Contents
1. What is a rectifier circuit?
A rectifier is an electrical device that converts alternating current from the mains voltage into a unidirectional direct current.
It works simplest by changing the main supply AC voltage from the power grids to DC voltage. Most importantly, many appliances we rely on require DC.
The term rectifier is used because the device straightens the directional flow of current. Electronic filters are being used to smoothen the rectifier output, a growing trend.
Consequently, modern silicon semiconductor rectifiers caused the exit of Selenium-based rectifiers, mechanical rectifiers, copper-oxide rectifiers, and vacuum tube rectifiers.
Mechanical and vacuum tube rectifiers (used in cathode ray tubes) were inefficient due to high internal resistance.
However, copper oxide and selenium-based rectifiers have better momentary voltage tolerance than SCR (Silicon Controlled Rectifier). It is a huge advantage over silicon diodes.
(Transformer AC power to DC power with diode bridge and capacitor)
2. Types of Rectifiers
Single-phase and three-phase rectifiers.
In both single-phase and three-phase rectifiers, they experience half-wave rectification and full-wave rectification.
Single-phase rectifiers have an input of 1-1-phase mains supply of AC power. The structures are very simple. They need one, two, or four diodes (depending on the type of system).
For single-phase AC, a high ripple factor is generated because the diodes connect to the secondary winding of the single-phase transformer.
Also, it uses only a single phase of the transformer secondary coil for rectification.
On the other hand, structures need three or six diodes in three-phase rectifiers. As all diodes connect to each phase of the transformer’s secondary winding, reduced ripple voltage occurs.
It further creates a high transformer utilization factor.
Advantages of single-phase rectifier
- Suitable for simple structures
Advantages of three-phase Rectifier
- Firstly, it is most preferred when using large systems
- Secondly, it delivers large amounts of power
- In addition, do not require any additional filter components to reduce RF
- It is efficient and has more TUF
Disadvantages of single-phase rectifiers
- To start with, it delivers a small amount of power.
- Moreover, has less transformer utilization factor(TUF)
(Diodes)
Half-wave and full-wave rectifiers
In half-wave rectification, the rectifier completely blocks one-half of the pulsating input signal and supplies only one-half in every full cycle.
It means that half of the AC power source supply gets wasted.
Half-wave rectification requires a single diode single-phase supply or three in a three-phase supp y.
The average rectified voltage is half the input volt.
However, the positive voltage has the same peak AC input voltage level as the input voltage.
There are two ways of designing a half-wave rectifier.
In the first model, the AC supply links directly with the output’s negative terms.
The next design has the alternating current supply attached directly to the output’s positive terminal.
Advantages
- First, it has a high-voltage output
- Also, it is cheap since it uses only one diode in power rectification.
Finally, it requires no supply transformer
Full-wave rectifier
This rectifier inverts lost or blocked negative input AC source sig al, improving the average value of the output sig al.
It also doubles the input AC voltage waveform frequency, a function the half-bridge rectifier can not per orm. And in the waveform produced, the input peaks and output peaks are equal.
Two commonly used methods in designing full-wave rectifiers are; center-tapped transformer and diode bridge cir uit.
It also works as an active regulator, allowing most current flow to the load circuit.
Advantages
- First and foremost, has high rectification efficiency (81.2%)
- Second, it has a lower RF (0.48)
- In addition, has a relatively high TUF
Disadvantages
- First, it requires a transformer to run
- Unfortunately, it undergoes fairly huge internal resistance from the AC mains supply.
- Lastly, it uses double diodes that can be expensive
Form Factor:
The form factor is the ratio of the RMS value of current to the DC output current.
FormFactor=RMS Value of Current DC Output Current Form Factor= RMS Value of Current DC Output Current.
The form factor of a full-wave rectifier is 1.11.
(Half-wave rectifier circuit picture)
Bridge Rectifier
A bridge rectifier is an AC to DC converter that rectifies main AC input to DC o tput.
The bridge circuit is a rectifier used in power supplies that supply DC voltage for electrical devices and electronic comp nents.
A simple bridge rectifier normally employs a load r sister, guaranteeing that the current flowing through it is equal throughout the negative and positive half cycles. The bridge rectifier is one of the most common parts of electronic power supplies.
The bridge rectifier arrangement has four adjacent diodes, also known as diode ridges.
Peak inverse voltage is the highest recorded voltage from the diode when connected in reverse bias in the negative ha f cycle.
During the positive half cycle, two diodes are in the conducting spot. The remaining pair is in the non-conducting position of the bridge rect fication. The rectifier output records occur across the load resistor.
Advantages of the bridge rectifier
- First, it has a higher rectification efficiency (81.2%)
- Also, it has lowered ripple voltage
- No transformer is needed in bridge rectifier operation
- In addition, has high TUF when weighed with a center tap rectifier
- Finally, it attains high frequencies by using simple filtering
Disadvantages
- First, has higher costs of bridge rectifier construction because it uses four diodes.
- Has reduced output voltage due to voltage drops in the system
- Again, the system configurations are quite complicated
- Lastly, it experiences great internal resistance when operated with lower voltages.
The bridge rectifier is good. In the first AC cycle, diodes D2 and D4 are forward biased, thus conducting. The positive voltage is on the anode of D2, whereas the cathode terminal of D4 has a negative voltage.
