Electronics

Light Emitting Diodes (LEDs)

Symbol

Anode--->|---Cathode; Anode = long lead; Cathode = short lead, flat side, or spot


DC Circuit

+V---R---LED---GND; R = (Vin - Vled)/Iled


TTL Drivers

LED = ON: TTL High---R---LED---GND or TTL Low---LED---R---+5V


Tri-Color Circuit

Rtotal = R1 + R2 = (+-V - Vred)/Ired, R1 = (+-V - (Vgreen + V1n914))/Igreen


Notes

Typical Forward Voltage Drop for LED (VLED) = 1.5 V to 2.5 V
VLED for a red LED = ~1.7 V
VLED for a green LED = ~2.5 V
 
Typical Forward Voltage Drop for silicon diode (Vdiode) = ~0.6 V
 
Typical Forward Current for LED (ILED) = 5 mA to 20 mA
 
Silicon Diode Polarity
Band indicates cathode (negative)
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DISCLAIMER

Page author: Dawn Rorvik (rorvikd@evergreen.edu)
Last modified: 05/20/2003