Analysis Methods for Transient CircuitsImpedance, ZLC BehaviorStep-by-Step ApproachStep-by-Step Approach (cont’d)Class ExamplesLect14 EEE 202 1Analysis Methods for Transient CircuitsDr. HolbertMarch 17, 2008Lect14 EEE 202 2Impedance, ZUsing Ohm’s Law, impedance (Z) can be defined via:V = I ZCircuit ElementImpedance (ohms)Resistor RCapacitor 1 / (sC)Inductor sLLect14 EEE 202 3LC Behavior•Recall some facts on the behavior of LC elements•Inductors (L):–The current in an inductor cannot change abruptly in zero time; an inductor makes itself felt in a circuit only when there is a changing current–An inductor looks like a short circuit to d.c.•Capacitors (C):–The voltage across a capacitor cannot change discontinuously; a capacitor makes itself felt only when there exists a changing potential (voltage) difference–A capacitor looks like an open circuit to d.c.Lect14 EEE 202 4Step-by-Step Approach1. Assume solution (only dc sources allowed): x(t) = K1 + K2 e-t/2. At t=0–, draw the circuit with C as open circuit or L as short circuit; find VC(0–) or IL(0–)3. At t=0+, redraw circuit and replace C or L with appropriate source of value obtained in step #2, and find x(0)=K1+K2 4. At t=, repeat step #2 to find x()=K1Lect14 EEE 202 5Step-by-Step Approach (cont’d)5. Find time constant ( )Looking across the terminals of the C or L element, form Thevenin equivalent circuit; =RThC or =L/RTh6. Finish upSimply put the answer togetherThis is essentially the inspection method except it is expressed in a systematic procedureLect14 EEE 202 6Class Examples•Drill Problems P6-6, P6-7, P6-8, P6-13, P6-14–We’ll use the inspection (step-by-step) approach for P6-7 and
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