Calculation of Parallel Resistors

Parallel Resistors Explained

Calculation of parallel resistors for basic electronic circuits – Parallel Resistors are resistors connected in parallel to other resistors. Two resistors, three resistors, and so on.

Well, previously we have studied the Explanation and function of series resistors. Now we will learn about Parallel Resistors.The basic circuit of a parallel resistor is as follows:

Parallel Resistor Functions are:

  • Decrease a specific resistance value.
  • Current Divider

A. Reducing Specific Resistance Values

Why should we reduce the resistance value?

Resistors have a standard value in their production. Resistor manufacturing companies, do not print resistors with many values.

Consider the following pdf, which contains 168 lists of resistor values with a tolerance of 5% that are commonly produced:

For example, a resistor with a value of 2819 ohms or 2.8K Ohm is needed.

However, only 2.7K and 3K Ohm resistors are available on the market.

Then, how can we make a resistor with a value of 2.8K ohms?

The trick is to make a parallel resistor using a resistor of 3.6K ohms and 13K ohms = 2.8K ohms.

The formula for parallel resistor circuit is:

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

R1 = Resistor 1
R2 = Resistor 2
R3 = Resistor 3
Rn = Resistor n

*n = next value

B. Parallel Resistor As Current Divider

Things to remember from this series are:

“The voltage of each resistor is the same, while the current of each resistor is different“.

By their nature, the resistor will cause a voltage drop or voltage drop across the series resistor.

Notice in the image below, there are three resistors connected in series.

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

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

When measuring the respective currents in the resistor, using a multimeter. The results are 3V, 2V and 5V.

  1. Find Rtotal
    1/ Rtotal = 1/R1 + 1/R2 + 1/R3
    1/ Rtotal = 1/3k + 1/2k + 1/5k
    1/ Rtotal = 0.000333333333333 + 0.0005 + 0.0002
    Rtotal = 1 / 0.00103333333
    = 967.7419 Ohm

  2. Find Current (I1)
    I1 = V / R1
    = 10V / 3K
    = 0.0033333333333333 A
    = 3.3333333333333 mA

  3. Find Current (I2)
    I2 = V / R2
    = 10V / 2K
    = 0.005 A
    = 5mA

  4. Find Current (I3)
    I3 = V / R3
    = 10 / 5K
    = 0.002 A
    = 2mA

  5. Find Total Current (Itotal)
    Itotal = I1 + I2 + I3
    = 3.3mA + 5mA + 2mA
    = 10.3333333333333 mA

  6. Check it
    R = V / I
    = 10V / 10.3333333333333 mA
    = 10V / 0.0103333333333333 A
    = 967.7419 Ohm

are you understand right now?

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