THEVENIN

1
THEVENINS THEOREM

• Thevenins theorem permits the reduction of a
  two-terminal dc network with any number of
  resistors and sources (Complex Circuit) to one
  Equivalent circuit having only one source and one
  internal resistance in a series configuration
  shown belw

2
Original and Thevenin Equivalent Circuit
3
Measuring CalculatingVth by MultiSim

• Circuit above shows how to measure the Thevenin
  Voltage (Vth). That is measured 4V.
• The Circuit below shows how to measure Thevinins
  Resistance (Rth)
• Conclusion To measure Vth, remove the load
  resistance (unknown), then measure the voltage
  across open circuit terminal
• (Vo.c. Vth).
• The Circuit below, shows how to measure and
  calculate the Thevinin Resistance (Rth)

4
Original and circuit to measure Rth
5
Measured and Calculated Rth

• To measure Rth, with load resistance removed,
  also remove and replace source voltage by a short
  (jumper wire), then measure and calculate the
  Thevenin resistance zacross the Open Circuit
  terminals
• Rth is measured 6 Ohms.
• Considering the jumper wire, 6 and 3 Ohms
  resistors are in parallel, and result is in
  series with 4 Ohm resistor.
• Rth (Cal.) (6 x 3)/(63) 4 2 4 6 Ohms

6
Original Thevenin Equivalent Circuit
7
Using Ohms Law to Calculate Unknown Current

• As you can see from this simple Tutorial Example,
  the load current for original and the Thevenin
  Equivalent Circuit are Identical.
• This verifies our solution and demonstrate how to
  measure and calculate the unknown element current
  by using Ohms Law for Thevnin Equivalent
  Circuit
• IL (Vth)/(Rth RL) (4V) / (66)
• IL 4/12 0.333A ?gt Calculated!
• Compare this with measured, they are exactly
  equal! Now you can apply this to other Problems.