Why is a BJT called a current controlled current source ?
A BJT (Bipolar Junction Transistor) is called a current-controlled current source because its collector current (I_C) is primarily controlled by the base current (I_B). In an NPN transistor configuration, for example, an increase in the base current causes a proportional increase in the collector current due to the transistor’s internal amplification process. This relationship means that the BJT acts like a current source where the collector current is determined by the amount of base current supplied, making it a current-controlled current source.
A controlled current source is a type of electronic circuit or device that maintains a constant current output regardless of changes in load resistance or other external conditions. It achieves this by adjusting its internal impedance to ensure a stable current output. Controlled current sources are essential in applications where precise current regulation is necessary, such as in sensor circuits, analog signal processing, and current-mode amplifiers.
A FET (Field-Effect Transistor) is called a current-controlled device because its drain current (I_D) is controlled by the gate-source voltage (V_GS). In a FET, varying the gate-source voltage modulates the conductivity of the channel between the source and drain terminals, thereby controlling the amount of current flowing through the device. This voltage-controlled current regulation distinguishes FETs from BJTs, which primarily rely on base current to control collector current.
A BJT is not considered a voltage-controlled device primarily because its output current (collector current) is predominantly controlled by the input current (base current). While the base-emitter voltage (V_BE) does influence the base current (I_B) to some extent, the key factor determining the collector current (I_C) is the base current itself. Therefore, BJTs are classified as current-controlled devices rather than voltage-controlled devices like FETs, where the output current (drain current) is mainly controlled by the gate-source voltage (V_GS).
A BJT is called a bipolar device because it operates with both majority charge carriers (electrons and holes) contributing to its operation. In an NPN transistor, for instance, current flow occurs due to both electron (majority carriers in the emitter and collector regions) and hole (majority carriers in the base region) movements. This dual carrier mechanism distinguishes BJTs from unipolar devices like FETs, which predominantly rely on one type of charge carrier (electrons or holes) for current conduction. The term “bipolar” reflects this characteristic of BJTs involving both types of charge carriers in their operation.
In this article, we will teach you various methods for filling and storing rainwater, focusing on cisterns and tanks to…