E72 (P)review
or
Things you should know
E72 takes off where E11 left off. Because of this, there is certain knowledge from E11 that will be assumed. You don't have to be able to easily apply all the various methods of solution that you used in those courses  the ones that are important will come back to you as you use them. There are, however, some fundamental things that you should know.
The rest of this indroduction is devoted to a restatement and review of the salient material from E11. Look it over to see if there are any topics with which you feel uncomfortable. If there are any, you may want to break out your E11 (and/or E12) book and review. Again  you don't need to be facile with all the fine points, but you should feel at ease with each topic.
The preview is broken up into four parts:
Passive Linear Circuit Elements
Resistor  Capacitor  Inductor  
Circuit symbol  
CurrentVoltage Characteristic  
Parallel Equivalent  
Series Equivalent  
Complex Impedance (Sinusoidal input) 

Other  . 
high frequency  acts as short circuit low frequency  open circuit 
high frequency  open circuit low frequency  short circuit 
Time Constant (with Resistor)  .  τ=RC  τ=L/R 
Resonance 
Voltage and Current Sources
Circuit Symbol  
Independent DC voltage source  Output voltage is constant (at any current)  
Independent AC voltage source  Output voltage varies sinusoidally.  
Current Source  Output current is constant (at any voltage).  
Voltage dependent voltage source (Voltage Amplifier) 
Output voltage is proportional to a control voltage, Vc (with proportionality constant Av  Av is unitless)  
Current dependent current source (Current Amplifier) 
Output current is proportional to a control current, Ic (with proportionality constant Ai  Ai is unitless)  
Current dependent voltage source (Transresistance Amplifier) 
Output voltage is proportional to a control current, Ic (with proportionality constant Rm  Rm has units of ohms) 

Voltage dependent current source (Transconductance Amplifier)  Output current is proportional to a control voltage, Vc (with proportionality constant Gm  Gm has units of Siemens (Conductivity)) 
v1v2v3v4=0, or v1=v2+v3+v4
As an example, consider the circuit below:
We can find the voltage across the 1kΩ resistor by consisdering the voltage source and the current source independently.
Consider Voltage Source Alone
(Current Source set to zero  an open circuit)Consider Current Source Alone
(Voltage Source set to zero  a short circuit)
Simplify Circuit
Voltage = 1.333 volts (by voltage divider)
Simplify Circuit
(333Ω=1k in parallel with 500  333=1k500)
Voltage = 0.333 volts (by Ohm's law)
Result
Therefore, the total voltage (by superposition)=0.333+1.333=1.666 volts.
When applying the Thevenin Theorem there are three cases.
 Case 1: Only independent sources  the typical case. In the typical case, there are no dependent sources in the circuit to be Thevenized. To find the Thevenin equivalent, first find the open circuit voltage, V_{oc}, this is the Thevenin voltage. To find the Thevenin resistance, set all sources to zero and find the resistance of the resulting circuit
Consider again the circuit from above,
and try to find the Thevenin circuit at the terminals (i.e., across the 1k resistor). From the discussion of superposition, we know the open circuit voltage, V_{oc}, is 1.666 volts. The Thevenin resistance, R_{T}, is found by finding the equivalent resistance of the circuit with all source set to zero, as shown below
Obviously the Thevenin resistance, R_{T}, is 1k500=333Ω. Therefore the resulting circuit is:
 Case 2: Independent and Dependent Sources. If the circuit to be Thevenized has both dependent and independent source, the method described above cannot be used to find the Thevenin resistance. Instead, you must find the short circuit current, I_{sc} (current through short circuit at terminals). Then the Thevenin resistance is given by R_{T}=V_{oc}/I_{sc}.
 Case 3: Only Dependent Sources. If only dependent sources are present, then the Thevenin voltage is zero, and the Thevenin resistance is determine by applying a test voltage V_{test} and the terminals and determining the resulting current, I_{test}. The Thevenin resistance is given by R_{T}=V_{test}/I_{test}. (Likewise, for this third case, you can apply a test current and measure the resulting voltage).
On to System Behavior
On to Problems
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