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Thread: 5W COB LED spotlight controller

  1. #1
    Join Date
    Jul 2019
    United Kingdom
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    Default 5W COB LED spotlight controller

    I thought I'd share the driver circuit I use throughout my garden lighting, just in case this is of use to anyone for driving LED spots for an installation.
    See lights in action here:

    I use the 12v 5W units from TOMSHINE throughout, there's not much to them other than a waterproof case, a 5W COB LED, and small driver unit (do a search for them, you'll find them on eBay and Amazon) They come in 'warm' and 'cool' models, come in packs of 4 for about £16, so £4 each! The cool LEDs are great for illuminating the garden and showing the plants at their best, the warm is more more pleasant for the seating areas - I found the cool a little harsh for this, so I have a mixture.

    The main issue with them is they can't be flashed quickly or dimmed as they stand, since the driver has a little 'lag'. So I realised early on that I was going to need to rethink the LED driver circuit. I'm going to describe my approach below, I'm sure some of the electronics wizards will find some holes in this, but it worked for me.

    Poking around with a voltmeter I measured 16V DC across the LED using the supplied driver (yes this is higher than the 12V DC input), about 300mA current through the LED. This is there the 5W rating comes from.

    The first step is to remove the driver from the lamps (it's super easy) which leaves you the two wires connected to the LED.

    For control I am using RGB LED striplight controllers, which gives 8 channels of PWM output from DMX input. I started designing my own, but realised I could buy them cheaper....

    This will work 'as is' for PWM control of 12-24v 'dimmable' items (like RGB strip)

    To interface to the Tomshine lights, my first step was to remove the 8 (Mosfets?) from the PCB. I then soldered a 4.7K resistor for safety between the micro controller pin and each of the 8 outputs. This can be done through two of the three holes where the mosfets were, the third goes to GND and isn't used from this application. So effectively this connects the 8 output pins of the micro controller to the RGBW output screw terminals, via 4K7 resistors. The resistors ensure that if accidentally grounded, this doesn't damage the micro controller IC.

    Next step is to build a simple constant current driver circuit which interfaces the LED to the 5V logic output fro the micro controller. You need 8 of these, one for each output.
    The basic concept I took from here:

    Here's my circuit:

    I use a 2.7 ohm resistor for 'sensing reistor', this needs to be reasonably high power (1 watt will do), but other than that it's just a general purpose NPN transistor and a logic-level Mosfet. The Tomshine COB LED is connected between 16v and the Mosfet drain, I also included a regular LED in parallel via an 800 ohm resistor, this gives a status monitor on the output.

    Some of the nice features of this:

    - 16v distribution around the garden (actually I use 30v and step it down at each controller) means less voltage drop.
    - If any of the spots get shorted out, it won't damage the driver since it's current limited to 300mA
    - I have a small 3mm red LED on each output which shows what's going on

    Hope that helps someone!
    Last edited by RichieNorthcott; 08-25-2019 at 11:49 AM.

  2. #2
    Join Date
    May 2009
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    Default Re: 5W COB LED spotlight controller

    very nice detail.
    I am quite familiar with TOMSHINE products. while no one can ever mistake these little gems for their high end counter parts. they do the job very well and at a fraction of the price of the big boys (like Chauvet, or AMDJ). of course they dont have near the bells and whistles, but for what most folks do with here, they work great.

    I used to use a REN48 controller to run most of my DMX stuff in my display. these are great little boards built to last! what I mean is they can take quite a beating and still keep ticking. they can control ANY type of non pixel light that is under 12VDC. they can run DMX, LED's (3 or 4 channel) simultaneously. but, they are not "smart" boards as they have be "built"to do what you want. please reference HERE for more information. the link is a WEALTH of information.
    note: MOST of us are using pixels now with the FALCON controllers (which also have full DMX capabilities built right in), you can see the full line HERE.
    there are lots of us who run our entire displays from a RASPBERRY PI and use falcon boards exclusively namely because the support provided BY falcon is second to NONE! they develop the software and the hardware. then we use software called XLIGHTS (you can read about it HERE), which integrates SEAMLESSLY into all the falcon boards.

    Sean Megan (founder of nutcracker (which later integrated into XLIGHTS)) and Dave Pitts (founder of Falcon) along with their crews have developed some of the best stuff to hit Christmas since the tree!

    again! good work!
    and good luck

    Last edited by Keebler; 08-25-2019 at 06:21 PM.
    all pix <70 univ)


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