What is Rectifier?
A
Rectifier is an electronic circuit or device that offers a low resistance path
(ideally zero resistance path) to current in one direction and high resistance
path (ideally infinite resistance path) in opposite direction.
This property allows the rectifier to convert a bidirectional waveform, such as sinusoidal waveform (AC signal), whose average value is zero, into a unidirectional waveform, which has non-zero average value and a constantly changing magnitude.
The constantly changing magnitude of the output waveform of the rectifier indicates the presence of the AC component and the non zero average value of this waveform indicates the presence of the DC component. Therefore, this waveform is referred to as a pulsating DC waveform and can be further filtered out as a pure DC signal with the help of different kinds of filters and freewheeling diode.
Thus,
a rectifier is most commonly known as an AC to DC converter.
Importance of Rectifier
Rectifiers are the fundamental circuits in electronics because most of the electronics circuit or device operates on DC power, while the universal supply of electricity is AC in nature, as it is less expensive and safer. Therefore, the conversion of AC to DC is the fundamental need of those electronic devices. Although, there are various DC power sources available but these sources are limited and not economical.
What is Rectification?
The process
of conversion of a bidirectional waveform into a unidirectional waveform is
known as rectification or in simple words we can say that the
process of conversion of AC waveform into DC signal is known as rectification.
There are
two types of rectification i.e. half wave rectification and full wave
rectification.
Half wave rectification means the conversion of half of the AC waveform into DC signal and the rectifier that offers half wave rectification is called half wave rectifier.
Full wave
rectification means the conversion of the full waveform of AC
signal into DC signal and the rectifier that offers full wave rectification is
called full wave rectifier.
Rectifier's Circuit Diagram
In rectifier circuits, we use semiconductor switches that allow the conduction of current in one direction only such as Diodes, SCRs, MOSFETs etc. As mentioned earlier, a rectifier itself allows the conduction of current in one direction only. These semiconductor switches are connected in different circuit configurations for half wave rectification as well as full wave rectification.
Let us explore the circuit configurations for both half wave rectifiers and full wave rectifiers separately.
Rectifier circuits can be either single phase or three phase, depending on the nature of supply. Since the universal supply is either single phase or three phase AC.
Further in this article, we will discuss the concept of rectifiers by using single phase rectifiers because it is easier to understand.
Half Wave Rectifier Circuit
Half wave
rectifier circuit employs only one semiconductor switch to convert half of the
AC waveform into DC signal. The circuit diagram for the half wave rectifier is
shown in the given figure.
Full wave Rectifier Circuit
For full wave rectification, we use two types of circuit configuration i.e. Centre tapped rectifier circuit and bridge rectifier circuit.
Centre Tapped Rectifier Circuit
A center tapped rectifier uses two semiconductor switches and a center tapped transformer, connected as shown in the given figure.
Bridge Rectifier Circuit
A
bridge rectifier circuit configuration uses four switches connected in a
bridge-like arrangement. The circuit diagram of the bridge rectifier is shown
in the given figure.
Note
:-
The above classifications of rectifiers are based on the rectification and
circuit configuration. Additionally, rectifiers are further classified as controlled
rectifiers, un-controlled rectifiers and semi-controlled
rectifiers on the basis of controlling the output or the switch used.
We have created a dedicated article on the types of rectifiers. You can check it out for detailed information on Rectifiers and their types.
Working of Rectifier
The working of the Rectifier depends on the biasing of the switch used in its circuit.
As
we discussed above, a rectifier circuit uses semiconductor switches that have
unidirectional current conduction property such as diodes, SCRs, MOSFETs, etc.
So according to the biasing of these switches, we ensure the direction of
current flow in the rectifier circuit. This allows us to effectively convert
the bidirectional waveform such as AC signal into a unidirectional waveform
such as pulsating DC signal.
Let us
understand the above discussed working of rectifiers in detail for both half
wave rectification as well as full wave rectification separately.
To make it easy to understand, we'll use rectifier circuits with diodes only.
Half Wave Rectification
As
we discussed above, for half wave rectification a rectifier circuit employs
only one semiconductor switch (diode). In this circuit the diode is connected
in such a way that it only conducts for the desired half of the AC
supply.
Typically,
it is desired that only the positive half of the AC supply is converted into DC
signal. So, we will focus on the working of half wave rectifiers for converting
the positive half of AC supply into DC signal.
However,
you can also convert the negative half of AC supply as well. To convert the
negative half of the AC supply, you can simply reverse the orientation of the
switch used in this circuit.
