Cree R-bin Vf??

hello again. I must say I am totally perplexed!

What is the Cree XR-E R2 and hopefully R4 Vf???

Some people here say it is lower right at the P4 neighboorhood, other seem they use 3.7+ at their mods.....hmmmm??? And a japanese Fenix T1 R2 review had a table with 3.8??? Vf...

BTW I tried to find the info in the Cree website but I could not locate any document that lists all the bins (P,Q,R) Vf.

so any references????

If its like any of the other Cree P3/P4/Q2/Q3/Q4/Q5 bins, then there is
no possible way to predict what the Vf is.

It varies from one led to another.

yes but then why do we drive the Q5s on 3.7Volts? because this is the bin average?

kosPap said:

yes but then why do we drive the Q5s on 3.7Volts? because this is the bin average?

Click to expand...

3.7v is kind of the standard for white LED's. This is due to the technology currently used to produce white LED's. As far as Cree as a company is concerned, the entire XR-E series has the same general Vf requirements, with the specific LED's having some variation.

The Cree's (among other's ) specs can be seen here:
https://www.candlepowerforums.com/threads/156772

kosPap said:

yes but then why do we drive the Q5s on 3.7Volts? because this is the bin average?

Click to expand...

We don't just "drive" the Q5s on 3.7 volts.

Flashlights with Q5s can be designed to be "driven" by cells with a whole
range of different voltages

ie. single AA/AAA NiMH 1.2V
single AA/AAA Alkanline 1.5V
single CR123A 3V
single li-ion RCR123 3.7V
2 AAs/AAAs NiMH 2.4V
2 CR123s 6V
2 Li-ions RCR123 7.4 V


and the list goes on.


It just so happens that if we don't use a driver to produce a fixed current,
ie. that we direct-drive the led instead that the 3.7V produced by a li-ion
usually is a fairly close match for the Vf of many leds.

This is far from accurate though, which is why its better to use a driver
supplying a known amount of current to the led which is within the limits
that its advertised for.

I meant why do manufacturers drive the Q5 at 3.7 V using PCBs or otherwise...

Is the Q5 designed to be supplied with 3.7Vby and large? What is the R2 design specs?
Pratically when you mod a flashlight to Q5 starting with a P4 it is siad that the Vf is too low at 3.2V....So enter a new driver.

When the R2s become widley available will I have to use a driver that outpus 3.2, 3.7 or a higher voltage to the LED????

kosPap said:

I meant why do manufacturers drive the Q5 at 3.7 V using PCBs or otherwise...

Is the Q5 designed to be supplied with 3.7Vby and large? What is the R2 design specs?
Pratically when you mod a flashlight to Q5 starting with a P4 it is siad that the Vf is too low at 3.2V....So enter a new driver.

When the R2s become widley available will I have to use a driver that outpus 3.2, 3.7 or a higher voltage to the LED????

Click to expand...

The Cree P4, Q5, R2 are not different LED's, they are the same LED, the Cree XR-E-7090. The letters are just a grading system for flux. The entire XR-E line has the same drive specs, which can be seen here:

http://img171.imageshack.us/img171/4668/vfee2.jpg

From my understanding, the driver will self adjust to the Vf of the LED(or whatever its supplying).

Each Cree XR-E has a slightly different Vf. Some Q5s have a Vf of 3.4v at 700 mA and others have a while some bad ones are 4v at 700 mA. A good driver should be able to supply both with power without problem. Locking a driver into a specific voltage would be a dumb idea for powering something that has variable Vf.

If a driver can power a P4 bin, it should be able to power the Q5, R2 Seoul P4, Luxeon I, or what ever thing with similar(not identical) voltage and current needs.

P2, R2, Q5 are just bins to grade the LED on how efficient and/or bright it is, each LED would be different.

The way lots of LED drivers work is to put out a high voltage, like 12-13V, but put it out at the desired current. The voltage drop (Vf) of the LED will change to accomodate the current.

Dang! now I get it...

So how I test that the driver is up to task? assemble and measure at the wire-led soldering points???

Damn! seems I was cheap when assembled this driver with a P4 instead of an available Q5 (driver goes short of 12V hooked straight to the DMM)....