cree board question

flashburn72 · Jul 28, 2007

Just got a cree p4 from dealsextreme. question is can I put six volts to it?
web site says typical input is 3.7. any help would be great. thank you in advance

mmmflashlights · Jul 28, 2007

No, that's too much. You'd need a regulator circuit to drop the voltage down to around 3.5-4V. Some batteries have their voltage sag under a load more than others, but not that much. You could get away with 3 1.5V alkaline cells, not 6 volts though.

Mash · Jul 28, 2007

Dx has the regulator board you need, if you intend to drive with volts. There is a range of them, differing in voltage range and drive current. Have a look and see which best fits your needs.

Curious_character · Jul 28, 2007

Tiny changes in voltage cause very large changes in current -- that's the nature of semiconductor diodes. Furthermore, as a diode heats up its voltage for a given current drops. That means that if you drive it with a constant voltage, the current can increase dramatically as it heats up.

That's why LEDs are always driven from constant current (or approximately constant current) -- not constant voltage -- sources. You apply the desired current, and let the voltage be what it will be.

c_c

flashburn72 · Jul 28, 2007

Thanks for the help guy's. I will just keep it around 3-4 volts

Curious_character · Jul 28, 2007

flashburn72 said:
Thanks for the help guy's. I will just keep it around 3-4 volts

A properly designed current regulator should have an open circuit voltage well above the LED voltage. Several volts greater than the nominal LED voltage of about 3.5 volts wouldn't be unusual.

c_c

NA8 · Jul 29, 2007

Curious_character said:
You apply the desired current, and let the voltage be what it will be.

c_c

In a nutshell, what is Fenix doing with their regulator circuit that gets such great performance ?

Curious_character · Jul 29, 2007

NA8 said:
In a nutshell, what is Fenix doing with their regulator circuit that gets such great performance ?

Fenix uses a current regulator like eveyone else. If they're getting a particularly good combination of run time and total light output, it means that their regulator is more efficient than most. That would be a result of competent design, and perhaps the willingness to spend a few more pennies on the necessary components. It's not hard to design a high efficiency regulator (I've done a couple myself). The challenge is in making it small and cheap.

c_c

cree board question

flashburn72

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flashburn72

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