BASIC KNOWLEDGE - SEMICONDUCTORS What you need to know about power semiconductors
Power semiconductors perform the same tasks as regular semiconductors—only on a much larger scale. These high-performance components are capable of handling extremely high electrical currents, voltages, and frequencies.
Power semiconductors are typically used for industrial applications and the longdistance transmission and distribution of electricity.
What is a power semiconductor?
Like all semiconductor devices, power semiconductors are used to rectify and amplify electrical signals or turn the flow of electricity on and off. Unlike regular semiconductors, however, these devices are designed to handle high electrical currents and high voltages of up to several gigawatts.
As components in power management subsystems, power semiconductors are typically used as switching devices and rectifiers (to convert electrical signals), as well as to change the voltage or frequency of an electrical current.
There are three types of power switches: metal-oxide-silicon transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs) and bipolar junction transistors (BJTs), the latter of which are either used discretely or as part of power integrated circuits (PICs).
The main industries that benefit from power semiconductors are power transmission and distribution, automotive and transport, renewable energy, consumer electronics, and other industrial applications. They play a key role in the sustainable and efficient use of energy, and can be used to transport energy over long distances with minimal losses.
Si, SiC, and GaN, explained
The semiconductor material silicon (Si) is still used for many high-voltage and high current applications today, though it has been joined by silicon carbide (SiC) and gallium nitride (GaN) in recent years. The latter two materials have a wider bandgap, which significantly reduces power loss and increases efficiency. Of these semiconductor materials, GaN offers the best performance.
An overview of power semiconductor categories
Power semiconductors employed in power management system can, as mentioned above, be devided into different categories. Below is a brief introduction to the four key categories of power semiconductors:
Power metal-oxide-silicon transistors are fully controllable power semiconductor switches designed to handle large amounts of power. They are the most commonly used type of power transistor and perform particularly well at high frequencies. As four-terminal devices, they feature gate, drain, source, and body terminals. Power MOSFETs offer low gate drive power, rapid switching speed, wide bandwidth, in addition to being easy to operate and repair. The input voltage controls the component’s output current.
Insulated-gate bipolar transistors are another type of fully controllable power semiconductor switch, and are often used for low-to-medium frequency applications. Like power MOSFETs, they have a high impedance gate, so they require very little power to switch a device on or off. IGBTs have high power ratings and low on-state voltage, and are typically used as a discrete device in power electronics units such as air conditioners and electric cars.
Thyristors are semi-controllable power semiconductor switches with two or three terminals. Also known as silicon-controlled rectifiers, they control the flow of an electrical current in unidirectional or bi-directional circuit configurations. These components are often used to protect circuits in home appliances, electrical tools and outdoor equipment.
Power diode (rectifier)
Power diodes are uncontrollable power semiconductor devices capable of rectifying very strong electrical signals. They can handle hundreds of amperes and thousands of kilovolts. These components feature an anode terminal, a cathode terminal and a semiconductor consisting of a P-N junction. The P-N junction in power diodes is larger than in regular diodes. The P and N layers are both doped, although one is doped more highly than the other.
Reliability and failure
Power semiconductors can easily fail if they are exposed to an excessively high operating voltage, or a high voltage and high current at the same time. Overvoltage can puncture an insulator, such as the gate oxide layer on a power MOSFET or IGBT. This is why it is often recommended to operate them at 20 percent below their stated voltage rating to ensure reliable operation.
Overheating is another major reason why power semiconductors can fail. Electronic components naturally heat up due to on-resistance, i.e. the resistance between the drain and source when a transistor is in operation. The greater the on-resistance, the higher the power loss and the more heat that is produced. It is therefore essential to take thermal management into consideration in any power electronics system. Research is currently being conducted into ways to reduce on-resistance and to better insulate and protect high-performance components.