emitterstrømtilførsel

emitterstrømtilførsel refers to the method by which current is supplied to the emitter terminal of a bipolar junction transistor (BJT). This is a fundamental aspect of transistor biasing, which determines the operating point and thus the transistor's behavior in a circuit. The emitter current (Ie) is crucial as it is directly related to the collector current (Ic) and base current (Ib) by the equation Ie = Ic + Ib.

Various circuit configurations are used to provide emitterstrømtilførsel, each with its own advantages and disadvantages in terms of stability, gain, and input impedance. Common methods include using a resistor connected to ground or a negative voltage supply, or employing a current source. The choice of emitterstrømtilførsel significantly impacts the AC characteristics of the transistor, such as its transconductance and overall voltage or current gain.

In common emitter amplifier configurations, a resistor in the emitter leg (RE) is frequently used for emitterstrømtilførsel. This resistor provides negative feedback, which helps to stabilize the transistor's operating point against variations in temperature and transistor parameters. While this improves stability, it can also reduce the AC gain of the amplifier. To overcome this gain reduction, a bypass capacitor is often placed in parallel with the emitter resistor, effectively short-circuiting it for AC signals.

Alternatively, a more stable and precise emitter current can be achieved using an active current source. This is typically implemented with another transistor and a few resistors. Current sources offer high output impedance and provide a constant current regardless of voltage fluctuations, leading to highly stable biasing and predictable amplifier performance. Understanding emitterstrømtilførsel is therefore essential for designing and analyzing transistor circuits effectively.