Reverse Conducting Thyristor (RCT)

Explore the structure, working principle, applications, advantages, and drawbacks of Reverse Conducting Thyristors (RCTs) in power electronics.

Reverse Conducting Thyristor (RCT)

Introduction to the Reverse Conducting Thyristor (RCT)

The Reverse Conducting Thyristor (RCT) is a semiconductor device that combines the features of both a thyristor and a diode in a single package. The unique structure of an RCT allows it to behave as a normal thyristor during the forward blocking and conduction modes, while during reverse blocking and conduction modes, it acts as a diode. This dual-functionality is one of the distinguishing features of an RCT that makes it a versatile component in power electronic circuits.

Structure of an RCT

The structure of an RCT is quite similar to a conventional thyristor but with an additional layer. A conventional thyristor is a four-layer (PNPN) device, while an RCT is a five-layer (PNPNN) device. This fifth layer is responsible for the reverse blocking capability of the device. The RCT can be considered as a combination of a thyristor and a diode integrated into one package, with the diode connected in anti-parallel to the thyristor.

Working Principle of an RCT

  1. Forward Blocking Mode: In this mode, the thyristor part of the RCT is reverse-biased and the diode part is forward-biased. However, due to the high potential barrier at the junction, the RCT remains off and does not conduct current.
  2. Forward Conduction Mode: When the gate terminal is given a positive pulse, the thyristor section of the RCT turns on and starts conducting current. During this mode, the diode part remains reverse-biased.
  3. Reverse Blocking Mode: In this mode, both the thyristor and diode sections are reverse-biased and the RCT does not conduct current.
  4. Reverse Conduction Mode: When a reverse voltage is applied, the diode part of the RCT becomes forward-biased and starts conducting current, while the thyristor part remains reverse-biased.

Given these operational modes, it’s clear that the RCT offers an increased range of functionality compared to traditional thyristors. However, the true value of an RCT becomes evident when examining its potential applications in power electronics.

Applications of Reverse Conducting Thyristor (RCT)

Reverse Conducting Thyristors are primarily utilized in power electronic circuits, such as inverters, choppers, and converters, where both forward and reverse current flow is required. Here are a few specific applications:

  • Inverters: RCTs are used in inverters for switching purposes. In inverters, a DC source is converted into an AC source. For such transformations, RCTs provide efficient switching and reverse blocking capabilities.
  • Choppers: In DC choppers, RCTs allow the conversion of fixed DC input into a variable DC output. The reverse conducting feature of the RCT is utilized in this application.
  • Induction Heating: RCTs are employed in induction heating circuits, where they function as efficient switching devices. The reverse blocking capability of RCTs is particularly useful in these applications.
  • Phase Control Circuits: In phase control circuits, RCTs are used to regulate the power supply. They offer excellent control over the output voltage, making them ideal for these types of applications.

Advantages and Disadvantages of RCT

RCTs offer numerous advantages, such as high blocking voltage capability, large surge current capability, and the ability to handle both forward and reverse currents. They also exhibit low conduction losses and excellent controllability. However, they do have some drawbacks. RCTs are complex devices and require precise control signals for operation. Additionally, their manufacturing process is more complex and expensive than traditional thyristors.


In conclusion, the Reverse Conducting Thyristor (RCT) is an innovative and versatile power electronic device. It integrates the functionality of a thyristor and a diode, offering both forward and reverse current handling capabilities. Its unique structure and operational modes make it an efficient choice for a variety of power electronics applications, including inverters, choppers, and phase control circuits. Despite its complexity and higher manufacturing costs, the benefits offered by RCTs, such as improved controllability and low conduction losses, make it a valuable component in modern power electronic systems.

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