The MOSFET or IGBT question is a recurring one. We all have faced this question once. Knowing which type of FET to go for. And the question is still going-on. You can look for the web, and you find an IGBT manufacturer’s e-book about how IGBT’s are such a good solutions for so many applications. But you may also find an e-book teaching you about MOSFETs, their superiority, and how you could use them in almost all of your designs. If this book happens to be written by a famous MOSFET manufacturer, it’s a total coincidence of course…

Certainly, the IGBT is the choice for breakdown voltages above 1000 V, while the MOSFET is for device breakdown voltages below 250 V. Device selection isn't so clear, though, when the breakdown. MOSFET full form is Metal Oxide Semiconductor Field Effect Transistor and IGBT full form is Insulated Gate Bipolar Transistor. What is MOSFET and its full form? There are two types of MOSFET viz. N-channel MOSFET and p-channel MOSFET. It can also be classified as Depletion MOSFET and Enhancement MOSFET.

It reminds me of Transphorm’s former CEO presentation during a Keynote at APEC. He showed us a slide (actually one that I made back when I was at Yole Développement), that he twisted to mock how SiC, GaN and Super Junction MOSFET actors view the same situation.

A great way to teach how marketing and vision alter a message supposed to be objective at first (and why consulting companies like Point The Gap have clear view :-) ).

Figure 1: Transphorm’s CEO presented these picture during APEC keynote sessions: The truth about marketing your products.

So, I’m not here to reveal you a hidden truth for generations (of IGBTs). There is no hidden truth.

It’s what « they » said… All the people you met and asked the question. But each time you read a new article on the subject, it becomes blurry. Let’s make things a little bit clearer for everyone.

There are a few cases where the MOSFET or IGBT question is non-applicable:

• All applications requiring 1700V or higher breakdown voltage for the switches
  • Rail traction, Wind turbines, Grid T&D, Central inverters for utility scale PV, high power motor drives…
  • This breakdown voltage requirement comes mostly from the DC-bus voltage. This bus in motor drive or generator as an example, is the one that conveys rectified DC power to the DC/AC conversion part. This bus, loaded with capacitors to stabilize and filter current, may have a design at 1000V+. This make you have to use 1700V devices or more.
• All applications at very low voltage:
  • Apart from flash light triggering in cameras (300V IGBTs). You will always go for a MOSFET. From 5V to 400V. Period. It’s smaller, faster, better and sometimes stronger.
  • This includes a load of consumer applications, embedded power conversion to power-up all sorts of functions inside all the electronics you have at home or carry everywhere.

So where does the question applies? For all the stuff between 400V and 1700V.

You can have:

• Consumer applications: like AC/DC adapters for laptops, tablets and electronics
• Renewable energy with PV inverter for residential, but also micro-inverters.
• All the industries using the medium and small range of motor drives (conveyors and/or belts)
• All small/medium power UPS, in data centers, SMEs, industries…
• And so many other applications…

MOSFETs are good because they are fast. Their switching frequency can go up to several 100MHz. And it’s their main advantage. You also have to think about and Include Super Junction MOSFET in the story. We will write an article about the history of Super Junction MOSFET. But remember that SJ MOSFET have even better characteristics compared to MOSFET. They are also more expensive.

On the other hand, IGBTs can handle more power, meaning that at a comparable voltage, they outperform MOSFETs in current handling capability.

This is the main idea and it comes from losses. All transistor have losses. If we highly simplify the problem, you end-up with two type of losses: Conduction losses and switching losses, respectively happening during conduction mode, or at switching on/off or off/on (you could guess that, right?).

So what happens is that:

• IGBT have lower conduction losses but higher switching losses compared to the best Super Junction MOSFETs
• MOSFETs in general and especially Super Junction MOSFETs, have low conduction losses (the famous RdsON they advertise everywhere) but have higher conduction losses compared to IGBT

And this is the key thing you have to keep in mind.

Next generation compound semiconductor devices are not in the party yet. They are too expensive for you, and you better let another niche applications and adventurous company put Wide band gap semiconductor on the market. But you better watch and try the devices, validate them and get ready to launch.

Though the choice is still blurry for now: GaN FeT should be used for voltages up to 1200V. SiC is giving it’s best at high and very high voltage: 1700V but, based on R&D, it’s outstanding at voltages up to 10kV.

It’s still an unclear boundary. So far, GaN is available at 600V only (1200V are samples).

SiC begins to be used, for very specific applications.

MOSFETs and IGBTs are now becoming a commodity: More and more Chinese companies are able to manufacture IGBTs. Only early generation and simple device designs are available from them, but that’s a sign. On the other side, Infineon recently announced that they are moving some MOSFETs (40V OptiMOS) to their Dresden 12in. (300mm) wafer fab. It’s becoming common and cheap to have Power MOSFETs and IGBTs.

But the market of GaN and SiC is not at it’s breakeven point. Investment is what make manufacturers survive, not sales. This makes us tell it’s early.

But mainly frequency. They are still king on their own voltage (low for MOSFET, and high for IGBT). but between 400V and 1700V, you have to choose. Look at the losses, the on and off time, the frequency of your applications, but also now you are looking at the footprint (MOSFET generally have small packages).

