What do converters output?

EatSleepRunBike

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I want to build myself an LED bike light using 3 XRE's. I already have a 6v battery pack from my old nite rider that I would like to use. I want to drive each LED at 500ma. I've been looking at converters and I am cofused on what they output. It sounds like you have an input voltage range, and it outputs a constant current. What is the output voltage? Does it matter? Will the Vf of the XRE's even matter if I use one of these converters?
 

LEDcandle

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Depends on the converter; if it is an 'auto-detect', it will bump or drop the voltage as necessary.

If it is a boost converter, then that'll allow you to use a lower voltage batt solution (within specs/capabilities of the converter) to drive an LED that requires more .

If it is a downboy type, you can use higher voltage batts to run a lower voltage LED.

The Vf of the emitter does matter to judge if you need a stepup or stepdown converter. Or get an auto-detect type to solve this problem (but it usually has lesser input range)

If your batt voltage is out of the converter spec range, usually it direct drives the LED (no regulation) or fries something.

I'm not an expert in electronics but I guess that's what I understand about it.
 

infinity of zero

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It is the most safe to connect te led's in serie with each other. The forward voltage of one led is approximately 3,4V when you drive them at 500mA. So you'll need a driver that can deliver more then 10V. A step up converter would do the job for you (from 6V to more then 10V to drive the leds at 500mA). You don't need a converter that can also stepdown.
 

chris_m

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LEDcandle said:
Or get an auto-detect type to solve this problem (but it usually has lesser input range)

Also generally less efficient than either a boost or a buck.

Fortunately if you want to drive 3 XR-Es from a 6V pack you have a nice easy solution - simply run the LEDs in series and use a boost driver such as a Fatman. That should work perfectly with those voltage ranges.
 

LightBright

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It's in the range of 3.1ish to 3.8ish. If you're going to be designing your own driver circuitry, you'll probably be studying for a while. There are some ready-made driver boards, you'll have to look around CPF.

There have been a few threads with bikers that did their own LED setups, so just keep browsing around.

I've been mtn biking at night with my Fenix PD1 CE, just one. So, your shortcut would be to buy three. Or one for the handlebar and one for your helmet.
 
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