Dimensionamento della Resistenza di Caduta per un LED

Summary

This educational video explains how to properly dimension the current-limiting resistor for an LED. It covers the basic properties of LEDs, including their voltage drops based on color, and the importance of selecting the correct resistor to prevent LED damage. The video demonstrates how to calculate the resistor value using Ohm’s Law and provides a practical example with a red LED. Key concepts such as Kirchhoff's Voltage Law and the role of resistors in regulating current are emphasized, ensuring safe and efficient LED operation.

Takeaways

• 😀 LEDs (Light Emitting Diodes) are electronic devices that emit light when electric current passes through them.
• 😀 The LED has two terminals: the anode (positive) and the cathode (negative). The LED emits light when current flows from the anode to the cathode.
• 😀 To identify the polarity of common LEDs, the anode has a longer lead than the cathode.
• 😀 The voltage required for a typical LED to function varies by color: 1.8V for red, 1.9V for yellow, 2.0V for orange, 2.0V for green, 3.0V for white, and 3.5V for blue.
• 😀 The current drawn by a common LED is typically around 15-20mA (milliamps). It is crucial to respect these values to prevent damaging the LED.
• 😀 To protect the LED, a current-limiting resistor is often used in series to prevent excessive current flow, ensuring the LED operates safely.
• 😀 The resistor is calculated based on the difference between the supply voltage and the LED's forward voltage. The formula is: R = (Vcc - V_LED) / I.
• 😀 Kirchoff's law applies to this circuit, ensuring that the sum of potential drops across the resistor and the LED equals the supply voltage.
• 😀 In practical terms, if the supply voltage exceeds the LED's forward voltage, a resistor is used to drop the excess voltage, maintaining proper current flow.
• 😀 An example calculation shows how to size the resistor for a red LED with a 5V supply voltage: the required resistor value is approximately 213 ohms, which can be approximated to 220 ohms for available resistor values.

Q & A

What is an LED?

An LED (Light Emitting Diode) is an electronic component that emits light when an electric current flows through it. It is made from semiconductor materials, typically silicon, which release photons (light) when the current passes through them.

What are the two terminals of an LED and what are their functions?

The two terminals of an LED are the anode (positive) and the cathode (negative). The current flows from the anode to the cathode, and the LED emits light when the current flows in this direction.

What happens if current flows in the opposite direction in an LED?

If current flows in the opposite direction (from the cathode to the anode), the LED will not emit light because the diode does not conduct in reverse polarity.

Why is a resistor needed in series with an LED?

A resistor is needed in series with the LED to limit the current flowing through it. Without the resistor, excessive current could damage the LED, causing it to burn out.

What are the typical forward voltage values for different colored LEDs?

The typical forward voltage values for LEDs based on their color are: Red LED - 1.8V, Yellow LED - 1.9V, Green LED - 2.0V, White LED - 3.0V, Blue LED - 3.5V.

What is Kirchhoff's Voltage Law (KVL) and how does it apply to LED circuits?

Kirchhoff's Voltage Law states that the sum of the voltage drops in a series circuit equals the total supplied voltage. In an LED circuit, the supply voltage is divided between the LED and the series resistor, so the voltage drop across the resistor plus the voltage drop across the LED must equal the total supply voltage.

How does Ohm’s Law help in dimensioning the resistor for an LED?

Ohm's Law, which states that resistance equals voltage divided by current (R = V/I), helps determine the value of the resistor needed to ensure the correct current flows through the LED, thereby protecting it from excessive current.

In the example provided, how is the resistance for a red LED calculated?

In the example, the resistance is calculated by first determining the voltage drop across the resistor (V_R = V_cc - V_LED = 5V - 1.8V = 3.2V) and then applying Ohm's Law (R = V_R / I). With a current of 15mA (0.015A), the resistance comes out to 213 ohms, which can be rounded to 220 ohms.

What is the role of the resistor in ensuring the LED functions safely?

The resistor ensures that the voltage drop across the LED is controlled, preventing excessive current from flowing through it. This protects the LED from burning out due to overcurrent.

What should be considered when choosing a resistor value for an LED?

When choosing a resistor value, the voltage supply (V_cc), the LED's forward voltage (V_LED), and the desired current (I) must be considered. The resistor value is calculated to ensure that the correct voltage is dropped across the LED and the current is limited to a safe level.