# Working with different LEDs

#### Rob1132

Joined Nov 4, 2010
36
I'm looking to put together a light that will consist of 2 different types of LEDs. I'm still learning a lot of this stuff, but I've had some luck lately working with LEDs. But what I have in mind is to take 2 different LEDs and combine them so they would be running off of a single power source. I'm not sure how I would figure out what kind of resistor to use. I've used the LED array wizard for everything so far and that only gives an option to put the value of one kind of LED in it. I'd appreciate any help and here's the values of each of the LEDs I was going to use...

1.5v
140mA

3.4v
100mA

I'd like to use 5 LEDs of each and run it off of a 9V battery. I should also mention that I've actually put together a light with 5 LEDs of the one with 1.5v already and it works great with a single 10ohm resistor.

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#### Markd77

Joined Sep 7, 2009
2,806
Just use the wizard for the 3.4V ones as well. It will probably give you 3 strings of LEDs with resistors. Just connect them to the 9V battery the same as the others. If it is a PP3 don't expect it to last very long, and also the current will probably be lower than you predict because they don't supply much current.

#### marshallf3

Joined Jul 26, 2010
2,358
A common 9V battery won't drive that large of a load. You're asking for 1.4A of current and it just isn't possible.

#### Wendy

Joined Mar 24, 2008
23,280
For that kind of current a buck puck or similar circuit would be a good way to go. These kinds of circuits can be expensive, thought there are several designs that have been developed here on AAC. The reason is conversion. If a LED takes 0.34W (0.1A X 3.4VDC) and the converter is 80% inefficient it will use 0.43W. This translates into 48ma for 9V or 36ma for 12V.

I also agree a small 9V is not going to provide this kind of power. Even AA batteries wired to create 12V would be kinda small. 9V batteries quickly drop to 7V with use, this is normal and expected.

Wiring these LEDs in series will improve some of the performances and reduce the number of buck puck converters.