In this tutorial, I will explain you the working of rectifiers. Rectifiers are one of the very basic circuits of electronics. At the start a comprehensive introduction of rectifiers is provided along with the types and uses of rectifiers and the effect of the type of rectifier on the output. After that the circuit of rectifiers is implemented on MATLAB’s Simulink. We will also discuss the difference between both the types of rectifiers and compare the output of the block diagram constructed on Simulink.
Introduction to Rectifiers
In electrical engineering rectifier is one of the very simple circuit used. The basic purpose of a rectifier is to convert the alternating current (AC) to Direct Current (DC). For the beginners, the definition of AC voltage can be taken as the voltage which changes its direction from positive voltage to negative across same terminal in a specified period of time over and over again. A simple sinusoidal wave is an AC wave. However, DC can be defined as a constant source of voltage which remains either positive or negative through the course of time.
Types of rectifiers:
Rectifiers can be classified into two major types
- Half wave rectifier
- Full wave rectifier.
Half wave rectifier:
Half wave rectifier is the one which only rectifies (converts to DC) the positive part of the AC voltage and skips the negative part. This rectifier is used very rarely in common practice because of the loss of power due to the wastage of negative part.
Full wave rectifier:
A full wave rectifier however uses both the positive and negative parts of the AC wave to rectify. It will pass the positive pat as it is and will invert the negative part of the wave to appear like positive on the load with the help of a bridge as you will see shortly. Along with some filters to remove ripples we can get a perfect DC wave at the output. Due to less power loss and closer resemblance to DC this circuit is used frequently compared to the former one.
Full wave rectifier simulation in Simulink
Open MATLAB and then open Simulink using the simulink icon on MATLAB as we have been doing in previous tutorials. Create a new blank model and save it in the first hand so you can access it in future. Now, click on the library browser icon on Simulink recently created model. And in the library browsers, search bar write diode as shown in the figure below. Remember that diodes are the main component in any type of rectifier and here we are going to design a full wave rectifier as the half wave rectifier is the simpler one and you can do it on your own.
Figure 1: Diode search
- From all the diodes select the most suitable diode. I prefer to select the one with protection as shown in the figure below,
Figure 2: Diode
- Place four such diodes. If you are familiar with rectifiers before, you must know that in a full wave rectifier there is a bridge of diodes. This bridge is made up of four diodes, hence place four such diodes. Place two diodes in series and the pair of two branches with two diodes each are then connected in parallel as shown in the figure below,
Figure 3: Bridge
- Know click on anywhere on the screen and from the search box search the AC voltage source as we have done previously as shown in the figure below,
Figure 4: AC voltage source
- Connect the positive side of the AC source between the two serially connected diodes and the negative side to other serially connected diodes as shown in the figure below,
Figure 5: Sources
- After the source is connected we also need a ground to complete the circuit. From the same search bar search ground as shown in the figure below,
Figure 6: Ground search
- Connect the ground at the bottom of the circuit connected, now from the search bar search series RLC branch as shown in the figure below,
Figure 7L RLC branch search
- Add the block to the model created. Double click on the RLC branch and from the parameters block select the resistor branch only as shown in the figure below
Figure 8: Resistor branch
- Connect this resistor branch at the load of the bridge rectifier and the diagram with load connected will look like the one shown in the figure below,
Figure 9: Diagram
- Now we need to set the input parameters of AC voltage source. Double click on the Input voltage source and set the peak amplitude of the voltage to 10V as shown in the figure below,
Figure 10: AC parameters
- Now if you run this block diagram you will encounter an error for the requirement of power gui. Power gui is a block which is the essential need in Simulink to run an electronic circuit. In the search bar search power gui as shown in the figure below,
Figure 11: Power GUI
- Next we need a voltage measuring device in order to see the voltage waveform at the output. Again in the search bar write voltage measurement as shown in the figure below,
Figure 12: Volt meter
- Place two such voltmeters on the model. Connect one of the voltmeters across the load resistor as are basically interested in measuring and viewing the voltage waveform at the load resistor. Refer to the figure to see how to connect the voltmeter at the load.
Figure 13: Load voltmeter
- Also we need a reference waveform to compare the output at the load with. Therefore, we will also measure the voltage at the input by connecting a voltmeter across the input AC source as shown in the figure below,
Figure 14: Input voltmeter
- Now, we also need to see the waveform at the load and the input to visualize actually what happened in a rectifier. To visualize a waveform what we need to place is an oscilloscope as we have been using in previous tutorials. In the search bar search scope as shown in the figure below,
Figure 15: Scope
- Place the block on the model near the load. As we want to view two waveforms, one of the input and other of the output. Therefore, we need two input ports of scope. Change the number of input ports of the scope to two as we have done in previous tutorials (Refer to RLC tutorial). At the two input ports connect the input voltmeter and the output load voltmeter as shown in the figure below,
Figure 16: Complete block diagram
- Run the model by pressing the run button and then double click on the scope. We want to see the legends on the waveform displayed by scope hence click on the view button and check the legends label as shown in the figure below,
Figure 17: Legends
- The rectified output at the load and the input AC are both shown in the figure below,
Figure 18: Rectified output
- The output is a pulsating DC. It can be converted to plain DC by using filters and regulators.
Exercise:
- Perform the analysis on half wave rectifier using MATLAB’s Simulink. It would be much simpler than the one performed in this tutorial.
(Hint: Number of diodes to be used will be one)