A brief analysis of the working principle and function of IGBT

 This article explains the working principle and function of IGBT in an easy-to-understand manner through equivalent circuit analysis, and briefly points out the characteristics of IGBT. It can be said that IGBT is an on-off switch that has the advantages of high input impedance of MOSFET and low conduction voltage drop of GTR.

IGBT (Insulated Gate Bipolar Transistor) is a composite fully controlled voltage-driven power semiconductor device composed of BJT (Bipolar Transistor) and MOS (Insulated Gate Field Effect Transistor). It has the high input impedance and GTR's low conduction voltage drop has two advantages. The GTR saturation voltage is reduced, the current carrying density is large, but the driving current is large; the MOSFET driving power is small, the switching speed is fast, but the conduction voltage drop is large, and the current carrying density is small.

IGBT combines the advantages of the above two devices, with low driving power and reduced saturation voltage. It is very suitable for use in converter systems with DC voltages of 600V and above, such as AC motors, frequency converters, switching power supplies, lighting circuits, traction drives and other fields.

At present, there is a lack of high-quality IGBT modules in China, and almost all of them are imported. The insulated gate bipolar transistor (IGBT) is the youngest member of the high-voltage switch family. A 15V high-impedance voltage source can conveniently control the current flow device, thereby controlling high current with lower control power.

An easy-to-understand version of the working principle and function of IGBT:

IGBT is a switch, it is either on or off. How to control its on or off depends on the voltage of the gate and source. When +12V (greater than 6V, usually 12V to 15V) is applied to the gate and source, the IGBT is turned on, and the gate When no voltage is applied to the source or negative voltage is applied, the IGBT is turned off. The purpose of adding negative voltage is to ensure reliable turn-off.

IGBT does not have the function of amplifying voltage. When it is on, it can be regarded as a wire, and when it is disconnected, it is regarded as an open circuit.

IGBT has three terminals, namely G, D, and S. After voltage is applied to both ends of G and S, the internal electrons are transferred (characteristics of semiconductor materials, which is why semiconductor materials are used as power electronic switches). Originally, There is a one-to-one correspondence between positive ions and negative ions. The semiconductor material is neutral, but after a voltage is applied, the electrons accumulate to one side under the action of the voltage, forming a conductive channel, because the electrons can conduct electricity and become a conductor. . If the voltage applied to both ends of GS is removed, the conductive channel in this layer will disappear, it will no longer conduct electricity, and it will become an insulator.

The working principle and function of IGBT circuit analysis version:

The equivalent circuit of IGBT is shown in Figure 1. As can be seen from Figure 1, if a positive driving voltage is applied between the gate and emitter of the IGBT, the MOSFET will be turned on, so that the collector and base of the PNP transistor will be in a low resistance state and the transistor will be turned on; if the IGBT When the voltage between the gate and emitter is 0V, the MOSFET turns off, cutting off the supply of base current to the PNP transistor, causing the transistor to turn off.

Figure 1 Equivalent circuit of IGBT

It can be seen that the safety and reliability of IGBT are mainly determined by the following factors:

--The voltage between IGBT gate and emitter;

--The voltage between the IGBT collector and emitter;

--Current flowing through IGBT collector-emitter;

--IGBT junction temperature.

If the voltage between the IGBT gate and emitter, that is, the driving voltage, is too low, the IGBT cannot work stably and normally. If it is too high and exceeds the withstand voltage between the gate and the emitter, the IGBT may be permanently damaged; similarly, if The allowable voltage applied to the IGBT collector and emitter exceeds the withstand voltage between the collector and the emitter, the current flowing through the IGBT collector-emitter exceeds the maximum allowable current of the collector-emitter, and the junction temperature of the IGBT exceeds its If the junction temperature exceeds the allowable value, the IGBT may be permanently damaged.

Insulated gate bipolar transistor (IGBT)