Circuit Theory/Lab4.5.1

thumb|the original circuit, R7 is the load, find thevenin equivalent of the rest of the circuit thumb|Finding Vth using ohm's law thumb|thevenin resistance is calculated by zeroing the sources and opening the load thumb|redrawing thevenin resistance network to make calculation easier Example, find the thevenin equivalent of this circuit, treating R7 as the load. Simulate the circuit, displaying load voltage and current as the load is swept through a range of resistance values Simulate the thevenin equivalent circuit and again sweep the load voltage and current through a range of resistance values Finding Thevenin Voltage Open the load (resistor R7), and find the voltage across it's terminals. R5 and R6 are dangling and can be removed. Vth = VA - VB VA = 2-VR1 = 2 - (2-5)*2.2/(2.2+4.7) .. voltage divider VA = 2.9565 VB = 5-VR3 = 5 - 5*6.8/(6.8+6.8) .. voltage divider VB = 2.5 volts Vth = 2.9565 - 2.5 = 0.4565 volts Can check with this simulation. Finding Thevenin Resistance Remove the load, zero the sources. Redraw up and down so the parallel/serial relationships between the resistors are obvious. Finding Norton Current IN = Vth/Rth = 0.4565/7.3986 = 0.0617 amp Simulating the original circuit In the simulation, can see the computed Norton's current when the load is 0 ohms. Can see the computed Thevenin voltage when the load is around 20 ohms which approximates an open. Comparing with the Thevenin Equivalent In this simulation, can see the same values, except this time the load voltage is relative to ground, so don't have to look at a drop or differences between two voltages as with the original circuit simulation.