An electrical device that is used to convert alternating current into direct current is called as rectifier. Every embedded system based circuit or project consists of micro-controller as major component. We know that, most of the micro-controllers operate at voltage range of 5V DC. Especially, 8051 micro-controller that is frequently used for maximum number of embedded systems based applications works at 5V DC. But, in general, the power supply available is 230V AC. So, we need to convert this 230V AC into 5V DC or required DC voltage level. This process of conversion of AC into DC is called as rectification.
The electrical and electronic circuit, which is used for rectification process is called as rectifier. There are different types of rectifiers such as half-wave rectifier, full-wave rectifier and bridge rectifier. The half-wave rectifier converts or rectifies only half cycle of input waveform. The full-wave rectifier converts or rectifies full cycle or entire input waveform. Bridge rectifier also converts or rectifies entire input waveform. But, mostly bridge wave rectifier is used for maximum number of applications as it is more efficient and advantageous than the half-wave rectifier and full-wave rectifier. Every micro-controller based power electronics project requires rectifier, as most of the components need power supply of around 5V DC voltage.
Bridge Wave Rectifier
Bridge rectifier consists of four diodes, which are connected in the form of bridge; hence, these types of rectifiers are termed as bridge-wave rectifiers or bridge rectifiers. Different types of diodes are used for designing bride-wave rectifier. These diodes are classified based on the voltage and current ratings of the diodes. Thus, bridge-wave rectifiers can be classified into different types based on the types of diodes used. Similarly, bridge wave rectifiers designed using diodes are called as uncontrolled rectifiers and rectifiers designed using thyristors are called as controlled rectifiers. Let us start with diodes 1N4007 that are typically used to implement bridge-wave rectifier.
Types of Bridge Wave Rectifiers
There are different types of bridge rectifiers that are classified based on different criteria. Consider different types of bridge rectifiers, which are classified based on the types of rectifiers such as uncontrolled rectifiers and controlled rectifiers. Diodes are called as uncontrolled rectifiers as diodes start conduction whenever the anode voltage is greater than the cathode voltage. But, in case of controlled rectifiers know as thyristors, even though the anode voltage is greater than cathode voltage, thyristors start conduction only when the gate terminal is triggered. Thus, we can trigger the gate terminal as per the requirement; hence, we can control the operation of the rectifier.
Bridge-wave rectifiers that are designed using thyristors are called as controlled bridge wave rectifiers. The operation of the rectification can be controlled by triggering the thyristors gate terminal whenever it is required. We know that the diode is a semiconductor device consisting of two layers (P-N) and thyristor is also a semiconductor device consisting of four layers (P-N-P-N). It can be used as open-circuit switch and also as a rectifier based on how the gate terminal of the thyristor is triggered.
Types of Bridge Rectifier Diodes
There are series of didoes form 1N4001 to 1N4007 with different current and voltage ratings, but frequently 1N4007 is used for designing bridge-wave rectifiers. 1N4007 diode has absolute maximum ratings including voltage rating as 1000V peak repetitive reverse voltage VRPM, 1A average rectified output current IF(AV), 30A non-repetitive peak forward surge current IFSM, which can be operated at -55 degrees to +175 degrees temperature. Thermal characteristics as 3W power dissipation, junction to ambient thermal resistance 50 degrees/W. The didoes that are occasionally used to design rectifiers are series of didoes from 1N5400 to 1N5408 and 6A4.
1N5408 bridge rectifier didoes are also used for some special applications and these are having ratings as maximum repetitive peak reverse voltage 1000V, maximum RMS voltage 700V, maximum DC blocking voltage of 1000V, maximum average forward rectified current 3A, operating junction and storage temperature range -50 to +150 degrees centigrade. ACPWM control for induction motor is a practical example in which a bridge wave rectifier designed using 1N5408 diodes.
These 6A4 bridge rectifier diodes have maximum ratings and electrical characteristics as maximum recurrent peak reverse voltage of 400V, maximum reverse voltage of 280V, maximum DC breaking voltage of 400V and maximum average forward rectified current of 6A. 6A4 diodes are used for bridge rectifiers in some special applications, an example is propeller display of message by virtual LEDs. Working of bridge rectifier circuit is similar irrespective of the diodes used to design rectifier, so let us consider the bridge wave rectifier circuit designed using diodes 1N4007, as it is used for bridge rectifiers in some special applicatins – for example a propeller display of message by virtual LEDs.
Working of the Bridge Rectifier Used to Convert 230V AC to 5V DC
Step-down transformers are used to convert 230V AC (high voltage) into 12V AC (low voltage). This 12V output is an RMS value and its peak value is given by the product of square root of two with RMS value of the output of step-down transformer, which is approximately 17V. The working principle of transformers is based on Faraday’s laws of electromagnetic induction.
Uncontrolled Bridge Wave Rectifiers
230V AC power is converted into RMS value of 12V AC or peak value of 17V (approx.), but 5V DC is the required power; for this purpose, 17V AC (peak value) power is converted into DC power, then it is stepped down to 5V DC. The 17V AC is converted into DC using a bridge-wave rectifier that consists of four diodes, which are called as uncontrolled rectifiers. Diode will conduct only in forward bias and will not conduct during the reverse bias. If anode voltage of diode is greater than cathode, then the diode is said to be in forward bias. Diodes D2 and D4 conducts during positive half cycle and diodes D1 and D3 conduct during negative half cycle.
This charging and discharging of the capacitor make the pulsating DC into pure DC, as shown in figure. A step-down converter namely IC 7805 voltage regulator is used to convert 15V DC to 5V DC.
Block diagram of IC7805 voltage regulator is shown in the above figure. It consists of an operating amplifier that acts as error amplifier, zener diode used for providing voltage reference.
In general, 7.2V to 35V is the operating voltage range of IC7805 regulator. If the input voltage is 7.2V, then it gives maximum efficiency and, as the voltage exceeds 7.2V efficiency will decrease as there will be loss of energy in the form of heat. So, heat sinks are used to protect the regulator from over heat. Even without using transformer, we can directly convert 230V AC into 5V DC using high-rating diodes. If we have 230V DC power supply, then we can directly convert the 230V DC into 5V DC using a DC-DC buck converter. Feel free to post your comments in the comment section below and encourage other readers to learn the basics about rectifiers.