Lecture 10 Thevenin and Norton Equivalent Circuits ECE
- Slides: 10
Lecture 10 Thevenin and Norton Equivalent Circuits ECE 205 Prof. Ali Keyhani
Equivalent Circuits • A two terminal interface: • Interface is the connection between circuits Thevenin equivalent circuit: Norton equivalent circuit:
Conditions for Existence of the Equivalent Circuits: • Theorem: If the source circuit in a two terminal interface is linear, then if the source circuit is replaced by the its Thevenin or Norton equivalent the interface signals i and v will not change • Thevenin and Norton circuits have the same i-v characteristics: – The two circuits can be replaced by each other – The equivalency conditions should be derived
Equivalency Conditions • In order to find the equivalency conditions the i-v relationship of two circuits should be compared • Thevenin Circuit: • Norton Circuit:
Equivalency Conditions • Norton and Thevenin circuits have the same i-v relationship, therefore: • Once one of the circuits is found the other can be determined by source transformation
• Parameters of the Norton and Thevenin circuits can be found by calculating the open-circuit voltage and shortcircuit current
Example 1 Find the load resistance to have a load voltage of 3 V.
Example 1 Solution: Thevenin equivalent circuit is found to simplify the circuit at the interface. To find the short circuit current first the equivalent resistance of the circuit is found to be able to calculate the input current.
Example 1 The resulting Thevenin equivalent circuit: Voltage division is used to find the load resistance:
Example 2 Find the Norton equivalent of the circuit to the left of the interface.
