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I'm wanting to build an LED light panel using this PWM dimmer. However, I'd like to have 2 different LED light strips that can be faded between using the pot. I need one light strip to take the power provided from the board and the other to use the remaining power (50/50, 90/10, etc). Is this at all possible, or is there a separate board I could search for (what terms could I use)? Would I simply need to use two different boards and control them separately?

Thank you.

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    \$\begingroup\$ I don't understand what you want. Do you mean you want both to be say 90% or one 90% The other 10%? \$\endgroup\$
    – Passerby
    Commented May 10, 2017 at 23:44
  • \$\begingroup\$ The latter - If one is 90%, the other is 10%. \$\endgroup\$
    – Firedan1176
    Commented May 10, 2017 at 23:47
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    \$\begingroup\$ A PWM cross fader. That's going to be a custom design I bet. \$\endgroup\$
    – Passerby
    Commented May 11, 2017 at 0:01
  • \$\begingroup\$ IF you are current limited, what are the specs and does it shut down or simply overheat. Define source and both loads and crossover current point. I did this using discrete power LEDS to fade from bright white to sunset colours then off for a 60W bay window custom ceiling light array. \$\endgroup\$
    – D.A.S.
    Commented May 11, 2017 at 0:33
  • \$\begingroup\$ But you cannot use this dimmer as a cross fader, it is only a single sided dimmer For this you need a half bridge with PWM on both drivers with a dead-time. then Output to V+ and output to -V does the cross fade to dual loads. \$\endgroup\$
    – D.A.S.
    Commented May 11, 2017 at 0:38

2 Answers 2

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It sounds as though what you want is something to provide two different PWM signals to an LED power controller that accepts one, where one PWM signal is the inversion of the other one:

schematic

simulate this circuit – Schematic created using CircuitLab

The PWM generator can be anything you can find that is able to let you create a 0% to 100% PWM output at whatever control voltage you need. The "INV" device is just a properly compliant inverter. It could be a transistor of some kind or an actual logic gate (if it is compliant.) It's output will be the inverse of the PWM generator's output. In this way you get the exact opposite percent for one and the other inputs feeding into the two remaining devices: the LED controllers.

The LED brightness controllers need to be appropriate for your LED strip, or LEDs, or whatever you are using. And they need to accept a PWM input that they use to linearly regulate the percent of time they apply the set current to the LED lights.

Now, one more point to keep in mind. The human eye does not translate 50% duty cycle as 50% brightness. (Worse, there are two completely different "systems" in your eye: scoptic and photopic.) In broad strokes, brightness in your eye is a logarithmic thing. You can check out another link here at EESE for something to consider on that topic, too. You may want to use an audio taper or some way of arranging things with your PWM generator so that the light levels appear to be more linear as you adjust the control. But it's not necessary. Just a suggestion.

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  • \$\begingroup\$ Thanks for the response! As far as I can tell, I'm wanting to wire the PWM directly to an LED light strip. I do not want to have to use an arduino or any code, so I'm simply wanting an analog way of changing the brightness of two different sets of LEDs where one will be the opposite brightness of the other. I don't care too much about a "linear"/accurate brightness, so I think if I'm able to find such an inverter that you describe, I will have exactly what I need. Using the linked PWM board I had in my original question, is there something I could add/use directly to get that inverted signal? \$\endgroup\$
    – Firedan1176
    Commented May 11, 2017 at 0:06
  • \$\begingroup\$ @Firedan1176 The inverter design depends on the PWM device and upon the LED controllers and their inputs, as well. Someone needs to do some thorough research about the PWM generator output's voltage and current compliance as well as the LED controller input drive requirements. Chances are, a transistor and a resistor or two could manage the job, though. (May require tracking down some power supply details as well.) \$\endgroup\$
    – jonk
    Commented May 11, 2017 at 0:15
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You can make a circuit utilizing an inverting op amp that will invert the PWM output. I (hastily) created one in Multisim. LED strip 1 would be receiving the red signal and LED strip 2 would be receiving your purple signal.

Crude inverting op-amp circuit

As you can see from the first chart, when the duty cycle is 80%, LED strip 2 duty cycle will be 20%. The second chart demonstrates the opposite: LED strip 1 is at 10% duty cycle and LED strip 2 is at 90%.

LED1- 80%, LED2 - 20%//LED1- 10%, LED2 - 90%

I hope this helps push you in the right direction! Good luck!!

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  • \$\begingroup\$ I'd be concerned about the power-handling capability of this. Op amps are not typically high-power devices, and those that are aren't cheap. If this is for illumination, it might not be an option, not without some kind of power transistor. \$\endgroup\$
    – Hearth
    Commented May 11, 2017 at 1:07
  • \$\begingroup\$ @Felthry I did not take not into consideration, thank you for pointing that out! From other comments it looks like OP has gotten a lot more (and probably better) suggestions :) \$\endgroup\$
    – L. Paw
    Commented May 11, 2017 at 14:50

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