<P> 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, usually a straight line, represents the response of the linear part of the circuit, connected to the nonlinear device in question . The points where the characteristic curve and the load line intersect are the possible operating point (s) (Q points) of the circuit; at these points the current and voltage parameters of both parts of the circuit match . </P> <P> 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 . The characteristic curve (curved line), representing the current I through the diode for any given voltage across the diode V, 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 </P> <Dl> <Dd> V D = V D D − I R (\ displaystyle V_ (D) = V_ (DD) - IR \,) </Dd> </Dl>

What is the difference between ac and dc load line