A rectifier, also known as, AC to DC Converter is one of the most important devices in any electrical circuit. It is used to convert one form of the current into another. And because of this property, we have electricity in our house. So, in this chapter, we will cover rectifier definition, uses, the process of rectification, circuit, and types.
In this Article You will learn:
- 1 What is a Rectifier
- 2 Rectifier Working Theory
- 3 Types of Rectifier Circuits
- 4 Rectifiers Comparison Table
What is a Rectifier
A rectifier is an electrical device that consists of one or more diodes allowing the flow of current only in one direction. It basically converts an alternating current into direct current. The process of converting Alternating Current into Direct Current is called Rectification Process. And it is also called AC to DC converter.
Rectifiers can be mold in several forms as per requirement like a semiconductor diode, silicon controlled rectifiers, mercury arc valves, vacuum tube diodes, etc.
For signal detection and power rectification, diode rectifier circuits are widely used in electronic circuits design. These are used in various devices includes radio signals or detectors, Dc power supplies, household appliances like laptops, video game systems, televisions, etc.
Now as we have understood the definition, it is time to learn how rectifier works. This can be easily understood by remembering “how a diode works”. As we know a diode only allows the flow of current in one direction. It blocks either the positive cycle of current or the negative cycle of current.
Now, the same property of Diode is used in the rectification of the signal. Here is how:
Rectifier Working Theory
In this section, we will learn how a rectifier works or how is rectification is achieved in a circuit.
As we know, Alternating current has two cycles; positive cycle and negative cycle. And Direct current flows straight in one direction.
When in a circuit having AC Current at the input side, we add a diode, it blocks a particular cycle of the alternating current. Hence producing an output current which will flow in one direction only that means Direct Current.
In this process, One Particular cycle of AC current gets wasted and it depends on the side of the connected diode. By this, we mean, whether an anode or cathode part of the diode is connected to the circuit. So to use both of the cycles, we add more than one diodes in a circuit.
This whole process is called Rectification.
The voltage we get at the output of the circuit after being rectified is not pure DC voltage. It is always a pulsating DC having some properties of AC voltage. Ripple Voltage is defined as the “residue of alternating voltage mixed with DC voltage obtained at the output of the rectifier circuit”.
To obtain a pure DC voltage, this pulsating Ripple voltage is processed through a filter circuit. And then it is regulated by a regulator to achieve DC voltage of the desired strength.
This can be easily understood by the example of the household Power Supply arrangement.
Household Power Supply:
For economical reasons, the electrical power is transmitted, distributed, and generated as a.c i.e. alternating voltage available at the mains.
Sometimes most of the electronic circuits need d.c voltage for their operation, for that purpose all electronic equipment includes a circuit that converts a.c voltage of the mains supply to d.c voltage. This circuit is known as the Power supply circuit.
The Power supply is the most important circuit of all electronic and electrical circuits. Without this all devices are useless.
The block diagram of the power supply is shown above. At the input of the power supply, a transformer is used to step down the voltage as per requirement. It is known as the power transformer.
After stepping down the voltage, this output voltage becomes the input of the next block i.e rectifier which converts this a.c to dc voltage.
This pulsating DC is fed back into the filter circuit which removes the spikes, pulsations and smoothes it out. After filtering, this d.c is fed back to the regulator which obtains regulated d.c at the output.
Efficiency of Rectifier
The efficiency of the Rectifier is defined as “The ratio of the DC output power to input power from the AC supply.”
Efficiency is always less than 100% because some of the output power is AC rather than pure DC. It can be improved by using smoothing circuits which reduce the ripple and AC content of the output.
Rectifier Efficiency Equation:
Pin = Input Power
Pout = output Power
η = Efficiency
As we know,
Pin = (Vpeak /2) * (I peak / 2)
Pout = (Vpeak / π) * (I peak / π)
η = Pout / Pin
η = (Vpeak / π) * (I peak / π) / (Vpeak /2) * (I peak / 2)
η = 4 / π2
You can also watch below Video by Simply Electronics
Types of Rectifier Circuits
There are different types of diode rectifier circuit available in the market, each has its own merits and demerits. Rectifier circuits may be single-phase or multi-phase.
For industrial applications, three-phase rectification is essential while for domestic applications single phase rectification is sufficient.
In half-wave AC to DC Converter, when A.C supply is applied at the input, only the positive half cycle appears across the load whereas the negative half cycle is suppressed.
In a single-phase supply, it requires a single diode while in a three-phase supply it requires three diodes. It is not efficient because only half of the input waveforms reaches the output.
To reduce the ripples or to eliminate the harmonics of the AC frequency from the output, more filtering is needed. For full details, read our detailed article on a half-wave rectifier.
In a full-wave rectification process, during both the half cycles when a.c. supply is applied to the input, current flows through the load in the same direction.
A full-wave circuit yields a higher average output voltage by changing both polarities of the input waveform to pulsating DC. This type of rectification can be achieved by using at least two diodes conducting current alternatively.
During the positive as well as the negative half-cycle of the input AC, the two circuits namely center tap full wave rectifier and full-wave bridge rectifier are employed to obtain the same direction of flow of current in the load resistor.
Center Tap Full-Wave Rectifier
The center tap circuit employs a transformer with secondary winding tapped at the center point. Two diodes are connected in the circuit so that each one of them uses a one-half cycle of the input AC voltage.
For rectification, one diode utilizes the ac voltage appearing across the upper half of the secondary winding while the other diode uses the lower half of the secondary winding.
The output and efficiency of this circuit are high because the AC supply delivers power during both the halves.
Full Wave Bridge Rectifier
Bridge Rectifier circuit is one of the efficient forms of full-wave AC to DC converter. It utilizes four diodes in a bridge topology.
In place of center tap transformer, in this case, an ordinary transformer is used. The AC supply to be rectified is applied to the diagonally opposite ends of the bridge and the load resistor is connected across the remaining two diagonally opposite ends of the bridge.
Rectifiers Comparison Table
The comparison between different rectifiers on the basis of various points are tabulated below.
|Properties||Half wave rectifier||Full-wave center-tap rectifier||Full-wave bridge rectifier|
|No. of diodes||1||2||4|
|D.C current||Im / π||2Im / π||2Im / π|
|Maximum Current value||Vm / (rf + RL)||Vm / (rf + RL)||Vm / (2rf + RL)|
|Output Frequency||fin||2 fin||2 fin|
|Peak Inverse Voltage||Vm||2Vm||2Vm|
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