Engineer Column

Harmonizing Circuit Design and EMC DesignPart 1 Summary of Semiconductors (1) Transistors and Diodes


Hello! My name is Inagaki, and I’m with ROHM.

This first part is about transistors and diodes. I did a quick search of the ROHM website to see how many different models of transistors and diodes there are. There are 3,463 kinds of discrete semiconductors (the breakdown being 685 kinds of MOSFET, 1,099 kinds of bipolar transistor, and 1,679 different diodes), and 1,865 kinds of power device (including 552 power transistors, 990 power diodes, 164 SiC power devices, 147 IGBTs, and 22 IPMs), for a total of some 5,338 models of transistors and diodes currently in mass production by ROHM. Truly amazing variety. The very fact that there are so many different kinds of devices means that they are provided for use in many diverse conditions and circumstances.

How in fact do all these various transistors and diodes differ from each other? One type of difference is the device structure (whether a MOSFET, a bipolar transistor, a power device, and so on); another type of differences is the electrical characteristics (rated voltage, maximum current, power, frequency). The former of these is directly related to the device operation. MOSFETs are mainly used in the role of a digital on/off switch, whereas bipolar transistors are primarily used for analog amplification of currents. Power devices, as represented by SiC (silicon carbide) devices and IGBTs (insulated gate bipolar transistors), feature high operating voltages (for example 1,200 V) and large output currents (such as 600 A). The latter differences are the characteristics of the transistors and diodes themselves. Among trends in recent years there have been steady increases in maximum output currents as well as rising operation frequencies.

Today, it is possible to simply select the optimum product from among these options. When selecting a desired product, a web search can be performed, and so by inputting the required characteristics, a list of candidate products is instantly displayed. The details can be checked by downloading PDF files of the data sheets. How convenient it all is today! If you still can’t find what you need, you should be able to obtain some further information by making inquiries via websites or directly asking sales engineers or the like.

Here I’d like to talk about the differences between transistors and diodes as discrete semiconductors (components), and transistors and diodes as part of semiconductor integrated circuits (ICs). Both are encased in resin sealing parts (molded packages), but there are major differences. To begin with, there are the numbers of elements; a discrete semiconductor incorporates a single transistor as a rule, whereas in a semiconductor integrated circuit, there may be as many as 500 million to one billion transistors present. Then there are operating voltages: discrete semiconductors operate at higher voltages (such as the 1,200 V mentioned earlier), whereas some semiconductor integrated circuit products operate at 1 V or less. Where output currents are concerned also, when comparing single transistors, the output current for a discrete semiconductor can be large (such as the aforementioned 600 A), whereas in a semiconductor integrated circuit it is of order 10 μA (10×10-6 A). These differences are due to the differences in the physical dimensions of the transistors. Conceptually, one might imagine a discrete semiconductor as a single huge transistor, whereas a semiconductor integrated circuit incorporates an enormous number of very tiny transistors. Operating frequencies are also very different, being vastly higher for integrated circuits (for example, 3 GHz or the like) than for discrete transistors. Even devices of the same type, whether transistors or diodes, are completely different in their guises as discrete semiconductors and as parts of an integrated circuit.

Finally, a word or two about electromagnetic compatibility (EMC), on which I have been working and which is the theme of this series. The two main types of electromagnetic compatibility (EMC) are electromagnetic interference (EMI) or emission, in which a device itself affects other devices or human bodies through electromagnetic noise, and electromagnetic susceptibility (EMS) or immunity, in which a device is affected by electromagnetic waves from outside and malfunctions. Because harm due to both of these must be prevented, they are referred to in this way. I expect that some readers will be somewhat bewildered at suddenly encountering the term “electromagnetic compatibility” or EMC, so we’ll stop here for today, but from the next article I’d like to explain it, bit by bit, in detail.

Thanks very much for reading!

Information on Downloading Technical Documents

Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.

Download Technical Documents

Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.