What is FBT(full-bridge thyristor)Rectifier?

Introduction

A thyristor is a semiconductor device that is used for switching and controlling electric power. The full-bridge thyristor rectifier(FBT) is a device that is used for converting AC voltage to DC voltage by using four thyristors in a bridge configuration. This configuration is known as a full-bridge rectifier. The device is commonly used in applications that require high power DC output such as in power supplies, welding equipment, battery chargers, and electric vehicles.

In this article, we will discuss the full-bridge thyristor rectifier in detail, including its working principle, advantages, disadvantages, and applications.

Working Principle

The full-bridge thyristor rectifier consists of four thyristors, which are connected in a bridge configuration. The bridge configuration allows the AC voltage to be applied across the two ends of the bridge, and the DC voltage is obtained from the two points in the middle of the bridge.

The four thyristors are arranged in pairs, with each pair consisting of two thyristors that are connected in anti-parallel. The anti-parallel connection ensures that the current flows through the load in the same direction, regardless of the polarity of the input voltage.

The thyristors are controlled by a trigger circuit, which ensures that they switch on and off at the appropriate times. The trigger circuit is usually a pulse transformer or a firing circuit that generates a pulse to turn on the thyristors.

When the input voltage is positive, thyristors T1 and T2 are forward-biased, and thyristors T3 and T4 are reverse-biased. As a result, the current flows through thyristors T1 and T2, and the load receives positive voltage.

When the input voltage is negative, thyristors T3 and T4 are forward-biased, and thyristors T1 and T2 are reverse-biased. As a result, the current flows through thyristors T3 and T4, and the load receives negative voltage.

The full-bridge thyristor rectifier can also be used for phase control of the output voltage by varying the delay angle of the thyristors. By changing the delay angle, the amount of power delivered to the load can be controlled, which is useful in applications that require variable speed control, such as in electric motor drives.

Advantages of FBT Rectifier

• High efficiency: The full-bridge thyristor rectifier has a high efficiency due to its low voltage drop and low power dissipation.

• High power handling capacity: The device can handle high power loads, making it suitable for high-power applications.

• Reliable and robust: Thyristors are highly reliable and robust, which makes the full-bridge thyristor rectifier a durable and long-lasting device.

• High input voltage capability: The device can handle high input voltages, making it suitable for applications that require high-voltage DC output.

• Low harmonic distortion: The full-bridge thyristor rectifier has low harmonic distortion, which reduces the amount of electromagnetic interference (EMI) generated by the device.

Disadvantages of FBT Rectifier

• Complex control circuit: The full-bridge thyristor rectifier requires a complex control circuit to ensure that the thyristors switch on and off at the right time.

• High cost: The device is relatively expensive due to the high cost of the thyristors and the control circuit.

• Requires cooling: The full-bridge thyristor rectifier generates a lot of heat, which requires cooling to prevent overheating.