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TOPIC: 3W 6500k LED Lighting Project - Need for some Analog Electricity Help

3W 6500k LED Lighting Project - Need for some Analog Electricity Help 1 week 6 days ago #17964

  • hop
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Greets Everyone! (Especially you Jon! )
And FOR Jon… I placed tags to allow you and others to move to the meat of this question without suffering through my long-winded preface. Lol
I have a project I am working on to help me with something that has ALWAYS plagued me with my projects. Proper lighting, and especially SPOT lighting. What comes from this project later is holiday lighting effects, accent lighting for my home, and even plant supplemental lighting.
I would LOVE to have a lab. A long bench with shelves, cabinets, endless test equipment, a long beautiful white surface covered with a sizeable anti-static mat. And of course, proper bright white lighting that allows my tired aging eyes to read all the small device print. But as reality has it, I am not an engineer but more of a hobbyist, drunk with the constant feed of the science behind my ideas and creations. Self-fulfilled with satisfaction by applying what little I know to furnish my house and family with something you cannot buy online, and cannot be done by anyone else in my neighborhood. I am stuck between the profitable inventor and production and the prototype.
It’s not as sad as I make it, but it does limit me somewhat. Without an electrical engineering degree, and most of the complex math forgotten with the faded years of my high school youth, I am left with endless searches via google, and posting my inquiries here and a few places elsewhere… hoping someone with the talent I wish I had will throw me a nugget. All I really need is a breadcrumb trail though most times.
So my lab is a place in our third bedroom, populated with minimal but at least somewhat respectable equipment. Not the lab I dream of but it’s a place to pursue my passion.
So to make it more productive for me, I need to tackle each item on my list of goals, and the one I will go after today is lighting!
I devised on paper an idea that IS available online but more expensive than I think it should be, and certainly not the exact design I want, so I went after it as a project.
The 3 watt LED in various spectrums of white has finally hit the market in large volumes and cheap prices. I found a place where I can get 50 of these in a snap-apart grid for $10. Certainly enough of them and cheap enough to prototype with. They are probably crap, but again, it’s a prototype.

Forward voltage is 3.6-3.8vdc with a max current of 700ma. They are supposedly 6500k wavelength and 180-200lm. This wavelength is great for vegetable production of indoor plants, but that is another project.
I am great with the digital aspect of things. MCU’s, C and C++, Linux, software development platforms, but when it comes to analog electricity, or better known as ohm’s law… well it was said a few times here. Ω’s Law + Hop = FIRE!
I have countless strips of WS2812B RGB LED’s and the means to control them. But when it comes to these white light strips and obviously individual LED’s like what I am working with here, individual control of brightness in an array is not possible with the existing design. An engineering friend of mine suggested that I look to getting small SMD WS2811 chips, adding P-Channel MOSFETS, a couple of resistors and a cap, and control each 3W LED using that scheme. I LOVE IT! It seems viable.
No I really do not care about controlling each LED in a 3x array individually, but the WS2811 is 3 channel because of the RGB aspect, so why not develop 3x LED arrays and just control the brightness of all of them in 3x LED pods? The goal is to be able to send digital data to control the pod’s brightness, and send more data to control other pods in a larger array. The device conditions the data signal and passes on additional data to the next node once the locally needed data is stripped off. In this case, 24 bits, or 3x 8 bit bytes for each channel’s brightness value. PWM is also supplied. I just need to use the mosfets to drive the LED’s.
The individual control of each 3w LED in the pod can be folded out into a straight line, allowing a string of these to need only one WS2811 for each group of 3. This is important for my lightning simulator effects for Halloween, and, that’s another project too for another thread.
For now? Spot lighting pods. I even found a nice diffuser for the project! I also found some nice gooseneck hardware with M8/M10 machined male and female ends for mounting. And, the end-point mounting hardware. I can equip one of these assemblies with a cheap MCU, capacitive touch controls for intensity, and I have my adjustable high-intensity spot lighting! WOOHOO!
Enter the brick wall I slammed into. Selecting components. The designs I have reviewed favor a P-Channel MOSFET with low RDS(ON) to minimize heat generated by the driver, especially during PWM control. I am absolutely lost picking the correct small SMD device to meet my needs and that is what I need help with. With drivers needed every 3 LED’s, cost is an issue. The funny thing is, the hardest part for me use to be designing and having the pod boards made. With all that Jon Chandler has offered here, I am confident I can do that pretty easily.
But I need to pick a P-Channel MOSFET.
Power I plan to supply is 5v 6a (or more depending on the application). Obviously, if I have 3x LED’s at max 700ma, I am looking at 2.1a per pod at full on.
The WS2811 power requirements are a bit of a mystery and need to research more. The datasheet shows a 100Ω resistor between 5vdc and VDD in, and not sure why. The datasheet says 6-7vdc with an output voltage of 12vdc. I will test this with my scope. My limited knowledge of analog has me asking… is that too high for a low RDS(ON) device?
3W LED forward voltage is between 3.6vdc and 3.8vdc. I need to make sure I do not exceed that and many have stated I should use at LEAST a 1w resistor of a value of about 1.4Ω to 4Ω.
I need a circuit and P-Channel MOSFET recommendations.
I hope someone can help me here. Jon? Wink Wink.
Thank you for your time!
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