Power Electronics Switches

Power Electronics Switches

Power electronics switches are known as solid-state switches or semiconductor switches. These switches can operate without any mechanical movement. According to the number of terminals, the power electronics switches classify into two parts;

1) Two terminal switches:

2) Three terminal switches:

1) Power Diode:

The power diode is a two-terminal P-N junction semiconductor device. It has two terminals; the positive terminal is known as an anode and the negative terminal is known as a cathode.

If anode terminal is at higher potential then the cathode terminal, the device works as forward bias and forward current will flow through the anode to cathode. In this condition, a very small amount of voltage drops across the device and this drop is the forward voltage drop. If you consider this diode as an ideal switch, then this forward voltage drop is zero.

If the anode terminal is at lower potential then the cathode terminal, the device works as reverse bias. In reverse bias, a very small amount of current will flow across the diode and this current is leakage current.


The MOSFET is the abbreviation for Metal Oxide Semiconductor Field Effect Transistor. The MOSFET is a voltage control device. Generally, MOSFET use for the switching and amplifying of the electric signal in electronics devices. Two types of MOSFET are available; N-type and P-type MOSFET.

The MOSFET has three terminals; Gate (G), Drain (D), and Source (S). The width of the channel is electronically varying along with the flow of the charge carrier. Electrons and holes are the charge carrier. The charge carriers enter from the source and exit by the drain. The gate voltage can control the width of the channel. The gate is located between the source and drain and it is insulated from the channel close a thin layer of metal oxide.

MOSFET can work in two modes; Depletion mode and Enhancement mode.

3) IGBT:

IGBT stands for Insulated Gate Bipolar Transistor. It is a hybrid combination of MOSFET and BJT. Like MOSFET, IGBT has high input impedance and switching frequency. Like BJT, low saturation of voltage.

It is a three-terminal device; Gate (G), Collector (C) and Emitter (A). The IGBT combines the insulated gate technology of MOSFET with the output characteristic of the bipolar transistor (BJT). So, it is known as Insulated gate bipolar transistor.

4) BJT:

BJT stands for Bipolar junction transistor. It has three terminals; Gate (G), Emitter (E), and Collector (C). If we connect two diodes in series, this will give us two PN junctions connected with common P or N and It makes three layers, two junctions, and three terminals device.

The bipolar transistors operate in three different regions:

Active – In active region, the transistor operates as an amplifier

Saturation – In this region, the transistor is “Fully-ON” operating as a switch

Cut-off – In this region, the transistor is “Fully-OFF” operating as a switch

It is a current regulating device. So, it can control the amount of current flowing through them from the Emitter to the Collector terminals. The current flowing through the BJT is in proportion to the amount of biasing voltage applied to their base terminal.

5) Thyristor:

Thyristor has three terminals; Gate (G), Anode (A), and Cathode (C). When the anode terminal is negative with respect to the cathode, the thyristor is in forward bias. It behaves like a diode. Once thyristor is turned on, it not need the gate pulse. If the gate signal is not given, then also it remains turned on.

It can only turn OFF by the forward current or anode current reduces to zero or below the holding current.

The thyristors include:

  • Silicon controlled rectifier (SCR),
  • triode for alternating current (TRIAC),
  • Gate Turn Off switch (GTO),
  • Unijunction Transistor (UJT),
  • Programmable Unijunction Transistor (PUT),
  • AC Diode (DIAC),
  • Silicon Controlled Switch (SCS).

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