What is a double-base diode, the structure, working principle, operation modes, characteristics, and application fields of a double-base diode 2

3. Working Modes of BJT

BJTs have three operating modes: amplification mode, cutoff mode, and saturation mode.

In the active mode, the emitter junction of the BJT is forward-biased, while the base-emitter junction is reverse-biased. When an input signal is applied to the base, the current in the base region changes due to the input signal's variation. This variation causes a change in the emitter current, which in turn affects the collector current. By amplifying the input signal, the output signal is amplified.diode

In cutoff mode, the emitter junction of the BJT is reverse-biased, and the base junction is also reverse-biased. At this point, regardless of changes in the input signal's magnitude, the base current remains very small, thereby affecting the emitter current and collector current, causing the BJT to be in cutoff.diode

In saturation mode, the emitter junction of the BJT is forward-biased, and the base junction is also forward-biased. When an input signal is applied to the base, the current in the base region changes, causing variations in the current of the emitter and collector regions. At this point, the BJT is in saturation.diode

IV. Characteristics of BJT

The BJT possesses many important characteristics, such as amplification factor, input resistance, output resistance, and switching speed.diode