Instructables

1.5A Constant Current Linear Regulator for LEDs for

Picture of 1.5A Constant Current Linear Regulator for LEDs for
STCS1_SIMPLE CIRCUIT.JPG
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So there are a ton of instructables covering the use of high brightness leds. Many of them use the commercially available Buckpuck from Luxdrive. Many of them also use linear regulation circuits that top out at 350 mA because they are highly inefficient. This instructable serves to let people know that there are other options out there to drive high power leds. We came upon this project in the work we are doing with a customer for a high power led strobe [www.ohararp.com/blog.html]

The heart of this project is the STCS1 from STM Electronics:
http://www.st.com/stonline/products/literature/ds/13415/stcs1.htm

Warning: Some parts of this project were designed and fabbed using professional software and hardware. However, all aspects of this design could be done using open source products or some perf board and wire wrap.
 
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Step 1: Read the Data Sheet!

Picture of Read the Data Sheet!
First step with any electronics project is to read the data sheet:

http://www.st.com/stonline/products/literature/ds/13415/stcs1.pdf

From this we can easily see some of the key features of this chip:
■ Up to 40 V input voltage
■ Less than 0.5 V voltage overhead
■ Up to 1.5 A output current
■ PWM dimming pin
■ Shutdown pin
■ LED disconnection diagnostic

Step 3: Layout the PCB!

Picture of Layout the PCB!
Using the connectivity of the schematic layout your board for the simplest wiring configuration as possible. This might take some time but your patience here will serve you well. This applies to all layout methods. Here you can clearly see we are using 1206 packages for all of our resistors, capacitors, and diodes.

Step 4: Wired Up!

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Here's everything wired up. Unfortunately we had to use the bottom plane and some vias to completely route this board.

Here are the Gerber Files of this board.

Step 5: Order and Assemble the Board

Picture of Order and Assemble the Board
BUCKPUCK_C_TOOLS_1 (Small).jpg
Using your favorite pcb vendor and assembly method you can put together the board pretty quickly. We prefer http://www.goldphoenixpcb.biz/ for our boards and then we use kapton stencils, kester solderpaste, and a reflow skillet or oven to assemble our boards.
hikira3 years ago
i have bin working with electronics all my life but im on my first big project

i can kinda read schematics but im confused is their a way you could post a schematic with pics of the parts in their spots or a pic of the board that is easier to see the traces
additionally i would want to run this at max voltage would i use the same resisters
Remi5053 years ago
Does anyone know where I would be able to buy these chips online?
musick7 Remi5053 years ago
You can go to the Maker of this Driver and request a Sample of the part or parts you need. In this case it would be, www.st.com Use the data sheet info to search for the part and add it to your basket on there website. Then select the Sample option. If it doesn't have a place on there website, which it should for samples, Contact ST and ask about samples for xxxxx product.

Simple. If your prototyping one device to see if it works, 99.999% of the IC Manufactures have a sample program. The few that don't you most likely request a few samples... The only thing you agree to when ordering samples is, you can't resale any parts you received for Free. If you make money on something, you have to buy it.

And yes I know it's an old post but thought i'd add my two cents... =)
ohararp (author)  Remi5053 years ago
I still have a ton of these boards still available if you are interested. sales@ohararp.com
KnH3 years ago
is there a way to build a driver to run 12 LEDs @ 750mA
ohararp (author)  KnH3 years ago
Hmmm, 12*3.7V=44.4V. You couldn't run these in series with this chip. Maybe 2 strings of 6 leds = 6x3.7=22V. You could then run these off of a 24V supply. I'd recommend runnning 2 drivers rather than running the 2 strings in parallel.
cahillicus4 years ago
Slowly getting this figured out.  A couple quick questions though.  D5 in the schematic is a Zener diode.  But in the BOM you list an LED driver for D5.  Confused.

Also, the schematic shows C1 and C3 as 4.7uF and the BOM lists them as10uF and 1uF.  Which should I use?
Thanks
conntaxman4 years ago
I just finished my three circuits. useing this circuit .So I connected all three and each circuit has 3 - 3watt leds.Well they worked ok,but I thought it would be brighter . Im trying to get the same brightness as the led flood light that I bought at costco's ,I think they have 21 super bright leds in them,and it cost me about $10.00 a few months ago.
       I think a 100watt incandescent  bulb =1750 Lumens and my 3 watt leds are about 100 Lumens.So I guess I only have a brightness of about 51 watt incandescent right?
oh well its fun anyway. Now I just have to see what different type of cap,I could use that would be smaller the the ceramic .01 cap.All the other parts i got are small and the cap,.now is too big.
well have fun.
Johnny

