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Industry
Num：33
See：2439
2020-10
10
MOS tube and IGBT tube differences
IGBT tubes are similar in appearance and characteristic parameters, so why do some circuits use MOS tubes? And some circuits use IGBT tubes, right?


1. Structure and classification of MOS tubes
There are two main types of fET: junction fET (JFET) and insulated gate FET (MOS).
MOS tube is MOSFET, the Full Chinese name is metal-oxide semiconductor field effect transistor, because the gate of this kind of field effect tube is isolated by the insulating layer, so it is also called insulated gate field effect tube.

MOSFET can be divided into N groove depletion type and enhanced type. There are four types of P-trench depletion type and enhanced type.

Some MOSFET will have a diode inside, this is the volume diode, or called the parasitic diode, continued flow diode.
There are two explanations for the role of parasitic diodes:
1) The parasitic diode of MOSFET is used to prevent the MOS tube from being burnt out under the condition of VDD overvoltage, because before the overvoltage causes damage to the MOS tube, the diode first breaks down in reverse to direct the large current to the ground, so as to avoid the MOS tube being burnt out.

2) To prevent the MOS tube from burning out when the source and drain of the MOS tube are reversely connected. It can also provide a path for the reverse induced voltage when the circuit has a reverse induced voltage to avoid the reverse induced voltage breakdown of the MOS tube.
MOSFET has high input impedance, fast switching speed, good thermal stability, voltage control current and other characteristics, in the circuit, can be used as an amplifier, electronic switch and other purposes.


2. Structure of IGBT
The IGBT (Party Gate Polaroid), Insulated Gate Bipolar Transistor, is a composite Transistor consisting of a Transistor Transistor and a MOS Transistor.
IGBT, as a new electronic semiconductor device, has the characteristics of high input impedance, low voltage control power consumption, simple control circuit, high voltage resistance, large current bearing and so on. It has been widely used in various electronic circuits.
The volume diodes inside the IGBT are not parasitic, but are specifically designed to protect the IGBT's fragile reverse pressure resistance, also known as FWD (continuous flow diodes).
It is not difficult to determine whether there is a body diode in IGBT. You can use a multimeter to measure the C and E poles of IGBT. If IGBT is good and the resistance value measured at the C and E poles is infinite, then IGBT does not have a body diode.
IGBT is very suitable for applications such as AC motor, frequency converter, switching power supply, lighting circuit, traction drive, etc.


3. Structural features of MOS tube and IGBT
The internal structure of MOS tube and IGBT tube is shown in the figure below.
The ideal equivalent circuit of IGBT is shown in the figure below. IGBT is actually a combination of MOSFET and transistor tride. MOSFET has the disadvantage of high on-resistance, but IGBT overcomes this shortcoming.

In addition, IGBT and MOSFET with similar power capacity may have a slower speed than MOSFET, because IGBT has a long time of turning off and towing, and the dead zone time will also be longer, which will affect the switching frequency.


4. Choose MOS tube or IGBT?
In the circuit, MOS tube is chosen as the power switch tube or IGBT tube, which is a problem often encountered by engineers. If factors such as system voltage, current and switching power are taken into consideration, the following points can be summarized:
The shaded area indicates that both MOSFET and IGBT can be selected. Represents a level that cannot be reached by the current process.
In general, the advantages of MOSFET are that it has good high-frequency characteristics and can operate at frequencies up to several hundred kHz and up MHz. The disadvantages are that it has a large conduction resistance and a large power consumption in high-voltage and high-current situations. And IGBT in low frequency and higher power occasions performance is excellent, its conduction resistance is small, high voltage.
MOSFET is used in switching power supply, ballast, high frequency induction heating, high frequency inverter welding machine, communication power supply and so on. IGBT is mainly used in welding machine, inverter, inverter, electroplating electrolytic power supply, ultra-audio induction heating and other fields.
 

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