Editing Bipolar junction transistor (section)

===== Etymology of ''h''<sub>FE</sub> =====
The ''h'' refers to its being an h-parameter, a set of parameters named for their origin in a '''''h'''ybrid equivalent circuit'' model (see above). As with all h parameters, the choice of lower case or capitals for the letters that follow the "h" is significant; lower-case signifies "small signal" parameters, that is, the slope the particular relationship; upper-case letters imply "large signal" or [[Direct Current|DC]] values, the ratio of the voltages or currents. In the case of the very often used ''h''<sub>FE</sub>:
* ''F'' is from '''''F'''orward current amplification'' also called the current gain. 
* ''E'' refers to the transistor operating in a ''common '''E'''mitter'' (CE) configuration. 
So h<sub>FE</sub> (or hFE) refers to the (total; DC) collector current divided by the base current, and is dimensionless. It is a parameter that varies somewhat with collector current, but is often approximated as a constant; it is normally specified at a typical collector current and voltage, or graphed as a function of collector current.

Had capital letters not been used for used in the subscript, i.e. if it were written ''h<sub>fe</sub>'' the parameter indicate small signal ([[Alternating Current|AC]]) current gain, i.e. the slope of the Collector current versus Base current graph at a given point, which is often close to the hFE value unless the test frequency is high.