Lecture 8 Source Transformation Thevenin Equivalent Circuit Norton Equivalent Circuit

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

Source Transformation Show that

i S =v S

/R for any

R L

Thevenin Equivalent Circuit

Finding the Thevenin Voltage

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

Getting A Norton Equivalent Circuit from Thevenin Equivalent Circuit

R TH

Thevenin Equivalent Circuit

V TH I N =V TH /R TH R TH

Norton Equivalent Circuit

Find the Thevenin Voltage

Details

Methods of Finding R TH • • • R TH =V TH /i SC – – If R L =0, the short circuit current from a to b (i.e. i should equal to i sc =V Th /R TH .

ab ) So R TH =V Th /i sc 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

Find the Thevenin Resistance

Details

Equivalent Thevenin Circuit

What is the Norton Equivalent Circuit ?

Determine the Thevenin Resistance

Thevenin Voltage

Thevenin Resistance

Methods of Finding R TH • • • R TH =V TH /i SC – – If R L =0, the short circuit current from a to b (i.e. i equal to i sc =V Th /R TH .

ab ) should So R TH =V Th /i sc 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 – Deativate INDEPENDNET voltage/current source – Apply a test source

Example 4.11: Find R TH

Simplified Schematic

Methods of Finding R TH • • • R TH =V TH /i SC – – If R L =0, the short circuit current from a to b (i.e. i should equal to i sc =V Th /R TH .

ab ) So R TH =V Th /i sc 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

Example 4.10

Determine the Thevenin Equivalent Voltage

Example 4.10

1. Determine the short circuit current 2. Determine R TH