Simple Buck LED Driver with PWM Input

High-power LEDs over 1W are now quite inexpensive. I'm sure many of you are incorporating LEDs as light sources in your projects.
However I realize that the finding and configuring the power supply is still not as simple as it can be; commercially available LED drivers are convenient, but often overkill or not flexible. Even my own Universal LED Driver can be overkill at times. Some projects call for a bear minimum, simple driver.

Poorman's Buck - Simple, Constant Current LED Driver

So I created the "Poorman's Buck" - simple switch-mode (buck) constant current LED driver that's built without a microcontroller or a specialized IC. All of the parts are easy to obtain, "off-the-shelf", though-hole parts.

Even though this driver is minimalistic, I added a current adjust function that doubles as a dimmer, and an input to control the output with PWM. This makes the "Poorman's Buck" perfect building block for Arduino or other microcontroller based LED projects - you can control many high-power LEDs from a microcontroller simply by sending PWM signal. With Arduino you can simply use "AnalogWrite()" to control the brightness of high-power LEDs.

Step 1: Features

• Inductor "switch mode" (buck) converter for high energy efficiency.
• Wide supply voltage range of 5 to 20V. Great with batteries as well as AC adaptors.
• Cycle-by-cycle, true constant current circuit
• Configurable output current up to 1A
• Up to 15W maximum output power. (at supply voltage 20V with five 3W LEDs connected)
• Current control potentiometer (trims the output current down to about 9%)
• Current control can be used as a built-in dimmer
• Output short-circuit protection
• PWM control input - controllable via external microcontroller including Arduino.
• Compact design - only 1 x 1.5 x 0.5 inches (excluding the pot shaft)

Comments

[murak]

Hi. If I am only interested in running a single CRee LED, could this be powered via a joule thief circuit , similar to those used in your other (i.e. night light) projects?

[ledartist]

You can hook up Cree LED (you mean high power LED, right?), and it'll light up, but not at its full brightness. Joule Thief circuits such as mine can only give 15 mA current through the LED at most.

Aki

[LazyCat]

at the request of greendq:
http://webfile.ru/6513782
(smd variant)

[SauliusPak]

I am not sure, but I think that C3 and C4 in schematic should be connected after the inductor, in parallel with LEDs. When I tried original schematic, I could not get higher current in the output than 0.44 A. When I moved C4 in paralel with LEDs, i.e. current output, driver started to behave as expected. However, current is somewhat lower with 5 V, than in the range 6 to 19 V.

Another question: is it possible to trim current even lower by reducing R3 or increasing pot value?

[hanlin_y]

When you cap the output, a smaller inductor can be used.
http://www.digikey.ca/Web%20Export/Supplier%20Content/NS_14/PDF/National_power_designer116%5B1%5D.pdf?redirected=1

[ledartist]

C3 and C4 are there to bypass the power supply and keep the noise from going out.
Connecting capacitors in parallel with the LEDs won't hurt, but that should not change the output current either. But when you mesure the current using a multimeter, you may not get the correct reading because the current has ripples. I suspect that that's what's happening in your experiment. The best way to see what's going on is to connect an oscilloscope to read the voltage on R10/11. You should see a nice triangular wave there.

[edgypyro]

where can i find the parts
GPN (5551, 2222, 3904, etc.) - Q1
GPP (5401, 2907, 3906, etc.) - Q2

[ledartist]

GPN means General Purpose NPN Transistor, and
GPP means General Purpose PNP Transistor.

You can use 2N5551, 2N2222, MPS2222A, 2N3904, and so on...

[LazyCat]

smd variant :
http://webfile.ru/6433982

[SauliusPak]

Could not post a reply, maybe a bug in Chromium support... Did not accept the captcha.

Thank you for reply. I know the limitations, but I don't have an oscilloscope. Would be quite an overkill for my own needs :-) But ripple from 0,4 A to 1 A... I think, that multimeter, as a "slow" device, should display some average of a current. Anyway, have taken a look at lots of buck converter schematics, they always have some "buffer" capacitor after the inductor. So I'll leave it there, as my perception is better with it :-D

[rbrenganathan]

can u send the circuit led driver


regards
renganathan

[pravardhan]

Hi,

I want a PWM generator circuit that can be used in your circuit which measures the output from your LED driver with a reference voltage from a zener diode or some reference IC so that the output voltage of your LED driver is reduced to the reference voltage.

I will be using a 12V zener diode for the IC, Q1 and Q2, but Q3 will operate at 40V. The reference voltage is 18V.

Bye,
PRAVARDHAN

[LazyCat]

Looks great and works great! )

[LazyCat]

dimension to break the wire LED - 600mA,
consumption of the power supply - 500mA,
the way it should be?

[ledartist]

Not sure what your question is...
If you are wondering why the current draw from the power source is less than the output, that's correct. Buck converter's input current is almost always less than the output.

[LazyCat]

Thanks Ledartist for your input.

[ledartist]

Looks great! Are you posting an instructable?

[pravardhan]

Hi, I have few questions:

1. Can you post the circuit without the potentiometer?
2. Is there any cheaper P channel MOSFET that is easily available?
3. If I have to use a N Channel MOSFET, what should i do to the circuit?

