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Class : Apprenti
Posts : 2
Registered on : 18/01/2008
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I bought the SFH485-P Infrared LED's that the site suggested and I'm trying to find a suitable power source. I have a power supply that's rated for 12V, 500mA output and I'm planning on using 3 LED's rated for 1.5V at 100mA. The wizard says I should use a 111 Ohm resistor. Is this correct?
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Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
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Hello skruis.
1) the SFH485 are rated for 100 mA when PCB mounted. Thats not the case in most of freetrack's setups.
So you'd better stick to 70mA max instead (thats the max value when the SFH485 is cable mounted).
2) the value was ok for the given infos.
Just be careful about the dissipated power in your resistor, which is gonna heat up.
3) if you use you power supply and 70 mA , you get :
3 x leds , serial wired.
1 x 160 ohms 5% 0.77w dissipated power
I would use a 160ohms 2w resistor, just to have a security factor (resistors are cheap components, so its ok to use a bigger one for security).
cya
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