When it comes to modern electronics, the MOSFET plays a vital role in everything from mobile phones to electric vehicles. A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is the backbone of power switching and amplification in electronic circuits. Whether you're designing a solar inverter, building a lithium battery management system, or working on an electric vehicle charger, understanding how a MOSFET works—and more specifically, the three modes of operation—is essential.
In this article, we’ll break down the three primary modes of MOSFET operation, explore its structure, types, and applications, and analyze how this versatile device functions in real-world scenarios. We’ll also explore the latest technologies, including SGT MOSFETs and enhancement mode MOSFETs, and how companies like Jiangsu Donghai Semiconductor are innovating in this field.
Understanding the Basics of a MOSFET
A MOSFET is a semiconductor device used to switch and amplify electronic signals. It's widely used due to its high efficiency, fast switching speed, and small size. The device has three terminals—Gate, Drain, and Source—and it operates based on the voltage applied to the gate terminal.
Before diving into the three modes of operation, it’s important to understand that MOSFETs come in different types, such as:
N-channel and P-channel MOSFETs
Depletion mode and enhancement mode MOSFETs
Power MOSFETs, including SGT MOSFETs (Shielded Gate Trench)
You can explore different product types of MOSFETs at Jiangsu Donghai Semiconductor’s official site:
The Three Modes of Operation of a MOSFET
Every MOSFET operates in three primary modes depending on the voltage applied between its terminals: Cut-Off, Triode (Linear), and Saturation (Active). Understanding these modes is crucial for designing efficient circuits.
| Mode of Operation | Gate-Source Voltage (Vgs) | Drain-Source Voltage (Vds) | Description |
| Cut-Off | Vgs < Vth | Any | MOSFET is OFF. No current flows. |
| Triode (Linear) | Vgs > Vth, Vds < Vgs - Vth | Low | MOSFET acts as a resistor. Used in analog circuits. |
| Saturation (Active) | Vgs > Vth, Vds ≥ Vgs - Vth | High | MOSFET is fully ON. Ideal for switching applications. |
Let’s explore each mode in simple terms:
1. Cut-Off Mode
In this mode, the gate-to-source voltage (Vgs) is less than the threshold voltage (Vth). The MOSFET remains off, acting like an open switch. There is no current flowing from drain to source. This mode is widely used in digital logic circuits where a clear ON/OFF state is necessary.
2. Triode Mode (Linear Mode)
When the gate voltage is higher than the threshold, and the drain voltage is lower than the gate voltage minus the threshold, the MOSFET acts like a variable resistor. This mode is used in analog applications where precise voltage control is needed, such as motor drives or amplifiers.
3. Saturation Mode (Active Mode)
Here, the MOSFET is fully on. Vgs is greater than Vth, and Vds is higher than Vgs - Vth. The drain current becomes stable and independent of Vds. This is the most common mode for switching applications like DC-DC converters, inverters, and power supplies.
MOSFET Types, Working, Structure, and Applications
Types of MOSFETs
There are several types of MOSFETs, each designed for specific applications:
Enhancement mode MOSFET: The most common type, normally OFF when Vgs = 0.
Depletion mode MOSFET: Normally ON, and needs a reverse gate voltage to turn OFF.
SGT MOSFET: A newer generation of MOSFET using a trench structure for better performance in low-voltage applications.
Structure and Working
A MOSFET consists of a semiconductor body (usually silicon), an insulating layer (usually silicon dioxide), and a conductive gate. When voltage is applied to the gate, it controls the current flowing between the drain and source.
For example, a SGT MOSFET (Shielded Gate Trench MOSFET) uses a trench structure to reduce on-resistance and gate charge, making it ideal for high-efficiency switching in power electronics.
Donghai Semiconductor specializes in advanced MOSFET technologies including SGT MOSFETs, available here:
Real-World Applications of MOSFETs
MOSFETs are everywhere today, powering devices in several sectors:
Inverters used in solar energy systems
EV motor controllers and battery management
High-frequency switching power supplies
Consumer electronics like TVs, air conditioners, and vacuum cleaners
Industrial tools such as welding machines and UPS systems
Donghai’s MOSFET products are widely adopted in these sectors, benefiting from high production standards and innovative designs.
