Who should use IGBT and MOSFET? Did you choose the right one?

“semiconductor power devices mainly include power diodes, power triodes, thyristors, MOSFETs, IGBTs, etc. Among them, MOSFET and IGBT are voltage-controlled switching devices, which have the advantages of fast switching speed, easy driving, and low loss. The full name of IGBT is insulated gate power transistor. It is a composite fully controlled voltage-driven semiconductor power device composed of bipolar triode (BJT) and MOSFET. It has both the high input impedance of MOSFET and the low on-state voltage drop of BJT. advantages.

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Author Doctor M

Semiconductor power devices mainly include power diodes, power triodes, thyristors, MOSFETs, IGBTs, etc. Among them, MOSFET and IGBT are voltage-controlled switching devices, which have the advantages of fast switching speed, easy driving, and low loss. The full name of IGBT is insulated gate power transistor. It is a composite fully controlled voltage-driven semiconductor power device composed of bipolar triode (BJT) and MOSFET. It has both the high input impedance of MOSFET and the low on-state voltage drop of BJT. advantages. With the rise of new energy vehicles, smart home appliances, 5G, rail transit and other industries, MOSFET and IGBT have also ushered in the spring of development.

However, in practical applications, engineers will encounter the same confusion: the selection of devices is really a headache. I feel the same way about this. Today, let’s take a look at the similarities and differences between MOSFETs and IGBTs, and what parameters should be focused on when selecting models.

Similarities and differences between MOSFET and IGBT

Both MOSFETs and IGBTs are solid-state semiconductor devices integrated on a single piece of silicon, and both are voltage-controlled devices. In addition, IGBTs and MOSFETs have isolation between the gate and other terminals, and both devices have high input impedance. In applications, both IGBTs and MOSFETs can be used as static Electronic switches.

Although there are many things in common, there are many differences between IGBTs and MOSFETs in terms of performance parameters and applications.

Structurally, MOSFETs and IGBTs look very similar, but are actually different. IGBT consists of emitter, collector and gate terminals whereas MOSFET consists of source, drain and gate terminals. The IGBT has a PN junction in its structure, and the MOSFET does not have any PN junction.

In terms of characteristic parameters, the main difference between MOSFET and IGBT is reflected in the following 9 aspects:

1. In the low current region, the on-voltage of the MOSFET is lower than that of the IGBT, which is also its advantage. However, the forward voltage characteristic of IGBT is better than that of MOSFET in the high current region. In addition, since the forward characteristics of MOSFETs have a strong forward dependence on temperature, IGBTs have better high-temperature characteristics and lower on-voltage than MOSFETs.
2. IGBTs are suitable for conduction and control of medium to very high currents, while MOSFETs are suitable for conduction and control of low to medium currents.
3. IGBT is not suitable for high frequency applications, it can operate well at 1000 Hz frequency. MOSFETs are particularly suitable for very high frequency applications, and they can operate well at megaHz frequencies.
4. The switching speed of IGBT is relatively low, and the switching speed of MOSFET is very high.
5. IGBTs can withstand very high voltages as well as high powers, MOSFETs are only suitable for low to medium voltage applications.
6. The IGBT has a larger turn-off time, and the MOSFET has a smaller turn-off time.
7. The IGBT can handle any transient voltage and current, but when a transient voltage occurs, the operation of the MOSFET is disturbed.
8. MOSFET devices are low-cost and cheap, while IGBTs are still relatively high-cost devices.
9. IGBTs are suitable for high power AC applications and MOSFETs are suitable for low power DC applications.

Because of these differences, MOSFETs and IGBTs have their own emphasis in application. Typically, MOSFETs are rated at around 600V, while IGBTs can be rated up to 1400V. From a voltage rating perspective, IGBTs are mainly used for higher voltage applications. From an operating frequency perspective, IGBTs are typically used at switching frequencies below 20kHz, where they have higher switching losses than unipolar MOSFETs.

On the whole, for low frequency (less than 20kHz), high voltage (greater than 1000V), small or narrow load or line changes, high operating temperature, and rated output power applications exceeding 5kw, IGBT is the first choice. The MOSFET is more suitable for low voltage (less than 250V), large duty cycle and high frequency (greater than 200KHz) applications.

Figure 1: Performance comparison of different types of transistors (Image source: TOSHIBA)

MOSFET key electrical parameters

The advantages of MOSFET determine that it is very suitable for high frequency and high switching speed applications. In switching power supplies (SMPS), the parasitic parameters of the MOSFET are critical, which determine performance such as transition time, on-resistance, ringing (overshoot while switching), and back gate breakdown, all of which are closely related to the efficiency of the SMPS .

As a power switch, the MOSFET should be chosen with very low on-resistance, low input capacitance (ie Miller capacitance), and very high gate breakdown voltage, even high enough to handle any peak voltages generated by the inductance. In addition, the parasitic inductance between the drain and source is as low as possible, because low parasitic inductance minimizes voltage spikes during switching.

For gate driver or inverter applications, it is often necessary to choose MOSFETs with low input capacitance (for fast switching) and higher drive capability.

IGBT key electrical parameters

The main advantages of IGBTs are the ability to handle and conduct medium to ultra-high voltages and high currents, have very high gate insulation characteristics, and produce very low forward voltage drops during current conduction, even when a surge voltage occurs, the IGBT operation will not be disturbed. The downside is that IGBTs are not suitable for high frequency applications. Compared to MOSFETs, the switching speed is slower and the turn-off time is longer.

In practical applications, the parameter requirements of inverter technology for IGBT are not static, and the requirements for IGBT are different.

Taken together, the following parameters are crucial in the selection of IGBTs.

