askvity

How do LED Resistors Work?

Published in Electronics 3 mins read

LED resistors, also known as ballast resistors, work by limiting the amount of current that flows through a Light Emitting Diode (LED). This prevents the LED from burning out due to excessive current.

Here's a breakdown of how it works:

  • LEDs are Current-Driven Devices: Unlike incandescent bulbs that are primarily voltage-driven, LEDs are current-driven. This means their brightness is directly related to the current flowing through them. Exceeding their maximum current rating leads to immediate damage and failure.

  • The Resistor's Role: Current Limiting: The resistor is placed in series with the LED and the power source (e.g., a battery or power supply). Its primary function is to introduce resistance into the circuit, which limits the current to a safe and appropriate level for the LED.

  • Ohm's Law in Action: The value of the resistor is calculated using Ohm's Law (V = IR, where V is voltage, I is current, and R is resistance). By knowing the voltage of the power source, the forward voltage of the LED (the voltage it drops when conducting), and the desired current for the LED, you can calculate the required resistance.

    • Formula: R = (Vs - Vf) / I
      • Vs = Source Voltage (e.g., 5V)
      • Vf = LED Forward Voltage (e.g., 2V, check the LED's datasheet)
      • I = Desired LED Current (e.g., 20mA or 0.02A, check the LED's datasheet)

  • Example: Let's say you have a 5V power supply and an LED with a forward voltage of 2V and a desired current of 20mA (0.02A).

    • R = (5V - 2V) / 0.02A
    • R = 3V / 0.02A
    • R = 150 Ohms

    Therefore, you would need a 150-ohm resistor to protect the LED. In practice, you might choose the closest readily available value, such as 150 ohms or 160 ohms.

  • Preventing LED Burnout: Without a resistor, the LED would draw excessive current, leading to overheating and rapid degradation or immediate failure. The resistor ensures the LED operates within its safe operating parameters.

In summary, LED resistors act as current limiters, preventing excessive current flow and protecting the LED from damage. By carefully calculating the required resistance value using Ohm's Law, you can ensure your LED operates safely and reliably.

Related Articles