We know that power devices are the core of power conversion and circuit control in electronic devices. They utilize the unidirectional conductivity of semiconductors to change voltage, frequency, phase, and DC/AC conversion functions within electronic devices. Based on controllability and other usage factors, power devices are classified into many categories, among which common classifications include:
1. MOS Controlled Thyristor (MCT)
MCT is a novel composite device combining MOSFET and bipolar transistors. It combines the high impedance and low drive characteristics of MOSFET, the power and fast switching speed of MCT, with the high voltage and high current characteristics of thyristor, forming a high-power, high-voltage, fast, fully controllable device. Essentially, an MCT is a MOSFET gate-controlled thyristor. It can be turned on or off by applying a narrow pulse to its gate, and it is composed of numerous parallel unit cells.
Its characteristics include: a simpler drive circuit than that of a GTO; and a forward voltage drop comparable to that of an SCR, lower than that of an IGBT and a GTR. MCTs feature high voltage, high current, high input impedance, low drive power, low forward voltage drop, fast switching speed, and low switching losses. Furthermore, MCTs have extremely high di/dt and du/dt withstand capabilities, which simplifies their protection circuitry.
2. IGCT Integrated Gate Commutated Thyristors
IGCT is a novel device developed based on thyristor technology, combined with IGBT and GTO technologies. It features high current handling, high blocking voltage, high switching frequency, high reliability, compact structure, and low conduction loss. It is a new type of power semiconductor device used in large-scale power electronic systems, suitable for high-voltage, high-capacity frequency conversion systems, and boasts low cost, high yield, and promising application prospects.
The IGCT integrates a GTO chip with an anti-parallel diode and gate drive circuit, and connects it to its gate driver externally in a low-inductance manner. It combines the stable turn-off capability of a transistor with the low on-state loss of a thyristor. It exhibits thyristor performance during the turn-on phase and transistor characteristics during the turn-off phase.
3. Integrated Power Electronics Modules (IPEM)
IPEM is a modular system that integrates numerous components of a power electronic device. It begins by packaging semiconductor devices such as MOSFETs, IGBTs, or MCTs with diodes into a single chip, forming a building block. These building blocks are then stacked onto an open-cell, high-conductivity insulating ceramic substrate. Below this, a copper substrate, a beryllium oxide ceramic plate, and a heat sink are arranged in sequence. On top of the building blocks, control circuitry, gate drives, current and temperature sensors, and protection circuitry are integrated onto a thin insulating layer using surface mounting. IPEM enables intelligent and modular power electronics technology, significantly reducing circuit wiring inductance, system noise, and parasitic oscillations, thereby improving system efficiency and reliability.
4. Ultra-high power thyristors
Since its invention, the power capacity of thyristors (SCRs) has increased nearly 3,000 times. In the past decade or so, due to the rapid development of self-turn-off devices, the application areas of thyristors have shrunk somewhat. However, due to their high voltage and high current characteristics, they still occupy a very important position in HVDC, static var compensators (SVCs), high-power DC power supplies, and ultra-high power and high-voltage variable frequency speed control applications.
The device's unique structural and fabrication features include: a long gate-cathode perimeter forming a highly interwoven structure; the gate area accounting for 90% of the total chip area, while the cathode area accounts for only 10%; and a long hole-electron lifetime in the base region, with the horizontal distance between the gate and cathode being less than a diffusion length. These two structural features ensure that the cathode area can be 100% utilized at the moment of turn-on. Furthermore, the cathode electrode employs a relatively thick metal layer, capable of withstanding instantaneous peak currents.
The characteristics of ultra-high power thyristors include:
1) When a thyristor is subjected to a reverse anode voltage, it will be in a reverse blocking state regardless of the voltage applied to the gate.
2) When a thyristor is subjected to a forward anode voltage, it will only conduct when a forward voltage is applied to its gate. At this time, the thyristor is in the forward conduction state, which is the thyristor's thyristor current-carrying characteristic, or controllable characteristic.
3) When the thyristor is in the conducting state, as long as there is a certain positive anode voltage, the thyristor will remain conducting regardless of the gate voltage. That is, once the thyristor is turned on, the gate becomes ineffective. The gate only serves as a trigger.
4) When the thyristor is conducting, it will turn off when the main circuit voltage (or current) decreases to near zero.
5) The condition for a thyristor to conduct is that a positive voltage should be applied between the anode and cathode, and an appropriate positive voltage should also be applied between the gate and cathode. To turn off a conducting thyristor, the positive voltage between the anode and cathode must be removed or reversed.
