1.5A Constant Current Linear Regulator for LEDs For





Introduction: 1.5A Constant Current Linear Regulator for LEDs For

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:

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.

Step 1: Read the Data Sheet!

First step with any electronics project is to read the data sheet:


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 2: What Else Do We Need? How Bout 5V@20mA

Because I wanted this design to have a nearly identical pinout as the BuckPuck from Luxdrive I decided to add a simple 5V@20 mA

Step 3: 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!

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

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.

Step 6: Let the Blinding Begin!

With the .1" spacing on the pinout of this board you can very easily breadboard your project. Here we are powering a string of 3 x K2 Luxeons (140 lumens per led) from a 12V wall wart capable of supplying 3000 mA.

The performance of this chip is pretty amazing. At 1500 mA the driver board is barely warm to the touch when driving leds continuously.

Note: This design is for a strobe light where the leds do not stay on very long. For continuously running the leds you MUST mount them to a heatsink to dissipate the heat that is produced.

All parts for this design can be found at Mouser or Digikey:
Here's the BOM

Driver IC - STCS1



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    40 Discussions

    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

    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... =)

    I still have a ton of these boards still available if you are interested. sales@ohararp.com

    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.

    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?

    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.

     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

    3 replies

     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?

    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.

    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.
    7 replies

    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.

    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.

     Sees like a pretty simple calculation to me - See Section 7.1 of the datasheet.

    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.

    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.
    reason is ,that it is a little bigger to solder with the pre made pc. board.
    tks again.
    very nice cir.