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Electronic Circuits Basics by John Derek

Electronic Circuits Basics

Designing and building electrical circuits is a fascinating hobby. Before building any electrical circuit we must learn the language called "electronics". Like any other language, there are some basic rules that we must know and understand. These rules will help us reading and designing simple and complicated electronic circuits.

This article's main target is to teach the electronics language to readers that are not familiar with electronics by using a group of rules and simple equations that describe the behavior of every electronic component and the relationship between the components in the circuit.

Basic electronic circuit can be separated to three sections: Power supply, wires, load.

The power supply (battery, wall mounted transformer etc.) drives current through the wires to the load (Lamp, Phone, motor, TV, etc.). If you would like to design electrical circuit to light a lamp or powering alarm or driving a motor with commands from a computer, you must understand the behavior of the components in the design according to their datasheets that are available from the component's manufacturers.

Understanding each component behavior will help you set the appropriate conditions to each of the components on your design. Your goal as a circuit designer is to know how to choose the best components to make your design work.

There are some basic electronic components that can be found in almost every electronic design. In the first article we will learn what are these basic components and their behavior in the electronic circuit, but first we must learn some basic terms and definitions.

Numbers Scientific notation

Scientific notation is a method for writing very small or very large numbers is a short way. For example: K [Kilo] = 1000, m [mili] = 1/1000. Large and small numbers are very common in electronics. Examples:

1. 0.003 ampere current = 3mA (3 mili ampere) or 3*10-3
2. capacitor with size of 0.0000000007 Farad = 7nF (7 Nano Farad) or 7*10-9
3. frequency with size of 20,000,000,000 Herz = 20GHz (20 Giga Herz) or 20*109

Electric wire (conductor)

Electric wire is called a conductor because it is made of a conductive material that can flow current. There are many types of conductors with many parameters and shapes, but don't worry, there are only several common conductors that can be used in an electronic circuit according to the signals that are active in the design. We will soon find out what type of conductor can be used for each of our electronic designs.

The conducting wire is like a pipe that helps the current flow from one point to another in the circuit. The conducting wire is usually covered with isolating material (usually plastic/nylon) that prevents the conductor to be shorted with other conductors on the electronic circuit. Many circuits are made of a printed card where the conductors are printed and are part of the card (some of them are hidden in internal layers of the card).

Electric current

Electric current is defined as a flow of electrons through a conductor (similar to water flow inside a pipe). Electric current is defined by size and direction. We can calculate the size of electric current in every conductor in the circuit according to the components and connections between them.

Size of electric current in a conductor

Electric current has the symbol "I" and measured with "ampere" units. The size of the electric current is relative to amount of electric charges flowing inside the conductor during time. We will see soon how to calculate the size of electric current in the electronic circuit.

Direction of electric current

In addition to the electric current size there is also a direction to the current flow inside the conductor. Direction of current inside a conductor is the opposite direction of the electric charges flow.

Electric voltage

Current flow inside a conductor is accomplished when there is a difference in the charge size between the two conductor edges. In other words, when there is a potential difference between two edges of the conductor. The potential difference is called electric voltage, this electric voltage drive the current flow inside the conductor. Electric voltage is marked as "V" and measured in "Volt" units.

Voltage source (power supply)

Voltage source (power supply) is a component that generates potential difference between its two terminals. This is the voltage of the power supply.

Total current consumption of an electric circuit

The total current consumption of an electric circuit is current consumed from the power supply of the electric circuit to power all electronic components. This is the current that flow inside the conductors that are connected to the power supply of the electric circuit. Simple electric circuit to light a LED triggered from a light sensor usually has total current consumption of around 50mA (50 mili ampere).

Complex electric circuit such as PC's mother board has total current consumption of several amperes. The size of current delivered by the power supply depends on the type of the components on the electric circuits, the circuit designer must know what are the parameters of the components in order to choose the appropriate power supply that can deliver the required current and voltage to the electric circuit as we will see in the article.

