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What would be the best way to drive 3 high-power RGB LEDs with one 18650 battery? The LEDs are 3 W a piece. Forward voltage is 3.2 V, forward current 350 mA per color.

I would like to use a mini RGB controller but they don’t function well at low voltage or practical with a large resistor. Can anyone give me basic direction on what components I should use to design a board with basic functionality to change colors and maybe brightness? I’m very sharp with ESP dev boards, I just need direction on hardware for LED controls.

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  • \$\begingroup\$ One very easy solution is to set up to 5v and then power a normal RBG controller with that. You could design something more clever to waste less power, but it sounds like you're looking for a simple solution. \$\endgroup\$
    – user1850479
    Commented Mar 27, 2023 at 1:02
  • \$\begingroup\$ I’m trying to conserve space as well. I’ve tried using a boost converter to bump the voltage higher but it makes the leds flash and the voltage drop is to much. \$\endgroup\$
    – Matthew Whitlow
    Commented Mar 27, 2023 at 1:26
  • \$\begingroup\$ You can get single ICs that contain the boost converter and the RGB controller all in one, so very compact. That'd take more design work though. Alternatively you could buy a better boost converter that works correctly (or design one yourself) and pair with an off the shelf controller. Lots of options, choose whatever works for your problem. \$\endgroup\$
    – user1850479
    Commented Mar 27, 2023 at 1:30
  • \$\begingroup\$ boost converter [makes the LEDs] flash and the voltage drop is to much sounds exceeding some current limit somewhere - if controlled individually and up to rated current, that's 3.15 A and more than 8 W - net. \$\endgroup\$
    – greybeard
    Commented Mar 27, 2023 at 1:30
  • \$\begingroup\$ The more I looked into it, I’ve learned that I need a constant current device. The only thing I’ve found that’s constant current is a step down converter which doesn’t help either. Where would you recommend I shop for quality electronics other than Amazon? \$\endgroup\$
    – Matthew Whitlow
    Commented Mar 27, 2023 at 1:39

1 Answer 1

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schematic

simulate this circuit – Schematic created using CircuitLab

This is a circuit that should provide a smooth current through the LED using a PWM signal. I was unable to get the proper PWM duty cycle to achieve continuous conduction mode. But this should be able to power your LEDs.

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  • \$\begingroup\$ (to achieve continuous conduction mode increase frequency, inductance (current down), or duty cycle(current up.)) What is the difference to using a square generator where now there is triangle+comparator? \$\endgroup\$
    – greybeard
    Commented Mar 27, 2023 at 7:04
  • \$\begingroup\$ I tried that and for some reason was unable to achieve CCM. Maybe I had the wrong values, but I think it's due to some peculiarities in the simulator. It seemed to work in another answer. There i think I was able to get the voltage to PWM device working properly. \$\endgroup\$
    – PStechPaul
    Commented Mar 27, 2023 at 18:23
  • \$\begingroup\$ Here are some successful simulations Only thing greatly different is power supply 12V and not 3.7V. electronics.stackexchange.com/a/659055/316329 electronics.stackexchange.com/a/660188/316329 \$\endgroup\$
    – PStechPaul
    Commented Mar 27, 2023 at 18:37
  • \$\begingroup\$ Fixed PWM, into a stiff load like an LED, from a variable supply, in CCM, is every ingredient in a recipe of disaster. Current mode control however is perfectly suitable. \$\endgroup\$
    – Tim Williams
    Commented Jul 14 at 23:18

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