Current Transfer Characteristics

The current transfer characteristic plots the variation of collector current $I_C$ against base current $I_B$, at a fixed collector-emitter voltage $V_{CE}$. Even when $I_B$ is reduced to zero, a small $I_C$ still flows, called the common-emitter leakage current $I_{CEO}$, carried by minority charge carriers (matching the cut-off-region behaviour already noted in the output characteristics). The forward current gain $\beta$ is defined as the ratio of a small change in collector current to the corresponding small change in base current at constant $V_{CE}$: $\beta=(\Delta I_C/\Delta I_B)_{V_{CE}}$ -- i.e. $\beta$ is read directly as the SLOPE of this transfer curve. Its value is very high, typically ranging from 50 to 200 depending on how the parti …