1. ECE 3301 General Electrical Engineering
Presentation 35
Circuit Laws and Phasors

2. Kirchhoff’s Voltage Law
Consider a circuit with circuit elements and voltages as shown below:

3. Kirchhoff’s Voltage Law
Assume the network is excited by independent sinusoidal sources at radian frequency w.

4. Kirchhoff’s Voltage Law
The voltage across any circuit element will be a sinusoid at the frequency w with some amplitude and phase angle.

5. Kirchhoff’s Voltage Law
Kirchhoff’s Voltage Law must be true around any closed loop.

10. Kirchhoff’s Voltage Law
The sum of Phasor Voltages around any closed loop is equal to zero.

11. Kirchhoff’s Current Law
Consider a circuit with circuit elements and currents as shown below:

12. Kirchhoff’s Current Law
Assume the network is excited by independent sinusoidal sources at radian frequency w.

13. Kirchhoff’s Current Law
The current through any circuit element will be a sinusoid at the frequency w with some amplitude and phase angle.

14. Kirchhoff’s Current Law
Kirchhoff’s Current Law must be true at any node.

19. Kirchhoff’s Current Law
The sum of Phasor Currents into any node is equal to zero.

20. Impedances in Series VS = V1 + V2 + … + Vn VS = I Z1 + I Z2 + … + I Zn
VS = I (Z1 + Z2 + … + Zn )
VS = I Zeq
Zeq = Z1 + Z2 + … + Zn

21. Impedances in Parallel

22. Impedances in Parallel

23. Impedances in Parallel

24. DC Circuits and AC Circuits
All of the techniques and theorems from DC Resistive Circuits also apply to AC Circuits, now using Complex Numbers.
Voltage Divider Equation
Current Divider Equation
Source Transformations
Node Voltage Analysis
Mesh Current Analysis
Matrix Equations and Cramer’s Rule
Superposition Theorem
Thevenin Equivalent Circuit
Norton Equivalent Circuit
Maximum Power Transfer (More on this later)
Operational Amplifier Circuits