Demonstrating Thevenin and Norton equivalence and a way to calculate open circuit voltage, short circuit current and calculate the Thevenin and Norton equivalent resistances.

SWthevenin with Csamphold_thev and SWnorton with Csamphold_nort sample and hold the open circuit voltages of the two sources.

The two ammeters measure the short circuit currents when the two switches change state at T=1s.

Plot expressions are then used to calculate the open circuit voltages divided by the short ammeter currents.

After T=1, these expressions show the Thevenin and Norton equivalent resistances respectively.

However, there are some problems with this simple simulation.

i) The equivalent resistance calculation should explode to infinity for T<1 because the ammeter currents are zero!

ii) CL does not show the calculated restances correctly for T<1, so in fact the plots look sort of OK although they are incorrect for T<1

iii) CL shows a nosensical slope on the resistance plots even though all values are 1.000.

Setting `Start Time = 1.1`

( i.e. after the switches change state)
is a way round this problem although CL still does not
show the T<1 behaviour correctly.

Simulate > Time Domain > Run Time-Domain Simulation

A correctly working LTspice version of this simulation:

Thevenin-Norton_calculations_01.7z

can be downloaded from:

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