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Figure 1: Basic NPN common collector circuit (neglecting biasing details).. In electronics, a common collector amplifier (also known as an emitter follower) is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a voltage buffer.
The remainder of the electrons recombine with holes, the majority carriers in the base, making a current through the base connection to form the base current, I B. As shown in the diagram, the emitter current, I E, is the total transistor current, which is the sum of the other terminal currents, (i.e. I E = I B + I C).
One-dimensional current; Negligible recombination-generation in space charge regions; Negligible electric fields outside of space charge regions. It is important to characterize the minority diffusion currents induced by injection of carriers. With regard to pn-junction diode, a key relation is the diffusion equation.
In a circuit with a three terminal device, such as a transistor, the current–voltage curve of the collector-emitter current depends on the base current. This is depicted on graphs by a series of (I C –V CE) curves at different base currents. A load line drawn on this graph shows how the base current will affect the operating point of the ...
One trick is to add a common-gate (current-follower) stage to make a cascode circuit. The current-follower stage presents a load to the common-source stage that is very small, namely the input resistance of the current follower (R L ≈ 1 / g m ≈ V ov / (2I D) ; see common gate). Small R L reduces C M. [2]
A diode-connected transistor is made by connecting the base and collector of a BJT; the drain and source of a JFET [1] the gate and drain of a MOSFET; Diode-connected transistors are used in current mirrors to provide a voltage drop that tracks that of the other transistor as temperature changes. [2] They also have very low reverse leakage ...
Reduction of the output impedance of the signal source connected to the base (e.g., by using an emitter follower or some other voltage follower). Using a cascode configuration, which inserts a low input impedance current buffer (e.g. a common base amplifier) between the transistor's collector and the load. This configuration holds the ...
The 2N3904 is an NPN transistor that can only switch one-third the current of the 2N2222 but has otherwise similar characteristics. The 2N3904 exhibits its forward gain (beta) peak at a lower current than the 2N2222, and is useful in amplifier applications with reduced I c , e.g., (gain peak at 10 mA for the 2N3904 but 150 mA for the 2N2222).