little as 0.6 volts higher than the output voltage."

Is this also determined by the "Vce Saturation (Max)" value for Q1? If not, then where does it come from?

3. "The power dissipated by R3 is approximately: 0.25 / R3."

Where does the 0.25 come from? Is it calculated as 1/2 of whatever the 0.5 volts is from my first two questions?

4. "Q2 can only handle 2/3 watt before you need some kind of heatsink. with a large heatsink, this circuit can handle a LOT of power & current - probably 50 watts and 20 amps with this exact transistor."

Is he talking about the MOSFET burning up 50 watts on it's own, or 50 watts for the entire circuit, LEDs included?

5. Considering that the "dropout" remains constant at higher voltages, and assuming that the input voltage stays tuned to this level; would it be true to say that this circuit becomes more efficient with higher power LEDs?

boredom.is.me3 months ago

I've been studying and designing some modules based off of your schematics.

I am interested in an *even simpler* setup to power two sets of 3W LEDs. They will both share a 24V power supply. The first set uses six 3W LEDs (3.2-3.8V). This should be straight forward. My concern pertains to the second set. The second set only has two 3W LEDs (3.2-3.8V). Will the circuit drop the voltage to what the LEDs only need?

I received my parts and can confirm that the "even simpler" takes care of the voltage difference too. :)

ozdenakca4 months ago

hello,

for step 10, how can i calculate the voltages and currents? I want to modify this curcuit for different types of power leds.

thank you and have a nice day! :)

Krolo made it!5 months ago

This is the first pcb I designed that uses this instructable to power 16 1w LEDs. I later made a 48 output design. The most I have daisy chained is 109 for a light wall in a reastruant.

2015-02-08 10.54.11.jpg2015-02-06 04.05.36.jpg
xenonion8 months ago

Hello,

I've had great success with Schematic #4. I'm dimming 4 - 3 watt LED's. I'm powering them with a 20 volt supply. My question is, since this is a constant current device, can I power a single 3 watt led (forward voltage of 4 volts) with the same 20 volt supply? Is this a good idea?

Thank You

Hi there, this is a very good instructable with nice presentation.

I am planning to build constant current source #1.

Led : 10 W

Forward Voltage : 9-11 V.

Forward Current : 1050 mA.

Input Voltage : 12 V 5 A.

I assume R3 is 0.476 ~ 0.5 Own. Is it right?

I can't find the parts you suggested in local electronic stores. I could find only 2N2222, BC547 (Q1) and IRF640N (Q2).

If I use those transistors instead of the ones in the guide, what changes do I have to make?

AjayV19 months ago

your circuit is good cost effective need thermal compassion .

dapackers made it!9 months ago

Thanks for your Instructable! Using your even simpler current source and a
10W RGB LED my pumpkin really glows!!!!!! I used the cheaper
LM1084IT-ADJ regulators and some IRLB8721PbF N-Channel Mosfets to
turn the circuit on and off using an Arduino UNO. The video can be
seen on YouTube http://youtu.be/ry2G-STAhl8

The
library for the Arduino UNO was another instructable here:
http://www.instructables.com/id/RGB-lamp-with-Custom-Moodlamp-Library/

Thanks
to great contributors like you, this week I made a pumpkin that can
be seen from blocks away and I found out that the Hedgehog averages
about 6 miles a night on his wheel! I'm off to start my next
Instructables project!

Owl.bmp
xenonion9 months ago

Hello,

This is a great tutorial, I have all of the parts and built the #4 circuit. Now I want to use it to power 4X - 4.1 Volt 700 mA LED's. I tried to test the current output using 18 regular green LED's and the circuit will only pull ~ 40 mA's according to my DMM at full on no PWM signal. I am powering with a 40 volt 2 amp powersupply. I have the components listed and am using a 0.18 ohm resistor (R3) with theoretical current available up to 2.5 amps. R1 = 100k and the zener is 5.1 volts. What am I missing?

Question: What can I use for a dummy load to test my circuit? I have seen tutorials that use regular diodes (1N4005's) in series and then a series resistor to give the proper current draw? I've got a bunch of 1N4007's around, so i'm tempted to make several strings and test with that?

Thank You!