One is the rated voltage. Under the condition of switching operation, the rated voltage of the IGBT is usually higher than twice the DC bus voltage.
The second is the rated current. Since the current is overloaded when the load is electrically started or accelerated, it is required that the IGBT can withstand 1.5 times the overcurrent within 1 minute.
The third is the switching speed.
The fourth is the gate voltage. The working state of the IGBT has a great relationship with the forward gate voltage. The higher the voltage, the smaller the switching loss and the smaller the forward voltage drop.

IGBTs and MOSFETs in new energy vehicles

The electrification of vehicles is the general trend. Now that governments have set their own carbon peaking and carbon neutrality goals, it is very important to switch from traditional ICE vehicles to pure electric vehicles. Tighter global CO2 emission requirements continue to accelerate the process of vehicle electrification, and the compound annual growth rate (CAGR(VOL)) of electric vehicles/hybrid electric vehicles (EV/HEV) is expected to reach 20.1% from 2021 to 2026. Battery Electric Vehicles (BEVs), known as Zero Emission Vehicles (ZEVs), will have a CAGR (VOL) of up to 29.7%.

Figure 2: EV/HEV growth in the next 5 years (Source: onsemi)

The motor control system, engine control system, and body control system of new energy vehicles all need to use a large number of semiconductor power devices, and its popularity has opened a window for growth in the automotive power semiconductor market. Among various semiconductor power devices, the products with the strongest growth in the future will be MOSFET and IGBT modules.

According to the analysis results of IC Insights, a research institute, in 2016, the global MOSFET market reached 6.2 billion US dollars, and the compound annual growth rate of the MOSFET market is expected to reach 3.4% from 2016 to 2022. The global MOSFET market size is expected to approach $7.5 billion by 2022.

IGBT is the core device of the high-voltage system of new energy vehicles. Its core application is the main drive inverter. In addition, it also includes high-voltage auxiliary systems such as on-board charger (OBC), battery management system, on-board air conditioning control system, and steering. IGBTs are also widely used in DC and AC charging piles. In new energy vehicles, MOSFETs are mainly used in automotive low-voltage electrical appliances, such as electric seat adjustment, battery circuit protection, DC motors for wipers, and LED lighting systems.

IGBT and MOSFET “core” product recommendation

The AFGHL25T120RHD is an onsemi automotive-grade low-cost 1200V 25A IGBT that is AEC Q101 compliant with a rugged and cost-effective Field Resistance II trench structure. Offers excellent performance in demanding switching applications with low on-state voltage and minimal switching losses, and can be used in EV/HEV systems such as PTC heaters, electric compressors, on-board chargers, and more.

Another MOSFET module from ON Semiconductor, FAM65CR51ADZ1, is a 650V power integrated module (PIM) with a boost converter, which is mainly used in the on-board charger (OBC) in EV/HEV. The system is designed to be more compact, efficient and reliable.

Infineon Technologies has an extremely rich portfolio of IGBT power modules with different circuit structures, chip configurations and current and voltage levels, covering most applications on the market. They are available in chopper, DUAL, PIM, four-cell, six-cell, twelve-cell, three-level, booster or single-switch configurations with current ratings ranging from 6A to 3600A. The applicable power of IGBT modules is as small as a few hundred watts and as high as several megawatts.

For example, Infineon’s HybridPACK series offers multiple versions based on 6 different packages, optimized for different inverter performance levels between 100kW and 200kW, expanding the power range of IGBT modules for EV/HEV. The HybridPACK Drive in this series is a very compact power module optimized for EV/HEV vehicle traction applications, with a power range of 100kW to 175kW, enabling maximum efficiency in the actual drive cycle of an electric vehicle, even in harsh environments The inverter can also operate reliably under the conditions.

Figure 3: Power module HybridPACK Drive IGBT module for electric vehicle main inverter (Image source: Infineon)

Among them, the HybridPACK Drive Flat module (FS660R08A6P2Fx) and the Wave module (FS770R08A6P2x) are low-performance products in the HybridPACK Drive product family, which are cost-effective and suitable for 100kW to 150kW inverters respectively. As a high-end product in the product portfolio, the HybridPACK Drive Performance module (FS950R08A6P2B) is targeted at 200kW inverters. Due to the use of special ceramic materials instead of the commonly used alumina, its heat dissipation performance has been improved by more than 20%, and a higher current carrying capacity can be achieved.

Infineon’s 600V, 650V and 800V N-channel power MOSFETs are mainly aimed at high-performance automotive applications. CoolMOS N-channel MOSFETs are the company’s representative product series, suitable for low-power to high-power applications. There’s a clever balance between high performance and price.

Epilogue

Power semiconductor devices, also known as power electronic devices, are the core devices for power electronic devices to realize power conversion and circuit control. The operating frequency of silicon-based MOSFETs developed in the 1980s has reached the megahertz level. With the emergence of silicon-based IGBTs, power devices have found a solution between high power and high frequency.

In switching applications such as uninterruptible power supplies (UPS), industrial inverters, power control, motor drives, pulse width modulation (PWM), and switching power supplies (SMPS), MOSFETs and IGBTs are outstanding in performance due to their superior characteristics. better than other switching devices. Among them, MOSFETs are mainly used in lower voltage and power systems, while IGBTs are more suitable for higher voltage and power applications.

Driven by the demand for new energy vehicles, smart home appliances, and 5G, the market size of IGBTs and MOSFETs has continued to expand, and more and more companies have entered this field. How to find the product that best suits your needs in a complex market is a headache. In fact, no matter how complicated it is, you only need to pay attention to the main parameters we have introduced above, and I believe that you will definitely find a satisfactory product.