Monday, 4 March 2013

TYPES OF CIRCUITS IN THEVENINS-1

Example:

 Determine the Thévenin equivalent of the circuit below, as seen by the load, RL.
  

Solution 
 
We want to create a Thévenin equivalent circuit of the circuit to the left of the terminals a-b.now separate RL from the circuit and find Rth from terminals a-b 

Finding Rth. 
Short circuit the current sources,open circuit the voltage sources

Now the circuit appears as follows

 

From the above figure, it can be seen that the Thévenin resistance RTH is a parallel combination of a 3W resistor and a 6W resistor, in series with a 2W resistor.

Rth = ( ( 6 * 3 ) / ( 6 + 3 )) + 2 = 4Ω 

                            Rth= 4Ω

Finding Vth

The open-circuit voltage VOC is determined from the circuit below. We (arbitrarily) choose nodal analysis to determine the open-circuit voltage. There is one independent voltage in the circuit; it is labeled as v0 in the circuit below. Since there is no current through the 2W resistor, VOC = Vth





Applying nodal at VTH

VTH – 18  +  VTH = 0
6               3

Solving above equation,we get VTH = 6 v

                         VTH = 6 v
Now the equivalent circuit  is

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