Equivalent Impedance

Impedance seen between two terminals of a circuit.

Method 1 - Impedances Only

  • Series combination:
  • Parallel combination:

Method 2 - Independent Sources Only

  1. Turn off Independent Sources:
    • Replace voltage source with short-circuit
    • Replace current source with open-circuit
  2. Apply method 1

Method 3 - Test Source Method

  1. Turn off Independent Sources:
    • Replace voltage source with short-circuit
    • Replace current source with open-circuit
  2. Apply a test Voltage () at terminals
  3. Find resulting Current ()
  4. Calculate

eq-impedance-test-source-method.svg > invert

Method 4 - Thevenin/Norton Equivalent Method

  1. Find Thevenin Voltage ( = open-circuit Voltage ()) across terminals
  2. Find Norton Current ( = short-circuit Current ()) between terminals
  3. Calculate

eq-impedance-thevenin-norton-method.svg > invert