Semiconductor Devices in Power Electronics

Background

Power semiconductor devices are at the heart of power electronics circuits. Overall system reliablity and efficiency depend on the quality of semiconductor switches and how these devices are used. Throughout the last 50 years, power electronics technology mostly evolved with the availability of new and improved power semiconductor devices. In the past few years, device technology has made tremendous progress. High power bipolar transistors have become mature products and have been used for many applications such as motor drives, uninterruptible power supplies(UPS), and solid-state relays.

The impact of the power MOSFET

During the same period, a wide variety of MOSFETs have become available and subsequently gained the acceptance of their users. Today, MOSFET switching frequency capability has increseased standard commercial power supply PWM frequencies of ten years ago from 20kHz to 50kHz and beyond. PWM frequency in the low hundred kilohertz range is no longer unusual and some products are already using PWM frequencies approaching the megahertz range. This trend is expected to continue.

Other types of devices

In the past ten years, noticeable progress has also been make in the GTO technology. Large GTOs have found applications in high power traction drivers, high power UPS systems, and other areas traditionally controlled by SCRs. The relatively recent introduction of insulated gate bipolar transistors (IGBT) has provided the user with a versatile device. This new device combines the MOS input and the bipolar output characteristics into one device. It has gained quick acceptance by users in the off-line, high-power moter drives field and in the UPS industry. Because of its relatively low chip area requirement, it is expected that in the future, this device structure will be commonly used in the intergrated power circuit.

Ongoing research and industrial development

No devices are without problems when first introduced. It takes strong interaction between users and manufacturers to perfect them. There are many examples of such efforts that subsequently led to better devices and solutions for many application problems. To name a few, there were the reverse recovery problem of diodes, the dv/dt false turn-off of the MOSFET parasitic bipolar transistors, the reverse-bias second breakdown problem of the bipolar transistor, the latching failure of the IGBT, and the dv/dt problem of a GTO. These problems, however, have been resolved in certain degree.

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