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### Topic: High Power Multiple-Channel LED Driver Questions (Read 1 time)previous topic - next topic

#### Phillip630

##### Sep 05, 2013, 08:26 am
I want to make a PWM controlled LED light for my room. To light up the room, I'm hoping to get 1,000 - 1,500 lumens out of it. For maximum coolness, I want to have at least four channels so I can have RGB + warm white. I've been googling about powering such a device all day and found many solutions, none of which looked particularly easy besides this shield. Being an electronics newbie, I don't quite understand exactly what the parameters my DC adapter would need for this. If I want 4 channels operating at 700 mA with 30V, then obviously it needs to supply at least 4 * 0.7 * 30 = 84 Watts.

But what exactly determines the output voltage of a current regulator? Is it just the same as the voltage of Vin? I am very confused on these points.

That shield also seems a little pricey considering single-channel 1-Watt led drivers with PWM like the CAT4101 are less than a dollar. Is there a way to power an arbitrary number of these from one DC adapter? If the DC adapter regulates the voltage to 30V or whatever and I wire up n (an arbitrary number) CAT4101's in parallel to it (and the adapter can supply up to n amps or more), then I could safely power n independent LED strings with the proper voltage and current, right?

Thank you for any help! This stuff is all so confusing to me.

#### Chagrin

#1
##### Sep 05, 2013, 02:51 pm
You want to look for a power supply that can provide more than (4 * 700ma =) 2.8A of power at more or equal to the forward voltage (Vf) of the individual LEDs. In this case it's not useful to look at a wattage. When you're driving LEDs the voltage can be anything that is higher than the Vf of the LEDs; it's the amount of current you push through that matters.

The output voltage is the same as the voltage of Vin. There will be a small "dropout" for the CAT4101 of .5V, however.

The CAT4101 is a linear regulator while the LED shield uses a PT4115 which is a switching regulator. A switching regulator will be more efficient in regulating the current and especially so when Vin is greater than the Vf of the LEDs.

Four LEDs at 30V and 700ma seems like a lot more than 1500 lumens. Can you provide links to the LEDs you're driving?

#### Phillip630

#2
##### Sep 05, 2013, 09:37 pm
Okay, looks like I may only use 18 or 24 volts with an adapter like this. I would buy 5 or 6 of these RGB LEDs and these warm white LEDs.Now I have an idea of what to buy for this project, although now I realize it's going to be fairly expensive to buy all the LEDs. I suppose it's worth it though for a customizable, programmable, long-lasting light source.

#### Headroom

#3
##### Sep 05, 2013, 11:34 pm
For hight power LEDs with 700mA a linear regulator is really not a suitable solution. The shield you've linked to is actually a very inexpensive solution and is a switched DC/DC converter in Buck configuration. A much better higher efficiency solution requiring no heat sinking at the shield as opposed to a linear regulator.
You will need to use heatsinks for the LED's.

This shield is limited to 4 independent channels and you cannot stack another of the same shield on top of it to get to 8 channels as the shield directly uses the Arduino PWM pins and there is a limited number of those ;-)

Frankly, the LEDs you've linked to are also dirt cheap!
http://trippylighting.com

http://ledshield.wordpress.com/

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