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12v 3w led project? Answered

Hello all

I am trying to build a "knight rider" light for my car using 3w led's.
I know enough that I want to per sections (8 sections), and to wire the led's in series.
They will be mounted to an aluminum bar so I don't think I need heatsinks.
They will be controlled by a "chaser light" sequential controller.
The specs are:
3w yellow led:
forward voltage:  2.9v - 3.3v
forward current:  750 mA
I have researched and found led driver's but they are a bit more expensive than I would like to pay right now.
Can you guys help me with what I need for this to work in my car.
Do I need transistors, what resistors do I need (values, wattage, etc).
 I need some help from you guys.

How do I do this?????


So the adj pin will go on the other end of the resistor before going to the led?
Also, the "in" pin will get connected to the control box portion of the project, yes??

You need some "active" electronics to do this reliably, because of the range of temperatures you'll need the LEDs to work over.

This circuit only needs two components to work - the version here adds adjustable brightness. Omit the 1k and the 500 R and connect just the "horizontal" resistor. The resistor should be 1.8 Ohms for your 750mA limit.

You can drive two or three LEDs in each string with one of these circuits, which should be very cheap to build.

If your effect is running all the time, they probably won't get too hot, but should always be mounted on a heatsink.

trimmable current source.JPG

PS the resistor should be 1W rated. The ADJ pin on the regulator is connected to the "current limited output"