For my new project I want to power multiple HIGH power 3w smd LED which requires voltage between 3.2 to 3.7 volts.
What I am trying to achieve is total 7 lamps with each including RGB + white + warmwhite with such 3watt bulbs (attached image) . So my each lamp will have following connected in series :
3no. x 3w white bulb
3no.x 3w warmwhite bulb
3no. X 3w RGB bulb
And some resistor making it requiring 12volts each series
So when there will be single colour ON with highest brightness each lamp will consume 9watt and total 63watts from 7 lamps (9w x7).
So my question is how to make it efficiently possible using arudino with the ability to control the BRIGHTNESS . Which mofsets / BJT or any other component I have to use .
LEDs are normally "current controlled". With the proper current the voltage "magically falls into place."
Like all diodes, LEDs are non-linear... Their resistance goes down as the voltage goes-up and vice-versa. If the voltage is slightly high (or as the LED heats-up) you can get a LOT more current and it can burn-up (and/or your power supply might burn-up). If the voltage is slightly low you don't get full brightness.
With regular little LEDs we use a series resistor to control/limit the current, usually with about half of the voltage across the LED and half across the resistor.
You can do that with high power LEDs but you need to use a high-power resistor and it requires double the voltage and double the power (wattage).
So, high power LEDs (1W and above) normally use a constant current power supply (or "controlled current" for dimming). And if you can wire them in series (and control/cim them together) a single constant-current supply can power/control them all.
Constant current power supplies are usually switchmode designs which makes them very efficient.
A constant current supply works differently than a regular (constant voltage) power supply. With an open circuit (or a high-resistance load) the voltage jumps up to the maximum the particular supply can put-out as it tries to push current through an infinite (or high resistance) load. And if you short the output, it (usually) happily supplies the current at (nearly) zero volts.
Meanwell makes LED power supplies and drivers or you can find boards from other suppliers more economically. (I wouldn't recommend trying to build something like that yourself.)
There is an industrial dimming standard of 0-10VDC or 10V PWM and most of the dimmable Meanwell power supplies need 10V PWM for dimming. The 10V is usually built-in (so you can dim with just a pot) but you need a transistor driver if you want to control it from a 5 or 3.3V Arduino.
Also, high power LEDs usually need a heatsink... (They run a lot cooler than a regular light bulb but they do get hot and the semiconductor material can't handle nearly the temperature of a tungsten filament.)
I understand that overcurrent will fry up LED sooner and so will it be okay if I use slightly lower constant current power supply , lets say 60w for 63w of LEDs ? I am ok with LED not achieving full brightness.
I have the spare 12v 60w power supply hand which is fully sealed. So is there anyway i can use some MOSFET
A 3watt RGB LED contains three 1watt LEDs, not three 3watt LEDs.
A current limiting resistor and a mosfet is a bad idea.
Power LEDs are best driven with a constant current driver (with PWM pin). Example here.
They can drive 1 to 3 LEDs in series from a 12volt supply, or 3 to 6 on a 24volt supply.
The example in the link has three channels (2watt per LED).
There are (cheaper) single channel LED drivers like that on ebay etc.
Leo..
