IGBT (Insulated Gate Bipolar Transistor) is a composite power semiconductor device that combines the high input impedance of MOSFETs with the low conduction loss characteristics of bipolar transistors (BJTs). It is designed specifically for high voltage and high current scenarios and is a core switching component in the field of power electronics.
Structure and Composition
IGBT is composed of a three terminal four layer structure:
Gate: Similar to MOSFET, the control device conducts through an insulating layer (such as silicon dioxide).
Collector: Connect the high voltage terminal and inject charge carriers.
Emitter: a carrier output terminal that forms a current loop with an external circuit.
It adopts a composite structure of "MOS gate+bipolar transistor" internally:
MOS gate structure: controls input signals and drives low power.
PNP bipolar structure: responsible for the main current path and reducing the conduction voltage drop.
Working principle
IGBT conducts and turns off through gate voltage regulation:
Conduction stage:
Applying a forward voltage to the gate forms a MOS conductive channel, allowing electrons to flow from the emitter to the collector.
The PNP bipolar structure is activated, and holes are injected from the collector, triggering the "conductivity modulation effect" and significantly reducing the on resistance.
Shutdown phase:
The gate voltage returns to zero, the MOS channel disappears, the bipolar structure carrier recombines, and the current gradually cuts off.
Type and Characteristics
Classified by voltage level:
Low voltage type (<1200V): home appliance frequency converter, UPS power supply.
Medium high voltage type (1200V6500V): electric vehicles, industrial frequency converters, photovoltaic inverters.
Ultra high voltage type (>6500V): high-speed rail traction system, smart grid.
According to the packaging form:
Single tube packaging: small and medium power scenarios.
Modular packaging: Integrated freewheeling diode, suitable for high-power systems such as wind power generation.
Core advantages
High Voltage Tolerance: Supports thousands of volts of voltage, far exceeding ordinary MOSFETs.
Low conductivity loss: The conductivity modulation effect reduces heat generation, and the efficiency can reach over 95%.
Moderate switching speed: faster than BJT, slightly slower than MOSFET, balancing speed and loss.
Simple driving: gate voltage control, no need for complex driving circuits.
Typical applications
Electric energy conversion:
Electric vehicle motor controller (DCAC inverter).
Solar inverter (DCAC conversion).
Industrial control:
The frequency converter adjusts the motor speed.
Welding equipment, induction heating power supply.
Power transmission:
Converter valves for high voltage direct current transmission (HVDC).
Rail transit traction converter system.
IGBT solves the contradiction between efficiency and withstand voltage in high-power scenarios by integrating the advantages of MOSFET and BJT, becoming the "electronic heart" of new energy, smart grid and other fields, promoting the advancement of power electronics technology towards higher energy efficiency.