EE 2115-01 - Lec 09 - 2026_09_14
Watch on YouTube →
Overview
Hiren Trada applies superposition to resistor circuits, showing how to deactivate ideal voltage and current sources, redraw nodes, and add source-by-source voltage or current contributions. Worked examples produce 1.91 V across a 20 kΩ resistor, a 5.45 kΩ equivalent resistance, and zero net current in a second circuit; the lecture then introduces pull-up and pull-down logic using switches and the CD4066.
Key takeaways
- In linear circuits, superposition obtains a target voltage or current by analyzing each independent source separately and summing the signed contributions.
- For superposition, an ideal voltage source becomes a short circuit when deactivated, while an ideal current source becomes an open circuit.
- Redrawing and labeling nodes can reveal that physically separated wire-connected points are the same node, making parallel relationships and equivalent resistance easier to identify.
- The 2 V and 3 V source contributions in the resistor example are about 1.09 V and 0.82 V, which combine to 1.91 V; the equivalent resistance is 5.45 kΩ.
- In the current-source example, a 10 V source contributes 1 A while the 2 A source contributes negative 1 A in the chosen reference direction, producing zero net current in the target branch.
- A pull-up or pull-down resistor establishes an output's default logic level, while limiting current when a switch connects the output to a supply rail.
Chapters
- For a linear circuit with multiple sources, analyze one active source at a time and deactivate the others.
- Record the voltage or current at the same point for each source, then add the contributions to obtain the total.
- The 20 kΩ resistor example uses the 2 V and 3 V sources to illustrate how separate voltage contributions combine.
- Deactivate an ideal voltage source by replacing it with a short circuit, which holds its two terminals at the same voltage.
- Deactivate an ideal current source by replacing it with an open circuit, eliminating its current path.
- Apply these substitutions before analyzing each source's contribution because the circuit connections may change.
- With the 3 V source shorted, 20 kΩ is parallel with 30 kΩ; that combination is in series with 10 kΩ, giving about 1.09 V across terminals A and B from the 2 V source.
- With the 2 V source shorted, 10 kΩ is parallel with 30 kΩ; that combination is in series with 20 kΩ, giving about 0.82 V from the 3 V source.
- Adding the two contributions gives 1.91 V across the 20 kΩ resistor, matching the earlier equivalent-circuit result.
- Trada recommends redrawing a circuit and labeling nodes to make changed connections and parallel branches easier to recognize.
- To find the Thevenin resistance at A and B, deactivate all independent sources and calculate the resistance looking between those terminals.
- Continuous wires make connected points the same electrical node; in the example, the resistors share two nodes and are all in parallel.
- The LTspice setup compares the original 2 V and 3 V source circuit with its equivalent circuit.
- A zero-valued current source is attached at the output so the simulation can measure the terminal voltage and resistance.
- The circuits produce the same 1.91 V and 5.45 kΩ values, verifying their equivalence.
- With a 10 V source active and the current source opened, three series resistors total 10 Ω, so the voltage source contributes 1 A in the reference direction.
- With the current source active and the voltage source shorted, its 2 A divides equally between two 5 Ω paths, contributing 1 A opposite the reference direction in the target branch.
- The contributions sum to 1 A minus 1 A, or 0 A; the zero-current result corresponds to equal voltages at the ends of the branch resistors.
- Digital logic represents two states as binary 0 and 1, commonly described as low and high voltage.
- Low is illustrated as 0 V, while high is commonly 5 V in older logic circuits; modern devices may use 3.3 V.
- A washing machine provides an example of logic translating a selected towel cycle into control actions such as setting water temperature and run time.
- In the 5 V switch example, closing the switch connects the output to ground and makes it low; opening the switch lets the resistor pull it high.
- A pull-up resistor connects the output toward the positive supply, while a pull-down resistor connects it toward ground.
- The resistor limits current and prevents a direct short between the supply rails when the switch closes; a real voltage-controlled switch can also reduce the output below 5 V.
- The CD4066 contains four voltage-controlled switches for implementing switch-based logic circuits.
- For the discussed 14-pin or 16-pin packages, the supply pins are 14 or 16 and ground pins are 7 or 8.
- The first quiz is scheduled for the first five minutes of Friday's class, in person, with rapid one-word or one-number answers.
Transcript excerpt
0:02 All right, let's continue on. What's left was lecture eight. We'll finish that up and then move on to lecture nine which is a completely different topic. Okay. So we stopped here. Now this circuit we solve using uh equivalent circuits like the and Norton. uh let's see and then in just a two three slides we're going to solve it using a different technique called a superposition. So let's look at what superposition is first. Now the principle of superposition states as far as circuit analysis goes superposition principle states that if you have a circuit with multiple sources in there now the resulting voltage or
0:51 current in that circuit at any point so let's say this was circuit 2 the voltage across 30 kiloohms or the 10 koohm resistor or the current that is flowing through these resistors It is a result of all of the sources working or acting at the same time. Right? So the voltage or current in a circuit it is a is a result of all the sources working at the same time. So superposition principle states we can analyze a circuit with only one source active at a time. Deactivate all the other sources. analyze it just once using that one source
1:38 and then [clears throat] note down the voltage or current of interest. Then you move on to source number two. Activate source number two. Deactivate all the other sources. Analyze it again one more time. Find the voltage and current again at those same points. Move on to source number three, source number four, so on and so forth. Now you have n number of sources. You'll have n number of results for each single voltage and each single current. If you add them all up together, that would be the resulting voltage or
This is the start of the transcript. Save this video free for the whole transcript, searchable and time-coded.
Related notes
Summary, takeaways, and chapters were generated by AI from the video's transcript and may contain errors. The video belongs to its creator, Hiren Trada.