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FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > IR LED SFH485P, which leg is the anode?

RSS > IR LED SFH485P, which leg is the anode?, The flat side (i.e. meplat) is on the long leg of my SFH485P?!

DPLUIGI	#1 23/01/2008 - 05h47 Top
Class : Beta Tester Posts : 50 Registered on : 04/01/2008 Off line	I am confused according to the doc_led.pdf the anode should be the long leg of the LED and the cathode the shorter leg on the flat side (i.e. meplat) of the LED head - where the anode and cathode are connected to the + and - of the power supply/battery respectively. It is seems to be the opposite convention for these IR LED SFH485P I just received from Digikey. That is to say the flat side is not on the side of the short leg. Further more the package outline in the datasheet indicates that the cathode is on the flat side with the long leg. Is this a case where I should only consider which side the flat side (i.e. meplat) is? In a nutshell shall I connect the + of my power supply to teh short leg et the - to the long leg (i.e.side of the facette/meplat)? Thank you for clarifying this before I fry few of these hard to get SFH485P IR LED. Thanks Donat-Pierre
Kestrel	#2 23/01/2008 - 06h18 Top
Class : Webmaster (admin) Posts : 780 Registered on : 13/07/2007 Off line	The flat side of the LED is the prime indicator of polarity. Breaking with convention, the short leg of the SFH485P is the anode (+), as stated in the datasheet. As a side note the short leg is still connected to the large internal base and the long leg is still connected to the small internal base, just like a normal LED, so it's really the semiconductor junction polarity and flat side that are opposite convention. Support FreeTrack
DPLUIGI	#3 23/01/2008 - 16h10 Top
Class : Beta Tester Posts : 50 Registered on : 04/01/2008 Off line	Thank you for the clarification. I looked through the forum and several point model tutorials and did not see anything pointing this out. In retrospect the doc_led.pdf document on LEDs did points this very clearly in French: << * l'anode est constituée par le picot le plus petit, la cathode par le picot le plus grand dans le corps de la LED. (SAUF POUR CERTAINES LEDS DE PUISSANCE POUR LESQUELLES LES TAILLES DE PICOTS SONT INVERSEES). * Il y a un méplat sur le boîtier de la LED du côté de la cathode * Le fil de raccordement de l'anode est plus long (s'ils n'ont pas été recoupés) En cas d'incohérence flagrante entre les tailles de picots et la position du méplat, ignorer les picots et ne se fier qu'au méplat >> So this implies that the SH485P IR LED must be a high power led, since the anode is conneted to the large internal base/the short leg, and the cathode small internal base/the longer leg, which is teh reverse of regular LED. I'll know now, trust the Flat side rather than the leg length. The flat side, the cathode is on the long leg for the SFH485P... Got it. THanks again, Donat Edited by DPLUIGI on 23/01/2008 at 16h15.
tankbuster	#4 26/01/2008 - 18h38 Top
Class : Habitué Posts : 66 Registered on : 28/08/2007 Off line	My head hurts! Do I connect the positive of my power supply to the short leg on my SFH485P? Paul
RomD	#5 30/01/2008 - 00h02 Top
Class : Apprenti Posts : 23 Registered on : 04/01/2008 Off line	Yup. Kestrel @ 23/01/2008 - 06h18 a dit: The flat side of the LED is the prime indicator of polarity. Breaking with convention, the short leg of the SFH485P is the anode (+), as stated in the datasheet. SFH485P: Short leg with big internal piece on top = (+)
tankbuster	#6 30/01/2008 - 21h51 Top
Class : Habitué Posts : 66 Registered on : 28/08/2007 Off line	Thanks. I wasn't sure of the polarity of the cathode and anode and googling it only made it worse. It goes on about current flowing in and out of the device.

FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > IR LED SFH485P, which leg is the anode?

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