Hybrid LED strip controller

[kande004]

Hello All,

I am working with some 24v LED strips that are not technically RGB, but are instead 3200k-5600k (one LED for each) . I have been on the search for a rotary-style or slider style dimmer pot that will allow me to control the color temperature of one of these Hybrid strips. Basically, I want to be able to adjust between 3200k and 5600k or create a mix of the two, all the while not affecting overall brightness levels. I have searched a lot on Google and have found controllers that perform this function but are either RF or IR remotes and, in this scenario,the one ide like to find/build has to be inline. I imagine that the dimmer would need to accommodate the two negatives (color LEDS) and the positive. Any thoughts? Thanks everyone

 

[BradtheRad]

You need for one output to rise while the other output drops.

This concept could be useful. I saw this schematic for balancing stereo channels. A single pot does the job. (No need for two ganged pots.)



The pot was dialed back and forth as the simulation ran.

All resistors are necessary.

You would not necessarily drive the led's directly from this, but the outputs could control 2 transistors as resistive drop, or to generate PWM signals.

 

[chuckey]

LEDs are current operated devices, so your 24V devices must be a chain of them and a series resistor. As they do not conduct any current below a certain voltage, normally about 1.5V you cannot relate their light output to the applied voltage. So either you look up their characteristics as to current and light output or set up two LEDs with different power supplies and increase the voltage on one while reducing the voltage of the other while maintaining the same overall light output and note the PSU voltages. Then you have to electronically duplicate these results.
Frank

 

[kande004]

Hi guys, thank you for the help here! Great advice. Bradtherad, would i need be looking for a linear taper pot then? The LEDS I am working with are 5.5w/ft and i would be needing this controller to not drive, but to control color for about 5' worth.

 

[Audioguru]

Our vision's sensitivity to brightness is logarithmic like our hearing so a log pot is needed to control brightness. But you need one linear balance pot, not two log pots.

 

[BradtheRad]

Bradtherad, would i need be looking for a linear taper pot then?

I agree with Audioguru, a linear pot is suitable.

There is a chance you might want to use the PWM method. Here is a square wave oscillator with variable duty cycle. It produces positive and negative polarity, however you would need to customize this to your LED requirements, since your OP mentions two negatives and a positive.



The scope trace shows a few cycles of equal time for high and low voltage, sandwiched between a few cycles of unequal time lengths.

It's also a question whether you want the led's to be on simultaneously or not, which determines whether you can use a certain method.