What condition exists when a transistor is in saturation?

A transistor is in saturation when both the base-emitter and collector-base junctions are forward biased. This condition allows maximum current to flow through the transistor from the collector to the emitter, as the transistor is fully turned on.

In saturation, the base-emitter junction being forward biased means that a sufficient voltage is applied to allow current to flow freely from the base to the emitter, effectively allowing the transistor to conduct. Meanwhile, the forward bias of the collector-base junction enables current to flow from the collector into the base, reinforcing the conduction path and minimizing voltage drop across the transistor.

This state is crucial for applications where a transistor is used as a switch, as it ensures that the maximum possible current can flow through the device with minimal resistance, leading to efficient operation.