Light Emitting Diodes (LEDs)

Learning Intentions

  • To learn how LEDs emit light
  • To learn how LEDs are modeled in electric circuits

Media

How Blue LEDs Changed the World (5:33)

Why It Was Almost Impossible to Make the Blue LED (33:44)

Shuji Nakamura worked for years and years to develop the blue LED.

Channeling Energy Into Innovation: The Shuji Nakamura Story (2:03)

 

Notes

The datasheet tells us a lot about the LED’s in our kits. Choose one of the LED’s, and answer the following questions.

  1. Find the following limits
    1. Absolute maximum continuous forward current
    2. Absolute maximum peak forward current
    3. Absolute maximum power
  2. What is the relationship between voltage and current?
  3. What is the relationship between current and luminous intensity (brightness)?
  4. Putting together the two previous questions, what is the relationship between voltage and brightness?
  5. How can you tell which leg of the LED is the anode (negative)?

Datasheet – LED White Round 3mm – BL-BZX3V4V-1-B02-ND

Datasheet – LED Yellow Round – 732-5010-ND

Datasheet – LED Green Round – 160-1131-ND

Datasheet – LED Red Round – 732-5005-ND

Datasheet – LED Blue Oval – C566D-BFE-CU0W0351-ND

 

Demonstration

  1. Choose an LED from your kit.
  2. Determine the forward voltage and absolute maximum continuous forward current of the LED from the datasheet.
  3. Find the voltage for VDD in this circuit such that the current through the LED is equal to the maximum continuous forward current.

    1. What is the power dissipated by the LED?
    2. What is the power dissipated by the resistor?
  4. Build the circuit with your LED in series with a 200 ohm resistor.
  5. Connect the power supply to Vdd (positive, red) and ground (negative, black). Starting at 0 V, gradually increase the voltage. You should notice that the LED turns on near the “forward voltage” value from the datasheet. Stop when you reach the voltage you calculated in question 3.