Rectifier is a device which converts the alternating current (AC) into direct current (DC) and contain one or more diodes. Diode has zero resistance in one direction and infinity resistance in the other direction, so it act like short circuit in one direction and open circuit in other direction.
- What is a rectifier?
- Types of a Rectifier
- Which is the best rectifier?
- Disadvantages of bridge rectifier
- Use of Rectifiers
What is a rectifier?
Rectifier is a device which contain one or more diodes and converts the alternating current (AC) into direct current (DC).
What is a diode?
Diode is a semiconductor device with two terminal, which allows the current to flow in only one direction. Diode has zero resistance in one direction and infinity resistance in the other direction, so it act like short circuit in one direction and open circuit in other direction.
Types of a Rectifier
Rectifiers are basically of two types
- Half Wave Rectifier
- Full Wave Rectifier
- Center tap full wave rectifier
- Full wave bridge rectifier
Half Wave Rectifier
Half wave rectifier is the simplest. As show in above diagram, half wave rectifier have one PN junction diode. so which allows the current to flow in only one direction. However, Look at the input waveform and output waveform.
The circuit has an alternative voltage source. firstly, one PN junction diode and secondly, one load resister. See the input signal waveform which is AC.
For the positive half cycle, the PN junction diode will be in forward bias then current will pass through the circuit and we can see DC output across the load resister.
For the negative half cycle, the PN junction diode will be in reverse bias so, If we consider it an ideal diode then the current will not pass through it in reverse bias condition. However, this cycle of diode’s changing bias will continuously run and this is how half wave rectifier will clip the negative part of the input and give the DC output.
The output frequency will be same as the input frequency and the peak input voltage and peak output voltage will be also same.
What is Frequency?
Frequency is the time required for completing one cycle (one cycle is completed when the wave start from zero and again reach to the zero)
To understand full wave transformer, firstly, we need to understand what transformer is.
Here is the short explanation of transformer:
Transformer is an electrical device which work on the principal of magnetic induction and used to raise or lower the current and the voltage.
Why transformer used in Rectifier?
There is diodes are connected in the circuit of it and These diodes have certain breakdown point. so, if we apply very high amount of voltage diodes will get burn. However, as mention in the definition of transformer it can lower the voltage. Therefore, we use transformer into it.
Full Wave Rectifier
Center tap full wave rectifier
As shown in the above circuit, Full Wave rectifier contain two PN junction diode and one load resistor. However, Two PN junction diode are connected with the secondary loop. And the secondary loop is center taped and connected with the ground. Because of two diodes are connected if opposite direction. For the first positive half cycle of input signal, one diode will be in forward bias and the other one will be in reverse bias. The diode in the forward bias will conduct the current and other one will not. Same thing will happen for the negative half cycle. This circuit converts both positive and negative half cycle into DC.
Its output frequency will be double of the input frequency but peak output voltage will be half of the peak input voltage.
Full wave bridge rectifier
Full wave bridge rectifier has four diodes. Its circuit looks like bridge that’s why we call it as full wave bridge rectifier. It is almost similar to the center taped full wave rectifier but here we can get peak output voltage equal to peak input voltage because of four diode. During the positive half cycle diode D1 and D2 will be in forward bias and diode D3 and D4 will be in reverse bias. so diode D1 and D2 will conduct the current and diode D3 and D4 will not conduct the current.
During the negative half cycle diode D3 and D4 will be in forward bias and diode D1 and D2 will be in reverse bias. so, diode D3 and D4 will conduct the current and diode D1 and D2 will not conduct the current. This way we can have double frequency and equal input output voltage with bridge rectifier. And also this type of it don’t requires bulky center tap transformer.
Which is the best rectifier?
The best rectifier is full wave bridge rectifier.
Half wave rectifier cannot provide as much efficiency in compare to bridge rectifier because it only convert positive half cycle into DC. Half wave rectifier’s peak output voltage are same as input peak output voltage but it waste many voltages.
Center tap full wave rectifier need a very bulky center tap transformer to work. And bridge rectifier don’t need center tap rectifier. Center tap full wave rectifier’s peak output voltage is half of the peak input voltage. When bridge rectifiers peak output voltage and the peak input voltage are equal.
Because, full wave rectifier’s efficiency is highest. Bridge rectifier have four diodes so they can convert positive as well as negative half cycle into DC and it also not requires bulky center tap transformer to work.
Disadvantages of bridge rectifier
Bridge rectifier have four diode in its circuit therefor, cost of making it increases. Also its output I s not pure DC, it has ripple in its output. Because of four diode voltage drop also increases and one of major advantage of bridge rectifier is it don’t requires the center tap transformer.
NOTE: no rectifier is 100% accurate. There is always some AC quantity in it. But Full wave bridge rectifier provides current which has highest DC quantity and lowest AC quantity. That’s why we consider it as a best rectifier.
Use of Rectifiers
The main application of it is for converting the Alternating Current(AC) into Direct Current(DC). No rectifier can convert the Alternating Current(AC)into 100 % Direct Current(DC). But still many rectifiers are developed such that they have more than 95 % accuracy.
There will always come AC quantity exist after rectifying it. There are many filter circuits are available which are made up of capacitor and many other electronic component. These filter circuits can help to remove the AC quantity and increase the DC quantity as much as it can.
- Rectifiers are used in the mobile charger because, the current we are getting from our home’s plug that is alternating current(AC ). But mobile phone, laptop and many other devices’ batteries need DC(direct current)for charging. And as we know they are majorly used for converting AC quantity into DC quantity. So this is why the rectifiers are used in mobile chargers.
- Half wave rectifier is used for demodulating the amplitude of modulated signal.
- Full wave rectifier is used in radio for detecting the amplitude of modulating signal.
- Rectifiers are also used in AM radios.
- Many of the devices we use are made working on DC so every appliance that works on DC have the rectifier in it. Examples: TV, monitor, mobile, laptop, etc.
A half wave rectifier is not as effective as a full wave rectifier. With a 1/2 wave, you are throwing away one hump of the sine wave…either positive or negative portion. With a full wave rectifier you get both humps…either positive or negative.
The resultant effective voltage is much greater with a full wave rectifier, because there is very little time when the voltage is zero. The half wave is zero for 1/2 of the cycle.
Ripple factor (γ) may be defined as the ratio of the root mean square (rms) value of the ripple voltage to the absolute value of the DC component of the output voltage, usually expressed as a percentage. However, ripple voltage is also commonly expressed as the peak-to-peak value.
Transformer Utilization Factor (TUF) is defined as the ratio of DC power output of a rectifier to the effective Transformer VA rating used in the same rectifier. … But in TUF, instead of AC power input, VA rating of transformer secondary is used for calculation.
For a rectifier, The PIV refers to the maximum reverse voltage that the rectifier circuit applies to the diodes. This means the whole Secondary Voltage of the Transformer is applied reverse biased to the diode. So, for a half wave rectifier, the PIV is equal to the Secondary Voltage Of Transformer.
The diode bridge circuit was invented by Polish electrotechnician Karol Pollak and patented in December 1895 in Great Britain and in January 1896 in Germany. In 1897, the German physicist Leo Graetz independently invented and published a similar circuit.
AC signals can not be stored and DC power or signals can be stored. Thus,to store the electrical energy we need to convert it into DC. AC can be transported over long distances because of it’s frequency and dc can not be transported as dc has zero frequency. Thus, we have AC power supplied in homes,industries.
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