LED

• 2 lead semiconductor device.
• Light emitting PN-junction diode.
– Visible or infrared light.
• Has polarity.
• Recall diodes act as a one way gate to current flow.
– A forward-biased PN-junction diode allows current flow from anode to cathode.
• An LED conducts and emits light when its anode is made more positive (approx.
1.4V) than its cathode.
– With reverse polarity, LED stops conducting and emitting light.

• Similar to diodes, LEDs are current-dependent devices.
– LED brightness is controlled by controlling current through LED.
• Too little current through LED  LED remains OFF.
• Small current through LED  dimly lit LED.
• Large current through LED  brightly lit LED.
• Too much current through LED  LED is destroyed.
• A resistor placed in series with LED accomplishes current control.