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RSS > Power Supply Question

Weyrman	#1 03/02/2008 - 21h23 Top
Class : Apprenti Posts : 14 Registered on : 26/01/2008 Off line	I have a switching mode selectable power supply that can provide the following voltages: 3/4.5/5V @ 2.5A 12.5VA max 6/6.5V @ 2A 13VA max lps 7V 1.9A 13.3VA max lps From the above possibilities, which setting would you recommend with 3 SFH485P IR Leds.
tristan68	#2 04/02/2008 - 09h47 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	Hello Weyrman. You need to use a PSU voltage a bit greater (about 1v is ok) than your LED BLOCK forward voltage. For a 3 SFH485 block (so 4.5v forward voltage), i'd suggest using about 5.5v REAL voltage. Since you use an unregulated PSU (seems so...), u should try using the 4.5v setting. this way , you'll need a 27ohms resistor for 50mA current in your leds. (using the led wizard) cya
Weyrman	#3 04/02/2008 - 23h28 Top
Class : Apprenti Posts : 14 Registered on : 26/01/2008 Off line	Ok, just a final check The power supply set on 5V gives a steady digital multimeter reading of 5.2V I therefore used the regulated power supply option in the LED wizard with 3 leds. 5.2V 1.5V forward V 50mA forward current which gave me a Ohms value of 14Ohms and specifying a 15Ohms 5% resistor Yes/No ????
tristan68	#4 05/02/2008 - 16h20 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	Yes Go on , it's all right (thumbs up) !

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