The first half of the signal passes through these wo diodes. During the second half of the cycle, diodes D1 and D3 are forward biased, thus onducting.
The overall effect is that the two halves of the AC can p ss through. After that, the negative half is inverted and becomes positive.
(Bridge rectifier)
Uncontrolled Rectifiers and controlled rectifiers
Uncontrolled Rectifiers
The name uncontrolled rectifiers refer to the rectifier type that provides fixed DC output voltage for a particula AC supply.
Uncontrolled rectifiers only use diodes and can either be; full wave controlled or a half-wave controll d rectifier. However, they are less efficient since diodes can only be on or off.
Controlled Rectifiers
This circuit converts AC to DC using thyristors to control the power supply to the load. A half-wave controlled rectifier consists of a single SCR ( Silicon Controlle Rectifier).
They have the same design as uncontrolled rectifiers but use SCR instead. Half-wave controlled rectifiers limit power wastage as they offer constant power control.
3. How Rectifier Circuits Work in Electronics
Working Principle of Rectifier Circuits
Rectifier circuits work simply by turning the AC power source into a DC power source. They comprise diodes interlocked across the system to create a forward-only movement of electrons to power devices.
When AC flows through a rectifier circuit, the diodes eliminate negative voltage swings from the AC source.
Therefore, it leaves the positi e voltage only. A simple diode only allows current flow in one direction, blocking current flow in the reverse direction.
This image depicts an AC voltage waveform from a ectifier diode.
The current waveform alternates between short increases in voltage and no-voltage periods.
It is a direct current as it only has a positive voltage.
(Diode ridge diagram)
4. Precautions for the Design of the Rectifier Circuit
There are precautions that you need to consider when designing a rectifier circuit in any lectrical device.
To clarify, we discuss the most important precautions that will affect the choice of rectifier design.
Positive Half-Cycle
During the positive half cycle, the voltage which appears across the anode and c thode is positive. It means that the diode is forward-biased.
Assuming that the circuit connects to an ideal diode and the power rating is constant. Peak voltage is Vm, referred to as the peak voltage value without voltage drops.
However, we should consider the voltage drop on certain diodes as a silicon diode with 0.7V(voltage drop).
It only gets forward biased when the applied input voltage exceeds the thre hold voltage (0.7V). Hence, the circuit starts conducting.
Peak voltage = Vm – 0.7V( voltage drop)
Negative Half-Cycle
It is different with a negative half cycle as the voltage appearing across the anode and cathode is negative.
The diode in the rectifier circuit gets reverse-biased, acting as an open switch. This leads to no current flow, resulting in a zero voltage reading at the output.
Moreover, even after considering the diode used in the negative half cycle, the voltage across the diode is negative, meaning that the reading at the output will still be 0V.
Voltage drops:
Mains voltage usually carries a lot of power. The partial power loss of a current’s electrical potential while moving through a circuit is called a voltage drop.
VD= ( 2*L*R*I) / 1000
Calculating heat dissipated in the rectifier:
Usually, this is the heat lost in the rectification process as voltage drops and resistance occ rs within the diodes.
Therefore, it is important to know the voltage drops of specific diodes used in the circuit.
Pheat (Power Loss) = Pmax ( Maximum output power of the system) / Eff (Efficiency of the rectifier module) – Pmax ( Maximum output power of the system.
The Peak inverse voltage:
PIV refers to the maximum voltage a diode can wit stand in reverse bias. Hence, if exceeded, the diodes can break down. The peak inverse voltage is equal to the input voltage.
The peak inverse voltage (PIV) = 2Vs max = 2Vs max.
5. The Smoothing Capacitor
A smoothing capacitor is a system that evens out variations in a signal’s supply. They are mainly applied after a record eir o power supply voltage. During the half cycles, smooth transitions are created when the capacitor charges and discharges. The charging process occurs when current flows through the positive half cycles.
Full-wave Rectifier with Smoothing Capacitor
The smoothing capacitor helps to improve the incomplete output ri ple across the diodes.
So, it is connected in parallel across the diodes to maintain steady voltage in the load circuit.
The load placement falls across the output of the full-wave bridge rectifier. The capacitor then increases the DC output.
As a result, the smoothing capacitor converts the rectifier’s rippled output into a smoother DC output.
The ripple voltage is inversely proportional to the soothing capacitor value. The two values are related by
Vripple = Iload/(fxC)
Alternatively, a voltage regulator integrated circuitcan be used for a constant DC supply.
5uF Smoothing Capacitor
The charge and capacitance through a 5uF Smoothing Capacitor vary depending on the conne tion within the circuit.
The equivalent capacitance will be the sum of all the capacitors connected in the circuit for a capacitor in a parallel connection.
50uF Smoothing Capacitor
Likewise, the same principle applies here for a 50uF Smoothing Capacitor. The voltage in a parallel circuit connection is th same for all capacitors.
However, the 50uF makes a stronger smoothing capacitor compared to the 5uF capacitor.
(Image of capacitors)
6. Conclusion
A wide range of devices that use rectifier circuits have been established in this article.
Voltage regulators are one application, while power supply components and amplitude modulation detectors (A Ds) used for radio signals are other common uses.
The device was also once commonly known as a crystal detector in early radio receivers.
We hope this article answers all your questi ns about rectifier circuits.
Feel free to contact us for the basic components of aking your rectifier circuit.
We look forward to assisting you in your projects.
