Introduction to circuit analysis

Have you thought about bringing your very own Arduino, ESP32 or Raspberry Pi ideas to life? Then a bit of circuit analysis will definitely help you on your way! Electronics can seem like pure magic but with some effort and a little circuit theory, you’ll develop your first electronics project in no time!

So what is circuit analysis? Simply put, a circuit is a path for the flow of electrons. The flow of electrons is considered an electric current. The purpose of circuit analysis is to gain an understanding of how to examine, manipulate and use these electrons. Therefore, circuit analysis is a fundamental tool in electrical engineering. This includes an understanding of Ohm's Law and of Kirchhoff's Law.

Ohms Law

Ohm's law is explained thoroughly in this blog, so it is only briefly covered here. It is recommended to visit the blog mentioned above, to get a good understanding of Ohm's Law! But we do continue with a quick runthrough of Ohm's Law.

Ohm's law is a fundamental principle in physics that defines the relationship between the electric current, voltage and resistance in an electric circuit.

Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance of the conductor. Mathematically, Ohm's Law can be expressed as shown in figure 1.



Figure 1: Ohm's Law.

The voltage, V, is measured in Volts.

The current, I, is measured in Amperes

Resistance, R, is measured in Ohms

See figure 2.


Figure 2: A table for the units in Ohm's Law.
* This table is an excerpt from the Ohm's Law blog. Check out that blog for a deeper understanding of Ohm's Law!

Kirchhoff’s Laws

Kirchhoff's laws are two other basic principles of circuit analysis. These laws describe current and voltage respectively in an electrical circuit and are used to analyze and understand the behavior of the circuit. In the following we will review these laws one at a time.

1 - KCL

Kirchhoff's Current Law (KCL - Kirchhoff's Current Law)

This law states that the total current entering a node must equal the total current leaving the node (an example and explanation of a node is given in the following figure). In other words, it can be expressed as the sum of all flows into a node is equal to zero.

To explain this law, a water analogy is often used. The amount of water flowing into a node is equal to the amount of water flowing out of the node. An illustration of a node can be seen in figure 3.

Figure 3: Illustration of Kirchhoff's Current Law (KCL - Kirchhoff's Current Law). The figure is a section of an electrical circuit. The currents entering the node (red) are equal to the currents leaving the node (blue).

To return to the water analogy: If one considers the paths of the currents, I1, I2, I3, I4 and I5 as water pipes, it is noted that the currents meet at the node. The red currents are directed towards the node and the blue are directed out of the node. The mass of water for the sum of the red flows must then be equal to the mass of water for the blue flows. This is the principle of Kirchhoff's Current Law (KCL - Kirchhoff's Current Law)

2 - KVL

Kirchhoff's Voltage Law (KVL - Kirchhoff's Voltage Law)

This law states that the total voltage around any closed loop in a circuit must be zero. A closed loop in an electrical circuit refers to a path in the circuit that starts and ends at the same point.

In other words, it can be expressed as the sum of all voltage drops in a closed loop is equal to the total voltage rise in the loop.

Figure 4: Is a circuit with a voltage generator, V1, and 2 resistors (the zig-zag symbols indicate resistors R1 and R2). The circuit shows a closed loop as it starts and ends at the same point, namely at V1. The current, I, is indicated by value and direction around the circuit in the center of the figure.

Figure 4 illustrates how the voltage drop around the closed loop is equal to the applied starting voltage from the voltage generator V1. The voltage across the red part of the circuit is the original 9 V from V1. The voltage across the green part of the circuit is 5.4 V and for the blue section the voltage is 0 V.

Let's apply Ohm's Law to each section of the circuit with the values ​​defined in Figure 5. The three sections are divided by the voltage drops V2 and V3. We calculate the voltage drop across V2 and V3, and when we take the sum of these voltages, we should to get 9 V. This is the concept behind Kirchhoff's Voltage Law (KVL - Kirchhoff's Voltage Law).

Figure 5: Calculates the voltage drops in the circuit seen in Figure 4

  • In Figure 5, we first define the values ​​in the circuit
  • Then we calculate the voltages across V2 and V3
  • And finally we take the sum of V2 and V3

Thus, Kirchhoff's Voltage Law (KVL - Kirchhoff's Voltage Law) is proved.

Together, Ohm's Law and Kirchhoff's Law form an effective set of tools for analyzing electrical circuits and provide the basis for several methods of circuit analysis. After reading this blog, you are now one step closer to bringing your electronics dreams and projects to life. We now have a better understanding of circuit analysis, and even though we have only gone through some of the basics, we are now ready to get even better and form a broader understanding of electronics.

Electronics is a limitless hobby - you can always improve and there is always more to learn. If you are interested in more circuit analysis there are several methods and principles such as Thevenin, Norton, Mesh and Nodal Analysis.

We also have a blog about a very useful sub-circuit - the voltage divider. Check it out! The voltage divider is used in countless electronic products and is one of the most important sub-circuits in electronics.

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