THEVENIN THEOREM & NORTON Lecture 06 THEVENIN THEOREM & NORTON
OBJECTIVES Apply Thevenin’s theorem to simplify AC circuits for analysis. List the steps for determining the Thevenin Equivalent of an actual electronic circuit. Using Thevenin’s theorem, analyze complex series-parallel circuits with multiple load values. Calculate the average power dissipated by a load.
THÉVENIN’S THEOREM Used to reduce an AC circuit to a single voltage source “VTH” in series with a single Impedance “ZTH “
THEVENIN VOLTAGE “VTH” is: the “Open Circuit Voltage” measured across the load, with the load removed.
THEVENIN IMPEDANCE “ZTH ” is: the “Total Equivalent Impedance” of the circuit as seen from the load position with the load removed and all sources zeroed.
Steps for Thevenin circuit Step 1: Open the two terminals between which you want to find the Thevenin circuit. Step 2: Determine the voltage across the terminals. Step 3: Determine the impedance viewed from the terminals with all sources zeroed. Step 4: Connect VTH and ZTH in series to produce the Thevenin Equivalent circuit.
Step 5: Redraw the Thevenin equivalent circuit as a single Impedance “ZTH” in series with the load impedance “ZL” and voltage source “ETH”.
Ex: Calculate the Thévenin Equivalent circuit. Given: Vs = 25<0 V; R1 = 100Ω ; R2 = 25 Ω; RL = 1kΩ, XL = 80 Ω, f = 509 Hz
Solution: Find VTH
Calculate VTH (open circuit)
Find ZTH
Calculate ZTH
Draw Thevenin equivalent circuit
Ex: NORTON THEOREM
STEP 1: Find ZN = ZTH
Calculate ZN = ZTH
STEP 2: Find IN = Isc
Calculate IN = Isc Note that,
Equation for Mesh 1
Equation for Mesh 2
Calculate IN
Norton Equivalent Circuit
NORTON THEOREM
THEVENIN THEOREM
RELATIONSHIP Keep in mind that the two equivalent circuits (Thevenin and Norton) are related as:
RELATIONSHIP