5.4 Bi-Colour LEDs

A bi-colour LED can be in two different forms: 2-pin and 3-pin. In a 2-pin LED, two different colour LEDs are combined in one package and wired in ‘inverse parallel’, that is one forwards, one backwards (see Figure 5.3). As shown in the truth table, only one LED is ON at any time, depending on the voltage applied to the pins.

Figure 5.3 Bi-colour 2-lead LED

In a 3-pin bi-colour LED, two different colour LEDs are usually connected in inverse, as shown in Figure 5.4. The common cathode pin is normally connected to the ground. Only one or both LEDs can be turned ON by supplying voltages to the anodes, as shown in the truth table.

Figure 5.4 Bi-colour 3-lead LED