Th

1
Thévenin and Norton Equivalent Circuits
Thévenin Equivalent Circuit
Norton Equivalent Circuit
How do we calculate RT, VT, iN, RN?
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Calculation of RT and RN

• RTRN, same calculation
• Setting all sources to be zero (killing the
  sources)
• Voltage source short
• Current source open
• Calculate equivalent resistance seen by the load.

3
Calculation of VT
Remove the load and calculate the open circuit
voltage
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3/3/03 Minute paper

• PPT slides on the web?
• There are other elements like inductors and
  capacitor. Does all the stuff we are learning
  not still apply to those components.
• Yes, these elements just have different i-v
  characteristic.

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Calculation of IN
short the load and calculate the short circuit
voltage
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Souse transformation
VThINRN RNRTh
Summary
Thévenin's Theorem

• Any two-terminal linear circuit can be replaced
  with a voltage source in series with a resistance
  which will produce the same effects at the
  terminals.
• VTh is the open-circuit voltage Voc between the
  two terminals of the circuit that the Thevenin
  generator is replacing.
• RTh is the ratio of Voc to the short-circuit
  current Isc.In linear circuits, this is
  equivalent to "killing" the sources and
  evaluating the resistance between the terminals.
  Voltage sources are killed by shorting them
  current sources are killed by opening them.

Detailed Example
7
Concept Check
Which of the following circuits is the correct
Thévenin generator?
Which of the following circuits is the correct
Thévenin generator?
B
C
A
Answer B
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Summary Norton Therorem

• Any two-terminal linear circuit can be replaced
  with a current source in parallel with a
  resistance which will produce the same effects at
  the terminals.
• IN is the short-circuit current Isc of the
  circuit that the Norton generator is replacing.
• Again, RN is the ratio of Voc to the
  short-circuit current Isc. Or calculating the
  equivalent resistance after killing the sources
• Note that for a given circuit, RN  RTh.

Detailed Example
9
Concept Check
Which of the following circuits is the correct
Norton generator?
B
C
A
Answer A
10
Maximum Power Transfer Impedance Matching

• Why Thévenin and Norton equivalents? Very easy
  to calculate load related quantity. One such an
  example is the maximum power transfer to the
  load.

RlRT
Impedance is a generalized term of resistance
when capacitors and inductors are included.