What is IGBT? Insulated Gate Bipolar Transistor

The Insulated Door Bipolar Transistor, also called IGBT for short, is a cross between the traditional Bipolar Junction Transistor (BJT) and the Field Effective Transistor (MOSFET), making it ideal as a semiconductor switching device.

The IGBT Transistor takes the best parts of these two types of common transistors, the high input impedance of a MOSFET and the low saturation voltage of a bipolar transistor with high switching speeds, and combines them to produce another type of transistor switching device. with almost zero gate current drive, it can process large collector-emitter currents.

IGBT
Typical IGBT

Insulated Door Bipolar Transistor (IGBT) combines MOSFET's insulated door (hence the first part of its name) technology with the output performance characteristics of a traditional bipolar transistor (hence the second part of its name).

IGBTs are used in power electronics applications such as inverters, converters and power supplies where the demands of the solid state switching device are not fully met by power bipolares and power MOSFeTs. High current and high voltage bipolars are available, but switching speeds are slow. Power MOSFETs may have higher switching speeds, but high voltage and high current devices are expensive and difficult to obtain.

The advantage of the ins isolated door bipolar transistor device over a BJT or MOSFET is that MOSFET offers more power gain than the standard bipolar type transistor, along with higher voltage operation and lower input losses. In reality, as shown, the Darlington type is a FET integrated with a bipolar transistor in the form of configuration.

Insulated Door Bipolar Transistor

IGBT
Insulated Door Bipolar Transistor

We can see that the bipolar transistor with insulated gate is a three-terminal transconductance device that combines an insulated gate N-channel MOSFET input connected in a kind of Darlington configuration with a PNP bipolar transistor output.

As a result, the terminals are labeled as Collector, Emitter and Gate. Two of its terminals (C-E) are associated with the passing conductivity path, while the third terminal (G) controls the device.

The amount of amplification obtained by the ins isolated gate bipolar transistor is a ratio between the output signal and the input signal. The amount of gain for a traditional bipolar connection transistor (BJT) is approximately equal to the ratio of the output current, called Beta, to the input stream.

Since the metal oxide semiconductor area is insulated from the main current transport channel within the effective transistor or MOSFET, there is no input current. Therefore, the gain of a FET is equal to the rate of input voltage change of the output current change, which makes it a conductivity device, which also applies to IGBT. Then we can consider IGBT as a power BJT provided by a MOSFET.

Insulated Door Bipolar Transistor can be used in the same way as BJT or MOSFET type transistors in small signal amplifier circuits. However, since IGBT combines the low transmission loss of a BJT with the high switching speed of a power MOSFET, an optimal solid state switch is available, ideal for use in power electronics applications.

In addition, IGBT has RON resistance in a much lower "case" than an equivalent MOSFET. This means that the I2R drop is much lower throughout the bipolar output structure for a specific switching current. The forward blocking process of the IGBT transistor is the same as a power MOSFET.

When used as a static controlled switch, the insulated gate bipolar transistor has voltage and current ratings similar to that of the bipolar transistor. However, the presence of an isolated gateway in an IGBT makes driving much simpler than BJT, as less drive power is required.

An isolated door bipolar transistor is simply made "ON" or "OFF" by activating and disabling the Door terminal. Applying a positive input voltage signal to the door and transmitter, while keeping the device in an "ON" state, making the input door signal zero or slightly negative, causes it to become "OFF" in the same way as a bipolar transistor. or eMOSFET. Another advantage of IGBT is that it has a much lower in-case channel resistance than a standard MOSFET.

IGBT Properties

IGBT

Since IGBT is a voltage-controlled device, unlike BJTs, which require the base current to be fed adequately to maintain continuous saturation, it requires only a small voltage on the Gate to maintain transmission through the device.

In addition, IGBT is a one-way device, that is, unlike MOSFETs with duplex current switching properties (controlled forward and uncontrolled in reverse), it can only switch the current "forward", that is, from collector to transmitter. .

The principle of operation of the ins isolated gate bipolar transistor and the Gate drive circuits are very similar to that of the N-channel power MOSFET. The main difference is that the resistance offered by the main conductive channel when the current flows from the device in the case of "ON" is much smaller in IGBT. Therefore, the available values are much higher compared to the equivalent power MOSFET.

The main advantages of using the Insulated Door Bipolar Transistor compared to other types of transistor devices, coupled with high voltage capacity, low ON resistance, ease of driving, relatively fast switching speeds and zero-gate drive current, make it a good choice for medium speed. high voltage applications such as pulse width modulation (PWM), variable speed control, switch mode power supplies or solar DC-AC inverter and frequency converter applications running in hundreds of kilohertz ranges.

A general comparison between BJTs, MOSFETs, and NSCTs is given in the following table.

IGBT Comparison Table

IGBT
IGBT Comparison Table

We found that the Ins isolated Door Bipolar Transistor is a controlled semiconductor switching device such as an effective transistor, MOSFET, which has the output properties of a bipolar connection transistor (BJT) but receives a metal oxide.

One of the main advantages of the IGBT transistor is that it can be made "ON" by applying a positive door voltage or "OFF" by allowing the door signal to be used in various ways by making it zero or slightly negative. switching applications. It can also be driven in the linear active zone for use in power amplifiers.

With lower condition resistance and transmission losses, as well as the ability to change high voltages at high frequencies without damage, the Insulated Door Bipolar Transistor makes it ideal for driving inductive loads such as coil windings, electromagnets and DC motors.