Different Types of Diodes and How They Work

Different Types of Diodes and How They Work

ElectronicPublished on November 10, 2024

Zener, Schottky, Rectifiers, Thyristor, Silicon and TRIACs

A diode is a two-terminal electrical device. Electrical diodes are made from semiconductors, mostly silicon but sometimes germanium. There are different types of diodes, but the ones discussed here are Zener, Rectifier, Schottky, Transient Voltage Suppressor, Thyristor, Silicon Controlled Rectifier, and TRIAC. Whether you want to compare zener diodes vs Schottky diodes or wondering, ‘How is a zener diode different from an ordinary diode,’ understanding each type and how they work is essential for choosing the right one for your electronic circuits.

Zener Diodes

Zener Diodes are silicon semiconductor devices that permit current to flow in either a forward (anode to cathode) or reverse direction. The highly doped p-n junction allows the device to conduct in the reverse direction when the breakdown voltage is reached. Unlike the other different types of diodes, the Zener reverse breakdown is due to electron quantum tunneling caused by a high-strength electric field.

When in forward-bias mode, Zener diodes operate like a standard diode. When connected in the reverse mode, there may be a small leakage current flowing. As the reverse voltage increases closer to the breakdown voltage, a current begins to flow through the diode. The series resistor determines the current maximum. Once the maximum is reached, the current stabilizes and remains constant over a wide range of applied voltages.

Rectifiers

Rectifiers are two-lead semiconductors that only allow current to pass in one direction. A rectifier is composed of one or more different types of diodes that convert alternating current (AC) to direct current (DC).

  • Half-Wave Rectifier: Only the positive half cycle becomes visible across the load; the negative cycle is blocked or lost.
  • Full-Wave Rectifier: Converts the full AC input signal (positive and negative half cycles) to a pulsating DC signal.

Applications include DC power supplies, radio signals or detectors, HVDC power transmission, and various household appliances such as laptops, video game systems, and televisions.

Schottky Diodes

Schottky Diodes are formed by the junction of a silicon semiconductor (n-type) with a metal electrode. Known for fast switching and low forward voltage drop (typically 0.15–0.45V), Schottky diodes have no depletion layer and are unipolar devices.

In comparing Zener diodes vs Schottky diodes: Zener diodes are ideal for voltage regulation, while Schottky diodes excel in fast-switching and power-efficient applications.

Transient Voltage Suppressor (TVS)

TVS diodes protect electronics from voltage spikes or surges by shunting excess current when the voltage exceeds breakdown levels. They act as clamping devices and are available in:

  • Unidirectional: Allows current in one polarity (above or below ground).
  • Bidirectional: Suitable for AC signals or bipolar DC signals.

Applications include data and signal line protection, microprocessors, AC power lines, telecommunications, and low-energy diversion circuits.

Thyristor Diodes

Thyristor diodes are three-terminal devices (gate, anode, and cathode). A small gate current triggers a larger current flow between anode and cathode. Once triggered, the current continues even after the gate signal is removed, until reset.

Variants of thyristors include:

  • Silicon Controlled Rectifier (SCR)
  • TRIACs

Silicon Controlled Rectifiers (SCRs)

SCRs are four-layer (P-N-P-N) solid-state devices with three terminals: anode, cathode, and gate. Made from silicon, SCRs are unidirectional and used in high-power applications where AC needs to be converted to DC.

SCR types include:

  • Standard SCR
  • Gate Turn-Off SCR (GTO)
  • Light-Activated SCR (LASCR)
  • Asymmetrical SCR (ASCR)

Common uses include motor control, lighting systems, induction heating, and relay switching.

TRIACs

TRIACs are also three-terminal thyristor family devices. The terminals are:

  • Gate: Acts as the trigger.
  • Anode 1 (Main Terminal 1)
  • Anode 2 (Main Terminal 2): Gate current must originate from this side.

TRIACs act like two SCRs in parallel but reversed. They conduct in both directions once triggered and are built from a single semiconductor substrate.

Applications include AC power control, motor control, dimmer switches, and low-power switching circuits.