MOSFETs

What Are MOSFETs?

MOSFETs, also known as MOSFET transistors, stands for ’Metal Oxide Semiconductor Field-Effect Transistors’. MOSFETs are transistor devices which are controlled by a capacitor. The "Field-Effect" means that they are controlled by voltage. The aim of a MOSFET is to control the flow of the current passing through from the source to the drain terminals. It acts very similarly to a switch and is used for switching or amplifying electronic signals.

MOSFETs are also integral components in a variety of power applications. They range from low-power MOSFETs, which are ideal for small-scale, energy-efficient devices, to high-voltage options designed to handle robust and high-demand applications requiring significant and swift switch mode power supply. This versatility makes MOSFETs essential in both consumer electronics and industrial systems.

Also, these semiconductor devices are ICs (integrated circuits) which are mounted onto PCBs. MOSFETs come in a range of standard package types such as DPAK, D2PAK, DFN, I2PAK, SOIC, SOT-223 and TO-220. For more information about MOSFETs, please see our complete guide to MOSFETs.

**Types of MOSFETs **

MOSFET transistors have two modes: depletion and enhancement. Here’s how they work:

Depletion Mode MOSFETs

Depletion MOSFETs operate like a closed switch where the current passes through by default, even when no voltage is applied to the gate. Applying a negative voltage to the gate of an n-channel depletion MOSFET, will stop the current flow, thus acting as a normally closed switch. Although less common than their enhancement counterparts, depletion mode MOSFETs are useful in applications where a default current path is necessary until specifically turned off.

Enhancement Mode MOSFETs

Enhancement mode MOSFETs function like a variable resistor and are typically more popular than their depletion mode counterparts. These transistors apply a positive voltage on the gate relative to the source to turn on, effectively acting as a normally open switch that closes in response to voltage. Manufacturers provide enhancement mode MOSFETs in both n-channel and p-channel variants, providing flexibility in different circuit configurations.

How Do MOSFETs Work?

The pins on a MOSFET package are the Source, Gate and Drain. When a voltage is applied between the Gate and the Source terminals, current can pass through from the Drain to the Source pins. When the voltage applied to the Gate changes, the resistance from the Drain to the Source will change, too. The lower the voltage applied, the higher the resistance. As the voltage increases, the resistance from the Drain to the Source will decrease. Power MOSFETs are like standard MOSFETs, but they are designed to handle a higher level of power.

N-Channel vs. P-Channel MOSFETs

N-Channel MOSFETs contain additional electrons which are free to move around. They are a more popular channel type. N-Channel MOSFETs work when a positive charge is applied to the gate terminal.

P-Channel MOSFETS substrate contains electrons and electron holes. P-Channel MOSFETs are connected to a positive voltage. These MOSFETs turn on when the voltage supplied to the Gate terminal is lower than the Source voltage.

MOSFET Applications

MOSFETs play a crucial role in various electronic applications due to their efficiency and versatility in managing power and signals. Here are some of the key areas where MOSFETs are commonly used:

• Power Supplies: In power supplies, MOSFETs control voltage and current delivery with high efficiency, which is crucial for minimising energy loss in devices ranging from mobile chargers to industrial power units.
• Amplifiers: MOSFETs boost weak signals to higher power levels without significant distortion, which is essential in applications ranging from home audio systems to communication infrastructure.
• Digital Circuits: They act as rapid on/off switches in digital circuits, enabling the fundamental logic operations necessary for computing and digital communications.
• Microprocessors: Within microprocessors, MOSFETs manage the flow of digital data through logic gates, directly influencing processing speed and power efficiency in computers and smartphones.

How to Choose the Right MOSFETs for You

Here are essential factors to consider when selecting the appropriate MOSFET for your application:

• Voltage Rating: Ensure the MOSFET’s voltage rating exceeds the maximum operating voltage in your application to avoid breakdown and ensure long-term reliability.
• Current Capacity: Choose a MOSFET with a current rating that can handle the maximum expected load plus a suitable margin to prevent overheating and potential failure.
• Power Dissipation: Consider the power dissipation capabilities of the MOSFET, which must be adequate to manage the heat generated during operation without exceeding the maximum junction temperature.
• Switching Speed: Evaluate the switching speed required for your application; faster switching can reduce losses in high-frequency applications but may increase electromagnetic interference (EMI).
• Package Type: The physical size and thermal resistance of the package are crucial, especially in compact or densely packed designs where heat dissipation is a concern.

If you’re unsure about selecting the ideal MOSFET, turn to RS Hong Kong for guidance. We offer a wide range of MOSFETs, including n-channel and p-channel types, with low to high voltages. From power cables and temperature data loggers to bipolar junction transistors and MOSFETs, our team will help you find the most effective and reliable components for your needs.

Delivery Options in Hong Kong

RS Hong Kong offers a range of convenient delivery options to ensure you receive your MOSFETs promptly and efficiently:

• Same-Day Delivery: This service is available for orders placed before noon Monday through Friday, provided the items are in stock locally.
• Next-Day Delivery: For items in our Hong Kong stock, next working day delivery is guaranteed when you place your MOSFET order during weekday afternoons. Expect working day delivery for orders placed during weekends and public holidays.
• Flexible Delivery Options: For especially urgent orders, RS Hong Kong offers an express delivery service that can be scheduled for any specific day within the next 12 months. Please note that this service incurs an additional delivery fee.

Please be aware that we do not offer delivery to GPO Boxes, restricted areas, or outlying islands. For more details on global stock availability and our Product Plus options, please contact our Customer Service team at HKEnquiry@rs.rsgroup.com or 852 2421 9898.