How do dual color LEDs work?

Dual color LEDs function by emitting different colors of light based on the direction of the applied voltage. Essentially, they house two LED dies within a single package.

Basic Functionality

The core principle behind a dual color LED is that it contains two separate LED emitters, each producing a different color. These emitters are connected in a way that allows for switching between colors. The key to this is the direction of the voltage applied:

• Forward Voltage: When positive voltage is applied to one specific terminal, the corresponding LED emitter activates, producing light of its specific color.
• Reverse Voltage: If the polarity of the applied voltage is reversed, the other LED emitter is activated instead, and it emits light of its color.

The Electrical Configuration

In practical use, only one pin can receive voltage at a time, meaning that you can activate only one color at a given moment. The following table summarizes the function of each pin:

Practical Example

For instance, consider a dual color LED with red and green emitters. If the positive voltage is applied to terminal A, the LED will emit red light. Conversely, if the voltage is reversed, with terminal B receiving the positive voltage, the LED will emit green light.

Advantages of Dual-Color LEDs

• Space Saving: They combine two LEDs into one package, saving valuable space on circuit boards.
• Cost-Effective: They are typically more cost-effective than using two separate LEDs.
• Versatility: They are ideal for applications that need to show different states or indications, such as:
  • Power indicators (on/off, standby)
  • System status indicators (error, active)
  • Traffic lights (red, green)
  • Signal flags (pass, fail)

Conclusion

Dual color LEDs work by alternating which internal LED receives a forward voltage, thus changing the color of light emitted. The direction of voltage is the key to activating a specific color.