1. Analysis of Resistive circuits and Revision
Week of 1st September 2008

2. Questions from last week

3. Operational Amplifier – Inverting and Non-Inverting inputs
Input V1 is called the non-inverting input because Vout is in phase with V1.
V2 is called the inverting input because Vout is 180° out of phase with V2.
In some applications, only the noninverting input is used and the inverting input is grounded. In other applications, only the inverting input is active and the non-inverting input is grounded ( LABS 4 and 5 )

4. Lissajous figures

5. Waveforms from lab – 4 ( VI Characteristics for Resistor, LDR, Thermistor)

6. Current Controlled Current Source

7. Current controlled Voltage Source

8. Version of Multisim

9. Page 77

10. Voltage and Current Sources

11. Node Voltage analysis of circuits with Current Sources - 103

12. The ideal model can be called the first approximation.
Ideal voltage source
Maintains a constant output voltage, regardless of the value of RL. RL
VRL= 10 Volts
10 V
The ideal model can be called
the first approximation.

13. Approximations Widely used in industry Useful for troubleshooting
Useful for circuit calculations

14. Voltage Sources An ideal source has no internal resistance
The second approximation of a voltage source has internal resistance
A stiff voltage source has an internal resistance that is 1/100 of load resistance

15. Real Voltage Source This model is called the the second approximation.
Has an internal resistance in series with the source RS RL
VRL< 10 Volts
10 V
This model is called the
the second approximation.
When RL is equal to or greater than 100 times RS, a real
voltage source is stiff and the first approximation can be used.

16. Ideal current source Maintains a constant
output current, regardless of the value of RL. RL
1 A
IRL= 1 Ampere
The ideal model can be called
the first approximation.

17. Real current source This model is called the the second approximation.
Has a large internal resistance
in parallel with the source RL
1 A RS
IRL< 1 Ampere
This model is called the
the second approximation.
When RS is equal to or greater than 100 times RL, a real
current source is stiff and the first approximation can be used.

18. Thevenin’s Theorem
Used to replace any linear circuit with an equivalent voltage source called VTH and an equivalent resistance called RTH

19. Thevenin Example Original Circuit

20. Thevenin’s theorem can be used to replace any
linear circuit with an equivalent voltage source
called VTH and an equivalent resistance called RTH.
6 kW
4 kW
VTH
72 V RL
3 kW
RTH
Calculate or measure
Thevenin’s resistance (RTH)
Remove the source.
Remove the load.
Calculate or measure VTH across the open terminals.

21. Thevenin’s Voltage

22. Voltmeter Tip The input impedance of
a voltmeter should be at least 100 times
greater than the Thevenin resistance to
avoid meter loading.
Meter loading errors cause inaccurate measurements.
DMMs are usually not a problem since they
typically have an input impedance
of 10 MW.

23. Original circuit Thevenin equivalent circuit
6 kW
4 kW
Original
circuit
72 V RL
3 kW
6 kW (RTH)
Thevenin
equivalent circuit RL
24 V (VTH)

24. Norton’s Theorem
Used to replace any linear circuit with an equivalent current source called IN and an equivalent resistance called RN

25. Norton’s Current
IN = 4 mA
RN = 6 KW

26. A Thevenin equivalent circuit The Norton dual
6 kW (RTH)
A Thevenin
equivalent circuit RL
24 V (VTH)
VTH
Circuit Conversion
RN = RTH
IN =
RTH
6 kW (RN) RL
4 mA (IN)
The Norton
dual

27. Superposition Theorem

28. 1st in-semester exam Two hours – Monday (8th ) 9 am to 11 am.
All that covered in class and lab
Focus on the problems from Dorf. Verification and Design problems are optional.

29. Two-loop problem – Superposition theorem – Current through R2

31. Circuit Theorems
Refer Chapter 5 from book of Dorf and/or Chapter 1 of Malvino.
Chapter 5 of Dorf is much more comprehensive.

32. Thevenin’s circuit application to two loop problem – Calculate current through R2

33. Norton’s theorem – Current through R2