I am a complete beginner at designing circuits and my English sounds like a 5-year-old talking. So, please beer with me.
I was thinking of building an aquarium light. As plants need a full spectrum of light to grow properly, this is the selection of colours I came up with by watching many YouTube videos about this topic. I also wanted to adjust each colour separately with an Arduino or esp8266.
The first problem was to control these LEDs based on colour. Which I think I have solved with help from the internet. Please check if there are any problems with the Mosfet driver section.
I am planning on powering these LEDs with a voltage and current-controllable buck converter. (The LEDs are 1W each. They are bead-type LEDs commonly used in horticulture)
Now the problem is the red and the yellow LEDs have a lower forward voltage than the rest and there is also a smaller number of yellow LEDs. So, my questions are:
Won't there be a lower resistance path through the red and yellow LEDs for the current to flow? Which in turn will make them brighter than the rest or possibly even damage them.
Is it ok to power LEDs with a higher voltage than the sum of forward voltages as long as the current is constant?
Is it ok to connect LEDs in parallel like in the schematic?
If this won't work, what are the other options I have to accomplish the goals I have?
And if this works (which I don't think it would) is the voltage and current (20.4V 12.6A) I'm planning on providing correspond with the need of the circuit?
No as a rule, even if they are the same color, as there are manufacturing variations in forward voltage drop.
You can connect LEDs in series, as the same current will flow through each one, regardless of color or forward voltage. You still need a current limiting resistor or constant current source for each series string.
These are readily available in my country. There is an output voltage range of DC180-240V written on the device does that mean I can use a string of LEDs with a forward voltage within that range? Are these devices safe? Are they efficient? And most importantly will I be able to use the existing PWM dimming system I have? (Of course with a MOSFET of greater voltage rating)
That's unusual. Usually a constant current source would be 0-240V, or something like that so you can drive one LED or a small number of LEDs and the voltage will go-down. Or usually you can even short it out and run current through zero Ohms at (nearly) zero volts.
Usually both, but don't touch the high voltage!
Usually no. When the MOSFET turns off during the PWM cycle it will try to continue to push current through an infinite resistance and the voltage will jump to the maximum.
Some LED power supplies are dimmable with a separate dimming-input. The "industry standard" is 0-10VDC, but often 10V PWM can be used. So that requires a transistor. Often the 10V is built-in so you can simply use a potentiometer as a manual dimming control or you can just use a transistor. Other's need a transistor and a (low current) 10V power supply.
I saw a "trick" once where a MOSFET was used to short-out the output. You wouldn't do that with a normal (constant voltage) power supply, but SOME constant current power supplies are happy putting current through a short, and theoretically no power is consumed/wasted because voltage is (nearly) zero. But I wouldn't trust that with all constant-current supplies.
If I use a MOSFET with a higher Vds than the maximum voltage the driver can create will this PWM dimming thing work? As the drivers with dimming capability are quite expensive buying one for each color is not economically feasible. And often they come with a higher current rating than what is necessary for this application.
