▁graph ▁of ▁the ▁current ▁vs . ▁the ▁voltage ▁in ▁a ▁non linear ▁device ▁like ▁a ▁di ode ▁or ▁trans istor . ▁ ▁It ▁represents ▁the ▁constraint ▁put ▁on ▁the ▁voltage ▁and ▁current ▁in ▁the ▁non linear ▁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 ▁non linear ▁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 . ▁ ▁The ▁example ▁at ▁right ▁shows ▁how ▁a ▁load ▁line ▁is ▁used ▁to ▁determine ▁the ▁current ▁and ▁voltage ▁in ▁a ▁simple ▁di ode ▁circuit . ▁ ▁The ▁di ode , ▁a ▁non linear ▁device , ▁is ▁in ▁series ▁with ▁a ▁linear ▁circuit ▁consisting ▁of ▁a ▁res istor , ▁R ▁and ▁a ▁voltage ▁source , ▁V DD . ▁ ▁The ▁characteristic ▁curve ▁( cur ved ▁line ), ▁representing ▁the ▁current ▁I ▁through ▁the ▁di ode ▁for ▁any ▁given ▁voltage ▁across ▁the ▁di ode ▁V D , ▁is ▁an ▁exponential ▁curve . ▁▁ ▁The ▁load ▁line ▁( di ag onal ▁line ) ▁represents ▁the ▁relationship ▁between ▁current ▁and ▁voltage ▁due ▁to ▁Kirch hoff ' s ▁voltage ▁law ▁applied ▁to ▁the ▁res istor ▁and ▁voltage ▁source , ▁is ▁ ▁Since ▁the ▁current ▁going ▁through ▁the ▁three ▁elements ▁in ▁series ▁must