EEE 302
Electrical Networks II
Dr. Keith E. Holbert
Summer 2001
Lecture 4
1
Thevenin/Norton Analysis
1. Pick a good breaking point in the circuit (cannot split a
dependent source and its control variable).
2. Thevenin: Compute the open circuit voltage, VOC.
Norton: Compute the short circuit current, ISC.
For case 3(b) both VOC=0 and ISC=0 [so skip step 2]
Lecture 4
2
Thevenin/Norton Analysis
3. Compute the Thevenin equivalent resistance, RTh (or
impedance, ZTh).
(a) If there are only independent sources, then short
circuit all the voltage sources and open circuit the current
sources (just like superposition).
(b) If there are only dependent sources, then must use a
test voltage or current source in order to calculate
RTh (or ZTh) = VTest/Itest
(c) If there are both independent and dependent sources,
then compute RTh (or ZTh) from VOC/ISC.
Lecture 4
3
Thevenin/Norton Analysis
4. Thevenin: Replace circuit with VOC in series with RTh, ZTh.
Norton: Replace circuit with ISC in parallel with RTh, ZTh.
Note: for 3(b) the equivalent network is merely RTh (or ZTh),
that is, no voltage (or current) source.
Only steps 2 & 4 differ from Thevenin & Norton!
Lecture 4
4
Independent Sources (Norton)
Isc
Circuit with one or
more independent
sources
RTh
Norton equivalent
circuit
Lecture 4
5
No Independent Sources
RTh
Circuit without
independent sources
Thevenin equivalent
circuit
Lecture 4
6
Class Example
• Extension Exercise E8.18
Lecture 4
7
PSpice Analysis of AC Circuits
• Should have done this in ECE 301
• We must use AC sources, and tell PSpice to
perform an AC analysis at specific frequency(ies)
• PROBE allows us to plot our results
• Take advantage of features (e.g., cursors) to assist
your analysis
• Completely annotate your schematic diagrams
• MOST IMPORTANT RULE: You will always get
an answer, you must judge its validity!
Lecture 4
8
Class Example
• Extension Exercise E8.19
Lecture 4
9