MOSFET vs. IGBT: Characteristics, Structure and Market Analysis

Ⅰ What is a MOSFET?

There are two main types of field-effect transistors, respectively, JFET and MOSFET.

MOSFET is metal-oxide-semiconductor field-effect transistor. Because the gate of this field-effect transistor is isolated by an insulating layer, so it is also called insulated-gate field-effect transistor.

MOSFETs can also be divided into four categories:

①N-channel depletion mode;

②N-channel enhancement mode;

③P-channel depletion mode; 

④P-channel enhancement mode.

MOSFET types and circuit symbols

Some MOSFETs will have a diode inside, which is a body diode, or a parasitic diode, or a current-continuing diode.

There are two explanations for the role of the parasitic diode.

The role of the Parasitic diode of MOSFET is to prevent the VDD over-voltage situation, burned MOSFET. Because the diode reverse breakdown before the over-voltage caused damage to the MOSFET, the high current directly to the ground, thus avoiding burning out the MOSFET.

MOSFETs have high input impedance, fast switching speed, good thermal stability, voltage control current, and other characteristics. In the circuit, a MOSFET can be used as an amplifier, electronic switch, and for other purposes.

Ⅱ What is an IGBT?

IGBT (Insulated Gate Bipolar Transistor), is a compound semiconductor device consisting of a crystal triode and MOSFET.

As a new type of electronic semiconductor device, IGBT has the characteristics of high input impedance, low power consumption for voltage control, simple control circuit, high voltage resistance, and high current withstand, etc... It is widely used in various electronic circuits.

IGBT and circuit symbol

The circuit symbol of IGBT has not been unified so far, and the symbol of triode and MOSFET is generally borrowed when drawing schematic diagrams, which can be judged from the model number marked on the schematic diagram as IGBT or MOSFET.

At the same time, we should also pay attention to whether the IGBT has a body diode. Not marked on the diagram does not necessarily mean that there is no. This diode is present unless specifically stated in the official data.

parasitic diode

The body diode inside the IGBT is not parasitic but is specially set to protect the fragile reverse withstand voltage of the IGBT. It is also known as FWD (Freewheeling Diode).

It is not difficult to determine whether there is an FWD inside the IGBT, you can use a multimeter to measure the C and E poles of the IGBT. If the IGBT is good and the C and E poles measure infinite resistance, it means that the IGBT does not have a body diode.

IGBT is very suitable for applications such as AC motors, inverters, switching power supplies, lighting circuits, traction drives and other fields.

Ⅲ Structural of MOSFET and IGBT

The internal structure of MOSFET and IGBT is shown in the figure below.

internal structure of MOSFET and IGBT

The IGBT is constructed by adding an additional layer to the drain of the MOSFET.

The ideal equivalent circuit of IGBT is shown in the figure below. IGBT is actually a combination of MOSFET and transistor triode. MOSFET has the disadvantage of high on-resistance, but IGBT overcomes this disadvantage, and IGBT still has low on-resistance at high voltage.

IGBT ideal equivalent circuit

In addition, if the IGBT and MOSFET have similar power capacity, the IGBT may be slower than the MOSFET because the IGBT has an off-drag time. Due to the long IGBT turn-off trailing time, the dead time is also lengthened, which will affect the switching frequency.

Ⅳ MOSFETs or IGBTs, Which one should we use?

In the circuit, the choice of MOSFET or IGBT as a power switching tube is a common problem encountered by engineers. From the system voltage, current, switching power, and other factors, we can summarize the following points.

MOSFET and IGBT application characteristics

We can also be seen from the following chart the conditions for the use of both. The shaded area indicates that MOSFETs and IGBTs can be selected, "?" indicates that the current process is not yet able to reach the level.

Common Application Areas for MOSFETs and IGBTs

In general, MOSFETs have good high-frequency characteristics. Its operating frequency can reach hundreds of kHz or even MHz. The disadvantage is that the on-state resistance is large and the power consumption is large in high voltage and high current situations. 100KHZ is almost the best operating limit of IGBT. IGBT has an excellent performance in low frequency and high power occasions. The on-resistance is small and the withstand voltage is high.

Finally, if the electronic components need to carry out high-speed switching action, MOSFETs have an absolute advantage, mainly because of the integration of BJT of the IGBT. BJT itself has a charge storage time problem, that is, in the OFF time, it takes a longer time, resulting in high-speed switching action can not be carried out.

MOSFETs are used in switching power supplies, ballasts, high-frequency induction heating, high-frequency inverter welding machines, communication power supplies, portable rechargeable batteries, and other high-frequency power supply fields; IGBTs are used in welding machines, inverters, inverters, electroplating electrolytic power supplies, super audio induction heating, electric motors, automotive power batteries, and other fields.

Ⅴ Identification of MOSFET and IGBT

MOSFET and IGBT are electronic components with a high frequency of use. The two are extremely similar in appearance and static parameters. Some electronic products have a technology monopoly, and sometimes their models are erased in the circuit. At present, there is still no uniform naming standard of MOSFET and IGBT. And their appearance and pin arrangement is similar. How to distinguish and judge becomes a necessary means.