Keeping in mind these points:

• IGBT have lower conduction losses but higher switching losses compared to the best Super Junction MOSFETs
• MOSFETs in general and especially Super Junction MOSFETs, have low conduction losses (the famous RdsON they advertise everywhere) but have higher conduction losses compared to IGBT.

The bipolar transistors were the only real power transistor used until the very efficient MOSFETs came along in the early 1970’s. The BJTs have gone through vital enhancements of its electrical performance since its inception in late 1947 and is still widely used in electronic circuits. The bipolar transistors have relatively slow turn-off characteristics and they exhibit negative temperature coefficient which may result in secondary breakdown. MOSFETs, however, are devices that are voltage controlled rather than current-controlled. They have positive temperature coefficient for resistance that stops thermal runaway and as a result secondary breakdown does not occur. Then, IGBTs came into the picture in the late 1980s. The IGBT is basically a cross between the bipolar transistors and MOSFETs and is also voltage-controlled like MOSFETs. This article highlights some key points comparing the two devices.

What is a MOSFET?

MOSFET, short for “Metal Oxide Semiconductor Field Effect Transistor”, is a special type of field effect transistor widely used in very large scale integrated circuits, thanks to its sophisticated structure and high input impedance. It’s a four-terminal semiconductor device that controls both analog and digital signals. The gate is located between the source and drain and is insulated by a thin layer of metal oxide which prevents the current from flowing between the gate and the channel. The technology is now used in all kinds of semiconductor devices to amplify weak signals.

What is an IGBT?

IGBT, stands for “Insulated Gate Bipolar Transistor”, is a three-terminal semiconductor device which combines the current-carrying capability of a bipolar transistor with the ease of control of that of a MOSFET. They are a relatively new device in power electronics typically used as an electronic switch in a wide a range of applications, from medium to ultra high power applications such as switched mode power supplies (SMPS). Its structure is almost identical to that of a MOSFET except the additional of a p substrate beneath the n substrate.

Difference between IGBT and MOSFET

1. Basic of IGBT and MOSFET

IGBT stands for Insulated-Gate Bipolar Transistor, whereas MOSFET is short for Metal-Oxide Semiconductor Field Effect Transistor. Although, both are voltage-controlled semiconductor devices that work best in switch mode power supply (SMPS) applications, IGBTs combine the high-current handling capability of bipolar transistors with the ease of control of MOSFETs. IGBTs are gatekeepers of current that combine the advantages of a BJT and MOSFET for use in power supply and motor control circuits. MOSFET is a special type of field-effect transistor in which the applied voltage determines the conductivity of a device.

2. Working Principle of IGBT and MOSFET

An IGBT is essentially a MOSFET device that controls a bipolar junction power transistor with both transistors integrated on a single piece of silicon, whereas MOSFET is the most common insulated gate FET, most commonly fabricated by the controlled oxidation of silicon. MOSFET generally works by electronically varying the width of the channel by the voltage on an electrode called the gate which is located between the source and the drain, and is insulated by a thin layer of silicon oxide. A MOSFET can function in two ways: Depletion mode and Enhancement mode.

3. Input Impedance of IGBT and MOSFET

An IGBT is a voltage-controlled bipolar device with high input impedance and large current-handling capability of a bipolar transistor. They can be easy to control as compared to current controlled devices in high current applications. MOSFETs require almost no input current to control the load current which makes them more resistive at the gate terminal, thanks to the isolation layer between the gate and the channel. The layer is made of silicon oxide which is one of the best insulators used. It efficiently blocks the applied voltage with the exception of a small leakage current.

4. Damage Resistance

MOSFETs are more susceptible to electrostatic discharge (ESD) as high input impedance of MOS technology in a MOSFET won’t allow the charge to dissipate in a more controlled fashion. The additional silicon oxide insulator reduces the capacitance of the gate which makes it vulnerable against the very high voltage spikes inevitably damaging the internal components. MOSFETs are very sensitive to ESDs. The third generation IGBTs combines the voltage drive characteristics of a MOSFET with the low on-resistance capability of a bipolar transistor, thus making them extremely tolerant against overloads and voltage spikes.

5. Applications of IGBT and MOSFET

MOSFET devices are widely used for switching and amplifying electronic signals in electronic devices, typically for high noise applications. The most application of a MOSFET is in switch mode power supplies, plus they can be used in class D amplifiers. They are the most common field effect transistor and can be used in both analog and digital circuits. IGBTs, on the other hand, are used in medium to ultra high-power applications like switch mode power supply, induction heating, and traction motor control. It is used as a vital component in modern appliances such as electric cars, lamp ballasts, and VFDs (variable frequency drives).

IGBT vs. MOSFET: Comparison Chart

Summary of IGBT Vs. MOSFET

Igbt Switching Circuit

Although both IGBT and MOSFET are voltage-controlled semiconductor devices mainly used to amplify weak signals, IGBTs combine the low on-resistance capability of a bipolar transistor with the voltage drive characteristics of a MOSFET. With the proliferation of choices between the two devices, it’s becoming increasingly difficult to choose the best device based on their applications alone. MOSFET is a four-terminal semiconductor device, whereas IGBT is a three-terminal device which is a cross between the bipolar transistor and a MOSFET which makes them extremely tolerant to electrostatic discharge and overloads.

Mosfet And Igbt Gate Driver

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Power Mosfet And Igbt