How to calculate the power dissipation of the resistor

Resistor - it is one of the main radioactive elements, which has a number of important parameters. Today we will focus on power dissipation, because this parameter is responsible for the safe and stable operation of each resistor.

What is power, and power dissipation

First, let's refresh memory, such that the DC power should recall for this very simple formula:

From the above, it is the expression it is clear that power depends on variables such as the voltage and current.

If we consider the real circuit, in the course of its work through the resistors located in the circuit, the current will flow a certain quantities, and since they (resistors) have a certain resistance, under the effect of the current on the resistor will generate heat. It is warm and have the power that is dissipated in the resistor.

So, if we set the resistor circuit with less power dissipation than is required, the resistor will overheat. This will lead to its rapid failure.

Therefore it is very important to observe the following rule: a replaceable resistor must meet the power dissipation smoked up resistor or this parameter must be greater than, but not less.

All manufactured resistors correspond to the standard range, which looks like this:

1. 0,125 W, 0.25 W, 0.5 W, 1 W, 2 W, and more

Usually, it observes the following rule: the greater size in the resistor, the greater the power dissipation it is designed.

Let's look at an example. Let's say we need to set resistor 100 OhmAnd current will flow through it 0.1 Amp.

In order to calculate the required power dissipation of our resistor we use the following formula:

So, it turns out that in this example, we will need a resistor with a power dissipation of one watt.

Note. For stable and reliable operation should necessarily take a resistor with a margin for power dissipation. This will ensure the desired reliability and durability of the circuit.

But what if you do not know what the current will flow through the resistor. To calculate the required power dissipation, you can use a different formula:

All of the above is true for the case when you need to replace a single resistor, but often enough to schemes possible to find the so-called composite resistor (several resistors connected in parallel, sequentially, or mixed).

So, let's look a serial connection.

In a series connection through resistors the same current will flow. And it turns out if we need to find a replacement resistor 100 ohms through which the current flows in 0.1 A and it is designed for power dissipation in 1 WIt can be replaced by two serially connected resistors on 80 Ohm and 20 Ohm.

If we use the above given formulas and calculate on how much power each resistor, we get the following result it should be calculated:

R1 - 20 ohms (0.2 W)

R2 - 80 ohm (0.8 W)

Now look at the table with standard and next choose the next largest denomination. It turns out that in this case suitable resistors with dissipation R1 - 0.5 W, R2 - 1 watt.

In the parallel connection, consider that a resistor with a lower resistance to flow a larger current.

Mixed compound, in practice, hardly used.

How to do without payment

In principle, one can dispense with formulas and calculations, just follow the following rule:

The power of each resistor which is included in the compiled circuit (parallel or serial) must be equal to the replaced power dissipation resistor. Simply put, if you want to replace the resistor 1W composite resistors, each of them should be not less than 1 watt of power dissipation.

That's all I wanted to tell you about calculating the power dissipation of the resistor and the rules of its replacement. If the article was useful to you, you will appreciate her huskies and thank you for your attention!