# 5 Resistor Application In Electronics Circuit

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## Resistor Application

Where is Resistor Application In Electronics Circuit? 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

Well, this is what most people know. Resistors are often used in circuits that require current resistance, such as turning on an LED.

The LED will work if it is supplied with sufficient current. Bright or not an LED depends on how much or a little current is applied to it. However, too much current applied to the LED will cause the LED to be damaged and burn out. Here it is important that we use resistors.

Let’s see an example:

Based on the dataseed of an LED, the current that makes the LED glow is 20 mA with a voltage of 2.2V.

In the circuit, the available source voltage is 5V. If the source voltage is given directly to the LED, it is certain that the LED will be damaged because the voltage limit that the LED can accept is 2.2V.

### 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.

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.

For example in our circuit design, we need a resistor with a value of 12.5K ohms.

However, in the market we get resistors with a value range of 12K ohms, 13K ohms.

How can we make a resistor with a value of 12.5K ohms?

The trick is to add a 12K ohm + 500 ohm resistor = 12.5K ohm.

The Resistor Series Circuit Formula is:

Rtotal = R1 + R2 + R3 + ….. + Rn

R1 = Resistor 1

R2 = Resistor 2

R3 = Resistor 3

Rn = Resistor n

*n = next value

#### 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“.

By their nature, the resistor will create a voltage drop or voltage drop across the series resistor. Notice in the picture below, there are three resistors connected in series.

The applied voltage at points A and B is 10V. Each resistor has a resistance value of 3K, 2K, and 5K Ohms connected in series.

When measuring each voltage on the resistor using a multimeter, the results are 3V, 2V and 5V.

How could this happen?

Explanation:

1. Get The Rtotal

Rtotal = R1 + R2 + R3
= 3K + 2K + 5K = 10K
2. 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
3. Get Voltage in R1

VR1 =  I * R1 = 1mA * 3K
= 3V
4. Get Voltage in R2

VR2 = I * R2
= 1mA * 2K
= 2V
5. Get Voltage in  R3

VR2 = I * R2
= 1mA * 5K
= 5V

#### Example of a Series Resistor

Here is an example and solution to a resistor voltage divider problem with two resistors in series. This formula is the basic formula of Ohm’s law.

1. First example

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

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

Second look for Vout1. The formula is Vout1 = I.R1

Third, look for Vout2. The formula is Vout2 = I.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.

First find the current I first. I = Vsource / 2K

Second find the resistance R1 the formula is R1 = (Vsource – Vout1) / I

Third find the resistance R2 the formula is R2 = (Vsource – Vout2) / I

### 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.

For example in our circuit design, we need a resistor with a value of 2819 ohms or the equivalent of 2.8K Ohms. However, on the market only 2.7K and 3K Ohm resistance resistors can be found.

Then, how can we make a resistor with a value of 2.8K ohms? The trick is to make a parallel resistor using a 3.6K ohm resistor and 13K ohm = 2.8K ohm.

The Resistor Series Circuit Formula is:

Rtotal = 1/R1 + 1/R2 + 1/R3 + ….. + 1/Rn

#### Parallel Resistors As Current Dividers

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

Notice in the picture below, there are three resistors connected in parallel.

The applied voltage at points A and B is 10V.

Each resistor has a resistance value of 3K, 2K, and 5K Ohms connected in parallel.

How could this happen?

Explanation:

1. Get the Rtotal

Rtotal = 1/R1 + 1/R2 + 1/R3
= 967.74 Ohm

2. Get the current (I1)

I1 =  V / R1
= 10V / 3K
= 0.0033333333333333 A
= 3.3333333333333 mA
3. Get the current (I2)

I2 = V / R2
= 10V / 2K
=  0.005 A
= 5mA
4. Get the current (I3)

I3 = V /  R3
= 10V /  5K
= 0.002 A
= 2mA
5. Get the Itotal

Itotal  = I1 + I2 +  I3
= 3.3mA + 5mA + 2mA
= 10.3333333333333 mA

6. Check again

R = V / I
= 10V / 10.3333333333333 mA
= 10V / 0.0103333333333333 A
= 967.7419 Ohm

### 4. Pull-Up Resistor Application

Pull-Up circuit is a resistor circuit that is used to make the voltage float or close to the source voltage.

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

If we play with digital electronic circuits, we will be dealing with two conditions 0 or 1.

This Digital Pin accepts digital logic input only, LOW (0) or HIGH (1).

In voltage, logic 0 is 0V and logic 1 is 5V.

However, if we want to know in more detail, actually logic 0 has a range of values, namely:

If Vsource 5V:

• 0 =    0V – 2.5V
• 1 = 2.6V – 5V

If Vsource is 3.3V:

• 0 =    0V – 2.4V
• 1 = 2.5V – 3.3V

The basic circuit of a pull-up resistor is as follows (left):

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

Notice in the picture above (left), when the button is not pressed, the Pin_Digital voltage will be in the 5V position, but when the button is pressed the voltage will change to 0V.

When the button is pressed, the resistor will become a resistance which will keep VCC and GND from short circuiting.

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

Let’s take the example of one of the uses of pull-up resistors is the reset button on the minimum microcontroller system.

On the microcontroller, a button will reset the microcontroller if the reset pin of the microcontroller is given a logic 0 or 0V (remember the voltage range above).

When the button is released (no longer at logic 0), the microcontroller will work by reading program starts from scratch.

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

This is a question that is often asked by new microcontroller users. The value of this pull-up resistor will be different according to the source voltage that drives the microcontroller.

• 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

### 5. Pull-Down Resistor Application

The difference between Pull-Down and Pull-Up resistors is only in their placement.

If Pull-Up, then the resistor is located on the “top” connected to VCC.

If Pull-Down, then the resistor is located on the “bring” connected to Ground.

For how it works is the same. If the button is pressed, then the output voltage is 5V, if not pressed the voltage is 0V.

The value of the Pull-Down resistor is the same as the Pull-Up.

Hopefully this Resistor Application article is useful.