The power grids from which we get power have alternating current. On the other hand, home appliances that we use require direct current. How is it possible that the alternating current we get from the power grids power direct current powered appliances? The answer lies in rectification. So, what is a rectifier?
Read on and you will know the answer. Here in this article, we will explain many things related to the rectifier. First, we start with the definition as we answer what is rectifier, then the types, comparison, and finally, the applications of this electrical device.
What Is Rectifier?
Let’s start with the definition first. What is a rectifier exactly? To put it simply, a rectifier is an electrical device that ‘rectifies’ the current. For example, a rectifier can be used to turn alternating current (AC) into direct current (DC).
You cannot know what is a rectifier if you don’t know what rectification is. So, what is rectification? Rectification is the conversion process of AC, which regularly changes direction, into DC, which flows in a single direction. This is what we call rectification.
Rectification produces a type of direct current that encompasses active currents and voltages. The currents and voltages are then adjusted, turned into a type of constant voltage DC. The current then is able to flow in a single direction without interruption. No current is able to flow in the opposite of said direction.
A rectifier consists of one or more diodes. A diode functions more or less like a one-way valve. It allows current to flow in one direction but not another. A rectifier comes in various physical forms. Some examples include vacuum tube diodes, solid-state diodes, mercury arc valves, and modern silicon-based designs.
There’s more to it, however. For instance, there are different types of rectifiers. The simplest type of rectifier is half-wave rectifiers, which converts alternating current into direct current. We explain the types in detail in the next section.
Types of Rectifiers
Due to their usefulness, rectifiers are used in many devices. There are many types of rectifiers. They are classified based on various factors. For example, bridge configuration, type of supply, and components used. As a whole, rectifiers are classified into two: single-phase and three-phase.
This is by no means the only classifications. Rectifiers can also be classified into three types: half-wave, full-wave, and bridge rectifiers, controlled and uncontrolled. To help you understand what is a rectifier and its types, we explain each below.
Single Phase and Three Phase
Single-phase rectifiers have quite simple structures. They require one, two, or four diodes, the amount which depends on what type of system is used. These rectifiers have an input of one-phase AC power. Due to their structures, this rectifier has less transformer utilization factor and delivers a small amount of power.
Single-phase rectifiers have a high ripple factor. Why? Because
- Its diodes are connected to single-phase transformer via the secondary winding of the said transformer
- For the current conversion, it uses a single phase of the secondary coil of the transformer
As for the three-phase rectifiers, they have an input of three-phase AC power. Their structures are a bit more complicated than their one phase counterparts. The structures of a three-phase rectifier consist of three or six diodes, with the diodes connected to each phase of the secondary winding of a transformer.
Compared to one phase rectifier, three-phase rectifiers have reduced the ripple factor. This is the reason why the latter is used in place of the former.
Also, three-phase rectifiers are the better choice when large systems are used. There are two main reasons why. First, there is no additional filter necessary to reduce the ripple factor. Second, these rectifiers are capable of delivering large amounts of power. Due to these reasons, these rectifiers are more efficient.
Half-wave, Full-wave, and Bridge rectifiers
Now you know what is a rectifier that has one phase and three-phase in the previous section. Let’s move on to the other common types of rectifiers: half-wave, full-wave, and bridge rectifiers.
· Half-wave rectifiers
Half-wave rectifiers convert only half of the cycle on the AC input. This half-cycle is converted into pulsating output. In other words, what is a rectifier does here is allowing one half to be converted while at the same time, blocking the other. Note that the half-cycle here can be either negative or positive.
Of all rectifiers, half-wave rectifiers are the simplest. Because of DC’s pulsating nature, these rectifiers have a high ripple factor. This is why half-wave rectifiers are considered to be inefficient. These rectifiers need filters so that their high ripple factor can be reduced.
· Full-wave rectifiers
Next, what is a rectifier with a full-wave waveform? Full-wave rectifiers are a bit similar to the half-wave rectifiers. Unlike half-wave ones, however, full-wave rectifiers convert both half cycles on the AC input. They don’t allow one half-cycle to be converted and block the other. They convert both of the cycles.
