Summary of Eletrônica - Módulo I - Eletroeletrônica - Agenda 9

Summary of Video: Eletrônica - Módulo I - Eletroeletrônica - Agenda 9

The video lecture focuses on special types of diodes beyond the common rectifier diode, emphasizing their functions, characteristics, and applications in electronic circuits, especially analog and digital systems. The primary diodes discussed are:

LED (Light Emitting Diode)
Zener Diode
Brief overview of Tunnel Diode and Schottky Diode

Detailed Breakdown:

1. Introduction

Agenda 9 covers special diodes other than rectifier diodes.
These diodes allow current in one direction and block it in the other but serve different functions.
The focus is on LEDs and Zener diodes, with brief mentions of tunnel and Schottky diodes.

2. LED (Light Emitting Diode)

Definition: A diode that emits light when current flows through it in the forward direction.
Physical Characteristics:
- Two terminals: Anode (longer terminal) and Cathode (shorter terminal, marked by a flat edge or chamfer).
- Current flows from anode to cathode to light up the LED.
Electrical Characteristics:
- Typical voltage drop: ~2 V at 20 mA current.
- Cannot be connected directly to high voltage sources (e.g., 5 V) without a Current-limiting resistor.
Circuit Considerations:
- Always use a series resistor to limit current and prevent damage.
- Calculation of series resistor (R):
  \( R = \frac{V_{source} - V_{LED}}{I_{LED}} \)
Applications:
- Indicators in calculators, measuring devices.
- Seven-segment displays (each segment is an LED).
- Displays can be common cathode or common anode types, affecting how LEDs are interconnected and controlled.
Representation:
- Symbol includes arrows indicating light emission.

3. Zener Diode

Function: Voltage regulator/stabilizer when reverse biased.
Operation:
- Must be reverse biased (positive connected to cathode, negative to anode).
- Stabilizes voltage at its Zener voltage (Vz) when supply voltage is higher than Vz.
- Cannot stabilize voltage below its Zener voltage.
Characteristics:
- Voltage remains constant (Vz) in breakdown region despite changes in current.
- Forward biased behaves like a normal diode with ~0.7 V drop.
Circuit Design:
- Requires a series resistor (Rs) to limit current:
  \( I_{max} = \frac{P_{max}}{V_z} \)
  \( R_s = \frac{V_{source} - V_z}{I_{max}} \)
Applications:
- Voltage regulation in power supplies.
- Ensures constant output voltage from rectifier circuits.
Important Notes:
- Direct polarization disables voltage regulation function.
- Must be used in reverse bias to operate as a Voltage regulator.

4. Tunnel Diode (Brief Overview)

Advantages:
- Low cost, low noise, high switching speed (nanoseconds).
- Immunity to environmental noise.
Disadvantages:
- Low power handling.
- No isolation between input and output.
- Small voltage variation at output.
Use:
- Mainly in high-speed, low-power applications.
Symbol and Operation:
- Operates between peak and valley voltages.
- Known for negative resistance region useful in oscillators and amplifiers.

5. Schottky Diode (Brief Overview)

Advantages:
- Low voltage drop.
- High switching speed.
- Operates with currents from 1 to 300 A.
Disadvantages:
- Leakage current higher than PN junction diodes.
- Maximum voltage typically limited (~100 V).
Applications:
- High-frequency circuits requiring fast switching.
Characteristic Curve:
- Starts conducting at ~0.7 V with current increasing proportionally.

6. Summary and Final Notes

LEDs and Zener diodes are the primary focus due to their frequent use in digital and analog circuits.
Tunnel and Schottky diodes are introduced for awareness but are less commonly used in the course context.
Emphasis on understanding LED operation and Zener Diode voltage regulation for future practical applications.
Reminder to always use current-limiting resistors with LEDs and Zener diodes to prevent damage.
Assessment activities will focus mainly on LEDs and Zener diodes.

Methodologies / Key Formulas:

LED Series Resistor Calculation:
\( R = \frac{V_{source} - V_{LED}}{I_{LED}} \)