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Muddiest Points – Week 5 1. Sign / Polarity Convention: See Node Voltage templates 2. What method to use and when: See the template of methods I’ve been giving you in class…. Consider what you are given in a problem, and what you want to obtain. Use the templates to plan how to solve the problem even before you start the math (or if you get stuck). Basically: Your workhorse methods are – Kirchoff (KVL/KCL) – solve for branch current Node Voltage – solve for node voltages Voltage & Current Dividers – Use if the geometry of the circuit permits, easiest of the methods. Which is more efficient? Dividers are easiest/most efficient when you can use them readily (geometry of the circuit). KVl/KCL and NodeV are pretty much equally efficient. KVL/KCL is used as a concept to derive almost all other methods. More efficient ways? Your multisim simulator is actually doing these method(s) to solve circuit equations. These really are the workhorse methods for ECE. 3. Lab 2 – See solution uploaded to website The "muddiest point" for me this week was from the lab. I understood what the voltage/current graphs meant and I thought I understood that each LED turns on at about 20mA <<This is correct>>, which corresponds to a different voltage for each color <<Yes!>>. When it came to checking the currents through the LED in the pre-drawn circuits, however, I could not understand why we were using 0A as the turn-on current <<Use 5 mA as the turn on, anything less is ‘off’>> and 20mA as the maximum burn-out current << LED spec sheet, or the curves max out at about 20 mA>>. I also couldn't figure out why we were considering the LED to be a voltage source that draws current yet has no resistance or why we could ignore the other resistor in parallel with the LED when we wanted all current to go through the LED. << You can read the LED resistance from the linear part of the curve (R=V/I, the slope of the line). It is a small resistance, so we can neglect it in most circuits. And, because R is small (let’s say 0), it does not impede the current, current can pass right on through like a short circuit. But, the linear part of the curves, instead of starting at V=0 like a resistor does, start at about VF=1.5V. So, it acts like a small resistor in series with a voltage source. <<We aren’t actually neglecting the parallel resistor. It has a fixed amount of current going through it , because of the voltage source created by the LED. It is a question of how much total current is in the circuit, and if it is greater than the current going through that resistor, we will get some through the LED to turn it on.