Full-wave rectifiers can convert both half cycles on the AC input into DC output because of its transformer. The transformer divides the input into two parts: positive and negative. No signal is wasted as both of the cycles are allowed simultaneously.
That is also the reason why full-wave rectifiers have lower ripple factor than half-wave rectifiers. Thus, full-wave rectifiers are considered to be a lot more effective than their half-wave counterparts.
· Bridge rectifiers
A bridge rectifier consists of a load resistor and three or mover diodes. This kind of rectifier is commonly used in power supplies as the electrical device supply the voltage to the components. The diodes of this rectifier are arranged in a way that two of them allow current during each half cycle.
These diodes work together in pairs. During the positive half cycle, a pair of diodes allows the electric current to flow. Likewise, during the negative half cycle, the other pair allows electric current to flow. Using these rectifiers, there is no need to use center-tapped transformers, which can be very expensive.
Controlled and Uncontrolled
What is a controlled rectifier? A controlled rectifier is a type of rectifier with an output voltage that can be changed or varied. To control the DC output, controlled rectifiers use thyristors. Diodes are limited only to either or off. As such, controlled rectifiers are used when current needs to be controlled accurately.
An uncontrolled rectifier is the opposite. It is a type of rectifier with an output voltage that cannot be changed or varied. Uncontrolled rectifiers consist of only diodes. This is why the output of uncontrolled rectifiers cannot be changed or varied accurately. They have a fixed output voltage which depends on the AC input
Comparison of Rectifiers
To give you a better understanding of what is a rectifier and its types, we compare three types of rectifiers here. These types are half-wave rectifier, full-wave rectifier, and full-wave bridge rectifier.
In a half-wave rectifier, the number of diodes is one.
- It has a DC current of Im / π.
- A transformer is not necessary for a half-wave rectifier.
- The maximum value of current is Vm / (rf + RL).
- It has a ripple factor of 1.21.
- The O/P frequency is fin.
- The maximum efficiency of a half-wave rectifier is approximately 40.6%.
- The peak inverse voltage of a half-wave rectifier is Vm.
Full-wave center-tap rectifier
- A full-wave center tap rectifier has two diodes.
- Its DC current is twice that of a half-wave rectifier, thus 2 Im / π.
- It requires a transformer.
- The maximum value of the current is Vm / (rf +RL).
- It has a smaller ripple factor, 0.482.
- The O/P frequency is 2 fin.
- The maximum efficiency of a half-wave rectifier is approximately 81.2%.
- It has a peak inverse voltage of 2 Vm.
Full-wave bridge rectifier
- Of the three, a full-wave bridge rectifier has the most diodes: 4.
- It has the same DC current as a full-wave center-tap rectifier, Im / π.
- A transformer is not necessary.
- The maximum value of current is a bit different being Vm / (2rf +RL).
- The ripple factor is 0.482, just like a full-wave center tap rectifier.
- The O/P frequency is 2 fin.
- The maximum efficiency is approximately 81.2%.
- It has a peak inverse voltage of 2 Vm.
Applications of Rectifiers
Now you know what is a rectifier. But what is this electrical device used for? What are the applications of rectifiers? The majority of electronic circuits use DC voltages. Of course, this includes electrical appliances in our house as well. That is not the only application of rectifiers, however.
Here are other common applications of rectifiers:
- Converting DC voltages into AC voltages
- Used to provide the polarized voltage needed in electric casting
- Half-wave rectifiers are used in soldering iron as well as a mosquito repellent
- Rectifiers are used in voltage multipliers, modulation, and demodulation
- Rectifiers are also used in rolling stock, traction, as well as three=phase traction motors, all being components used for running trains
So, what is a rectifier? A rectifier is an electrical device that rectifies the current as needed (from alternating to direct, for example). There are many types of rectifiers, each operates differently from the other. How a rectifier is applied is also different, depending on which type it is.