Powering x-opto white LEDs

[Alex Bird]

Hi,
I'm making some LED lights for illumination as part of some costumes,
in fact I have to put these things together tomorrow!

In my prototype I used some ultra-bright reds I had lying around, and
my series resistance calculations were fine. The device is simply a
D-type flip-flop, reed switch and npn transistor, enabling the light
to be switched on and off by waving it near a magnet.

For the real things I ordered these:

http://www.rapidelectronics.co.uk/r...CAT_CODE=30319&STK_PROD_CODE=M61376&XPAGENO=2

Made by X-opto. Who they?? I cannot find any online presence.

Lens Material V F max V R max Chromaticity Int.mcd@20mA View angle
water clear GaN 4.2V 5V X=0.31, Y=0.32 3000 15°

As the intensity is quoted for 20mA, I factored in the forward drop of
0.7V per LED and calculated the resistance. Nothing. I Checked all
my cables, measured voltages.
Eventually I tried upping the current, and finally with 5V connected
directly across them they are putting out what looks like 3000mcd to
me!

Am I right in thinking that I can do this because VFmax is 4.2V, and
4.2 + 0.7 = about 5? Am I wrong to assume a forward drop of 0.7V?
Does anyone know anything about these LEDs?

Thanks for any help,
Alex

 

[Tim Wescott]

Hi,
I'm making some LED lights for illumination as part of some costumes,
in fact I have to put these things together tomorrow!

In my prototype I used some ultra-bright reds I had lying around, and
my series resistance calculations were fine. The device is simply a
D-type flip-flop, reed switch and npn transistor, enabling the light
to be switched on and off by waving it near a magnet.

For the real things I ordered these:

http://www.rapidelectronics.co.uk/r...CAT_CODE=30319&STK_PROD_CODE=M61376&XPAGENO=2

Made by X-opto. Who they?? I cannot find any online presence.

Lens Material V F max V R max Chromaticity Int.mcd@20mA View angle
water clear GaN 4.2V 5V X=0.31, Y=0.32 3000 15°

As the intensity is quoted for 20mA, I factored in the forward drop of
0.7V per LED and calculated the resistance. Nothing. I Checked all
my cables, measured voltages.
Eventually I tried upping the current, and finally with 5V connected
directly across them they are putting out what looks like 3000mcd to
me!

Am I right in thinking that I can do this because VFmax is 4.2V, and
4.2 + 0.7 = about 5? Am I wrong to assume a forward drop of 0.7V?
Does anyone know anything about these LEDs?

Thanks for any help,
Alex

LEDs have a different forward drop from a silicon diode -- red ones can
range from 1.5V on up. In your case I think you need to use the 4.2V
instead of 0.7V in your calculations.