load line analysis

• What is load line analysis?

In graphical analysis of nonlinear electronic circuits, a load line is a line drawn on the characteristic curve, a graph of the current vs. the voltage in a nonlinear device like a diode or transistor. It represents the constraint put on the voltage and current in the nonlinear device by the external circuit.

The load line analysis of transistor means for the given value of collector-emitter voltage we find the value of collector current. This can be done by plotting the output characteristic and then determine the collector current I_C with respect to collector-emitter voltage V_CE.

• What is load and line?
  Line is the side of the device where the wires from the panel (or other equipment feeding the device) are connected. Load is where any devices that are to be protected by the GFCI device are connected

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  What is the importance of load line?

  
  

  The purpose of the load line is to ensure that a ship has sufficient freeboard (the height from the waterline to the main deck) and thus sufficient reserve buoyancy (volume of ship above the waterline). It should also ensure adequate stability and avoid excessive stress on the ship's hull as a result of overloading.

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  What is meant by load line?

  
  

  In graphical analysis of nonlinear electronic circuits, a load line is a line drawn on the characteristic curve, a graph of the current vs. the voltage in a nonlinear device like a diode or transistor. It represents the constraint put on the voltage and current in the nonlinear device by the external circuit.
• The example at right shows how a load line is used to determine the current and voltage in a simple diode circuit. The diode, a nonlinear device, is in series with a linear circuit consisting of a resistor, R and a voltage source, V_DD. The characteristic curve (curved line), representing the current I through the diode for any given voltage across the diode V_D, is an exponential curve. The load line (diagonal line) represents the relationship between current and voltage due to Kirchhoff's voltage law applied to the resistor and voltage source, is

• Transistor load line[edit]

  
  The load line diagram at right is for a resistive load in a common emitter circuit. The load line shows how the collector load resistor (R_L) constrains the circuit voltage and current. The diagram also plots the transistor's collector current I_C versus collector voltage V_CE for different values of base current I_base. The intersections of the load line with the transistor characteristic curves represent the circuit-constrained values of I_C and V_CE at different base currents. ^[2]
  If the transistor could pass all the current available, with no voltage dropped across it, the collector current would be the supply voltage V _CC over R_L. This is the point where the load line crosses the vertical axis. Even at saturation, however, there will always be some voltage from collector to emitter.
  Where the load line crosses the horizontal axis, the transistor current is minimum (approximately zero). The transistor is said to be cut off, passing only a very small leakage current, and so very nearly the entire supply voltage appears as V_CE.
  The operating point of the circuit in this configuration (labelled Q) is generally designed to be in the active region, approximately in the middle of the load line for amplifier applications. Adjusting the base current so that the circuit is at this operating point with no signal applied is called biasing the transistor. Several techniques are used to stabilize the operating point against minor changes in temperature or transistor operating characteristics. When a signal is applied, the base current varies, and the collector-emitter voltage in turn varies, following the load line - the result is an amplifier stage with gain.
  A load line is normally drawn on I_c-V_ce characteristics curves for the transistor used in an amplifier circuit. The same technique is applied to other types of non-linear elements such as vacuum tubes or field effect transistors.

• References

Edit

^ Adel Sedra, Kenneth Smith. Microelectronic Circuits, 5th ed.

1. ^ Maurice Yunik, Design of Modern Transistor Circuits, Prentice-Hall Inc., 1973 ISBN 0-13-201285-5 section 4.6 "Load Line Analysis" pp. 68-73

• Author :- Hrishikesh Patil .