What Is A Current-Limiting Resistor And What Does It Do To Protect Electronic Components

I.Calculation Method OF Current Limiting Resistance

The method of calculating the current limiting resistance needs to be determined according to the specific circuit requirements. There are mainly two cases as follows
1. Calculate according to the required current
When it is necessary to control the current in the circuit does not exceed a certain value, the resistance value of the current limiting resistance can be calculated according to Ohm's law, the formula is:
R =(V-VF)/1
Where, R is the resistance value of the current limiting resistor, V is the power supply voltage, VF is the forward voltage drop of the diode and other components in the circuit, and is the current to be controlled
The calculation is based on the required power
When it is necessary to control the power of the components in the circuit does not exceed a certain value, the resistance value of the current limiting resistance can be directly calculated according to the power formula, the formula is:
R =(V^2 - VF^2)/P
Where R is the resistance value of the current-limiting resistor, V is the supply voltage, VF is the forward voltage drop of the diode and other components in the circuit and P is the power to be controlled

II.Selection Principle OF Current Limiting Resistance

III.Additional Knowledge About Current Limiting Resistors

A current limiting resistor is utilized in an electric circuit to decrease the current flowing through it.

An instance of its application is when a resistor is connected in series with an LED.

fi-simplest-circuits
To regulate the current passing through the LED, it is advisable to include a current limiting resistor in series with it.

If an excessive amount of current flows through the LED, it will quickly burn out. Conversely, if insufficient current passes through it, the LED may not light up adequately.

Determining the Resistor Value

A current limiting resistor in series with an LED
Refer to the datasheet of the component to obtain information about the LED's voltage drop and the recommended current.

In the absence of a datasheet, experimentation can be conducted.

Connect the LED and a resistor in series to a variable voltage source. Begin with 0 volts and gradually increase the voltage until the LED illuminates.

Measure the voltage across the LED and the current passing through it.

Let's assume that the LED requires 15 mA and has a voltage drop of 2 volts. You intend to power it using a 5 V power source. What value of resistor is needed?

To determine the resistor value, start by calculating the voltage drop across the resistor. Since the LED exhibits a 2 volt drop, the resistor will have a 3V drop.

Therefore, we have 3V and a desired current of 15 mA flowing through the resistor and the LED.

To find the required resistor value, apply Ohm's law.

V = R * I \Rightarrow R = \frac{V}{I}

This yields

R = \frac{V}{I} = \frac{3V}{15mA} = 200 \Omega

Hence, the current limiting resistor should have a value of 200 Ohms.

Selecting the Appropriate Resistor

Now that you know the required resistor value is 200 Ohms, you discover that there are various types of resistors available.

The key consideration is the wattage rating of the component, which indicates its power-handling capability.

Therefore, determine the power dissipated in your resistor.

To calculate this, utilize the following formula for power:

P = I*V

This equation states that power equals the current multiplied by the voltage. Thus, we obtain

P = 15 mA * 3V = 45mW

Consequently, your resistor must be capable of handling a minimum of 45 mW.

Typically, most resistors can handle 250 mW or higher, making it easy to find a suitable one.