Resistance

Every material has the ability to resist to current flow through it. As long as the resistance of the material is high, less electronic charges can flow through it during time, meaning less electric current. Materials with extremely high resistance are called isolators, materials with low resistance are called conductors. As long as the resistance of the material is low we can say that the material is a better conductor.

Resistance is marked with "R" and measured in ohm units. Examples: Resistor with resistance of 10 Kohm(10000 ohm), The resistance of ideal conductor is 0 ohm.

Isolating and conducting materials

Resistance of isolator/conductor depends on the material and physical dimensions. Every material has its unique "Electrical resistivity". Conductors are materials with low electrical resistivity; isolators are materials with high electrical resistivity. Examples: Cupper is a very good conductor because its electrical resistivity is very low; plastic is a very bad conductor because its electrical resistivity is very high.

More examples for conductors: aluminum, gold, silver, steel. More examples for isolators: glass, wood, paper.

Basic terms in electronics can be illustrated with a water delivery system analogy:

Water pipe = electric wire
Water flow = current flow
Water pump/tower = power supply
Water Sprinkler/tap = electric load

In order to deliver water in the pipe to the sprinkler, a water pump must push the water from one edge of the pipe to the other edge. As long as the water pipe is thinner, less water can flow in a time unit. This is exactly how the electronic circuit works, as long as the wire is thinner, less current can flow in a time unit. We will learn soon about a component in the electronic circuit called "resistor", this component resist to part of the current flow through it. The analogy to "resistor" is a valve that adjusts the water flow in the pipe.

Ohm's law

First and most important law in electronics is ohm's law. This law is a formula that represents the relation between voltage, current and resistance as follows:

R = V/I

R = resistance
V = voltage
I = current

Playing with the formula can show another two representations:

I = V/R

V = I * R

We can see by ohm's law that when resistance rises, the current is reduced. If we will measure the resistance of a resistor in the electronic circuit and the voltage between its two terminals we will be able to calculate the current that flow through the resistor with ohm's law.

Resistor

Resistor is a component with constant and known resistance. The resistor includes two terminals that connect to the electric circuit. Resistors are manufactured on a large range of resistances as requested in each section of the electric circuit. The resistance of the resistor is defined during the manufacture process and usually marked on the resistor package with letters or color stripes code. The main function of the resistor in the electric circuit is to adjust currents and voltage in places where it is connected. Resistor in the electric circuit is marked with the letter R.

Electric power

Electric power is marked with the letter "P" and measured in Watt [W] units. Electric power is calculated with the three basic parameters of ohm's law: R, I, V and can be represented with the following formulas:

P = I*V
V = P/I
I = P/V

Where: P - electric power, V - voltage, I - current, R - resistance.

Resistors combinations in the electric circuit

There are many resistors with almost every resistance needed for the designer, but sometimes we have some resistors that are not exactly in the required resistance. In this case we can connect resistors in serial and/or parallel to each other to get the required resistance. There are three connection types: serial, parallel, mixed.

What is a "Total resistance"?

This is the measured resistance between two points in the electric circuit. For example: the total resistance between two terminals of one resistor is the resistance of the resistor itself. But how can we calculate the total resistance of a complex electric circuit like this one? We will see how to do that in a moment.

Connecting resistors in serial

The resistance of two resistors connected in serial is the sum of the two resistances.

Connecting resistors in parallel

Resistors (or any components with two terminals) connected in parallel is defined when the two terminal of the first resistor connected to the two terminal of the other resistor. The total resistance of two resistors connected in parallel is:

R = (R1*R2)/(R1+R2)

The || sign is used to mark a parallel connection between two components. The four resistors from the last example can be written:

RAB = R1||R2||R3||R4

Adding more resistors in parallel to each other will decrease the total resistance. We can see that the total resistance of two or more resistors connected in parallel is always less than the resistance of each on of them separately.


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