advertisement

Thevenin, Norton and Maximum Power Transfer Theorems Why Thevenin’s Theorem is useful Everything in the original circuit, except the load, maybe replaced by an equivalent circuit. The equivalent circuit consists of a series combination of a voltage source and a resistance. Write these on white board RTH = 5kΩ VTH = 10V Now you can place any load in the circuit you want and the calculations are EASY! .66mA =10kΩ Determine VTH Solving for VTH 10V 5V VTH = VA – VB = 5V Determine RTH What is the resistance from point a to b? http://www.youtube.com/watch?v=SWWt9I C7mGs&NR=1&feature=fvwp https://www.facebook.com/photo.php?v=133 641650156241 Everything in the original circuit, except the load may be replaced by an equivalent circuit. The equivalent circuit consists of a parallel combination of a current source and a resistance. Norton Current IN 2mA Norton Resistance There are a bunch of rules for how to calculate the Norton Current and Norton Resistance. However, a shortcut is to find the Thevenin Equivalent circuit and then convert it to a Norton 2mA Besides using traditional circuit analysis using Ohm’s Law, or Superposition, Mesh Analysis, Thevenin’s Theorem, and Norton’s Theorem, there are other circuit analysis techniques. A couple include: Nodal Analysis and Millman’s Theorem Do more hw problems from back of chap 12 (9, 10, 11, or 12) if time In the following circuit solve for VTH, RTH, IN, RN, IL and VL Solve for VL using traditional Ohm’s Law technique, Mesh Analysis, and Thevenin Analysis See notes RL (Ω)0 VT (V) I (A) PL(W) Pi (W) PT (W) Eff (%) 0 0 20 0 2000 2000 0 1 16.7 16.7 278.9 1394 1673.4 16.7 2 28.6 14.3 409 1022 1431.5 28.6 3 37.5 12.5 468.8 781.3 1250.1 37.5 4 44.4 11.1 492.8 616.1 1108.9 44.4 5 50 10 500 500 1000 50 6 54.5 9.1 496 414.1 910.05 54.5 7 58.3 8.3 483.9 344.5 828.35 58.3 8 61.6 7.7 474.3 296.5 770.75 61.6 9 64.3 7.1 465.5 252.1 717.55 64.3 10 66.7 6.7 446.9 224.5 671.35 66.7 20 80 4 320 80 400 80 30 85.7 2.9 248.5 42.05 290.55 85.7 40 88.9 2.2 195.6 24.2 219.8 88.9 50 90.9 1.9 172.7 18.05 190.75 90.9 ? What circuit analysis technique can we use to solve for this? Thevenin’s Theorem. RTH = 5kΩ I’ve checked this technique using Ohm’s law and it works. See following numbers: 5mW @ 5kOhm 4.94mW @ 4kOhm 4.96mW @ 6kOhm SPST SPDT DPST DPDT