Igbt Fet

Posted : admin On 1/29/2022

An IGBT (Insulated Gate Bipolar Transistor) is essentially an MOSFET (Metal Oxide Field Effect Transistor) controlling a bipolar junction power transistor (BJT) with both transistors are integrated on a single piece of silicon. Een transistor (samentrekking v.Eng. Transfer en resistor, = lett.: overdrachtsweerstand) is een halfgeleidercomponent met meestal drie aansluitingen.Als elektronisch onderdeel dient een transistor onder meer als versterkend of schakelend element in een elektronische schakeling. IGBT and MOSFET are both voltage-controlled but, one main noticeable difference is that IGBT is a 3-terminal device and MOSFET is a 4-terminal device. Although they are very similar, both of them have a few differences between the two transistors. IGBT: IGBT product selection provides a broad variety of different devices. These products address a wide range of applications in the field of automotive, traction, industrial and consumer systems. Our solutions offer very low power losses in the forward and blocking state, require only low drive power and have a high efficiency. . No formula was provided for IGBT, therefore a MOSFET and Bipolar Junction Transistor (BJT) was modeled in series to represent an IGBT. Failure rate is calculated by multiplying a base failure rate with several conditional factors. For example: where λ P = part failure rate λ b = base failure rate π T = temperature factor λ A.

Igbt Fet

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

Difference between mosfet and igbt

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.

  1. 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.

  1. 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.

  1. 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.

  1. 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

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.

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MOSFET Vs IGBT

Igbt inverter basics

In today’s world there are wide varieties of solid-state, switch-mode, power-supply transistors to perform switching operations in power-electronic systems. All these have their own specifications in terms of current, voltage, switching speed, load, driver circuitry and temperature. Each one has its limitations and advantages as well, but its usage depends on the requirements of the application.

In most of the switching applications Metal-Oxide Semiconductor Filed Effect Transistor (MOSFET) and Insulated Gate Bipolar Transistors (IGBTs) are predominant than the other switching devices due to their superior characteristics. These applications include Uninterruptable Power Supplies (UPS), Solar Inverters and Converters, various motor driver systems, Pulse Width Modulation (PWM) technique based applications, Switch Mode Power Supplies (SMPS), etc.

Let us see the prominent differences that make these switching devices suitable for appropriate applications. In this regard, the description of the following two switching devices is pertinent.

High-Voltage Power MOSFET

Power MOSFET

MOSFET is a most commonly used switching device, which is voltage-controlled power device unlike the BJT, which is a current controlled device. MOSFET is a low-current, low-voltage and high-frequency switching device. It consists of three terminals: gate, drain and source. It comes with two different modes: enhancement and depletion modes and the MOSFETs can be P-channel or N-channel MOSFETs. MOSFETs vary depending on the voltage level of the gate terminal.

In a depletion mode, maximum conductance takes place between the source and the drain if there is no voltage at the gate terminal, whereas a positive or negative voltage at the gate decreases the conductivity. In an enhancement mode, the MOSFET doesn’t conduct if there is no voltage at the gate terminal, and if the voltage is more, conduction takes place.

If the positive voltage is more than the threshold level applied between the gate and the source, then it creates a conduction layer by accumulating electrons. This layer is formed between the oxide layer and the P-substrate layer by pushing away the holes from the P-substrate and attracting the electrons in the N-layer. With the increase in the gate to source voltage, the size of this conduction layer increases resulting in the flow of more current from the source to the drain. In this way, MOSFET comes into conduction mode by the application of voltage across the gate and source.

MOSFET can be turned off by decreasing the gate to source voltage to below the threshold level of it. Sometimes a BJT current is required to trigger it though the MOSFET is a voltage controlled switch. It also has a body-drain diode useful in dealing with freewheeling current applications. Because its on-state resistance is low, on-state losses are also lower. MOSFETs can operate at high frequencies and low voltages and are perfectly suitable for faster switching operations with low-voltage drops. But these are restricted to be used at higher operating voltages in the range of around 500V.

IGBT (Insulated Gate Bipolar Transistor)

IGBT is designed by combining the features of both MOSFET and BJT in monolithic form. As the BJTs have high current handling capacity and MOSFET control is easy, IGBTs are preferred for medium to high-power applications. It is a minority charge carrier device and has high input impedance.

It has three terminals: Emitter, Collector and Gate. The Gate is a control terminal, whereas the collector and emitter terminals are associated for conduction path. IGBT is a four-layer structure P-N-P-N same as that of thyristors. The below figure shows different layers of IGBT, wherein the flow of electrons through the drift region and the channel draw more holes into the drift region towards the emitter. Because the current flow is composed of the holes and electrons, the current is of bipolar nature.

IGBT Structure

Similar to the MOSFET, when the positive gate bias is applied, it allows the inversion of P-base region under the gate and creates N-channel. During this state, the resistance of n- layer is reduced rapidly when the positive holes are injected from the p+ layer to the n- layer. This makes the IGBT to handle more currents than the MOSFET due to lower conduction losses. For turning it off – the negative bias at the gate or lowering the gate voltage to a threshold level makes it off due to no injection of holes to the N region.

Igbt switching circuit

Difference between Insulated Gate Bipolar Transistor (IGBTs) and High-Voltage Power MOSFETs

Difference Between Mosfet And Igbt

  1. MOSFET is a majority carrier device wherein the conduction is by electrons’ flow, whereas IGBT is a current flow comprising both electrons and holes. As discussed above, the injection of minority carriers (holes) to the drift region significantly reduces on-stage voltage due to conduction modulation. This is the advantage of low on-state voltage drop compared to MOSFET which is a smaller chip size and less expensive device.
  2. IGBT is made up of emitter, collector and gate terminals, whereas MOSFET consists of source, drain and gate terminals.
  3. IGBT usage is predominated for higher voltage applications as it is unipolar and requires additional freewheeling diode for the reverse flow of current. Because of this additional diode across the IGBT – it gives very high performance compared to the MOSFET.
  4. MOSFET and IGBT structures look very similar except for the P-substrate below the N substrate. Due to this extra layer, the conductivity is increased by the injection of holes that also reduces the on-state voltage as discussed above.
  5. MOSFET is rated at a voltage of about 600 volts, whereas IGBT is rated at a voltage of about1400V range. Therefore, at high voltages current becomes low eventually resulting in low switching losses.
  6. IGBT is preferred for low frequency (Less than 20 KHz), high voltage (more than 1000V), small or narrow load or line variations; low duty cycle, high operating temperature; and, more than 5kw output power rating applications; whereas MOSFET is preferred for wide load or line variations, low voltage (Less than 250V), large duty cycles and high frequency (more than 200KHz) applications.
  7. IGBT typical applications include Uninterruptable Power supplies (UPS), low-power lighting, motor control and welding applications, Switch Mode Power Supplies (SMPS), battery charging, etc., but compared to MOSFET, IGBT is predominated in several applications.

Difference between IGBT and MOSFET

In the above diagram, you can observe some comparisons of IGBT and MOSFET based on their model with ratings. Therefore, for choosing switching devices, especially IGBT and MOSFET devices there are larger parameters to be considered for the corresponding applications in power electronic field. For any application-based projects on these devices, you can contact us by commenting below.

Mosfet Igbt

Photo Credits:

Igbt Vs Mosfet Inverter

  • Power MOSFET by nlvocables
  • MOSFET Structure by circuitstoday
  • Insulated Gate Bipolar Transistor by cloudfront
  • IGBT Structure by lchu
  • Difference between IGBT and MOSFET by powersystemsdesign