The figure given below shows the rectifier circuit using a diode for half wave rectification.
In this
circuit :
- During the positive half-cycle of the AC
input, the diode D is forward-biased and conducts current, allowing the
positive half of the AC waveform to pass through the load
- During the negative half-cycle, the diode D is reverse-biased and does not conduct current, blocking the negative half of the AC waveform.
This results in a pulsating DC output that consists only of the positive half-cycles of the input AC signal.
The
working and the output waveform for the half wave rectifier can be visualized
with help of the given figure.
Full Wave Rectification
As
we mentioned earlier, for full wave rectification, there are two types of
rectifier circuit configurations used that are center-tapped circuit and bridge rectifier circuit.
Let us understand the working of both circuits of full wave rectifiers separately.
Center Tapped Full Wave Rectifier Working
The circuit diagram for center-tapped full wave rectifier using diodes is shown in the given figure.
In this circuit:
- During the positive half-cycle of the AC input supply, the terminal A is positive with respect to B, therefore the Diode D1 is forward biased and it allows the conduction of current and D2 is reverse biased and it does not allow the conduction of current. In this condition the current flows through the diode D1, the load and the center taping of the transformer and the output voltage across the load is the same as the input waveform.
- During
the negative half-cycle of the AC input supply, the terminal A is negative
with respect to B, therefore the Diode D2 is forward biased and it allows
the conduction of current and D1 is reverse biased and it does not allow
the conduction of current. In this condition the current flows through the
diode D2, the load and the center taping of the transformer and the output
voltage across the load is the negative of the input waveform.
The working and the output waveform for the center tap full wave rectifier can be visualized with help of the given figure.
Bridge Rectifier Working
The
circuit diagram for bridge rectifier using diodes is shown in the given figure.
In
this circuit the two diagonally opposite diodes conduct for each half
cycle of AC input supply.
- For
the positive half cycle of the AC input supply, diodes D1 and D3 are
forward biased, therefore these diodes conduct the current, and the diodes
D2 and D4 are reverse biased, therefore these diodes will not conduct the
current. During this condition the voltage across the load is the same as
that of the input supply.
- For the negative half cycle of the AC input supply, diodes D2 and D4 are forward biased, therefore these diodes conduct the current, and the diodes D1 and D3 are reverse biased, therefore these diodes will not conduct the current. During this condition the voltage across the load is the negative of the input supply.
The
working and the output waveform for the bridge rectifier can be visualized with
help of the given figure.
The
working of the rectifiers typically involves converting the AC waveform into DC
signal. But what happens when we put DC supply through a rectifier? This
question was asked several times on different online platforms on the internet
and deserves some attention, so we have taken this question into
consideration.
Working of Rectifier on DC Supply
Let
us understand what happens when DC supply is given to different rectifiers
separately.
Working of Half Wave Rectifier on DC Supply
Consider
the half wave rectifier circuit discussed previously.
In this circuit if we apply the DC voltage, then the diode either conducts continuously or blocks the conduction of current continuously until the supply is given. The conduction and blocking of current depend on the polarity of supply and the orientation of the diode used.
You
can visualize this phenomenon by the help of the given figure.
Working of Full Wave Rectifier on DC Supply
Working of Center Tapped Rectifier on DC Supply
Consider the same center tapped rectifier circuit using diode that was discussed previously.
Working
of Bridge Rectifier on DC Supply
Consider the same bridge rectifier circuit that was discussed previously.
In this
circuit if we apply the DC voltage of positive polarity (polarity that is shown
in the given figure) then the diodes D1 and D3 become forward biased and they
will conduct the current continuously to the load until the supply is given.
The polarity of the voltage across the load terminals is equal to the supply
voltage.
And
if the DC supply of negative polarity is applied, then the diodes D2 and D4
become forward biased and they will conduct the current continuously to the
load until the supply is given and the polarity of voltage across the load
terminals is reversed.
Output waveform of rectifier
In
the above discussion of the working of the rectifier, we see that the output
waveform for half wave rectifier and full wave rectifier is shown as the given
figure.
If
we observe the output waveform of the both types of rectifiers, we will find
that these are not the pure DC waveform. They are unidirectional waveforms that
constantly change their magnitude.
As
we discussed previously in the definition of rectifier, these
waveforms contain both DC and AC components of voltage, and therefore referred
to as pulsating DC.
Related Posts
No comments:
Post a Comment
Please feel free to provide feedback and suggestions, and also don't hesitate to ask your questions.