Types of Diodes: A Beginners Guide

Diodes are fundamental semiconductor devices that allow current to flow in one direction while blocking it in the other. Understanding different diode types helps you select the right component for your application.

How Diodes Work

A diode is formed by joining P-type and N-type semiconductor materials, creating a P-N junction. When forward-biased (positive to P, negative to N), current flows. When reverse-biased, current is blocked (until breakdown voltage is reached).

Standard Rectifier Diodes

The most basic diode type, used to convert AC to DC.

Characteristics:

• Forward voltage drop: 0.6-1.0V (silicon)
• Current ratings: mA to hundreds of amps
• Relatively slow switching

Common Types: 1N4001-1N4007 series, 1N5400 series

Applications: Power supplies, battery chargers, AC/DC conversion.

Schottky Diodes

Use a metal-semiconductor junction for lower forward voltage and faster switching.

Characteristics:

• Forward voltage drop: 0.2-0.4V
• Very fast switching (nanoseconds)
• Higher leakage current
• Lower reverse voltage ratings

Applications: High-frequency switching, power supplies, solar panel bypass, RF detection.

Zener Diodes

Designed to operate in reverse breakdown, providing voltage regulation.

Characteristics:

• Specific breakdown voltage (2.4V to 200V+)
• Maintains constant voltage under varying current
• Used in reverse-bias mode

Applications: Voltage references, overvoltage protection, voltage regulation.

Light Emitting Diodes (LEDs)

Emit light when forward-biased through electroluminescence.

Characteristics:

• Forward voltage varies by color (1.8-3.3V)
• Require current limiting resistors
• Available in many colors and packages

Applications: Indicators, displays, lighting, optocouplers.

Photodiodes

Generate current when exposed to light.

Characteristics:

• Convert light to electrical signal
• Can operate in photovoltaic or photoconductive mode
• Fast response times

Applications: Light sensors, optical communication, solar cells.

TVS (Transient Voltage Suppressor) Diodes

Protect circuits from voltage spikes and transients.

Characteristics:

• Very fast clamping response
• High power handling during transients
• Unidirectional and bidirectional versions

Applications: ESD protection, surge protection, automotive electronics.

Varactor (Varicap) Diodes

Capacitance varies with applied reverse voltage.

Characteristics:

• Voltage-variable capacitance
• Used in tuning circuits
• Operate in reverse bias

Applications: Radio tuning, voltage-controlled oscillators, phase-locked loops.

Tunnel Diodes

Exhibit negative resistance due to quantum tunneling.

Characteristics:

• Very fast switching (picoseconds)
• Negative resistance region
• Low voltage operation

Applications: High-frequency oscillators, microwave applications.

Comparison Table

Diode Type	Forward Voltage	Primary Use
Silicon Rectifier	0.6-1.0V	AC/DC conversion
Schottky	0.2-0.4V	Fast switching
Zener	N/A (reverse)	Voltage regulation
LED	1.8-3.3V	Light emission
Photodiode	N/A	Light detection
TVS	Clamping voltage	Protection

Diode Selection Guide

For Power Supplies: Rectifier diodes (1N4007) or Schottky for efficiency.

For Voltage Reference: Zener diodes at required voltage.

For Protection: TVS diodes rated for your application.

For Indicators: LEDs with appropriate color and brightness.

For RF/Tuning: Varactor diodes or tunnel diodes.

Common Diode Packages

• Through-hole: DO-41, DO-201, TO-220
• SMD: SOD-123, SMA, SMB, SMC
• LED: 3mm, 5mm, SMD 0603/0805/1206

Conclusion

Different diode types serve specific purposes. Rectifier diodes convert AC to DC, Zener diodes regulate voltage, LEDs emit light, and Schottky diodes enable fast switching. Select based on your application's voltage, current, speed, and function requirements.