Hi Dilshan, I am building a battery powered LED torch with 4X1.2V 1200mA batteries, and 3X3W LEDs I am trying hard to find a driver which could do the job of connecting them together

the LEDs I have are,
LED, HIGH POWER, 5000K, 70CRI, 275LM
Series: LUXEON TX
LED Colour: White
Luminous Flux @ Test: 369lm
Forward Current @ Test: 1A
Forward Current If Max: 1.2A
Forward Voltage @ Test: 2.86V.

could you please help me what should be the specifications of the driver??

.your voltage is very near so no need of regulators why not a resistor actually this regulator is needed if supply is fluctuating its output.

according to your calc.=0.64ohm resistance will work

so use 2=1ohm and 2 ohm 5w resistances in parallel to get .66 ohm

1.94/0.66=2.93A for 3 led and 0.97A for 1 led

remember NI-MH cells have voltage somewhat1.35-1.15 volts in my different calculations but doesn't makes difference too much i.e. doesn't kills led. Especially if led are connected to heat sink

I would avoid cranking them to their maximum current (If Max of 1.2A) because that will shorten their life span (and also increase heat output).

4x 1.2V = 4.8V (when fully charged, of course). Batteries are very likely 1200mAh (the little h is important: milli Amp HOURS)

3 of your LEDs in series = 3x2.86V = 8.58V, so nearly 2x your max battery voltage: you'd need a boost circuit to achieve that (i.e you won't get far with this circuit driving them because your input voltage isn't high enough). In series, you'd pull the 1A (at test), which is near the total Ah capacity of your batteries (but this would first require your batteries to provide 8.58V+, which they do not). Assuming you added 3 more 1.2V batteries (7x1.2 = 8.4V), you wouldn't have especially bright LEDs, and your battery voltage would still plummet like a rock, and eventually not actually drive the LEDs.

If you instead ran the LEDs in parallel (requiring lower voltage but higher current), you could drive them at a little more than 1/2 of your battery voltage (a switching regulator would be a decent approach). In such a configuration however, you would need to provide _3_AMPS_, which would cause your batteries to heat up, and their voltage would drop even faster.

In general, lower current, higher voltage (LEDs in series, not parallel) is preferable. Ohms Law will kick your butt: high current causes small resistances (including what occurs within the batteries as they heat under load) to result in larger voltage drops. This is the basic premise behind high voltage power transmission lines.

LEDs like this are intended to run off of something more than a few rechargeable AA batteries. An 18650 Li-Ion gives you 3.7V rated at say 2.4Ah (2400mAh, but that's at 3.7V not 1.2V). One such battery would be circa 1 hour of runtime for your lighting setup, and as the power supply for Dan's circuit, would not require a significant voltage drop (and thus dissipation).

I've had decent results from using a switching "buck" converter driving a 3W LED using a partially depleted 9V battery. At 8V or so, the 9V has outlived it's useful life as a 9V in whatever plug-in application it had, but clear on down to as low as 5V or so, it's still a good power source for a buck converter - you can drive a 3W LED quite nicely. Not for hours, but the battery was essentially trash to start with.

fche4141 year ago

Hi,

Could l know how do you come up with the equation I = 0.5/R3 please?

splud fche4141 year ago

An easier to understand and use explanation might be, given a known LED current rating of say 20mA (0.020 A), to determine the necessary resistance of R3:

R3_in_ohms = 0.5 / (desired_current_expressed_in_amps)

0.5 / 0.020 = 25 (ohms)

Does that help?

ThorstenP splud11 months ago

I have also a problem with this equation, were do you get the 0.5 from?

Hi!

(I apologize for my crappy english)...

This is the way I see it. As you can see on the diagram, the NPN transistor emitter is wired to ground and the base is wired to the power resistor. When the transistor is well... "polarized" (don't know how else to say it), a fixed voltage should appear between the base and the emitter. In the case of a 2N3904, the base to emitter voltage is approximately 0.58V, which is the same voltage drop on the power resistor... So, if you use this transistor, the current flowing would be I = 0.58/R3 (this is Ohm law V = I*R).

I hope you can understand my english...

splud Juan ManuelP10 months ago

"biased" is likely the term you're looking for.

