Loading in 5 sec....

Thévenin’s and Norton’s Theorem PowerPoint Presentation

Thévenin’s and Norton’s Theorem

- 218 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Thévenin’s and Norton’s Theorem ' - sawyer-simon

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

### Thévenin’s and Norton’s Theorem

Objective of Lecture

- State Thévenin’s and Norton Theorems.
- Chapter 4.5 and 4.6 Fundamentals of Electric Circuits

- Demonstrate how Thévenin’s and Norton theorems ca be used to simplify a circuit to one that contains three components: a power source, equivalent resistor, and load.

Thévenin’s Theorem

- A linear two-terminal circuit can be replaced with an equivalent circuit of an ideal voltage source, VTh, in series with a resistor, RTh.
- VTh is equal to the open-circuit voltage at the terminals.
- RTh is the equivalent or input resistance when the independent sources are turned off.

Circuit Schematic:Thévenin’s Theorem

Definitions for Thévenin’s Theorem

Linear circuit is a circuit where the voltage is directly proportional to the current (i.e., Ohm’s Law is followed).

Two terminals are the 2 nodes/2 wires that can make a connection between the circuit to the load.

Definitions for Thévenin’s Theorem

+

Voc

_

Open-circuit voltage Voc is the voltage, V, when the load is an open circuit (i.e., RL = ∞W).

Definitions for Thévenin’s Theorem

- Input resistance is the resistance seen by the load when VTh = 0V.
- It is also the resistance of the linear circuit when the load is a short circuit (RL = 0W).

Steps to Determine VTh and RTh

- Identify the load, which may be a resistor or a part of the circuit.
- Replace the load with an open circuit .
- Calculate VOC. This is VTh.
- Turn off all independent voltage and currents sources.
- Calculate the equivalent resistance of the circuit. This is RTH.
- The current through and voltage across the load in series with VTh and RTh is the load’s actual current and voltage in the originial circuit.

Norton’s Theorem

- A linear two-terminal circuit can be replaced with an equivalent circuit of an ideal current source, IN, in series with a resistor, RN.
- IN is equal to the short-circuit current at the terminals.
- RN is the equivalent or input resistance when the independent sources are turned off.

Definitions for Norton’s Theorem

Open-circuit voltage Isc is the current, i, when the load is a short circuit (i.e., RL = 0W).

Definitions for Norton’s Theorem

- Input resistance is the resistance seen by the load when IN = 0A.
- It is also the resistance of the linear circuit when the load is an open circuit (RL = ∞W).

Steps to Determine IN and RN

- Identify the load, which may be a resistor or a part of the circuit.
- Replace the load with a short circuit .
- Calculate ISC. This is IN.
- Turn off all independent voltage and currents sources.
- Calculate the equivalent resistance of the circuit. This is RTH.
- The current through and voltage across the load in parallel with IN and RN is the load’s actual current and voltage in the originial circuit.

Source Conversion

- A Thévenin equivalent circuit can easily be transformed to a Norton equivalent circuit (or visa versa).
- If RTh = RN, then VTh = RNIN and IN = VTh/RTh

Value of Theorems

- Simplification of complex circuits.
- Used to predict the current through and voltage across any load attached to the two terminals.
- Provides information to users of the circuit.

Example #1 (con’t)

Find IN and RN

Example #1 (con’t)

- Calculation for IN
- Look at current divider equation:
If RTh = RN= 1kW, then IN = 6mA

Why chose RTh = RN?

- Suppose VTh = 0V and IN = 0mA
- Replace the voltage source with a short circuit.
- Replace the current source with an open circuit.
- Looking towards the source, both circuits have the identical resistance (1kW).

Source Transformation

Equations for Thévenin/Norton Transformations

VTh = IN RTh

IN = VTh/RTh

RTh= RN

Alternative Approach: Example #1

IN is the current that flows when a short circuit is used as the load with a voltage source

IN = VTh/RTh = 6mA

Alternative Approach

VTh is the voltage across the load when an open short circuit is used as the load with a current source

VTh = IN RTh = 6V

Example #2

Simplification through Transformation

Example #2 (con’t)

Current Source to Voltage Source

Example #2 (con’t)

0.3V

Example #2 (con’t)

Current Sources in Parallel Add

Example #2 (con’t)

Transform solution for Norton circuit to Thévenin circuit to obtain single voltage source/single equivalent resistor in series with load.

Summary

- Thévenin and Norton transformations are performed to:
- Simplify a circuit for analysis
- Allow engineers to use a voltage source when a current source is called out in the circuit schematic
- Enable an engineer to determine the value of the load resistor for maximum power transfer/impedance matching.

Download Presentation

Connecting to Server..