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Another useful characteristic is the common-base current gain, α F. The common-base current gain is approximately the gain of current from emitter to collector in the forward-active region. This ratio usually has a value close to unity; between 0.980 and 0.998. It is less than unity due to recombination of charge carriers as they cross the ...
The current gain is very nearly unity as long as R S ≫ r E. An alternative analysis technique is based upon two-port networks . For example, in an application like this one where current is the output, an h-equivalent two-port is selected because it uses a current amplifier in the output port.
Generalised h-parameter model of an NPN BJT. The term "x" in the model represents a different BJT lead depending on the topology used. For common-emitter mode the various symbols take on the specific values as: x = 'e' because it is a common-emitter topology; Terminal 1 = Base; Terminal 2 = Collector; Terminal 3 = Emitter; i in = Base current (i b)
Collector current is approximately β (common-emitter current gain) times the base current. It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for high-power applications. Unlike the field-effect transistor (see below), the BJT is a low-input-impedance device.
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.
Some models base the collector current correction factor on the collector–base voltage V CB (as described in base-width modulation) instead of the collector–emitter voltage V CE. [3] Using V CB may be more physically plausible, in agreement with the physical origin of the effect, which is a widening of the collector–base depletion layer ...
Current gain in the common emitter circuit is obtained from the base and the collector circuit currents. Because a very small change in base current produces a large change in collector current, the current gain (β) is always greater than unity for the common-emitter circuit, a typical value is about 50.
current: 01:52, 23 August 2006: 740 × 400 (87 KB) Matt Britt == Summary == Energy band diagram of a simple NPN bipolar junction transistor in forward-active mode showing electron energy versus position. The depletion regions of the emitter-base and base-collector junctions are marked. <math>E_c</math> is