Modern insulated gate bipolar transistors (IGBTs) are commonly deployed as voltage-controlled bipolar device having metal-oxide semiconductor (MOS)-like input characteristics and bipolar output features. The introduction of the IGBT has allowed electronics engineers to reap the benefits of both the power MOS field-effect transistor (MOSFET) and the small-signal bipolar transistor (BJT) as a single piece of hardware that combines the functionality of power MOSFET and BJT components. The structure combines the simple gate-drive characteristics of MOSFETs with the high-current and low-saturation-voltage capability of bipolar transistors.
The term "insulated gate" describes the high input impedance of the MOSFET's input as it uses the voltage at its gate terminal rather than an external supply. The term "bipolar" describes the BJT's output region, where current flows via two charge carriers: electrons and holes. Because of this, it is able to manage enormous currents and voltages with only a little signal voltage. The IGBT is a voltage-controlled device due to its hybrid construction.
The value of IGBTs in power electronics
Power electronics find widespread use for IGBTs, particularly in pulse width modulation (PWM) servo and three-phase drives that call for precise control over a wide range of speeds with minimal background noise. These devices can also be utilized in power circuits that need frequent switching, such as uninterruptible power supply (UPS) and switched-mode power supply (SMPS) systems. IGBT boosts efficiency and reduces noise, making it a more dynamic performer in inverter circuits in automobiles and trucks, as well as in industrial motors and household appliances like air conditioners and refrigerators.
Additionally, IGBTs are also commonly used in renewable energy systems such as solar and wind power inverters, where they help to efficiently convert DC power into AC power for use in homes and businesses. They can handle high voltage and current levels, making them ideal for these applications. The technology works just as well in resonant-mode converter circuits and induction cookers. Commercially available IGBTs have low switching and conduction losses.
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Common uses of IGBTs
Let's take an example of an inducting heating circuit. Zero-voltage switching or zero-current switching is used in induction heating to minimize switching loss. IGBTs are frequently preferred as a switch here because of a high resonance voltage or current. Particularly, induction microwave ovens, induction rice cookers and other induction cooking appliances are all possible because of the use of IGBTs. Similarly, in UPS systems, IGBTs are available in both medium and large capacity (several kVA or greater capacity) types, which contribute to both space saving and high efficiency.
Another example is a voltage source converter (VSC). IGBTs have high voltage and current ratings, which allows for a level of control and flexibility not attainable with thyristors. Their use supports the implementation of multiterminal DC lines, and the difficulty of filtering the current harmonics on the AC side of the converter is reduced by the application of PWM and multilayer converter techniques. Since high voltage DC (HVDC) employing VSCs is becoming more widespread at higher voltages and currents thanks to the relentless advancement of the IGBT, DC lines emerge as a more appealing alternative for shorter lines since they allow for greater control of flow routes on the grid.
Benefits of IGBTs over BJT and MOSFET
- The conductivity modulation results in an extremely small on-state voltage drop, and a high on-state current density. This allows for a reduction in chip size and price.
- Input MOS gate layout provides low driving power capability and a straightforward drive circuit. In high current and voltage applications, this allows for simpler regulation than current-controlled devices.
- Large safe operating area. In comparison to the bipolar transistor, it is much better at conducting current, and proves superior in both forward and reverse blocking capabilities.
Drawbacks of IGBTs over BJT and MOSFET
- Because of the four alternating PNPN-layered internal construction, latch-up can occur. Once an IGBT enters latch-up, the gate no longer has any control over the collector current and turning it off requires forced commutation of the current much like a regular thyristor. IGBTs are easily damaged by the significant power dissipation that results from a prolonged latch-up state.
- The switching speed is slower than a power MOSFET but faster than a BJT. Turnoff time is slow because of collector current tailing caused by the minority carrier.
Conclusion
IGBTs are voltage-controlled bipolar devices with MOS-like input characteristics and bipolar output features, used in power electronics circuits such as inverters, UPS, VSCs and inducting heating circuits. Commercially available IGBTs have low switching and conduction losses, and offer many advantages over BJT and MOSFET, such as small on-state voltage drop, high on-state current density, low driving power, simpler regulation, a large safe operating area, and superior forward and reverse blocking capabilities. Additionally, IGBTs have a fast-switching speed and are capable of handling high power levels, making them ideal for use in power electronics applications such as HVDC transmission systems.
