Darlington Transistor vs MOSFET | Understanding the Key Differences

Transistors are essential parts of electrical circuits because they act as switches and amplifiers. Darlington transistors and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) are two common types of transistors to choose from. 

To better grasp when and how to employ Darlington transistors and MOSFETs, we will examine their properties, applications, and essential formulae in this article.

Darlington Transistor

The Darlington configuration, also known as a Darlington pair, is a circuit consisting of two bipolar transistors connected by an emitter, amplifying the current. Its current gain is significantly larger than each transistor alone and is often packaged like a transistor. Created by Sidney Darlington in 1953.

Figure 01: Darlington Transistor

Characteristics of Darlington Transistors

A bipolar junction transistor (BJT) design called a Darlington transistor consists of two transistors wired in series. This configuration has a very high current gain and input impedance, which makes it useful for devices like power amplifiers and motor control circuits that need a lot of current amplification. 

Darlington transistors are less effective in some high-frequency applications due to their larger voltage drop and slower switching speed when compared to other transistors, such as MOSFETs.

MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)

MOSFET, invented by Julius Edgar Lilienfeld in 1925, is a field-effect transistor fabricated by controlled silicon oxidation. Its insulated gate determines conductivity, used for amplifying or switching electronic signals. Common in digital circuits, MOSFETs can be made with p-type or n-type semiconductors for low power consumption.

Figure 02: MOSFET

Characteristics of MOSFETs

The ability of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), a voltage-controlled semiconductor device, to control the flow of current between its source and drain terminals based on the voltage supplied to its gate terminal (VGS), distinguishes it from other semiconductor devices. 

It is often used in amplification, switching, and digital logic applications in electronics because it functions well with minimal power dissipation, enables quick switching speeds, and is available in a range of voltage ranges.

Key Differences between Darlington Transistor & MOSFET

The Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) and the Darlington Transistor are two types of semiconductor devices that are often employed in electronic circuits for switching and amplification. Let’s examine the main distinctions between them as they have different qualities and uses:

Basic Operation

Following is a basic explanation of how a MOSFET and a Darlington transistor operate.

Darlington Transistor:

• A Darlington transistor is a combination of two bipolar junction transistors (BJTs) connected in such a way that the output of the first transistor drives the base of the second transistor.
• It is a current-controlled device, and its operation depends on the flow of current through its base terminals.

MOSFET:

• A MOSFET is a voltage-controlled device that operates based on the voltage applied to its gate terminal.
• It uses an electric field to control the flow of current between its source and drain terminals.

Voltage vs. Current Control

Below is an explanation of the differences in the “Voltage vs. Current Control” relation between a MOSFET and a Darlington transistor. 

Darlington Transistor:

• Controlled by current. The input signal controls the current flowing into the base of the first transistor, which in turn controls the current through the collector of the second transistor.
• Typically used in applications where high current amplification is required, such as in power amplifiers.

 MOSFET:

• Controlled by voltage. The voltage applied to the gate terminal determines the current flow between the source and drain terminals.
• Ideal for switching applications and for controlling high-frequency signals in digital circuits.

Power Dissipation

Electronic components used for switching and signal amplification include Darlington transistors and MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors). When it comes to power loss, they exhibit specific traits:

Darlington Transistor:

• Generally, Darlington transistors have a higher power dissipation compared to MOSFETs because they have a voltage drop (VCEsat) across their collector-emitter terminals when conducting.

MOSFET:

• MOSFETs have very low on-resistance (RDS(on)), resulting in minimal power dissipation when they are fully turned on. This makes them more efficient for high-current applications.

Voltage Rating

Darlington transistors and MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors) differ from one another in a number of areas, including their voltage ratings:

Darlington Transistor:

• Darlington transistors are available with voltage ratings suitable for various applications. However, they are typically used in low to medium-voltage applications.

MOSFET:

• MOSFETs are available in a wide range of voltage ratings, from low-voltage logic-level MOSFETs to high-voltage power MOSFETs, making them suitable for a broad spectrum of applications, including power electronics.

Switching Speed

Darlington transistors and MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors) vary from one another in a number of respects, including switching speeds:

Darlington Transistor:

• Typically slower switching speed compared to MOSFETs due to the inherent characteristics of bipolar transistors.

MOSFET:

• MOSFETs can switch on and off very quickly, making them ideal for high-frequency and high-speed switching applications.

Frequently Asked Questions and Answers – (FAQs)

When should I use a Darlington transistor?

When you require high current amplification, such as in power amplifiers or motor control circuits, use Darlington transistors.

When should I choose a MOSFET over a Darlington transistor?

If low power dissipation is crucial, as it is in digital circuits or power electronics, use MOSFETs for voltage-controlled switching applications, high-speed switching, or other switching scenarios.

Can Darlington transistors and MOSFETs be used interchangeably?

No, never. The decision is based on the particular needs of your application; each has advantages and disadvantages of its own.

To Conclude

In conclusion, the precise needs of the application determine whether a MOSFET or a Darlington transistor should be used. MOSFETs outperform Darlington transistors in voltage-controlled switching applications with excellent efficiency and speed, although Darlington transistors are frequently chosen for their current amplification capabilities.