Other new power electronic devices

Other new power electronic devices

MOS control thyristor

MOS controlled thyristor (MOS Controlled Thyristor, MCT) is a composite device that combines a pair of MOSFETs and thyristors. MCT effectively combines the MOSFET’s high input impedance, low drive power, fast switching process and the high voltage, high current, and low on-voltage drop characteristics of the thyristor. An MCT device is composed of tens of thousands of MC elements, and each element is composed of a thyristor, a MOSFET that controls the thyristor to turn on, and a MOSFET that controls the thyristor to turn off, as shown in Figure 1a, the graphic symbol of MCT is shown in Figure 1b.

MCT was once regarded as one of the most promising power electronic devices. It became a research hotspot in the 1980s, but because its voltage and current capacity have not been broken through, it has not been put into practical application.

Other new power electronic devices
Figure 1 – MCT equivalent circuit and graphical symbols

Static induction transistor

The Static Induction Transistor (SIT) is a junction field effect transistor, which was born in 1970. SIT is a multi-sub-conducting device (unipolar device), which has the advantages of high output power, low distortion, high input impedance, good switching characteristics and good thermal stability. Its operating frequency is comparable to that of power MOSFETs, and even exceeds that of power MOSFETs. SIT devices can easily realize multiple synthesis in structural design, so they are suitable for high-frequency, high-voltage and high-power applications. Recently, it has been widely used in professional fields such as radar communication equipment, ultrasonic power amplification, pulse power amplification and high-frequency induction heating.

SIT is a multiple integrated structure, which is composed of hundreds of small units connected in parallel. Figure 2a shows the structure of SIT elements. The three poles of the SIT are gate G, drain D, and source S, and their graphic symbols are shown in Figure 2b. SIT is divided into N-channel and P-channel. The arrow in Figure 2b indicates the direction of the gate current when the gate-source junction is forward biased.

Other new power electronic devices
Figure 2 – SIT structure and graphic symbols

SIT is turned on when no signal is applied to the gate, and turned off when the gate is negatively biased. It is called a normal conduction device and is not convenient to use; in addition, the on-state resistance of the SIT is large, which makes the on-state loss also large. SIT can be made into a normally off-type device, but the on-state loss will be greater, so SIT has not been widely used in power electronic equipment.

Static induction thyristor

The Static Induction Thyristor (SITH) was born in 1972 and is obtained by adding an emitter layer with a different conductivity type to the drain layer on the drain layer of SIT. Its working principle is similar to that of SIT. Both the gate and anode voltage can control the anode current through the electric field, so SITH is also called Field Controlled Thyristor (FCT).

SITH is essentially a bipolar device with two types of carrier conduction, with conductance modulation effect, reduced on-state voltage, and strong current flow capability. Many of its features are similar to GTO, but dynamic performance such as switching speed is much superior to GTO, and it is a high-capacity fast device.

According to different structures, SITH is divided into normal on type and normal off type. The SITH of the normal conduction type is developing rapidly at present.

The SITH manufacturing process is more complicated and the cost is high, so its development is affected to a certain extent.

Integrated gate commutated thyristor

Integrated Gate-Commutated Thyristor (IGCT) is sometimes called GCT (Gate-Commutated Thyristor) and is a new type of power electronic device that appeared in the late 1990s.

IGCT is a new type of high-power semiconductor switching device based on the GTO structure, the use of an integrated structure for gate drive, and the use of a buffer layer structure and anode transparent emitter technology. It has the advantages of stable turn-off capability of the transistor and low on-state loss of the thyristor. This type of device integrates a freewheeling diode with good dynamic characteristics on a chip, thereby realizing the organic combination of the low on-state voltage drop, high blocking voltage of the thyristor and the stable switching characteristics of the transistor in its unique way.

Compared with GTO, the capacity of IGCT is equivalent to that of ordinary GTO, but the switching speed is 10 times faster than that of ordinary GTO. Because IGCT has high-speed switching capability and does not need a snubber circuit, it simplifies the large and complex snubber circuit in ordinary GTO applications, and the reliability of operation is greatly improved; but the required driving power is still very large.

IGCT has the characteristics of large current, high blocking voltage, high switching frequency, high reliability, compact structure, low conduction loss, low manufacturing cost and high yield. It is currently mainly used in power systems.