* Spice As A Curve Tracer * Plot of iC versus Vce vCE 1 0 DC 0V iB 0 2 DC 1u * Note the current direction. The current is * injected into the base for an NPN transistor. * The base node is numbered as 2. * Q means a bipolar junction transistor (BJT) Q1 1 2 0 my_npn_tran * | | | * | | | * Collector | | * Base | * Emitter .model my_npn_tran npn(Is=1.8104e-15 bf=100 Vaf=35) * Note: Is is the scale current, bf is the beta * (the common-emitter-current gain). * Vaf is the Early voltage. Run pSpice twice, first with Vaf=35 * and a second time after deleteing Vaf=35 from the model * parameter. Vaf then assumes the default value of infinity. * Study the difference. * Vary the Vce from 0 to 10. * Draw 10 curves -- each for a fixed value of the base * current iB. The lowest curve is for 1uA and the highest * curve is for 10uA and the increament is 1uA. .dc vCE 0 10 0.1 iB 1u 10u 1u * When you use probe, add the trace of IC(Q1) to view the * output characteristics. You may want to change the Y-axis * Setting (look under Plot menu) from 0 to 1.5mA (click on User * Defined). .probe .end