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I’m buying a 10 or 20W RGB led chip and I plan to power it with a Li-ion 18650 battery. For big led’s like I’m using, they specify voltages from 6-30VDC depending on the individual led and range from 500-1000ma draw per channel. I’m somewhat of a novice in EE so I need help figuring out what to do from here. I know I will need a voltage booster step up module to get up to the higher voltages I need. To maintain constant voltage as the battery drains, do I also need a voltage regulator module? Or is there some alternative piece of hardware that can manage all of this for me? Let me know the best option.

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  • \$\begingroup\$ If you're using RGB, you may well want to go looking at drivers first. Are you thinking an RGB COB? \$\endgroup\$ – K H Sep 9 '18 at 6:09
  • \$\begingroup\$ @KH yes an RGB COB \$\endgroup\$ – Ryan Sep 10 '18 at 21:38
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Normally LED's of most any size are driven by a constant-current source, so the voltage can vary (to some degree) yet the LED will maintain the same brightness. LED's in series need more voltage but still an LED is a current driven device. Suggest you look up "LED Drivers" and you will find hundreds of options, from ICs to ready-to-use modules that adjust brightness and allow for series and/or parallel operation (expensive, so go basic first).

Cheap LED flashlights often just use resistors but they waste unused power as heat and do not keep the LED current constant. Also, having the option to boost the voltage to put many LEDs in series is a big plus because the LED current remains the same for the entire string.

Parallel strings do consume more current (the sum of all the strings) but that maybe going beyond what you had in mind. Spend the money for the right LEDs and the right LED power supply (adjustable) and have good results the first time. Later on you can think about series/parallel expansion.

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To keep it simple lets just say you have three 3 Watt LEDs, an R, G, and B.

I assume you want to adjust the current in each LED to get the same functionality as a Phillips Hue light bulb.

It is easiest if you find green and blue LEDs with a forward voltage below 3V which is just under the 3.2V cutoff discharge voltage of an Li-ion battery.

Rather than an RGB I would recommend using the Luxeon C Color line LEDs. They are small, have excellent color mixing, and very wide viewing angle (170°). Some good alternatives are the OSRAM Oslon SSL 150 and Cree XP-E and XP-E2

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If you are stuck on a single RGB then I would recommend the LED Engin LZ4 which is an RGB and White. You do not have to use the white.


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You will need three LED drivers, one for each color. Here you have to design your own or use an off the shelf DC-DC constant current buck step down driver. If your forward voltages get too high then you'll need a buck-boost constant current driver.

The only off the shelf driver I would use would be the Mean Well LDD (buck) or LDB (boost-buck) but they have a minimum input voltage of 9V. You could use 3 batteries in series. The efficiency of the LDD driver is 97% so you will still be using most of the battery's energy to drive the LEDs.

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The big problem with LED drives is the overhead voltage required. Some buck drivers need 4V over the forward voltage. You need a driver with a very low overhead or use serial batteries.

There are two methods you can use to dim the LEDs. PWM or a varying voltage level.

If I knew more about your application and you had the desire to design your own driver I could recommend some driver chips.

If you were to go with a NiMH or NiZn rather than Li-ion you could use a very simple boost driver. The Nickel-zinc (NiZn) is an excellent LED battery with a very flat discharge curve but best of all it is 1.65V rather than 1.5V.


Microchip Boost Driver

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