Usually, electronic devices have rectifier circuit that enable AC to DC conversion in power supply systems. This circuit usage is in low power devices, such as battery chargers, to rectify the low voltage produced in rectification.
To understand the rectifier circuit, we must learn about the rectification process. Rectification is responsible for changing negative bits of AC from the mains supply into positive DC voltages. When setting up your ideal system, you need the right rectifier. Therefore, understanding the rectifier and configuration of diodes will be important for you to set up your system.
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 because the device straightens the directional flow of current. The use of electronic filters to smoothen the rectifier output is 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- 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, there is a high ripple factor generated. This is because its 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, in three-phase rectifiers, structures need three or six diodes. Reduced ripple voltage occurs as all diodes get connected to each phase of the transformer secondary winding. 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
- 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)
Half wave and full-wave rectifiers
In half-wave rectification, the rectifier completely blocks one-half of the pulsating input signal. Then, 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 supply. The average level of the rectified voltage is half the level of input voltage. 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. For instance, in the first model, the AC supply links directly with the output’s negative terminal. The next design has the alternating current supply attached directly to the output’s positive terminal.
- 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
This rectifier inverts lost or blocked negative input AC source signal. As a result, it improves the average value of the output signal. It also doubles the input AC voltage waveform frequency, a function that the half-bridge rectifier can not perform. 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 circuit. It also works as an active regulator, allowing the majority of current flow to the load circuit.
- First and foremost, has high rectification efficiency (81.2%)
- Second, it has a lower RF (0.48)
- In addition, has a relatively high TUF
- 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
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)
A bridge rectifier is an AC to DC converter that rectifies main AC input to DC output. The bridge circuit is a rectifier used in power supplies that supply DC voltage for electrical devices and electronic components. A simple bridge rectifier normally employs the use of a load resistor. As a result, this guarantees the current flowing through it is equal throughout both 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 bridges. Peak inverse voltage is the highest recorded voltage from the diode when connected in reverse bias in the negative half 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 rectification. 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 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
- 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 two diodes. During the second half of the cycle, diodes D1 and D3 are forward biased, thus conducting. The overall effect is that the two halves of the AC can pass through. After that, the negative half gets inverted, and it becomes positive.
Uncontrolled Rectifiers and controlled rectifiers
The name uncontrolled rectifiers refer to the rectifier type that provides fixed DC output voltage for a particular AC supply. Uncontrolled rectifiers only use diodes and can either be; full wave controlled or a half-wave controlled rectifier. However, they are less efficient since diodes can only be either on or off.
This circuit converts AC supply to DC supply using thyristors to control the power supply to the load. Half-wave controlled rectifier consists of a single SCR ( Silicon Controlled Rectifier). They have the same design as uncontrolled rectifiers, but they 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. It comprises 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 positive 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 rectifier diode. The current waveform has alternating intervals in between short increases of voltage as well as no voltage periods. It is a direct current as it only has positive voltage.
(Diode bridge 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 electrical device. To clarify, we discuss the most important precautions that will affect the choice of rectifier design.
During the positive half cycle, the voltage which appears across the anode and cathode 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 threshold voltage (0.7V). Hence, the circuit starts conducting.
Peak voltage = Vm – 0.7V( voltage drop)
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 hence acting as an open switch. It leads to no flow of current. This results in zero voltage reading at the output.
Moreover, in the negative half cycle, even after considering the diode used, the voltage across the diode is negative. Meaning that the reading at the output will still be 0V.
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 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 occurs within the diodes. Therefore, knowledge of voltage drops of specific diodes used in the circuit is important.
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 withstand 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 = 2Vsmax.
5. The Smoothing Capacitor
A smoothing capacitor is a system that evens out variations in the supply of a signal. They are mainly applied after a rectifier or power supply voltage. During the half cycles, smooth transitions are created when the capacitor charge 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 ripple across the diodes. So, the smoothing capacitor gets connected in parallel across diodes to maintain steady voltage into 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 rippled output of the rectifier into a smoother DC output.
The ripple voltage is inversely proportional to the smoothing capacitor value. The two values are related by
Vripple = Iload/(fxC)
Alternatively, one can use a voltage regulator integrated circuit for a constant DC supply.
5uF Smoothing Capacitor
The charge and capacitance through a 5uF Smoothing Capacitor vary depending on the connection 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 the same for all capacitors. However, the 50uF makes a stronger smoothing capacitor compared to the 5uF capacitor.
(Image of capacitors)
A wide range of devices that use rectifier circuits have been established in this article. One application is voltage regulators, while another common usage includes power supply components and amplitude modulation detectors (AMDs) used for radio signals. The device was also once commonly known as a crystal detector in early radio receivers.
We hope this article answers all your questions about rectifier circuits. Feel free to contact us for the basic components of making your rectifier circuit. Looking forward to assisting in your projects.