RFMOSFET vs IGBT: Understanding Key Differences and Applications
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This article compares MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors), highlighting their differences and providing a table to aid in selecting the appropriate device for a given application.
What is a MOSFET?
MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. There are two main types of MOSFETs: n-channel and p-channel. They can also be classified as Depletion MOSFETs and Enhancement MOSFETs.
Figure 1: 600 Volt SJ-MOSFET structure and circuit symbol.
What is an IGBT?
IGBT stands for Insulated Gate Bipolar Transistor.
Figure 2: 600 Volt G6H Trench IGBT structure and circuit symbol.
While the structures of MOSFETs and IGBTs might appear similar at first glance, a crucial difference lies in the addition of a p-substrate beneath the n-substrate in the IGBT.
There are two primary IGBT structures:
- NPT-IGBT: Also known as a homogeneous structure.
- PT-IGBT: Also known as an epitaxial structure. PT-IGBTs exhibit characteristic epitaxial layers with an N+-doped region (buffer layer) and an N—region on a p-doped substrate wafer. NPT-IGBTs utilize a homogeneous N—doped wafer. A specially formed p-layer is created on the backside during wafer processing.
MOSFET vs IGBT: Choosing the Right Device
When deciding between an IGBT and a MOSFET, consider the breakdown voltage requirements. Generally:
- IGBTs are preferred for breakdown voltages greater than 1000V.
- MOSFETs are preferred for breakdown voltages less than 250V.
Figure 3: Comparison of output characteristics between MOSFET and IGBT.
Tabular Comparison: MOSFET vs IGBT
The following table summarizes the key differences between MOSFETs and IGBTs, aiding in device selection based on application and design needs.
| Feature | MOSFET | IGBT |
|---|---|---|
| Preferred device based on conditions | ||
| High Switching Frequency | > 100kHz | <20kHz |
| Wide line and load conditions | High Power levels (above say 3 kW) | |
| dv/dt on the diode is limited | High dv/dt needed to be handled by the diode | |
| High light load efficiency is needed | High full load Efficiency is needed | |
| Preferred device based on applications | ||
| Motor Drives | <250W | > 250W |
| Power Supplies | Universal input AC-DC flyback and forward converter power supplies | UPS and Welding H Bridge inverters |
| PFCs | Low to Mid power (75W to 3 kW) | High power (> 3kW) |
| Solar Inverters | Solar Micro Inverters | High Power Solar/Wind Inverters (> 5kW) |
| Applications | • SMPS (Hard switching greater than 200 KHz), • SMPS (ZVS less than 1000 watts), • Battery charging | • UPS(constant load, typically at low frequency), • Welding(high average current, low frequency <50KHz, ZVS circuitry), • Motor control(frequency <20KHz, short circuit/in-rush limit protection ) • Low power lighting(low frequency < 100 KHz) |
This comparison should provide a clear understanding of the differences between MOSFETs and IGBTs, facilitating informed decision-making for your specific application.
