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3W RGB LED's + PWM?

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things

New Member
Hi, I have 4 3W (Combined) RGB LED's on the way for a project.

I want to be able to control the colour of all 4 LED's at once from an Arduino, but kinda stuck on how to do it. My limiting factor is that I need to be able to get all the parts from Jaycar Electronics - Better. More Technical. only.

I was thinking of doing it like this:

**broken link removed**

But there has to be an easier way? Could anyone suggest any ways I could do this with parts from Jaycar?

EDIT: Looks like my little 2N2222A's wouldnt be able to handle 700ma! Maybe I need to use 3 2N2222A's to switch some TIP41C's then ...

Cheers,
Dan :)
 
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audioguru

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Most Helpful Member
Your circuit is missing current-limiting resistors so the LEDs will blow up.
 

things

New Member
I made the diagram in MS word, and decided to leave the resistors out to save time. I know very well they need current limiting. I should have noted that in my post sorry.

So will using a 2N2222A to drive a TIP41C work?

Thanks :)
 
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audioguru

Well-Known Member
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If you make your own darlington transistors then their voltage loss of 1V might be too much.
 

Blueteeth

Well-Known Member
Doesn't jaycar do any MOSFET's ? Look for the ones with the lowest gate threshold, otherwise you'll need bootstrapping which just over complicates matters.
 

audioguru

Well-Known Member
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Doesn't jaycar do any MOSFET's ? Look for the ones with the lowest gate threshold, otherwise you'll need bootstrapping which just over complicates matters.
The threshold voltage for Mosfets is when they are still turned off (the current is only 0.25mA), not when they turn on like a switch.
You need to look at the gate voltage when the max on-resistance is guaranteed.
 

Blueteeth

Well-Known Member
Oops, good call :)

To the op: You could use a higher supply voltage if the MOSFTE you use requires a larger gate voltage, then you could use your LED's in series as opposed to parallel. Green's and blues generally have a max Voltage of 3.8V (ish), so with a 12V supply, they'll drop 3*3.8 = 11.4V, giving a resistor voltage of 0.6V, meaning you can use a lower power resistor.
 
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