# Ohm Law, Symbol of Resistor, Types, and Defenition

__Symbol of Resistor__ - In electronic devices, if you have ever seen a component like the picture below, its name is Resistor. But resistors are not just like the following picture, there are many versions, you will read the article below.

This component is the most basic component and Symbol of Resistor that you must know if you want to play in the field of electronics, because it will be very widely used.

## Definition of Resistor

** Resistor is a passive** component to reduce current flowing in an electrical circuit. Resistor comes from the word "Resist" which means to reduce, hold, block, reject or inhibit.

The ability of a resistor to carry current is called **resistance**.

We can analogize that electric current is like water. While the resistor is a water pipe.

When water flows in a clean pipe, the amount of water entering is equal to the water leaving. However, if the pipe is dirty inside, has a lot of moss or there are lumps of soil, then the amount of water that enters is not the same as the water that comes out.

Well, the pipe was also called the Resist component, because it has blocked the flow of water with the presence of moss and lumps of soil. The amount of the resistor's ability to block electric current, depends on the resistance value.

The greater the resistance value, the greater the ability to inhibit electric current. Resistors are called passive components because these resistors do not require an energy source from other components to be able to inhibit electric current.

### Symbol of Resistor

Resistor symbols such as jagged or zigzag are American and Japanese standard resistor symbols often known as **ANSI** (*American National Standards Institute*), while square is a European standard and is often known as **IEC** (International Electrotechnical Commission). Some Symbol of Resistor are as follows:

### Ohm's Law and Units

The unit value of this resistor is “**Ohm**”. The current flowing in the resistor (A) is equal to the voltage across the resistor (V) divided by the resistance (R).

I = V / R

While the power consumption (P) of a resistor is equal to the current flowing (I) times the voltage across the resistor (V).

P = I x V

Using another formula, the power consumption of a resistor is equal to the square of the current (I^2) times the resistance (R).

P = I^2 x R

The complete formula is as follows::

## Resistor Types

### 1. Based on Value

When talking about resistance values, resistors are divided into two types, Fixed Resistors and Variable Resistors..

**a. **Fixed Resistor

Fixed resistors are resistors that have a fixed value of resistance. Usually this resistance value can be known based on the color of the bracelet or the number written on the resistor body.

In addition to having a fixed value, this resistor also has a tolerance value, temperature coefficient and power capability.

For self-tolerance, these fixed value resistors have a range from 0.001% to 20%. The smaller the tolerance value, the more accurate the resistance value.

For the temperature coefficient value, this fixed resistor starts from the value range of -1500/ -900ppm/degree Celsius to 1800ppm/degree Celsius.

For power capabilities, these resistors have power capabilities ranging from 0.05W (1/2W) to 150W.

Fixed Resistors are very many derivatives or types depending on the material that makes up the resistor itself, but in general, based on the material of manufacture, it is currently divided into four major groups, namely:

- Carbon Resistor (resistor made with carbon material)
- Film Resistors (resistors made of metal oxide are usually low-power)
- Wire-wound resistors (resistors made with wire windings are usually high power)
- Semiconductor Resistors (resistors made with semiconductor materials) .

**b. ****Variabel ****Resistor **

- Potensiometer
- Rheostat
- Thermistor
- Magneto Resistor
- Photoresistor
- Humistor
- Force Sensitive Resistor

### 2. By Shape

- THT
- SMD
- MELF

### 3. Based on Raw Material

Resistors have many types that can be made based on the composition of the material. Each resistor material has its own advantages and disadvantages.

As for based on the material, the various resistors are::

- Carbon Resistor
- Metal Element Resistors
- Metal Film Resistor
- Thick Film Resistors
- Thin Film Resistors
- Wire Wound Resistors
- Semiconductor Resistor

### 4. Based on Usage

Because the use of this resistor is very wide, it would be nice if we know the type of resistor based on its application, including:

- Power Resistor
- Current Sense
- Resistor Automotive
- Resistor Safety Resistive
- Moisture Resistant Resistor

## How to Calculate Resistor Value

There are two ways to find out the resistance value of a resistor. The first is based on the color band and the second value is listed directly on the body of the resistor. The most basic thing to know the resistor color value is to remember the resistor value table.

### 1. Based on Resistor Color Table

#### a. How to Read the Bracelet Color Code Resistor Value

**b. **First Example

Here in Figure 1 there is a resistor that I provide. This resistor has 4 colored bands on the body of the resistor.

**c. **Second Example

How to read the second example resistor is:

In the two examples above are resistors with 4 color bands, but on the market there are resistors that have 5 to 6 colored bands. Well, to be clearer how to read it, you can look at the following picture

### 2. How to Read SMD Resistor Value

**a. **First Example

Examples of SMD resistors read 3,300 Ohms or 3K3 Ohms or 3.3K Ohms

**b. **Second Example

## Package Shape and Resistor Size

- SMD (Surface Mount Technology)
- Axial
- MELF (Metal Electrode Leadless Face).

SMD and MELF resistors are often used in small dual layer devices. Because of its small size and the soldering position is directly on the PCB without holes, these resistors are used in almost all digital electronic devices such as computers, smartphones, LCD TVs and others.

