The Different Types of Rectifiers In Telecommunications

  Rectifiers are used in a variety of devices and can be applied to modify network systems. They are categorised in different ways dependent on factors such as type of supply, bridge configuration and components used. On the whole, rectifiers can be classified into two types – single phase and three phase rectifiers. Drilling down another level, they can then be separated into half wave, full wave and bridge rectifiers.

 

What is a Rectifier?

Before we get into the different types of rectifiers, it is worth going over what rectifiers are. A rectifier is a diode which converts alternating current (known as AC) to direct current (DC). DC only flows in one direction whereas AC regularly reverses direction. Rectifiers allow current to flow in a single direction.

 

Rectifiers take alternating voltage and converts it into high quality direct voltage needed for your telecom equipment. Traditional telecommunications equipment generally requires DC input power but mains power runs off AC. Such power systems consist of multiple rectifiers that convert AC power to DC power, so they can operate.

 

Without the right rectifier, there is little chance of configuring your ideal system. They are the heart of a power system as they offer optimised solutions for each application. Using rectifiers means that you can tailor your power system without having to rebuild every element.

 

The Different Types of Rectifiers

So, it is clear that rectifiers are a key component to any network system but we need to dip deeper to understand the carious types. Depending on the situation, different rectifiers are used conditional to the system it is used in. The top two levels are single phase and three phase, which indicate how many diodes are used in the circuit. Then we come to half wave, full wave and bridge rectifiers, which affect what half cycles are produced. Let’s go into each type to better understand what rectifier should be used.

 

Single Phase & Three Phase Rectifiers

Single phase rectifiers have an input of one phase AC power. The structures are very simple, needing one, two or four diodes (dependent on the type of system). This means that the single phase rectifier delivers a small amount of power and has less transformer utilisation factor (TUF). A single phase rectifier uses only single phase of transformer secondary coil for the conversion and diodes are connected to the secondary winding of single phase transformer. This causes high ripple factor.

 

Three phase rectifiers have an input of three phase AV power. Structures need three or six diodes and these are connected to each phase of the transformer secondary winding. Three phase rectifiers are used in place of single phase rectifiers to reduce ripple factor.

 

Comparing the two types of rectifiers, three phase is preferred when using large systems. This is because they can deliver large amounts of power and do not require any additional filter to reduce ripple factor. Because of this, three phase rectifiers are more efficient and have more transformer utilisation factor.

 

Half Wave & Full Wave Rectifiers

Half wave rectifiers convert one half cycle on the AC input into pulsating DC output. This allows half cycle of the AC input while blocking the other half cycle. The half cycle can be either positive or negative. It is the simplest rectifier as only one single diode is used. Figure 1 (below) shows a positive half wave rectifier whereas a negative half wave rectifier would show the diode being reverse biased (facing the opposite way). Due to the pulsating nature of the direct current, ripple factor is high. This means that half wave rectifiers are not considered to be efficient and they often need filters to reduce ripple factor.

 

Diagram illustrating half wave rectifierFigure 1: half wave rectifier

 

Full wave rectifiers convert both (positive and negative) half cycles on the AC input into pulsating DC output. As figure 2 (below) shows, these circuits use a center tapped transformer which is connected across the middle of the secondary winding of a transformer. These types of transformer divides input AC into two parts – positive and negative. Due to this, full wave rectifiers are considered much more effective as the ripple factor is much lower in comparison. Also, as both cycles are allowed at the same time, it means that no signal is wasted.

 

Diagram illustrating full wave rectifier

 

Figure 2: full wave rectifier

 

Bridge Rectifiers

Bridge rectifiers are widely used in power supplies to supply direct current voltage to the components. They use four or more diodes and a load resistor (see figure 3 below).

 

Diagram illustrating bridge rectifier

 

Figure 3: bridge rectifier

 

The four diodes are arranged in series with only two diodes allowing electric current during each half cycle. The diodes are considered to work in pairs, with one pair allowing electric current through the positive half cycle and the other half allowing current during the negative half cycle. The input alternating current is applied across two terminals and the output direct current is obtained across the resistor inductor which is connected between the other two terminals.

 

Bridge rectifiers allow electric current during both positive and negative half cycles of the input AC signal. These circuit configurations do not require center tapped transformers, which can be very expensive.

 

Uncontrolled & Controlled Rectifiers

Uncontrolled rectifiers are when only diodes are used in the circuit. All the rectifiers we have covered so far are uncontrolled rectifiers. Controlled rectifier circuits use thyristors to control the DC output. These are used when current needs to be controlled more accurately as diodes can only be on or off. Controlled rectifiers allow for continuous control and ensure there is no wastage of power.

 

How Are Rectifiers Used in Telecommunications?

When it comes to the telecommunications industry, rectifiers are essential for building network systems. Their use means that you won’t have to start from scratch when things need changing. The different types of rectifiers allow telecommunication companies to switch the layout of systems with relative ease. They also allow telcos to tailor their systems to suit their needs as and when they need modifying.

 

Applications of rectifier products include fixed access network, wireless access network, transmission network and communication network of enterprise. Rectifiers can provide stable and reliable power for main suppliers and efficiently reduce power consumption. Because of this, every telecommunications company should take into consideration the different types of rectifiers before setting up or making alterations to their system.