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| === Common-Emitter === | === Common-Emitter === | ||
| The given load line diagram is for the ] configuration. ]The load line diagram illustrates all possible values of collector current (I<sub>C</sub>) and the collector voltage (V<sub>CE</sub> in this case) for a given load resistor (R<sub>C</sub>). | The given load line diagram is for the ] configuration. ]The load line diagram illustrates all possible values of collector current (I<sub>C</sub>) and the collector voltage (V<sub>CE</sub> in this case) for a given load resistor (R<sub>C</sub>). | ||
| The point on the load line where it intersects the collector current axis is referred to as ''saturation point''. At this point, the transistor current is maximum and voltage across collector is minimum, for a given load. For this circuit, I<sub>C-SAT</sub>= V<sub>CC</sub>/R<sub>C</sub>. | |||
| The ''cutoff point '' is the point where the load line intersects with the collector voltage axis. Here the transistor current is minimum (approximately zero) and emitter is grounded. Hence V<sub>CE-CUTOFF</sub>=V<sub>cc</sub>. | |||
| The ''operating point'' of the circuit in this configuration is generally designed to be in the ''active region'', approximately between middle of the load line and close to saturation point. In this region, the collector current is proportional to the base current, and hence useful for ] applications. | |||
| ==References== | ==References== | ||
Revision as of 04:16, 27 October 2007
The load line of a transistor circuit shows the voltage-current characteristic (V-I Graph) of that particular circuit or configuration, over a range of Base currents. As the Collector-Emitter Voltage (VCE) varies from zero to its maximum value, the current at the Collector varies accordingly. It must be noted that this is the dc load line for the circuit for a fixed load. The saturation current and cutoff voltage determine the intersections of the graph on the Y and X axes respectively. Intersections of the base voltage curves with the IC-VCE graph indicate realistic operating conditions for those base currents.
Load lines for common configurations
Common-Emitter
The given load line diagram is for the Common emitter configuration.
The load line diagram illustrates all possible values of collector current (IC) and the collector voltage (VCE in this case) for a given load resistor (RC).
The point on the load line where it intersects the collector current axis is referred to as saturation point. At this point, the transistor current is maximum and voltage across collector is minimum, for a given load. For this circuit, IC-SAT= VCC/RC.
The cutoff point is the point where the load line intersects with the collector voltage axis. Here the transistor current is minimum (approximately zero) and emitter is grounded. Hence VCE-CUTOFF=Vcc.
The operating point of the circuit in this configuration is generally designed to be in the active region, approximately between middle of the load line and close to saturation point. In this region, the collector current is proportional to the base current, and hence useful for amplifier applications.
References
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