Hello, /diy/.
I'm making a project where I'll be using a lot of 3W LEDs, from various colours. As so, each colour have a different tension to be used. I will not buy a LED driver module, so I decided to build something similar to the pic related here. I was drawing mine, but I ran out of time.
Anyway, the question is: I want to adjust the brightness of all LEDs together, but every colour is under a different tension, controlled by an LM317 (or some similar, doesn't matter for the question).
Does a simple potentiometer before the regulators could be used? They would be in parallel, and would be probably 5 or more of them.
>>999544
Seriously, did you even read the datasheet? The circuit for an lm317 current regulator contains the lm317 itself and a single potentiometer. Just adjust the potentiometer to adjust the current.
>>999577
No, my dear friend. You are the one that didn't read what I said.
The potentiometer that you are referring to is the one to correct the tension of the output of the LM317. I am aware of it, and that is exactly why I am using these.
My question is, considering the LM317 adjusted to 2,6V, another one to 3,6V and other 3 to 4,1V, how could I control the intake current of all of them together, so all the LEDs are regulated together, from zero volts to the desired tension adjusted on the LM317.
>>999577
Better yet. The circuit in your image. I want to control the intake of various of them together. Think about 5 of those in your image, each one with a different setting on the potentiometer shown.
From zero to the desired tension, of all of them. This is the question. Simply putting a potentiometer before them? (before the intake?)
>>999592
I'm assuming that every time you say tension, you actually mean current.
Anyway, it's clear that your not seeing the difference between a constant current source and a constant voltage source. The pic that I posted is a current source, which is what you would use to control leds. It doesn't matter what the forward voltage of an led is if you are sending a constant current through it.
Your problem is that you want to connect the leds in parallel, which can result in different brightness even if you have identical leds in the different branches. It would be a lot easier to make a series circuit so that you can guarantee the same amount of current is moving through each led.
>>999597
Ok. I want to control 87 LEDs together, reducing or increasing its brightness at once. The 50 of them work with 2,6V, and the rest with 3,6V. Current for all is 0.7A.
How would you do it?
>>999601
Jesus, I can't beleive I have to spell this out for you. See pic related.
>>999620
Also, you're going to need a minimum of 184 watts to do this.
>>999592
Check the circuit at >>999577 again, it is a current source, while the one you posted in >>999544 is a voltage source.
Since led brightness depends on current, >>999577 circuit would be apropiate. Asuming you connect all the leds in series, the will draw the same current (the one provided by the regulator) and the output voltage would be autoadjusted as the sum of the foward voltages of each led at that current.
Keep in mind if the leds are 3W, the regul will heat and be kinda inefficient, as it is a linear regulator.
Whoops, forgot to add the adj terminals. See updated picture.
>>999622
I think you have me and OP confused. I drew a series parallel combo because, even though I originally recommended a series circuit, I realized that the current source would require an input voltage of atleast 263 volts. Breaking it in to a series/parallel combo will reduce that voltage requirement, but you will have to have a seperate regulator for each of the two colors.
In reality, if OP uses lm317, he's going to need a lot of them to dissipate 200 watts, so this simple circuit that I drew will have to be expanded to somewhere between 10 and 50 of these regulators or so, all controlled by a single potentiometer that is the size of a brick. Good luck OP.
For driving so many LEDs, a simpler solution is to power them mains AC using a capacitor/inductor as a current limiter. You don't need to worry about voltage, just the current and power going through each LED.
