Power Semiconductor Devices

Power semiconductor devices first appeared in 1952 with the introduction of the power diode. The thyristor appeared in 1957.Thyristors are able to withstand very high reverse breakdown voltage and are also capable of carrying high current.

One disadvantage of the thyristor for switching circuits is that once it is ‘latched-on’ in the conducting state it cannot be turned off by external control.

The first bipolar transistors devices with substantial power handling capabilities were introduced in the 1960s. These components overcame some limitations of the thyristors because they can be turned on or off with a control signal.

With the improvements of the Metal Oxide Semiconductor technology, power MOSFETs became available in the late 1970s. These devices allow operation at higher frequency than bipolar transistors, but are limited to the low voltage applications.

The Insulated Gate Bipolar Transistor (IGBT) developed in the 1980s became widely available in the 1990s. This component has the power handling capability of the bipolar transistor, with the advantages of the isolated gate drive of the power MOSFET.

Semiconductor devices are extensively used for various applications such as

  • Rectification
  • Amplification
  • Modulation etc.

Nowadays, the semiconductor devices are also used for power conversion applications. Necessary modifications are carried out on a single particular device to improve its ratings and current handling capabilities.

To handle power at a large amount and operate successfully, these devices must have these following requirements:-

  • These devices must have high current and voltage ratings.
  • These devices must have fast switching operations. The faster is the switching operation the faster is the system output.
  • These devices must have very less ‘ON’ state losses for the device to sustain for a longer period.
  • These devices must have lower random failures.
  • These devices must have high power and temperature cycles and high blocking capability.
  • These devices must have lesser parts to avoid the occupancy of a large area on the circuit board.


Classification of power semiconductor switches

  • Power devices is divided into terms of their number of terminals:
  1. The two-terminal devices (diodes) whose state is completely dependent on the external power circuit they are connected to.
  2. The three-terminal devices, whose state is not only dependent on their external power circuit, but also on the signal on their driving terminal (gate or base).
  • A second classification has to do with the type of charge carriers they use:
  1. Some devices are majority carrier devices (Schottky diode, MOSFET, JFET) – use only one type of charge carriers (i.e., either electrons or holes)
  2. Others are minority carrier devices (p-n diode, Thyristor, BJT, IGBT) – use both charge carriers (i.e. electrons and holes).
  • A third classification is based on the degree of controllability: uncontrollable switches (diodes), semi-controllable switches (thyristors), and fully-controllable switches (BJT, MOSFET, JFET, IGBT, GTO, MCT)

Power semiconductor devices
usually have two main different structure:-



  1. Thyristor structure: – These devices have low on state conduction losses.
  2. Transistor structure: – These devices have faster turn off capability i.e. their switching speed is faster.

Sometimes, these two structures are also combined to make a one single structure possessing both the properties of Thyristor as well as transistor.
Power devices are broadly classifiedas:-



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