CIRCUIT I DISCUSSION #4-5
EE220D
SUMMER 2015 TBE-B348
Wenlan Wu
ECE
University of Nevada-Las Vegas
OUTLINE
Thevenin’s Equivalent
 Norton’s Equivalent

THEVENIN’S EQUIVALENT
Between two terminals, any combination of sources
and resistances can be replaced by a signal voltage
source Vth and a single series resistor Rth
Ref: hyperphysics.phy-astr.gsu.edu/hbase/electric/thevenin.html
NORTON’S EQUIVALENT
Between two terminals, any combination of sources
and resistances can be replaced by a signal current
source In and a single parallel resistor Rn
Ref: hyperphysics.phy-astr.gsu.edu/hbase/electric/Norton.html
CIRCUIT EXAMPLES
CIRCUIT EXAMPLES
CIRCUIT EXAMPLES
THEVENIN VS NORTON
THEVENIN VS NORTON
THEVENIN
Resistors with independent sources:
1) Find Vth:
find the open circuit voltage Voc between A and B
nodes
2) Find Rth:
Deactive the independent sources: voltage means
short, current means open
Find the Rth by series and parallel theory
THEVENIN
Resistors only with dependent sources:
1) Vth:
Only dependent sources, the equivalent network is
merely Rth, no current or voltage sources. Vth=0
2) Find Rth:
Connect a current source (1A) flowing from B to A.
Calculate the Rth=Voc/1A
THEVENIN
Resistors with dependent and independent sources:
1) Vth:
Use KCL and KVL to find the open voltage between A
and B. Voc = Vth.
2) Find Rth:
Connect a short circuit between A and B
Determine the current between A and B
Rth = Voc/ Iab
NORTON
Resistors with independent sources:
1) Rn:
Voltage means short, current means open
Find out the Rn by using series and parallel theory
2) Find In:
Connect an short circuit between A and B
Find the current across the short circuit which is In
NORTON
Resistors only with dependent sources:
1) In:
Only dependent sources, the equivalent network is
merely Rth, no current or voltage sources. In=0
2) Find Rn:
Connect a current source (1A) flowing from B to A.
Calculate the Rn=Voc/1A
NORTON
Resistors with dependent and independent sources:
1) In:
Connect a short circuit between A and B
Find out the current across the A and B, that is In.
2) Find Rn:
Connect a open circuit between A and B
Determine the voltage between A and B
Rn = Voc/ In
THEVENIN VS NORTON
THEVENIN VS NORTON
THEVENIN VS NORTON
MATERIALS FOR LTSPICE
LTspice models on cmosedu.com
 LTspice Yahoo Discussion Group
 EE220D course web
 Email to wuw2@unlv.nevada.edu
 LTspice HELP

REFERENCES
Charles K. Alexander,《Fundamentals of Electric
Circuits》
 Jacob R. Baker, 《CMOS Circuit Design, Layout
and Simulation》
