1. Lecture 5 Source Transformation Thevenin Equivalent Circuit
Norton Equivalent Circuit

2. Circuit Techinques Ohm’s Law P=VI KCL, KVL Voltage/current divider
Series/parallel resistance
Mesh/Nodal Analysis
Source Transformation
Thevenin/Norton Equivalent Circuit
Superposition Principle
Maximum Power Transfer

3. Source Transformation
Show that iS=vS/R for any RL

4. Thevenin Equivalent Circuit

5. Determine the Thevenin Voltage (VTh)
If RL=∞ (load across a-b is removed), then Vab=VTH
RTH does not play a role!

6. 3 Bit Digital to Analog Converter
741 Op-Amp
Chapter 5

7. Sample DAC Waveform
DAC
Output
Digital Input

8. Applications
Most modern audio signals are stored in digital form (e.g. MP3 and CDs) and in order to be heard through speakers they must be converted into an analog signal

9. Thevenin Equivalent Circuit

10. Determine VTH

11. Methods of Finding RTH RTH=VTH/iSC
If RL=0, the short circuit current from a to b (i.e. iab) should equal to isc=VTh/RTH.
So RTH=VTh/isc
If the network contains only independent sources:
Deactivate a voltage source by replacing it with a short
Deactivate a current source by replacing it with an open
If the network contains dependent sources
Apply a test source

12. Calculate the Thevenin Resistance
RTH

13. If the network contains only independent sources
RTH?

14. RTH

15. Methods of Finding RTH RTH=VTH/iSC
If RL=0, the short circuit current from a to b (i.e. iab) should equal to isc=VTh/RTH.
So RTH=VTh/isc
If the network contains only independent sources:
Deactivate a voltage source by replacing it with a short
Deactivate a current source by replacing it with an open
If the network contains dependent sources
Apply a test source

16. Degenerated Common Emitter Amplifier (from last lecture)

17. What if we drive the base with a small signal?
Vin, m=1 mV
Vout, m=46 mV

18. Mesh Analysis (Last Lecture)
ne=2 essential nodes
be=3 essential branches
3-(2-1)=2 equations

19. Mesh Analysis (Last Lecture)1 2
Loop 1: clockwise
Loop 2: counter-clockwise
Clockwise around loop 1:
+Vin-i1rπ-(i1+i2)RE=0
Counter-clockwise around loop 2:
i2=gmi1rπ
Vout =-i2RC

20. Mesh Analysis (Details)

21. Determine RTH when a Dependent Source is PresentIT

22. Methods of Finding RTH RTH=VTH/iSC
If RL=0, the short circuit current from a to b (i.e. iab) should equal to isc=VTh/RTH.
So RTH=VTh/isc
If the network contains only independent sources:
Deactivate a voltage source by replacing it with a short
Deactivate a current source by replacing it with an open
If the network contains dependent sources
Apply a test source

23. Another Way to Find RTH
isc

24. RTH Calculation iSC=10V/100 KOhms=0.1 mA VTH=10V/2=5V
RTH=VTH/iSC=5V/0.1 mA=50 KOhms

25. Norton Equivalent Circuit
A Norton Equivalent circuit consists of
Short-Circuit Current
Norton Equivalent Resistance, which is equal to Thevenin Equivalent Resistance

26. Getting A Norton Equivalent Circuit from Thevenin Equivalent Circuit
RTH
Thevenin Equivalent Circuit
VTH
Norton Equivalent Circuit
IN=VTH/RTH
RTH

27. Derivation of Norton Equivalent Circuit
RTH
VTH
IN=VTH/RTH
RTH

28. Extra Credit Assignment
Derive

29. More about the Extra Credit Assignment

30. Extra Slides on Thevenin

31. Determine vab
Show that VTH=vab

32. Determine iSC and RTH

33. Example 4.10
Determine the Thevenin Equivalent Voltage

34. Example 4.10
Determine the short circuit current
Determine RTH

35. Slides on Source Transformation

36. RTH

37. Application Determine whether the 6V source is
absorbing or delivering the power.

38. Step-by-step simplification

39. Redundant Resistor (1)
Prove that the left circuit and the right circuit are
equivalent for any load resistor.

40. Redundant Resistor (2)
Prove that the left circuit and the right circuit are equivalent for any load resistor.

41. Example 4.9

42. Simplified Circuit