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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)
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 ...
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 ...
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.
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
In other words, the circuit has current gain (which depends largely on the h FE of the transistor) instead of voltage gain. A small change to the input current results in much larger change in the output current supplied to the output load. One aspect of buffer action is transformation of impedances.
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: 00:06, 23 August 2006: 740 × 400 (87 KB) Matt Britt: Removed redundant curve. 23:44, 22 August 2006: 740 × 400 (87 KB) Matt Britt: Fixed arrows. 23:41, 22 August 2006: 740 × 400 (86 KB) Matt Britt: Energy band diagram of a simple bipolar junction transistor under equilibrium showing electron energy versus position.