Copyright © 2009 Pearson Education, Inc.

Admin for next week:Mid-term date Friday March 20th.•Review lecture Monday (16th). Any requests?•Labs as usual•NO DISCUSSION SECTIONS NEXT WEEK•Extra Office hours

• 2-4pm Monday: Dr Holder Sharp Lab 222• 2-4pm Tuesday: Dr Holder Sharp Lab 222• 2-4pm Wednesday: Seth Sharp Lab 308• 2-4pm Thursday: Zach Sharp Lab 320

•Email is also OK – or stop by my office any time Monday or Tuesday

•I will be away Wednesday – Friday. •Dr Ji will give Wednesday’s class and the exam.

Copyright © 2009 Pearson Education, Inc.

Admin:

•Assignments:

• Fourth assignment due Monday (16th)• Any questions?

• Fifth Assignment is posted.• Not due until Monday (23rd), but good exam practice• Three questions on Thevenin circuits

Thevenin and Norton Equivalent Circuits

vTH= open circuit voltage at terminal (a.k.a. port)

RTH= Resistance of the network as seen from port(Vm’s, In’s set to zero)

Any network of sources and resistors will appear to the circuit connected to it as a voltage source and a series resistance

Thevenin and Norton Equivalent Circuits

vTH= open circuit voltage at terminal (a.k.a. port)

RTH= Resistance of the network as seen from port(Vm’s, In’s set to zero)

Léon Charles Thévenin1857-1926

Norton Equivalent Circuit

Any network of sources and resistors will appear to the circuit connected to it as a current source and a parallel resistance

Ed Norton – Bell Labs, 1898-1983

The Thevenin and Norton equivalent cicuits are just different representations of the same thing.

They are used to simplify circuit analysis

VTH=INRTH : so you only usually need IN or VTH

RTH=RN

Calculation of Thevenin and Norton Resistance (RTH = RN)

• RTH=RN ; same calculation (voltage and current sources set to zero)

• Remove the load.• Set all sources to zero (‘kill’ the sources)

– Short voltage sources (replace with a wire)– Open current sources (replace with a break)

• Calculate the equivalent resistance

Remove the load.Kill the sourcesCalculate the equivalent resistance

RTH=R3 + R1 || R2

Calculation of the Thevenin Voltage (VTH)

• Put the sources back. Remove the load and calculate the open circuit voltage

Note:

How much current flows through R3?

What is the Voltage across R3?

The Thevenin equivalent is then just VTH in series with RTH

Calculation of the Thevenin Voltage (VTH)

• Put the sources back. Remove the load and calculate the open circuit voltage

Note:

How much current flows through R3?

What is the Voltage across R3?

Voltage divider!

The Thevenin equivalent is then just VTH in series with RTH

Exercise: Draw the Thevenin Equivalent as seen by the 40Ω load resistor

• To find RTH, remove the load, kill the sources (short voltage sources, break current sources) and find the equivalent resistance.

• To find VTH Remove the load and calculate the open circuit voltage

Exercise: Draw the Thevenin Equivalent

• To find RTH remove the load, kill the sources (short voltage sources, break current sources) and find the equivalent resistance.

Exercise: Draw the Thevenin Equivalent• Replace the sources

• To find VTH remove the load resistor and calculate the open circuit voltage

VAB = 20 - (20Ω x 0.33amps) = 13.33V

Exercise: Draw the Thevenin Equivalent• Draw the Thevenin equivalent

What about the Norton equivalent?

What about the Norton equivalent?

But what if we don’t know VTH?

Remember – if you suppress the “kilo” in the resistance, the current calculated is in milliAmps

STOP HERE for mid-term 1

• Anything you’d like me to cover in detail on Monday?

• Requests so far:

mesh analysis 2

voltage divider & current divider

light bulbs

Thevenin