Methods for Finding Thevenin Model

1. Reduce the circuit using source transformations.

2. Find open circuit (o.c.) voltage, v_oc, and short circuit (s.c.) current, i_sc. This requires two separate analyses of the circuit. Then V_Th = v_oc and R_Th = v_oc / i_sc.

   More generally, attach two (or more) different load resistor values R_L to the terminals, and measure the corresponding voltage v_L and current i_L across/thorough R_L. Then solve for V_Th and R_Th using at least two equations of the form v_L = V_Th - R_Th i_L.
   The method above corresponds to R_L = infinity (o.c. so i_L = 0) and R_L = 0 (s.c. so v_L = 0).

3. An alternative for finding R_Th that does not require i_sc is as follows.

   Deactivate independent voltage and current sources (set them to zero values). This step may make the analysis simpler than finding i_sc.

   • If the circuit contains only independent sources, then R_Th is the equivalent resistance of the circuit.
   • If the circuit contains dependent sources, then apply a test voltage or current source, and R_Th is the ratio of the test source voltage and current.
     If the circuit contains only dependent sources, then you must use a test source to find R_Th.

   V_Th = v_oc is obtained from an open circuit analysis of the circuit (and is zero if the circuit contains only dependent sources).