In electronic circuits, diodes are among the most fundamental, common, and indispensable components. With their unidirectional conductivity, unique PN-junction physics, and diverse material structures, their functionality has expanded far beyond simple rectification. Today, diodes can regulate voltage, tune frequencies, limit current, detect signals, emit light, and absorb surges—covering almost every low-power and high-power application scenario.Many distributors offer a wide range of electronic components to cater to diverse application needs, like BSS84
This article provides a systematic breakdown of nine commonly used diodes, covering their operating states, structural principles, and typical applications. It aims to help beginners build a solid foundation and allow engineers to efficiently review key technical concepts.
The Two Operating States of a Diode
A diode consists of a PN junction, and its behavior depends on the applied bias. Understanding biasing is the foundation for mastering the functions of different diode types.
Forward Bias: The Fundamental Conductive State
When a forward voltage is applied, the potential barrier is overcome and carriers cross the PN junction, allowing current to flow. In this state, the diode exhibits its characteristic one-way conduction, which is used in rectification, switching, and light emission. Rectifier diodes, Schottky diodes, fast-recovery diodes, and LEDs all operate under forward bias.
Reverse Bias: Using High Impedance or Breakdown Characteristics
Under reverse bias, the depletion region widens and the diode exhibits a very high impedance, effectively cutting off current. Some special diodes, however, operate specifically in this state: Zener diodes use controlled breakdown for voltage regulation, TVS diodes absorb surge energy through avalanche breakdown, and photodiodes achieve high sensitivity under reverse bias.
Master the Bias, Master the Application
Forward bias is associated with conduction, rectification, and light emission, while reverse bias is used for regulation, protection, and light sensing. Once you understand this, identifying the intended use of any diode becomes straightforward—this is the core of electronic design.
Nine Common Diodes: Principles & Applications
Below are concise, professional explanations for each diode type (1–2 paragraphs each).
Rectifier Diode
Rectifier diodes, typically made from silicon, exhibit a forward voltage drop of about 0.6–0.7 V and very low reverse leakage. They are essential for converting AC to DC and form the backbone of power-conversion circuits.
They are commonly used in bridge rectifiers, power adapters, clamping circuits, and freewheeling paths for inductive loads—fundamental components in almost all power electronics.
Photodiode
A photodiode generates electron-hole pairs when exposed to light, producing photocurrent even without external bias. Under reverse bias, it offers faster response and better linearity.
It is widely used in light sensors, optocouplers, IR receivers, automatic brightness systems, and optical communication, making it indispensable in optical-detection applications.
Varactor Diode
A varactor diode changes its junction capacitance with the applied reverse voltage, effectively functioning as a voltage-controlled capacitor. As the reverse voltage increases, the depletion layer widens and the capacitance decreases, enabling precise tuning.
It is crucial in RF tuning, VCOs, PLLs, and antenna-matching networks, forming an essential part of modern frequency-control systems.
LED (Light-Emitting Diode)
An LED emits light when electrons and holes recombine under forward bias. Different semiconductor materials produce different wavelengths, enabling a wide variety of colors. LEDs offer high efficiency, long life, and small size.
They are used in indicators, lighting, backlight modules, display panels, traffic signals, and optical communication—core technologies in modern optoelectronics.
Current Regulator Diode
A current regulator diode maintains a nearly constant current over a specific voltage range through its internal regulating structure.
It is commonly used in LED drivers, current-source circuits, and protection circuits to prevent current fluctuations that could cause brightness variations or device damage.
Fast Recovery Diode (FRD)
Fast-recovery diodes use a PIN structure to minimize copyright storage, enabling much faster reverse recovery than standard rectifier diodes. Their recovery time can reach the tens-of-nanoseconds level.
They are essential in switching power supplies, inverters, motor-drive circuits, and any application requiring high-speed rectification.
Schottky Diode
A Schottky diode uses a metal-semiconductor junction, giving it an extremely low forward drop (0.2–0.4 V) and very fast switching with negligible reverse recovery.
It performs exceptionally well in high-frequency, low-voltage, and high-current designs and is widely used in DC-DC converters, CPU VRMs, battery protection, and solar-power systems.
TVS Diode (Transient Voltage Suppression Diode)
Under normal conditions, a TVS diode remains in a high-impedance state. When a surge, ESD, or lightning strike occurs, it rapidly enters avalanche breakdown and clamps the voltage to protect downstream components.
It is standard in communication ports, power lines, USB/HDMI, industrial control systems, and automotive electronics—an essential component in EMC protection.
Zener Diode
A Zener diode maintains a stable breakdown voltage under reverse bias, providing a nearly constant output voltage. It is widely used as a reference voltage source and in voltage-regulation circuits.
Beyond regulation, it is applied in over-voltage protection, clamping, and reference-generation circuits, making it a staple in analog-design applications.