cahillicus4 years ago
 Is there a way to up the output?  I want to be able to drive 6  3.7V LEDs at 800-1000mA from a car power source (14V).  Thanks
ohararp (author)  cahillicus4 years ago
 You'll need to do some reading up on leds.  But basically you will only be able to run 3-4 leds in series based on the forward voltage of your supply (14V in this case).  You could run more, but you would need to run them in parallel to do this using a single driver.
I am actually trying to build 2 light housings running 6 LEDs each.  However, I want to power each light separately.  Do you think i should just run 2 drivers per light (3 LEDs per driver)?  Or, would running them in parallel as you previously mentioned.  If so, how would you go about it?
ohararp (author)  cahillicus4 years ago
Since these are high power led's I would avoid running them in parallel (because offsets in resistance can cause one led to be driven harder than anot her-leading to shortened led life). 2 drivers for 3 series leds would be the way to go IMHO.
conntaxman4 years ago
Would the STCS2PR driver work using the same pin connection?This one has 10 pins as the STCS1PHR only has 8 pin connections.Just the STCS2PR is bigger to work with.
TKS
Johnny
 
ohararp (author)  conntaxman4 years ago
 Glad to see you got everything working!
ohararp, Could you answer me a question seeing that you seem to know alot about these chips.With the "STCS1" in the [Blue dia].Application diagram they dont connect the "EN" pin ,but in the cir. in DIY. they connect the EN pin to the "VCC". Also it is the same for the "" STCS2 "" it is the same,they dont connect the EN pin. So in both dose the EN pin have to be used?it is called the Shut down pin.
I connected it in your or the DIY. dia. and it works fine.I didn't disconnect it to see if that would have any effect.
I want to wire up one useing the STCS2.but don't know  either to connect it or not.
Tks
Johnny

hello ohararp. Would you know if I would be able to use a 10 ohm resistor in place of a .05 ohm in the cir. when using a "STCS2" it is coming from pin [ FB ] and [Source] .
Is that being used to regulate the voltage? I don't know.First time using these chips.
tks
Johnny
ohararp (author)  conntaxman4 years ago
 Sees like a pretty simple calculation to me - See Section 7.1 of the datasheet.
RF=VFB/ILEDS=100mV/700ma=142mOhms
Hi ohararp. I just read your reply.After which i just laughed at myself because I didn't know how to figure out how to make a cir. My trade was Plumbing/heating. I didn't read "section 7.1" yet. I guess what I'll do is just try a 10 ohm in place of the 5 ohm and see what happens.Hope that I don't see smoke.lol. well then i'll know that you can't use a 10 ohm.
I glad the other cir. works very good.
Thank for the reply and have a nice day.
Johnny
Would the STCS2PR driver work using the same pin connection?This one has 10 pins as the STCS1PHR only has 8 pin connections.Just the STCS2PR is bigger to work with.
TKS
Johnny
reason is ,that it is a little bigger to solder with the pre made pc. board.
tks again.
very nice cir.
ohararp (author)  conntaxman4 years ago
 It looks very similar...you'll have to compare datasheets though...

www.st.com/stonline/products/literature/ds/13968.pdf
conntaxman4 years ago
CORRECTION. below I said that this cir. did not work and was dim.I was my fault, I wired in a led the wrong way. After if fixed my mistake the cir. works VERY well,and the LEDs are VERY Brite, but the parts are VERY SMALL.
Tks for the CIR.
########################
Would the STCS2PR driver work using the same pin connection?This one has 10 pins as the STCS1PHR only has 8 pin connections.Just the STCS2PR is bigger to work with.
TKS
Johnny
conntaxman4 years ago
I built this cir. with 3 /3watt x700 ma x 3.5volt and the leds were not brite at all,the leds were only about 1/4 of their briteness.Im going to play around with different resistors,and see if I could get them briter
conntaxman4 years ago
I can't see were he is useing the 2 diodes in this cir. Is their one on the input for the 12vdc? Like some one said, the schematics are too small,and you only can enlarge it so much.
 could you make them larger?
ewertz4 years ago
These schematics are too small to read, and I don't get any usable GIF when I try to right-click-save them to view them another way.

Any chance of putting this up on a blog entry (or elsewhere) on your website...?

