A Bipolar Junction Transistor is a solid-state device in which the current flow between two terminals (the collector and the emitter) is controlled by the amount of current that flows through a third terminal (the base).
A Bipolar Junction Transistor can be used for analog circuits, especially for very-high-frequency applications, such as radio-frequency circuits for wireless systems. Bipolar transistors can be combined with MOSFETs in an integrated circuit by using a BiCMOS process to create innovative circuits that take advantage of the best characteristics of both types of transistor.

R_c = Collector Resistance
R_e = Emitter Resistance
V_s = Supply Voltage
V_c = Collector Voltage
V_e = Emitter Voltage
V_b = Base Voltage





I_c = Collector gain x I_b
V_e = I_C x R_e
V_b = V_e x Base to Emitter Drop
V_c = V_s - I_C x R_c
If (V_in < V_b) then,
V_c = V_s

V_e = 0
V_b = Base to Emitter Drop
I_c = 0
I_b = 0

R_b = Base Resistance
V_in = Input Voltage
R_c = Collector Resistance
R_e = Emitter Resistance
V_s = Supply Voltage
V_c = Collector Voltage
V_e = Emitter Voltage
V_b = Base Voltage



I_c = Collector gain x I_b
V_e = I_C x R_e
V_b = V_e x Base to Emitter Drop
V_c = V_s - I_C x R_c
If (V_c < V_e) then,


V_c = V_e
V_b = V_e + Base to Emitter Drop