Bye,
PRAVARDHAN

[ledartist]

1. Just replace the pot with a 10k ohm resistor, and connect the pin to the IC as though the pot is at the top extreme.
2. The one I used is the cheapest i could find.
3. I wanted to use N channel as well, but the circuit gets way too complex.

[pravardhan]

So, can i use IRF9540N. It's a P-Channel Mosfet in TO-220 package. The package is not a problem for me and this Mosfet is available in India for $0.80

[ledartist]

That should work.

[LazyCat]

RFD15P05 - 15A, 50V , 0.150 Ohm, P-Channel Power MOSFETs

I want to rewind the existing inductor at the desired nominal - here and asked and the diameter wire.
Sorry for my english.

[ledartist]

Ok RFD15P05 should work then.
I don't know how to wind inductors to get the specific value. I just purchase what I need...

[greendq]

Hi!
Hope, this will not be considered as necroposting, but I just found this article :)

Is it possible to do the same trick with 230V input? By using other components, of course. Can you point me to some circuit diagrams, it they exists?

Thanks in advance.

[ledartist]

It should in theory, but DO NOT TRY IT. Making buck converter to deal with such a high voltage is extremely difficult, not to mention dangerous!

[LazyCat]

RFD15P05 transistor can be used?
And one more question - tell me the diameter of the wires L1.

[ledartist]

You can't easily substitute bipolar transistor for MOSFET.
L1 is not just a wire - it's an inductor.

[LazyCat]

2903D JRC is a complete analog LM393 ?
Thanks in advance.

[gopalyajur]

Hello, Seems to be pretty interesting project.
I am planing to make a emergency lamp with 10 -12 white LEDs
(Vf=3.2, I= 20mA) using 4 NiMH batteries (2100mAH) connected in
series.

Would it be possible to adapt your circuit for my needs. If so what do I need to do?

| Thanks a lot in advance

[ledartist]

Yes you can, but for 10-12 regular LEDs using buck converter might be overkill. You can just use a resistor in series with each LED. Energy loss here is about (4.8V - 3.2V)/4.8V = 0.333 or 33.3%. Not small, but not that bad. Buck converter can lower the loss to less than 20%, but resistors are so cheap...

[RexHex]

the arduino pwm is set to 16mhz. would i need to drop this down to 1khz? also how would this be done if i do.

[ledartist]

Arduino's PWM frequency is about 500Hz. You can simply use analogWrite() command to control Poorman's Buck.

See: http://www.arduino.cc/en/Tutorial/PWM

[RexHex]

Ok that would work then. I was reading this and got 16mhz from it all and was trying to reduce it down.

http://www.arduino.cc/playground/Main/TimerPWMCheatsheet

Im using this driver and apparently its pwm control does not work then. http://www.parts-express.com/pedocs/manuals/073-048-parts-express-manual-7169.pdf

do you know where i could get a good driver with pwm control? i would build yours but i dont have the time, projects due nov 10th and i have lots of work to do.

thanks.

-Rex

[Scott McKie]

Hi,
I'm asking my question here because the subject is the LM339 comparator and I have a question about it.
My question is:
"Can an LM339 comparator's output drive an IRF740 MOSFET without a driver? Help!!!

Scott

[ledartist]

I think you are looking at the answer right here. Those two transistors are the FET driver.
If your application only needs slow switching speed, you might be able to get away without a driver. If that's the case simply pull-up the output of LM339.

[Scott McKie]

Thanks Ledartist for your input.
If the two transistors were not there, and the 339 was to operate by itself with an extremely small cuty cycle at 60+ kHz; and the 339's output was the only signal going into the IRF740 MOSFET, would the signal degrade in voltage and shape? The MOSFET is meant to switch the ground on and off in a circuit where the MOSFET is wired in an open collector configuration and I'm trying to test it to see if it is "breaking" the ground.

[ledartist]

By all means test it out. But my gut feeling is that 60 kHz is fast enough to require transistors or some other driver. Frequency below, say 10 kHz might be ok without.

Poorman's Buck operates at about 100 kHz. I observed the signal at the MOSFET gate and did not like what I saw without a proper driver. I tried a single transistor driver as well, and that did not cut it either. 

[tech industries]

Hi,
Is is possible to supply higher currents with this circuit? I'm looking at the Cree xm-l, which has a maximum forward current of 3A. Is it just a matter of using higher rated parts, or do some resistors need to be changed?
Thanks!

[ledartist]

Yes, you can use larger inductor (at least 4A rated in your case) and use larger Schottky diode to handle the higher current.
Then use 2.7k ohm for R2, adjust the R10/11 so that they total 0.16 ohm - paralel connect 6x 1 ohm resistors.

This is just a theory though. I haven't tested anything higher than 1A.

[skmdmasud]

HI.. i am a newbie so it might sound dumb..

1. Do i need regulated power supply to runt his circuit.

2. If i use 15V AC transformer and use full wave rectifier i get 15 X 1.414= 21.21 V DC will that be ok.

Can you please name some more cheap P channel Mosfets because this one is not available in my area.

Regards