60 led array what i need to power?

KJ6EAD

Joined Apr 30, 2011
1,581
I took 2 leds off the one board and put them in series and solo and got these measurements

supply voltage= 9.05 vdc
resistor value measured = .670 ohms
Vf across the 2 leds in series = 5.610 vdc
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supply voltage= 9.05 vdc
resistor value measured = .670 ohms
Vf across 1 led (solo not in series) = 2.885 vdc
That's not useful. You need to find the Vf while the current is exactly 20mA. Why don't you set up a small constant current source using an LM317L and 100Ω trimmer pot on a breadboard and adjust the current to 20mA, then measure the Vf. Remember, the pins are not shown in their true order in the application schematic.

Figure 906413 in the datasheet:
http://www.national.com/ds/LM/LM317L.pdf.
 
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