Why SGT MOSFETs Are Changing the Game
SGT MOSFETs are a breakthrough in power semiconductor technology. Thanks to their trench structure and shielded gate, they offer:
Lower on-resistance (Rds(on))
Higher efficiency in switching
Better thermal performance
Reduced gate charge (Qg)
These advantages make SGT MOSFETs a top choice for inverter applications, electric vehicles, and lithium battery systems—three of the fastest-growing markets in electronics.
Data Comparison: SGT vs TrenchMOS vs Planar MOSFETs
| Feature | SGT MOSFET | TrenchMOS | Planar MOSFET |
| On-Resistance (Rds(on)) | Very Low | Low | Moderate |
| Switching Speed | High | Moderate to High | Lower |
| Gate Charge (Qg) | Low | Moderate | High |
| Cost | Moderate | Low | Low |
| Application Suitability | EV, Inverter, BMS | Consumer Electronics | Low-cost circuits |
Trends in MOSFET Development
As the world moves toward electrification and renewable energy, the demand for efficient MOSFET solutions is skyrocketing. Key trends include:
Growth of EV and energy storage systems needing high-efficiency enhancement mode MOSFETs
Rise in SGT MOSFET adoption in compact, high-performance applications
Increased demand for low-loss MOSFETs in inverter systems
Industry shift toward wide-bandgap semiconductors like SiC, which complement standard MOSFETs
Donghai Semiconductor is keeping pace with these trends by offering advanced MOSFET products with high reliability and scalability. Their production capacity of 500 million devices annually supports global demand, especially for high-growth industries like new energy, 5G, and smart vehicles.
Integrating MOSFETs in Inverter Applications
Inverter circuits convert DC to AC and are at the heart of solar energy systems, EV drives, and UPS systems. Choosing the right MOSFET for inverter applications depends on:
Donghai’s MOSFET lineup is optimized for inverter use, with features like low Rds(on), enhanced thermal stability, and robust packaging (TO-220, TO-247, etc.).
For example, TO-247 packaged MOSFETs are ideal for high-power inverter circuits due to their large surface area for heat dissipation.
Why Donghai Semiconductor is a Trusted MOSFET Supplier
Jiangsu Donghai Semiconductor Co., Ltd. is a leading Chinese manufacturer with:
20+ years of experience in power device R&D
Strong expertise in SGT MOSFET, IGBT, and SiC technologies
15000 production area and 500 million units annual capacity
Advanced labs for reliability, application, and failure analysis testing
Recognition as a national high-tech enterprise and R&D center
Their products are widely used in:
EV controllers and onboard chargers
Solar inverters and lithium BMS
Industrial drives and automation systems
Consumer devices and 5G infrastructure
FAQs
A1: What are the three modes of operation of a MOSFET?
Q1: The three main modes are cut-off (MOSFET is off), triode (MOSFET acts like a resistor), and saturation (MOSFET is fully on for switching).
A2: What is the difference between enhancement mode and depletion mode MOSFETs?
Q2: Enhancement mode MOSFETs are normally off and require a positive gate voltage to turn on. Depletion mode MOSFETs are normally on and require a negative gate voltage to turn off.
A3: Which MOSFET is best for inverter applications?
Q3: SGT MOSFETs are ideal due to their low on-resistance, fast switching, and better efficiency in high-power environments.
A4: What makes Donghai’s MOSFETs different from others?
Q4: Donghai offers high-reliability, high-efficiency MOSFETs with advanced packaging and cutting-edge trench technology, suited for EVs, solar inverters, and industrial controls.
A5: Can I use Donghai MOSFETs in consumer electronics?
Q5: Yes, their MOSFETs are widely used in TVs, air conditioners, power tools, and smart home devices.
Understanding the three modes of MOSFET operation is foundational for engineers and designers working on everything from basic circuits to advanced energy systems. Whether you're dealing with enhancement mode MOSFETs, exploring the benefits of SGT MOSFETs, or selecting devices for inverter applications, choosing the right component is key.
Jiangsu Donghai Semiconductor provides a full range of MOSFET solutions to meet the growing needs of smart electronics, clean energy, and efficient power conversion. With a strong R&D team, advanced manufacturing, and a proven track record, Donghai is your go-to partner for reliable, high-performance semiconductor devices.
