12 Lesson Comparison of Analysis Techniques (Chapter 3 review)(CLOs 3-1thru 3-5) This lesson offers students with the ability to sit back and review all of the different analysis techniques we have been teaching them. They need practice in deciding which analysis tool to use when. Often it does not matter since they will get the right answer regardless of which method they choose, but at other times it does matter and choosing the wrong tool will cost them time and maybe even getting the right answer. In presenting this lecture, approach it with two goals in mind. First, show the students how to choose between analysis techniques when to use Node Voltage vs. Mesh Current or when Thvenin or Superposition makes the most sense. Second, use the lesson to briefly discuss Evaluation of competing interface designs. For the first goal, suggest using the following circuit. Then depending on what is asked for choose the following analysis technique: If the problem asks to solve for all voltages and all currents in the circuit, one should use mesh _ I1 R1 + V3 current analysis to solve the problem since there are two unknown nodes but only one unknown _ R3 mesh. IS If the problem asks to find how much power is R2 V2 I VS IA B delivered to the circuit by either source the + technique to use would be superposition. However, the total power dissipated in the circuit cannot be found by simply adding the contributions of each source. Why? If the problem asks how to select R2 for maximum power transfer to it, then Thvenin would be the best tact to take. If the problem asks to find I1. Mesh current would be the easiest approach. If the problem asked to find V2. Mesh current would probably be easier than Node Voltage. the If problem was to find V3 then Ohms Law would suffice (ISR3). For the second goal, we have introduced the concept of making smart engineering judgments. Benjamin Bloom in his Taxonomy called this Evaluation; choosing between alternatives the better or best solution to meet a set of constraints. It is the highest form of learning and an essential one for engineers. To practice this goal, suggest using the following example: Select the best interface design that would deliver 5 10% volts to a 100- load from an ideal 15 V source. The constraints are as follows: The best design will have minimized the part count, it will have used only standard value resistors and, most importantly, it will use the least amount of source power. Three options are provided in this problem. They are shown below.
Option #1 100 15 V 100 Option #2 100 Desired 100 I nt erf ace Option #3 220 100 + 10 V _
Option #1 delivers exactly 5 V but uses 1.5 W. It uses two standard value resistors. Option #2 delivers exactly 5 V uses 750 mW of power and uses two standard value resistors. Option #3 delivers only 4.69 V, but uses 703 mW of power and uses only one standard value resistor. Option #1 uses too much power. Option #2 provides an exact output and uses less power than Option #1. Option #3 delivers less than the perfect value of output voltage, but is within the tolerance range of 10%; it uses only one standard value resistor and the least power of the three. This comes down to an engineering decision. In balance, considering everything, which is the best solution? Probably, choose Option #3. Note that in Evaluation problems it is always useful to ask the student to explain why they selected the option they did.