White power LED with V(f) = 1.75V?.....too low?

[grizedale]

Hello,

We are using Cree XPEHEW White LEDs in our 460mA LED Lamp.

Cree XPEHEW Datasheet
**broken link removed**


These XPEHEW LEDs can be binned (sorted) on Forward Voltage [V(f)]

Binning & Labelling document:
**broken link removed**

Now, our three Cree XPEHEW LED part numbers from our BOM are the following:-

XPEHEW-L1-000-00 BE7

XPEHEW-L1-000-00 CE7

XPEHEW-L1-000-00 DE7



...The third character from the right hand end of the part number refers to the voltage bin (As stated on pages 2 & 8 of the binning document)

However, page 8 of the binning document says that "B" refers to a forward voltage of 1.75V to 2V....

-Surely this cannot be right?.....a white LED couldn't possibly have a forward voltage as low as 1.75V?

 

[chuckey]

Looking at P.8 of the Cree binning spec, they give Vfs from 1.75 -> 3.5, so it would be obvious that the LEDs are sorted, and while we would say LEDs about 2 Volts, there is a big tolerance on the Vfs for otherwise OK diodes. The only real problem is that if you wanted 10,000 @ 1.75 Volts then they might have to make 10,000,000 to get these end of tolerance devices. This is reminiscent of transistors in the 1960s, where they were sorted into, AF,RF, high gain, low gain. . . then labelled.
Frank

 

[grizedale]

Yes, but what i am saying is that surely it cannot be possible to make a white power LED with Vf as low as 2V .

White LEDs are always around 3V.

Red LEDs are foten about 2.2V, but surely you cannot get a white LED less than say 2.8V with 350mA current in it?

 

[BradtheRad]

The ledmuseum.org website shows a list of white led's. It's gone mostly archival, but even a few years ago there were white led's which operated below 2.2 V.

If white led's still have a blue led underneath, then it depends on what modern-day manufacturing has done as far as lowering blue led's operating volt levels.

I saw one description saying:

"This white LED has circuitry built-in, so it can operate from less than the 3.6 volts most other white LEDs require."

So built-in circuitry might have something to do with it.

 

[FvM]

However, page 8 of the binning document says that "B" refers to a forward voltage of 1.75V to 2V....
-Surely this cannot be right?.....a white LED couldn't possibly have a forward voltage as low as 1.75V?

It's all about reading.

You apparently overlooked, that the binning document describes beside white also red/amber/green LEDs. So there's is a trivial answer to your question. It's not said anywhere in the document that white LEDs are available in a B bin.

 

[grizedale]

Thanks FvM,

You are saying what i was thinking.............however, on our BOM, we have white LEDs....and these are with the "B" binning code in their part number....and they are definetely white.

-so i am wondering now if someone has made a mistake with the part number in our BOM.

-So do you believe that a white LED is almost certain to never be below Vf = 2.5V, say, at 350mA?

 

[FvM]

- so i am wondering now if someone has made a mistake with the part number in our BOM.

Yes something like this.

-So do you believe that a white LED is almost certain to never be below Vf = 2.5V, say, at 350mA?

Yes, by state of the art and semiconductor materials used for white LEDs.

 

[godfreyl]

Perhaps this advise I gave a couple of days ago is relevant here too.

If you can't find the information you want online, you need to make inquiries i.e. pick up the phone or send an email.

Bear in mind that if you want e.g. detailed information about Cree products, it is far better to direct your questions to Cree, rather than random strangers on an internet forum.

Similarly, if you have questions about a BOM, and the BOM was created by someone at your company, then surely (s)he's the best person to ask?

 

[grizedale]

No, they are very busy malheuresement..........they are working on somehing else now....if any problem now, we must sort it, not them....

I have emailed Cree before but no reply, ill try again though on your advise.

These are called "high efficiency" white LEDs, so maybe it is possible that they could have a forward voltage thats that low (~2V) at 350mA ?

 

[FvM]

It seems like the bin classes in the binning and labelling document don't correspond to the usage in the XP-E datasheet. The latter lists also bin classes 8 and 9 that aren't mentioned in the binning document. It's not a problem of your BOM.

These are called "high efficiency" white LEDs, so maybe it is possible that they could have a forward voltage thats that low (~2V) at 350mA ?

If they had managed this breaktrough, they won't keep it a secret. You can be pretty sure, that the typical datasheet Vf numbers around 3.5 V don't include exemplars with 2 V and below. It's like finding a Si BJT with 0.4 V Vbe :smile:
You should ask the manufacturer for a corrected binning document.

 

[grizedale]

incidentally , do you know why the above cree XPEHEW white LED is called "high efficiency"?

-Surely it is no more highly efficient than the MX6AWT LED from Cree, and thats not called "high efficiency" and only costs half the price.

MX6 LED datasheet:
**broken link removed**

Cree XPEHEW datasheet
**broken link removed**

 

[zhoubin]

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Web: **broken link removed**