commoncathode

Common cathode is a configuration used with LED-based displays and LED matrices in which the cathodes of all individual LEDs in a group are connected to a single common conductor, typically tied to ground. Each LED or segment has its own anode lead that is driven by a control circuit.

In seven-segment displays, common cathode means all segment cathodes are tied together to a common pin. To illuminate a segment, the corresponding anode is driven high; current flows from the supply through the segment to the common cathode. This contrasts with common anode displays, which share a common anode.

Multiplexing often uses common cathodes for digits; the display is driven by activating one digit's common cathode while applying appropriate voltages to the segment anodes. Current-limiting resistors are used to set LED current, either per segment or per digit, depending on the drive scheme.

Electrical characteristics vary by LED color; typical forward voltages range from about 1.8–2.2 V for red to 2.8–3.4 V for green/blue at a few milliamperes. In low-voltage microcontroller applications, a driver transistor or buffer may be used to sink or source current since microcontrollers often cannot drive large currents directly.

Common cathode arrangements are widely used in consumer electronics, instrumentation, and educational kits due to their straightforward grounding and compatibility with simple low-side drivers.