Design a circuit to dim and control color temp of a bicolor 12V LED Strip

Thread Starter

Rotbart

Joined Jul 28, 2017
5
Hello people,

I have done alot of experimenting with 12V LED strips for my cinematography endeavors - which works pretty well. Those new High CRI LEDs are effecient, very bright and sooo small.
Always single color for now and my knowledge of voltage regulators and PWMs sufficed.
My new project is to build a system of bicolor tubes that are dimmable and also color controllable, they will be in different length and have mini XLR connectors on both ends so I can take as many as I want and put them into a set as "practical lighting" solutions. (think lamps that are in frame to provide something for the eye to see but not to actually light subjects)

I sourced all the parts for this, only the dimmer itself seems to be a problem, as there are no affordable commercial ones available.

Id like to use these strips: https://store.yujiintl.com/products/bc-series-dual-cct-ribbon-120led-2835

I have basically no idea how to built this dimmer to do what I want. I just soldered a circuit with 2 10K PWM dimmers so I can basically dim both strips independently, but thats not practical on a film set.

Id love some insight how you would go about that.
Greetings from Germany,
Tim
 

Bernard

Joined Aug 7, 2008
5,788
Greetings, Rotbart, from USA. I could not bring up strip data. Does light pattern conform to an external
stimulus or could it be controller by two random voltage generators ?
 

Thread Starter

Rotbart

Joined Jul 28, 2017
5
Greetings, Rotbart, from USA. I could not bring up strip data. Does light pattern conform to an external
stimulus or could it be controller by two random voltage generators ?
So how it works,
You have three possible connectors:
+
- Cold light
- Warm light

The simplest solution would be to connect 2 voltage regulators, both positive wires from the regulators to the anode and the negative wires to either -W or - C
So I can mix both colors until I have the desired temp. Just not really practical.
Hope I understand you correctly.

Other than that Vf= 12V and the Leds will light up somewhere between 7-9V.

My ideal would be to, in the end, have one potentiometer to control overall brightness and a second to dial in overall color temperature.
Which would also mean that the relative brightness of both cold and warm stays the same when dimming.
 

Bernard

Joined Aug 7, 2008
5,788
I'm not sure of your colors, but suppose they are yellow & blue. Hot color might be full blue with a pinch of yellow & cold, full yellow with a pinch of blue. Overall brightness controlled by supply voltage? Sounds doable
but let the experts chime in.
 

Thread Starter

Rotbart

Joined Jul 28, 2017
5
Hey Bertus. That's what I already setup. On a film set thats not practical. I need a solution to just dial in the Color Temp. So I have one potentiometer with a scale that goes from 2700K to 6000K.
But thanks!
So if anyone can think of sth Id be glad.
 

bertus

Joined Apr 5, 2008
21,588
Hello,

You could try a circuit that will raise the PWM of cool, it will lower the PWM of warm.
This would be an idea:

Inverting_dual_SimplePWMcircuit.PNG

The circuit will run fine on 12 Volts.

Bertus
 

Bernard

Joined Aug 7, 2008
5,788
It might be possible to carry post #9 by Bertus, a step further by adding dimming by feeding normal output of
U1A & inverted output of U1D into one each of U1B & U1C, the other inputs to another NAND like U1A but at a higher frequency, C2 maybe 1 nF. For inverters would use 4049's rather than another 4093.
It seems that there is a loss of about 5 % per m so might run parallel lines of something like 14 ga. & attach sockets at desired spacing.
 
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