The FET is effectively a voltage controlled variable resistor. It (and well, the diode series) forms one half of the voltage divider circuit (coming from Vcc reference), which R3 is the other half of (going to ground reference). The lower the R3 resistance, the "closer to ground" the base of Q2 will be, and therefore the higher current (in the form of a lower FET D-S resistance) can flow through Q1. Raise R3, and the base of Q2 will be more positive, thus conducting the Q1 gate to ground, causing the Q1 D-S to have a higher resistance, and reducing the flow through the diodes.

The 0.5 figure seems like a reasonable ballpark figure for the voltage at which the Q2 base would be within the "region of operation", while not being saturated. The value would vary with the transistor being used - chiefly with the part type (refer to the data sheet), but also individual characteristics.. If one had a good transistor tester, you could get the Vbe(sat) of an individual candidate transistor and tune the resistor value to that.

Note that use of a Q2 with a higher Vbe(sat) voltage would allow for use of a nominally higher resistance value for R3, which may be easier to acquire. You don't want to use too low a resistance value, or the BJT will burn itself up.

Vbe(sat) for the PN2222A transistor is 0.6-1.2V for 15mA base current and 150mA of collector current. This represents _saturation_ (full-on), which is not where the transistor will (or should) be operating while it is regulating the current

Remember, the total resistance between the resistors and the ground is R3 + whatever the FET has been regulated to. The FET is the primary current regulator here.

FTR, your English is entirely understandable, and better than many who presumably communicate in it as a first language...

The Freak1 year ago
Link to PWM 555 thingy is dead (end of step 8).
ChronoX5 made it!11 months ago

Thanks for the shematic! The LM317 driver is too wasteful for one LED but this is just perfect. I used a 2N2222 NPN Transistor which has a Base Emitter Saturation Voltage of 0.6V. I didn't have any 1 Ohm resistors so I had to take about ten 10 Ohm ones ;)

2014-08-31 19.08.46.jpg
synthdood made it!11 months ago

I have built a bunch of these little circuits, and they work really well. Thank you for posting this! Here I built four driving a color LED with an micro controller and a pot. I encased it with liquid plastic for protection. You can adjust the LED cycle speed with the pot. I use a single lipo to power everything. Fun!

IMG_20140826_173203.jpg
pratham1231 year ago

I need to drive 5 3W RGB LEDs in series using an arduino. The maximum current required is 350mA each for R G and B dyes.
and minimum current requirement is 2.4V, 2.4V and 3.5V respectively.

What should I use to interface the LEDs with my arduino as the output current of each arduino pin is 50mA maximum

You need MOSFETs my friend (though a darlington may well suffice), i would recommend you read up on the topic of signal amplification and driving power using transistors :)

Hi Pratham, were you able to solve your query since I am also looking for the response to a similar query

yuenong1 year ago

Hi, I was into final exam on making LED lamp.

May i know which circuit the best for driving 48 LEDs simultaneously?

the LED forward voltage will be 2.8-3.2v and max forward current is 20mA.

thanks.

sbadgujar1 year ago

How to Connect 10*1w led to this circuit. what changes I have to make in circuit

Would a TIP41C be a good substitute for Q1 (the 2N5088)? I'd like to make sure I have enough headroom heat-wise, as I plan on putting the circuit in an enclosed area with no ventilation. Are there any other possible modifications I might have to make to the circuit (adjusting the value of R3, etc) to accomodate this? Thanks!

Upon looking at the TIP41C's datasheet more closely, it seems the forward gain is significantly smaller than the 2N5088. Would perhaps a TIP122 be a better replacement instead?

ovenam made it!1 year ago

Muy bueno!!!! Ya lleva poco más de dos años funcionando!!!

400209_10151080151406502_2042246309_n.jpg

Ref to http://www.instructables.com/id/Yet-Another-Daft-P... any idea how I can get y query solved.

I want the same matrix display on the higher powered LEDs ( 3 W would be good enough).

Thanks in advance

remi.serriere made it!1 year ago

Thank you for these schematics. I used them on my sequential taillights for my car : http://www.dodgeintrepid.net/showpost.php?p=269747...

I shared the link to your article in this forum, I hope you don't mind. There's also a video of the final result.

The picture included is just a "fly bug" design ^^ IRF640 and BC547B, I used it for testing ;)

RSCN4671.JPG
cfsterpka1 year ago

Awesome tutorial on LEDs and drivers thereof, thank you!

1-40 of 438Next »