The size of the SMD resistor is marked with a numeric code such as 0805. The numeric number contains the length and width of a resistor.

## Resistor Application

We now understand that a resistor is an electronic component that can block an electric current and have a Symbol of Resistor.

But in electronic circuits, what exactly or when are resistors used in circuits?

This is what we must master in designing and assembling electronic circuits. By knowing the basics of this resistor application, it is hoped that you can easily understand the repair of errors that occur.

There are at least 5 uses of resistors including Current Blockers, Series Resistors, Parallel, Pull-Ups, and Pull-Downs.

### 1. Reduce Current

Let's see an example:

### 2. Series Resistor

#### a. Definition of Series Resistor

A series resistor is a resistor that is connected in series with another resistor. Either two resistors, three resistors and so on.

In addition, resistors can also be connected in parallel and a combination of the two. This is the basics of electronics.

The series resistor circuit is basically like this:

#### b. Series Resistor Function

In electronic circuits, at least the most basic function is to add a certain resistance value and voltage divider.

Adding a Specific Resistance Value

Why do we have to increase the resistance value?

Resistors have standard values in their production. Resistor manufacturers don't print resistors with that many values.

Take a look at the following pdf, which lists 168 resistor values with a tolerance of 5% commonly produced:

The Resistor Series Circuit Formula is:

_{total}= R

_{1}+ R

_{2}+ R

_{3}+ ..... + R

_{n}

_{1}= Resistor 1

_{2}= Resistor 2

_{3}= Resistor 3

_{n}= Resistor n

#### Series Resistors As Voltage Dividers

The thing to remember from this series is:

“The voltage across each resistor in series is different, while the current for each resistor is the same“.

**How could this happen?**

- Get The Rtotal

Rtotal = R1 + R2 + R3

= 3K + 2K + 5K = 10K - Get Current Flow

I = V/R

= 10V / 10K ohm

= 0.001 A = 1mA

This means that the current through R1, R2 and R3 is 1 mA. The Current remains the same in the series resistor circuit.

Itotal = IR1 = IR2 = IR3 - Get Voltage in R1

VR1 = I * R1 = 1mA * 3K

= 3V - Get Voltage in R2

VR2 = I * R2

= 1mA * 2K

= 2V - Get Voltage in R3

VR2 = I * R2

= 1mA * 5K

= 5V

#### Example of a Series Resistor

**1. First example**

If Vs, R1 and R2 are known, how to find Vout1 and Vout2?

**answer:**

First find the current I first because the current in the series resistor is the same. The formula is I = Vsource / (R1 + R2)

**2. Seconds example**

If Vs, Vout1 and Vout2 are known, how to find R1 and R2?

**Jawab:**

Since R1 and R2 are unknown, the only way is to determine their total. For example, let's say Rtotal is 2K Ohms.

**3. **Parallel Resistor

**a. **Definition of Parallel Resistor

**Parallel Resistors are**resistors that are connected in parallel to another resistor. Either two resistors, three resistors and so on. The basic circuit of parallel resistors is as follows:

**b. **Parallel Resistor Function

The function of the Parallel Resistor is to reduce a certain resistance value and to divide the current. The explanation is as follows:

#### Reducing Certain Resistance Value

Why should we reduce the resistance value? Resistors have standard values in their production. Resistor manufacturers don't print resistors with that many values. Take a look at the following pdf, which lists 168 resistor values with a tolerance of 5% commonly produced:

The Resistor Series Circuit Formula is:

_{total}= 1/R

_{1}+ 1/R

_{2}+ 1/R

_{3}+ ..... + 1/R

_{n}

#### Parallel Resistors As Current Dividers

“The voltage across each resistor in parallel is the same, while the current for each resistor is different“.

**How could this happen?**

- Get the Rtotal

Rtotal = 1/R1 + 1/R2 + 1/R3

= 967.74 Ohm

- Get the current (I1)

I1 = V / R1

= 10V / 3K

= 0.0033333333333333 A

= 3.3333333333333 mA - Get the current (I2)

I2 = V / R2

= 10V / 2K

= 0.005 A

= 5mA - Get the current (I3)

I3 = V / R3

= 10V / 5K

= 0.002 A

= 2mA - Get the Itotal

Itotal = I1 + I2 + I3

= 3.3mA + 5mA + 2mA

= 10.3333333333333 mA - Check again

R = V / I

= 10V / 10.3333333333333 mA

= 10V / 0.0103333333333333 A

= 967.7419 Ohm

### 4. Pull-Up Resistor

#### a. What are pull-up resistors used for?

- 0 = 0V - 2.5V
- 1 = 2.6V - 5V

- 0 = 0V - 2.4V
- 1 = 2.5V - 3.3V

#### b. How do pull-up resistors work?

#### c. Examples of Using Pull-Up Resistors

#### d. What is the Rated Pull-Up Resistor used?

- If Vcc is 5V, can use a 10K Ohm . resistor
- If the Vcc is 3.3V, you can use a 4.7K or 4K7 Ohm resistor

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