Identification of damped NPN type IGBT and N-channel enhanced MOMS tube: The damped NPN type IGBT and N-channel enhanced MOMS tube have the same gate position. The C pole of the IGBT corresponds to the D pole of the MODS tube. The e pole position of the IGBT corresponds to the S pole position of the MODS tube. Judging and distinguishing between good and bad can be done by dynamic and static measurement methods.

Static measurement to distinguish MOSFET and IGBT

We first short-circuit the pins of the two tubes to discharge the static electricity.

There is a PN connection between the D pole and the S pole of the MOSFET. Forward conduction and reverse end. So Rgd=Rgs=Rds=infinity, Rsd=several thousand ohms.

The resistance from the G pole to the c and e poles of the IGBT should be infinite, that is, Rgc=Rge=infinity, and there is a damping diode between the IGBTs, so it has unidirectional conduction reverse cutoff characteristics, that is, Rce=infinity, Rec= Several thousand ohms.

From here, you can only use the resistance file of the multimeter to judge the quality of the tube, but you can't tell which kind of tube it is. The measured resistance value is very small, indicating that the tube is broken down, and the measured resistance value is very large, indicating that the internal circuit of the tube is open.

Dynamic measurement to distinguish MOSFET and IGBT

First, use a multimeter to apply a voltage to the grid of the tube to make the field-effect tube establish a channel. Then measure the resistance between D, S and c, e, and distinguish between MOSFET and IGBT according to the difference in resistance.

Use the resistance profile of a multimeter to measure the resistance between D, S, and c and e of the two tubes. Since the field effect tube has already established a channel, Rds=Rsd≈0. There is a resistance Rce between Rce, the on-resistance of the transistor in the amplified state, and Rec is the on-resistance of the internal damping diode, both of which are several thousand ohms.

Therefore, according to the measurement, the conduction degree of the two tubes is different, and the resistance value between D and S of MOSFET is much smaller than the resistance value between IGBTc and e, so MOS and IGBT can be distinguished.

Ⅵ MOSFET and IGBT market analysis

Power semiconductors are the core of electrical energy conversion and circuit control in electronic devices. They are mainly used to change the voltage and frequency in electronic devices, and DC-AC conversion, etc.

Basically, power semiconductors can be broadly divided into two categories: Power Discrete and Power Integrated Circuits (Power IC).

MOSFETs and IGBTs are mainly used to transform the current generated by power generation equipment with different voltages and frequencies into currents with specific electrical parameters through a series of conversion and modulation to supply various terminal electronic devices.

The global power semiconductor market, the highest proportion is industrial control, accounted for 34%, followed by the automotive and communications sector accounted for 23% each, consumer electronics accounted for 20%.

In recent years, power semiconductor applications have been expanded from industrial control and consumer electronics to new energy, rail transportation, smart grid, inverter home appliances, and other markets. According to the IHS Markit forecast, the global power components market size in 2018 is about 39.1 billion U.S. dollars. It is estimated that the market size will rise to 44.1 billion U.S. dollars in 2021with a compound annual growth rate of 4.1%.

IC Insights points out that among the various types of semiconductor power components, the most promising products in the future will be MOSFETs and IGBT modules.

MOSFET is a field-effect crystal that can be widely used in analog circuits and digital circuits, with the advantages of low on-resistance, low loss, a simple driving circuit, good thermal resistance characteristics. It is suitable for PC, cell phones, mobile power, car navigation, electric vehicles, UPS power supply, and other power control fields.

In 2016, the global MOSFET market size reached $6.2 billion, and it is estimated that by 2022, the global MOSFET market size will be close to $7.5 billion, and the compound annual growth rate will reach 3.4% in between.

The IGBT is a compound semiconductor power device consisting of a dual carrier junction transistor (BJT) and a MOSFET. With the advantages of the high input impedance of MOSFET and low on-resistance of BJT, IGBTs are ideal for variable current systems with DC voltage of 600V and above, such as AC motors, inverters, switching power supplies, lighting circuits, traction drives, etc.

Source: IHS, Secondary, MOSFETs, and IGBTs by value ($ billion)

As consumers' requirements for charging efficiency gradually increase, mobile phone charging has a fast charging mode, which means that high-current and high-power charging can be achieved by increasing the voltage. However, high voltages have safety concerns and need to be adjusted by adding rectifier MOSFETs.

Later, a safer flash charging mode appeared, mainly to achieve high-speed charging through low voltage and high current, which placed higher requirements on synchronous rectification MOSFETs.

On the other hand, it is the changes in the automobile industry. At present, the development of the automobile industry has moved from traditional cars to electric vehicles. The biggest beneficiary of the increase in automotive electronics is power semiconductors. In traditional fuel vehicles, power semiconductors are mainly used in fields such as start, stop, and safety, accounting for only 20%. According to the traditional car, the value of the power component is about 70 US dollars based on the value of the semiconductor bicycle of 350 US dollars.

But entering the generation of electric vehicles, its battery power modules require a lot of power equipment, and power equipment contains power semiconductors. The power components of hybrid vehicles account for 40%, and the power components of pure electric vehicles account for 55%. According to the calculation of the value of a single-vehicle semiconductor of a pure electric vehicle of US$750, the value of a power semiconductor is about US$413, which is about 6 times that of a traditional car.