Kollektorivirran

Kollektorivirran refers to the collector current in a bipolar junction transistor (BJT). It is the current that flows from the collector terminal to the emitter and is the primary controlled current in the transistor’s active operation.

In the forward-active region, Ic is primarily determined by the base current Ib and the transistor’s current gain β (also called hFE). The relation is Ic ≈ β Ib. A common way to express this is via the Ebers–Moll model: Ic ≈ Is exp(Vbe/VT), where Is is the reverse saturation current, Vbe is the base–emitter voltage, and VT is the thermal voltage (~25 mV at room temperature). Both descriptions capture how a small change at the input (base or base-emitter) controls a much larger current in the collector.

Ic is relatively insensitive to the collector–emitter voltage Vce in the active region, with a slight dependence caused by the Early effect. In saturation, Vce is low and Ic is limited by the external circuit rather than by β Ib; the transistor cannot increase Ic beyond what the circuit allows, and the device no longer follows the simple Ic ≈ β Ib relation. This makes the transistor useful for switching applications as well as amplification.

Measuring and using Ic involves standard units (amperes, typically milliamperes in small-signal devices). In many circuits, the collector current is converted to a voltage by a collector resistor, yielding Vout ≈ Vcc − Ic Rc. Ic and its dependence on temperature and manufacturing variations are central considerations in transistor biasing and circuit design.