Download Thevenin/Norton (Source transformation)

Thevenin and Norton Cookbook:
Why? There are many kinds of complicated sources in electrical engineering, and we basically want to
know how they ‘drive’ a load. We can either calculate or measure the voltages and currents at the
nodes where the load will be connected, and we then know how the loaded circuit will behave.
Isc
Rth
Norton Equivalent
1. Open Circuit Method to find Vth: (Ok for dependent and/or independent sources)
a. Open (remove) the load. That means shorting out voltage sources and opening up current
sources. Find VTH. If there are no independent sources, VTH=0.
b. VTH = Voc
2. Short Circuit Method to find Isc: (Ok for dependent and/or independent sources)
a. Short circuit the load. Find IL = Isc.
b. If Rth is known. Then VTH = Isc RTH
c. If Rth is not known. Rth = Vth/Isc
3. Equivalent Resistance Method to find Rth: (Ok for independent sources only)
a. Open (remove the load). Find RTH
4. External Source Method: (Ok for dependent and/or independent sources)
a. Open (remove) the load. Remove independent sources. ( Short out voltage sources and open up
current sources.) Find VTH. If there are no independent sources, VTH=0.
a. Remove independent sources. (That means shorting out voltage sources and opening up current
sources.) Leave dependent sources in place. (‘Diamonds are forever.’) Apply external voltage
Vex source to terminals. Know Vex. Find iex. RTH = Vex/Iex.
** Note: All of these methods can be used for calculation, simulation, or measurement. BUT be careful
of shorting a real device (Method 2.), it may burn out your wire or the device.