Diode vs. Thyristor: Key Differences Explained

Diodes and thyristors are semiconductor devices that share common foundational characteristics. Both devices are built upon P-N junctions, allowing them to control the flow of electric current. They operate as rectifiers, permitting current to flow in one direction while blocking it in the opposite direction. Furthermore, diodes and thyristors are essential components in electronic circuits, each playing a role in controlling and regulating electrical signals. However, a notable distinction is that while diodes are passive components with a straightforward one-way current flow, thyristors, with an additional control terminal (gate), offer active control over the conduction of current, making them suitable for applications requiring controlled power rectification.

Diode

A diode is a semiconductor device that allows current to flow in one direction only. It has two terminals viz. an anode and a cathode; separated by a P-N junction. The P-N junction is formed by combining a P-type semiconductor (which has an excess of positive charge carriers or “holes”) with an N-type semiconductor (which has an excess of negative charge carriers or electrons). The diode symbol is shown in the figure-1.

The primary function of a diode is rectification, converting alternating current (AC) into direct current (DC) by permitting current flow in one direction while blocking it in the opposite direction. Diodes have various applications, including rectifiers in power supplies, signal demodulation in communication systems, and protection against reverse voltage in electronic circuits. There are several types of diodes, each designed for specific applications. The common types are rectifier diodes, zener diodes, LEDs, Schottky diodes, varactor diodes, tunnel diodes, photo-diodes etc.

Thyristor

The term “thyristor” is often used as a generic name for a family of semiconductor devices that includes various types of controlled rectifiers. SCR is a specific type of thyristor that acts as a controlled rectifier. In many contexts, the terms “thyristor” and “SCR” are used interchangeably. The other thyristors designed for specific applications include triac, diac, GTO (Gate Turn Off Thyristor), IGBT (Insulated Gate Bipolar Transistor) and MCT (MOS-Controlled Thyristor).

SCR is a four-layer, three-terminal device that acts as a controllable switch for high-power applications. The three terminals are anode (A), cathode (K), and gate (G). The SCR is used in electronic circuits where controlled power rectification is required. The figure-2 depicts SCR symbol and its cross-section view. The operation of an SCR involves turning it on and off using a control signal applied to the gate terminal. The SCR remains in the off-state until a triggering voltage is applied to the gate. The key phases of SCR operation are forward bias (Off-state), Triggering (On-state), Conduction (On-state) and reverse bias (Off-State).

Difference between Diode and Thyristor

They serve different purposes and have distinct characteristics. Here are the key differences between diodes and thyristors.

Conclusion

In summary, while both diodes and thyristors are semiconductor devices, diodes are passive devices allowing current flow in one direction, whereas thyristors are active devices that can be controlled to allow or block current flow in a controlled manner using gate terminal.