tkx

ohararp (author)  ewertz4 years ago
 ewertz, I added a .pdf schematic that should be much easier to read to step 2.
cap9qd4 years ago
What schematic capture and PCB suite are you using?  I have been using Eagle since there is a script for creating g-code for milling boards with a CNC (which is one of the coolest things ever).  Thanks for the great instructions!
ohararp (author)  cap9qd4 years ago
 I use Proteus from www.labcenter.co.uk .  Its a great product, not free, but very inexpensive and very capable.  You can even simulate a lot source code for your microprocessor using the spice libraries.  Very handy for development.
bronx684 years ago
Nice approach but sorry but this doesn't look like a true replacement for BuckPuck. 1) I don't believe you can overdrive the BuckPuck. Not sure how this is handled but as long as you don't violate Vcc you are fine. Not true with this. 2) I believe a BuckPuck has an inductor built in it. 3) I don't believe they use a linear regulator.
mathieulj5 years ago
This is a linear driver and not a buck regulator.
jolshefsky5 years ago
Your title is in error: the STCS1 is a linear constant-current regulator, not a buck regulator. A buck regulator will achieve over 80% efficiency (i.e. power out = 80% of power in; 20% as heat) whereas a linear regulator like this has no fixed efficiency -- the higher the current, and the higher the voltage drop from input to output, the lower the efficiency.
jsbarrie5 years ago
Hi- I am working on a Solar/LED light design to replace kerosene lamps in the developing world. We have settled on a 12v system, in part because you can use an automotive outlet to charge cell phones. We need to come up with a really efficient circuit to power a pair of 3.4v 350ma LEDs. The more efficient the circuit, the less we spend on the solar panels. Any ideas where I could find this? Of course cost is also an issue. Any help is very appreciated. jsbarrie
ohararp (author)  jsbarrie5 years ago
jsbarrie,

You should drop me a line at sales(at)ohararp.com . As a teaser I do alot of low power stuff and think you best bet would be to use a single li-ion setup with a 12V tolerant charge setup. I would recommend using this buck-boost led driver for good efficiency and best use of the available power of a li-ion battery (see page 9 figure 10 http://www.st.com/stonline/products/literature/an/10232.pdf)

Ryan O'Hara
I am wondering what the power waste of this circuit is. Could you tell me the voltage and current of the input and output?
romp0015 years ago
Can the STCS1 be hand soldered to a PC board? I do not have the pre printed board or SMD equipment. What is the best way to wire and solder manually?
ewitte6 years ago
Whats the best I can get for always on LED source. Wanting to power (probably off 12v rail on computer power supply) 27 3w RED (700ma), 12 3w Blue (700ma) and 10 5w DEEP RED (1000ma). Doesn't matter if I can only do 3 or so per chip.
ohararp (author)  ewitte6 years ago
Despite which regulator you choose you will more than likely only be able to power 3 LEDS in series due to the forward voltage of the LEDs. You could then run your led matrix by putting other LEDs in parallel with these series LEDs. You'll have to remember that once you start putting LEDs in parallel that will reduce the amount of current each one receives. With such a large matrix of 27 LEDs I think using a uController and some mosfets with an led driver is going to be one of your best bets.
greed86 years ago
I was hoping that this would be a cheap alternative to the LED Dynamics Buckpuck. I went out and ordered a few of these and I can't say that I'm happy with my purchase. These things get really hot! Try to heat sink the bottom of an SMD component that is the size of this -> M. Let me explain, I am running a power SO-8 floating off a breadboard with a scrap piece of copper hanging off the center, and I can run less than 0.2A. At 0.2A, the pad reaches 120C within about 20 seconds and clips the output. If you had a pcb printed on an aluminum heatsink, like a Luxeon star, then you might be fine. With a nice fan and additional heatsink, 1.5A just might be possible as an output. Another note: Rfb is an annoyingly low value, this will add expense to this project as these resistors are uncommon. A trimpot is not an option, your only option for current limitations are parallel resistors. PWM is definitely a preferable option to this.

As an alternative to this instructable, I would highly recommend option 6 of Dan's great instructable http://www.instructables.com/id/Circuits-for-using-High-Power-LED_s/?ALLSTEPS. The FQP50N06L is a great TO-220 package that also gets hot, but is designed to deal with the generated heat. It is also a lot cheaper and easier to work with unless you have a specially made aluminum heatsink with a printed on power SO-8 pad footprint and SMD equipment readily available.
ohararp (author)  greed86 years ago
I have been using this driver board to power a high power strobe and have not had any issues with power. In fact this driver is perfect for those wanting a nice flashy bicycle light to let people know you are there. You don't mention the input voltage that you are using for your LED's. In this pcb design I placed thermal vias under the power pad of the SO-8 chip and tied them to a thermal ground plane on the bottom of the pcb. Mounting this driver on a piece of aluminum should dissipate much of the generated heat in a continuously on device.
greed86 years ago
Technically speaking, the title of this instructable should be a 0.5A Constant Current Buck Regulator for LEDs for < $10. As you show a 0.2 Ohm Rfb, the output will be 500 mA as defined by the STCS1PHR (IC LED DRIVER CC 1.5A POWERSO-8) that you are using. In the datasheet, the output amperage is defined by: RF = VFB / ILEDs = 100 mV / 500 mA = 0.2 Ω. So, if you truly want 1.5A output to your output, you would want an 0.067 Ohm resistor. RF = VFB / ILEDs = 100 mV / 1500 mA = 0.067 Ω. Cheers!
skrubol6 years ago
I don't see anything in the data sheet of that driver to indicate that it's a buck driver. Just looks like a linear driver to me.