Dave.H said:
I have an upcoming project involving running three LEDs off a single 9
volt battery, what resistors would I need, and would I also need a
capacitor, as in this circuit?
The specifications for the LED's I am planning to use, (the same one's
I used for the radio dial) are
5mm (T1 1/2) round with flange
16,000mcd (typical) output
Water Clear Lens
High Brightness
620 - 625nm Wavelength (Orange-Red)
15o Viewing Angle
Forward voltage, Vf = 2.0V (min), 2.3V (max)
Forward current, If = 20mA
Two simple options:
9V battery, 3x 2V (min), 3V to be dropped across a resistor X at 20mA -
V=IR, R=V/I R=3/0.020, R=150 ohms.
9V battery, 3x 2.3V (max) 9-6.9=2.1V headroom - you could use an LM317
set up as a current source. That would allow driving reliably with 20mA
(actual voltage not that big of an issue for LEDs, and not a very
reliable number). The LM317 acts as whatever size resistor is needed to
run 20mA (when it's set up to act as a current source). There are also
newer devices that do that as a unit, with no external parts.