MOSFET and IGBT Working Principle and Structure

Working principle and structure

MOSFET is the abbreviation for metal oxide semiconductor field-effect transistor. It is a voltage-controlled device that controls the drain current by controlling the gate voltage. The structure of MOSFETs can be divided into two types: enhanced and depleted. Enhanced MOSFETs are cut off when the gate voltage is zero and require a certain forward or reverse voltage to conduct; The depletion type MOSFET is conductive when the gate voltage is zero and requires a certain reverse or forward voltage to cut off. The main advantages of MOSFETs are fast switching speed, low switching loss, small input capacitance, and simple driving. However, they also have some drawbacks, such as high conduction resistance, high conduction loss, and weak breakdown resistance, and are not suitable for high-voltage and high-current applications.

IGBT is the abbreviation for insulated gate bipolar transistor, which is a current-controlled device that controls the collector current by controlling the gate current. The structure of IGBT is to add a P-type substrate layer on top of MOSFET, forming a PNP type bipolar transistor. The main advantages of IGBT are small conduction resistance, low conduction loss, strong breakdown resistance, and suitability for high-voltage and high-current applications. However, there are also some drawbacks, such as slow switching speed, high switching loss, large input capacitance, and complex driving.

Switch Characteristics

The switching speed of MOSFETs is fast, but there is a reverse recovery current, which increases the turn-on loss. The switching speed of IGBT is slow, but there is no reverse recovery current, so the opening loss is small. In high-frequency applications, MOSFETs have lower switching losses, while IGBTs have higher switching losses.

Conduction characteristic

The conduction resistance of MOSFETs is proportional to temperature, so as the temperature increases, the conduction loss increases. The conduction voltage of IGBT is inversely proportional to temperature, so as the temperature increases, the conduction loss decreases. In low-voltage applications, MOSFETs have smaller conduction losses, while IGBTs have larger conduction losses.

Safe Work Area

The safe working area of MOSFETs is limited by diodes and cannot withstand reverse voltage. The safe working area of IGBT is limited by transistors and cannot withstand excessive current. In high-voltage applications, MOSFETs have a smaller safe working area, while IGBTs have a larger safe working area.

drive circuit 

MOSFET is a voltage control device that needs to provide a constant gate voltage to drive. IGBT is a current control device that needs to provide a constant gate current to drive. Therefore, the driving circuit of MOSFETs is relatively simple, while the driving circuit of IGBTs is more complex.

Application scope

MOSFETs are suitable for low-voltage and high-frequency applications, such as switching power supplies, inverters, etc. IGBT is suitable for high voltage and low-frequency applications, such as motor control, frequency converters, etc.

In summary, MOSFETs and IGBTs have their own advantages and disadvantages in different application scenarios. If the application is low voltage and high frequency, requiring fast switching and small switching losses, MOSFETs can be chosen; If the application is high voltage and low frequency, and requires a smaller conduction resistance and greater resistance to breakdown, IGBT can be chosen. In practical applications, other factors such as cost, reliability, etc. need to be considered before selecting suitable devices.