Diodes and LEDs

What is a Diode?

A diode allows current to flow in only one direction. It has two terminals:

• Anode (+): Positive side
• Cathode (-): Negative side (marked with a stripe)

Diode Symbol

---|>|---  (Anode → Cathode)

The triangle shows current flow direction.

Real Diodes and LEDs

Here's what LEDs look like:

Red, green, blue, and yellow LEDs glowing - each color has different forward voltage

Types of Diodes

rectifier Diode

• General purpose
• Common: 1N4001-1N4007

Zener Diode

• Allows reverse current at specific voltage
• Used for voltage regulation

Schottky Diode

• Low forward voltage drop
• Fast switching

Light Emitting Diode (LED)

• Emits light when current flows
• Forward voltage: 2-3V

LED Polarity

Long leg = Anode (+)
Short leg = Cathode (-)
Flat side = Cathode (-)

LED Circuit

# Connect LED to 9V battery
battery_voltage = 9
led_voltage = 2  # typical LED forward voltage
led_current = 0.02  # 20mA
resistor_value = (battery_voltage - led_voltage) / led_current
R = (9 - 2) / 0.02 = 350Ω

Using LEDs Safely

1. Always use a resistor - prevents burnout 2. Check polarity - LED only works one way 3. Current limiting - keep under 20mA typically

Summary

• Diodes allow current one direction only
• LEDs emit light when forward biased
• Always use a current-limiting resistor with LEDs

Next Lesson

In the next lesson, you'll learn about series and parallel circuit connections.