One way of understanding the basic operation of a bipolar transistor is by looking at its Vce-Ic curves, i.e., the plots of its collector current Ic versus the voltage Vce across its collector and emitter for different values of base current Ib.
These curves are derived from a transistor in common-emitter configuration, and basically describe the transistor's common-emitter output characteristics.
A transistor circuit is said to be in common-emitter configuration if the emitter is the terminal common to both the input and the output.
In the analysis of transistor circuits, the input current and output voltage are usually considered the independent variables.
Thus, for the common-emitter configuration, the independent variables are the input current Ib and the output voltage Vce, while the dependent variables are the input voltage Vbe and the output current Ic.
The family of input characteristic curves may therefore be described by the function f1 wherein Vbe = f1(Vce, Ib), while the family of output curves may be described by the function f2, wherein Ic = f2(Vce, Ib).
The output curves corresponding to f2 are drawn with the collector-to-emitter voltage Vce as the abscissa, and the collector current Ic as the ordinate.
Different output curves are generated for different values of base current Ib, which are all drawn on the same plot.
These common-emitter Vce-Ic curves are useful in choosing the optimum operating point of a transistor used as an amplifier.
A transistor used as an amplifier must be operated in the active region, wherein the change in the collector current (output) is proportional to the change in the base current (input).
This linear region is ideal for amplification use because it allows the output waveform to be an enlarged 'faithful' copy of the input waveform
The active or linear region in the Vce-Ic curve is its flat portion on the right side.
Note that the change in collector current Ic is most sensitive to the change in base current Ib in this region.
The slope of the curve in this operating region represents the reciprocal of the transistor's collector or output resistance Rc, i.e., Slope = Ic/Vce = 1/Rc.
This means that in this region of the curve, the output resistance is relatively high (between 10-50 kΩ). An average Rc value of 30 kΩ in this region may be assumed.
Note that in this flat portion of the curve, the collector current Ic doesn't change much with the collector-emitter voltage Vce for any given base current Ib.
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One way of understanding the basic operation of a bipolar transistor is by looking at its Vce-Ic curves, i.e., the plots of its collector current Ic versus the voltage Vce across its collector and emitter for different values of base current Ib.
These curves are derived from a transistor in common-emitter configuration, and basically describe the transistor's common-emitter output characteristics.
A transistor circuit is said to be in common-emitter configuration if the emitter is the terminal common to both the input and the output.
In the analysis of transistor circuits, the input current and output voltage are usually considered the independent variables.
Thus, for the common-emitter configuration, the independent variables are the input current Ib and the output voltage Vce, while the dependent variables are the input voltage Vbe and the output current Ic.
The family of input characteristic curves may therefore be described by the function f1 wherein Vbe = f1(Vce, Ib), while the family of output curves may be described by the function f2, wherein Ic = f2(Vce, Ib).
The output curves corresponding to f2 are drawn with the collector-to-emitter voltage Vce as the abscissa, and the collector current Ic as the ordinate.
Different output curves are generated for different values of base current Ib, which are all drawn on the same plot.
These common-emitter Vce-Ic curves are useful in choosing the optimum operating point of a transistor used as an amplifier.
A transistor used as an amplifier must be operated in the active region, wherein the change in the collector current (output) is proportional to the change in the base current (input).
This linear region is ideal for amplification use because it allows the output waveform to be an enlarged 'faithful' copy of the input waveform
The active or linear region in the Vce-Ic curve is its flat portion on the right side.
Note that the change in collector current Ic is most sensitive to the change in base current Ib in this region.
The slope of the curve in this operating region represents the reciprocal of the transistor's collector or output resistance Rc, i.e., Slope = Ic/Vce = 1/Rc.
This means that in this region of the curve, the output resistance is relatively high (between 10-50 kΩ). An average Rc value of 30 kΩ in this region may be assumed.
Note that in this flat portion of the curve, the collector current Ic doesn't change much with the collector-emitter voltage Vce for any given base current Ib.
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