Power MOSFETs or Power Metal-Oxide-Semiconductor Field Effect Transistors are a key component in modern electronic devices and circuits that require switching or amplifying electric power. They combine the simple gate-driven structure of MOSFET devices with the high-current and high-voltage capabilities required for switching power electronics applications. Power MOSFETs allow efficient switching of both high voltages and high currents. Their high input impedance, fast switching speeds and ruggedness make them ideal for a variety of applications.
History and Development
The power MOSFET was invented by Kurt Lehovec, Mohamed Atalla and Dawon Kahng at the Stanford Industrial Park in the late 1950s. It was the seminal metal-oxide-semiconductor field-effect transistor (MOSFET) invented by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959. The power MOSFET added the ability to handle large currents and voltages. This made it suitable for use in energy-efficient power electronics products.
The first power MOSFETs began production in 1968 by several companies including Fairchild Semiconductor. They quickly found use in switching power supplies and other applications that required efficient switching of voltages greater than 40V. During the 1970s and 1980s, advances in MOSFET technology substantially improved performance. Devices became available that could handle hundreds of volts and amps of current. This paved the way for their widespread use in modern switch-mode power supplies, motor controls, and other applications.
Types of Power MOSFETs
There are several common categories and types of power MOSFETs based on design, structure and usage:
- Trench MOSFET: This type uses a trench structure for the gate electrode. It provides lower on-resistance than comparable planar MOSFET designs. Trench MOSFETs are commonly used in automotive and industrial applications requiring high current capabilities.
- Planar MOSFET: An older design approach with the gate electrode sitting on the surface rather than recessed in a trench. Not as efficient as trench types but cheaper to manufacture. Used where lower performance is acceptable.
- LDMOS (Lateral Diffused MOS): Features a lateral diffused structure allowing higher voltages of 600V or more. Commonly used in RF power amplifiers and linear switching applications.
- NFET (N-channel MOSFET): Uses n-type doping allowing it to conduct when a positive voltage is applied to the gate. Commonly used in switching circuits as an electron device.
- PFET (P-channel MOSFET): Uses p-type doping allowing it to conduct when a negative voltage is applied to the gate. Often used as a complement to NFET in CMOS circuits.
- Fast Switching: Designed for very high frequencies up to tens of MHz. Used in resonant converters, DC-DC converters and other fast switching power supply circuits.
- Slow Switching: Lower switching speed types optimized for frequencies below 100kHz. Used in appliances, industrial equipment and other less demanding applications.
Features and Operation
Power MOSFETs exhibit several defining characteristics that make them well-suited for switched-mode power conversion and control applications:
- Gate Input: The gate terminal uses a floating insulated gate design similar to other MOSFETs. This allows extremely high impedance and minimized power consumption for control signals.
- Low On-Resistance: Advanced structure designs like trench gate allow an extremely low “on” resistance between the drain and source terminals when turned on by the gate. This results in high efficiency power switching.
- High Voltage Blocking: The metal-oxide-semiconductor structure provides a robust barrier that supports blocking voltages as high as several thousand volts.
- Fast Switching: Power MOSFETs can transition between full "on" and "off" states in nanoseconds, enabling very high frequency switching needed for miniaturized power supplies and other applications.
- Ease of Driving: The high impedance gate makes power MOSFETs easy to turn fully on or off with minimal control circuitry. Even complex multimedia systems can drive them directly from digital outputs.
- No Reverse Conductivity: Unlike bipolar transistors, power MOSFETs do not allow current to flow between source and drain when the gate is off, preventing short circuits.
- Rugged & Durable: Properly designed power MOSFETs can handle overloads, transients, and hundreds of amps of current switching reliably for many years. This makes them suitable for industrial control and motor drive applications.
Some common applications that take advantage of the unique capabilities of power MOSFETs include:
- Switch Mode Power Supplies: Used almost universally for high-efficiency switching in desktop, server, telecom and other power supplies from 20W to 1000W or more. Allows very compact low-loss design.
- Motor Controls: Used extensively in variable speed motor drives, white goods, industrial equipment to efficiently switch high currents up to hundreds of amps used by motors.
- Appliance Controls: Control circuits for washing machines, HVAC systems, refrigerators, microwave ovens and other appliances utilize power MOSFETs due to their robust high current switching.
- Audio/Hifi Amplifiers: High current audio power amp designs for home cinema and audiophile use power MOSFETs to deliver 100W to 500W or more amplification with low noise/distortion.
- Electric Power Steering: Automotive power steering systems rely on power MOSFET H-bridge circuits and drivers to control electric motors with currents up to 30 amps or more.
- Solar & EV Power Electronics: Charge controllers, battery chargers and power distribution systems for electric vehicles and solar/renewable energy use many power MOSFET stages for high voltage/current switching up to 600V.
Power MOSFETs have revolutionized switched-mode power electronic systems by enabling precise, efficient control of high voltages and currents. Years of improvements continue extending their capabilities. Their versatility, robustness, and ease of use has made power MOSFETs integral to applications ranging from personal electronics to electric vehicles, industrial equipment and beyond. With ongoing innovations, they will remain a critical semiconductor component enabling new technologies well into the future.
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