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Beginner Electronics - Cree LED circuit

Ploh

Feb 15, 2014
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Feb 15, 2014
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Hi everyone!
I recently joined this forum to get some help on fixing my camping head lamp (the ones that go around your head).
It was a cheap item and the LEDs soon broke, however rather than buying a new one, I thought it'd be interesting to try and fix it.

I'm thinking of replacing the LEDs with these -
http://www.jaycar.com.au/productView.asp?ID=ZD0298

This is a circuit I drew up. I'd just like to know if this would work and why is it I see circuits online that include transistors and what not. Why is it so complicated!?

Each resistor would have to be at least 224 ohms right?

Thanks guys. I hope to learn more from this forum and create bigger and better circuits!
 

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Ploh

Feb 15, 2014
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Yes, that will work, but it will be inefficient.

You need to read this: https://www.electronicspoint.com/got-question-driving-leds-t256849.html (especially section 2)

And yeah, 220 ohm resistors will give you about 25mA in that circuit.

Thank you for the reply steve. I had a read of it before posting this thread however I want to use a 9V battery supply. Thus 3 LEDs in series would mean that I would need a source larger than 10.2V.
I intend to install 5 LEDs into the headlamp and thus, the parallel would work better for a 9V source right?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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If you have 5 LEDs, have 2 strings of 2 and one LED on its own.

Beware that 75mA from a small (type 916) 9 volt battery will mean that it won;t last long.

If you're using a larger battery you should be fine.
 

BobK

Jan 5, 2010
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Also be aware that 5 of those LEDs will produce about 3 lumens. A typical LED flashlight is more like 100 lumens, so don't expect it to be very bright.

The reason LED lights use more complicated circuits is for efficiency and consistency of the light output. Typically, they would use a buck / boost converter current source that will keep the current constant as the batteries wear down. I built a reading light that operators off a 9V (the ones I take out of my smoke detectors every 6 months, and still have useful life) and I got 30 hours of operation at 30 mA from these half discharged batteries. The light output was constant until the battery terminal voltage was down to about 4V. I used a single LED that puts out 8 lumens at 30mA, much more efficient than the ones you are using.

Bob
 
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