The Ultimate Guide to Power Semiconductor Devices: Everything You Need to Know

1. Uncontrolled turn-on and off devices (e.g. diode)
2. Controlled turn-on and uncontrolled turn-off (e.g. SCR)
3. Devices with controlled turn-on and off features include BJTs, MOSFETs, GTOs, SITHs, SITs, MCTs, and IGBTs. Notably, IGBTs combine MOSFET input control with the current-handling capability of traditional transistors. As a result, these components offer efficient and precise switching for advanced power applications.

• In the power circuit, the switching of diodes is carefully managed. Specifically, control signals are used to turn thyristors ON, while turning them OFF necessarily requires direct intervention from the power circuit. In contrast, control signals can directly turn controllable switches—such as BJTs, MOSFETs, GTOs, SITHs, IGBTs, SITs, and MCTs—both ON and OFF. Consequently, these fundamental differences in switching control mechanisms are crucial for designing effective and reliable power electronic systems. Ultimately, understanding these distinctions enables engineers to select the appropriate devices for specific applications.
• Firstly, BJT, MOSFET, IGBT, and MCT are unipolar voltage devices, while thyristors and GTOs handle voltages of both polarities. Moreover, BJT, MOSFET, IGBT, and SIT need a continuous gate signal to stay ON. In contrast, SCR, GTO, SITH, and MCT turn ON with a short gate pulse and continue conducting without ongoing gate drive. As a result, these differences help engineers select suitable devices for each application.
• Specifically, Triac and RCT (reverse conducting thyristor) possess bidirectional current capability, whereas all other devices—such as diodes, SCRs, GTOs, BJTs, MOSFETs, IGBTs, SITs, SITHs, and MCTs—are unidirectional current devices. Consequently, this distinction plays a key role in determining their applications in AC or DC circuits.
• As the evolution of new and advanced devices continued, the voltage and current ratings and electrical characteristics of the existing devices began improving dramatically. In fact, the device evolution along with converter,control and system evolution was so spectacular in the last decade of 20th century, that we define it as the "decade of power electronics".
• Engineers use thyristors for high-power, low-frequency applications. Devices are available with 8000 V and 4000 A ratings. ABB recently introduced a monolithic ac switch that has the voltage ratings of 2.8 kV-6.5 kV and current ratings of 3000-6000 A. The advent of large GTOs push the thyristor voltage-fed inverter from the market. Currently, GTOs are available with 6000 V, 6000 A (Mitsubishi) ratings for large voltage-fed inverter applications.
• Power MOSFET has grown in rating, but it's primary popularity is in high frequency switching mode power supply and portable appliances. The BJT appeared and then fell into obsolescence due to the advent of IGBT at the higher end and power MOSFET at the lower end. The invention of IGBT is an important milestone in the history of power semiconductor devices.
• Commercial IGBTs are available with 3500 V, 1200 A, but upto 6.5 kV and 10 kV devices are under test in laboratory. Trench gate IGBT with reduced conduction drop is available upto 1200 V, 600A. IGBT intelligent power modules (IPM) from a number of vendors are available for 600 V, 50-300 A and 1200 V, 50-150 A to cover upto 150 hp ac drive applications.
• Integrated Gate-Commutated Thyristor (IGCT) is basically a hard-driven GTO with built-in gate driver, and the device is available with 6000 V, 6000 A (10kV devices are under test). Recently, ABB introduced reverse blocking IGCT (6000 V, 800 A) for use in current-fed inverter drives. Large band gap power semiconductor device with silicon carbide (SiC) that has high carrier mobility, high electrical and thermal conductivities and strong radiation hardness is showing high promise for next generation power devices.
• Manufacturers can fabricate these devices for higher voltage, higher temperature, higher frequency, and lower conduction drop. They have already introduced SiC diodes commercially, and they expect to release other devices in the future.

The Various Kinds of Power Semiconductor Devices

1. Diodes: Diodes are basic semiconductors allowing current in one direction. They’re used in rectifiers to convert AC to DC and in circuits to catch voltage spikes, protecting other parts.
2. Transistors: These three-terminal devices—emitter, base, and collector—are widely used in power electronics, mainly as BJTs and MOSFETs.
3. BJT: BJT are very reliable and can handle the high current flow. Engineers more often use them for amplification and switching circuits.
4. MOSFET:The MOSFET have greater switching speeds and lower power losses as compared to the BJTs, they are therefore compatible with high frequency switching applications such as the inverter drives in the power system and switching power supplies.
5. Insulated Gate Transistors (IGTs): These devices combine the fast switching of MOSFETs with the high current-handling ability of traditional power transistors. Engineers commonly use them in motor drives, solar inverters, wind systems, and industrial automation.
6. Thyristors:Thyristors are four-layer semiconductors that handle large currents under voltage. Engineers use them widely in high-power switching for motor control, voltage regulation, and AC power management.

Working Principles of various Power Semiconductor Devices