Introduction

We will be adding new articles related to “power devices” to Tech Web’s “Basic Knowledge”. Recently, discrete devices such as diodes and transistors for handling large power with small loss, known as “power devices” or “power semiconductors”, have gathered attention. The reason is that power devices with higher efficiency and higher performance are needed to address “energy savings” and “miniaturization”, which are issues throughout the world.

However, what specific definitions should we use to categorize these “power devices” that one hears so much about today? Certainly there are no clear categories, but for example there are diodes and MOSFETs for AC-DC conversion or power switching with high voltage and high power, and then there are power modules that are modularized for output stages of power supply.

Here we will break things down into “silicon (Si) power devices” that are based on the conventional silicon semiconductor devices, and “silicon carbide (SiC) power devices” that have low loss and excellent characteristics in high-temperature environments compared to Si devices, and which are therefore expected to be the next generation low-loss elements. For power devices it is natural that attention is focused on new materials such as SiC, but there also are stunning performance improvements in the Si power devices that currently cover a wide range of markets and applications. At the present time one uses the best power devices according to the application and the specifications, so we will cover power devices in a rather wide sense.

Si Power Devices

We will break down our discussion of Si devices into four sections:

1. Si Diodes
   • Classification and Characteristics
   • Schottky Barrier Diodes
   • Fast Recovery Diodes
2. Si Transistors
   • Classification and Characteristics
   • High-Voltage MOSFETs
3. Methods of Selecting Transistors
   • Selection Process
   • SOA, Ratings, Temperature
4. Application Examples with Special Characteristics

There are many types of Si diodes and MOSFETs, and they have a lot of variation with regard to voltage rating and current. Among these, we will mainly consider power supply applications, and with regard to Si diodes we will cover Schottky barrier diodes and fast recovery diodes. For MOSFETs we will concentrate on high-voltage super-junction MOSFETs.

We will introduce the procedures and the decision methods for selecting transistors based on the required specifications, giving application examples that make use of the characteristics of diodes and transistors.

For each of these we will include basic information. For a power supply of several tens of watts, the power device is incorporated in a power supply IC, and it has become rare to choose a separate MOSFET and verify its operation. However, it is important to master the use of discrete parts in a high-power circuit. Future articles will check again the characteristics and specification values of diodes and transistors, and they will provide an opportunity to learn about the latest Si power devices characteristics and performance.

• Si power device
• SiC power device
• MOSFET
• Schottky barrier diode
• Fast recovery diode