Although in our daily life we use A.C. current devices. But rectifier
is a ‘Electronic device which converts A.C. power into D.C. power’.
The study of the junction diode characteristics reveals that the junction
diode offers a low resistance path, when forward biased, and a high
resistance path, when reverse biased. This feature of the junction
diode enables it to be used as a rectifier.
The alternating signals provides opposite kind of biased voltage at the
junction after each half-cycle. If the junction is forward biased in
the first half-cycle, its gets reverse biased in the second half. It
results in the flow of forward current in one direction only and thus the
signal gets rectified.
In other words, we can say, when an alternating e.m.f. signal is applied
across a junction diode, it will conduct only during those alternate half
cycles, which biased it in forward direction.
Mainly we have two types of rectifier :
Half wave rectifier.
Full wave rectifier.
junction diode as half
When a single diode is used as a rectifier, the rectification of only
one-half of the A.C. wave form takes place. Such a rectification is called
half-wave rectification. The circuit diagram for a half-wave rectifier
is shown in Fig.
It is based upon the principle that junction diode offers low resistance
path when forward biased, and high resistance when reverse biased.
The A.C. supply is applied across the primary coil(P) of a step down
transformer. The secondary coil(S) of the transformer is connected to
the junction diode and a load resistance RL.
The out put D.C. voltage is obtained across the load resistance(RL)
Suppose that during the first half of the input cycle, the junction diode
gets forward biased the conventional current will flow in the direction of
the arrow-heads. The upper end of RL will
be at positive potential w.r.t. the lower end. During the negative
half cycle of the input a.c. voltage, the diode is reverse biased. No
current flows in the circuit, and therefore, no voltage is developed across
(RL). Since only
the positive half cycle of the input appears across the load, the a.c. input
is converted into pulsating direct current (d.c.).
1. Half wave rectification
involves a lot of wastage of energy and hence it is not preferred.
2. A small current flows
during reverse bias due to minority charge carriers. As the output
across (RL) is
3. The resulting d.c.
voltage is not steady enough for some purpose. The following device is
used when a very steady d.c. voltage is required.
junction diode as a
“A rectifier which rectifies both waves of the a.c. input is called a full
:- It is based upon the principle that a
junction diode offers low resistance during forward biased and high
resistance, when reverse biased.
The main difference is that in full wave rectifier we use two diodes.
For this when we apply a.c. current to the rectifier then the first half
wave get forward biased due to first diode. And when the second half
wave comes. Then at that time the second diode comes in action and
gets forward biased. Thus output obtained during both the half cycles
of the a.c. input
:- The a.c. supply is applied across the primary coil(P) of a step down
transformer. The two diodes of the secondary coil(S) of the
transformer are connected to the P-sections of the junction diodes (D1)
and (D2). A load
resistance (RL) is
connected across the n-sections of the two diodes and at centre of the
secondary coil. The d.c. output will be obtained across the load
Suppose that during first half of the input cycle, upper end of (S) coil is
at positive potential. And lower end is at negative potential.
The junction diode (D1)
gets forward biased, while the diode. (D2)
get reverse biased. When the second half of the input cycle comes, the
situation will be exactly reverse. Now the junction diode (D2)
will conduct. Since the current during both the half cycles flows from
right to left through the load resistance (RL)
the output during both the half cycles will be of same nature.
Thus, in a full wave rectifier, the output is continuous but pulsating in
nature. However it can be made smooth by using a filter circuit.
on a junction
A P-n junction is said to be reverse biased if the positive terminal of the
external battery B is connected to n-side and the negative terminal to
p-side of the p-n junction. In reverse biasing, the reverse bias
voltage supports the potential barrier VB.
(Now the majority carriers are pulled away from the junction and the
depletion region become thick. There is no conduction across the
junction due to majority carriers. However, a few minority carriers
(holes in n-section and electrons in p-section) of p-n Junction diode cross
the junction after being accelerated by high reverse bias voltage.
Since the large increase in reverse voltage shows small increase in reverse
current, hence, the resistance of p-n junction is high to the flow of
current when reverse biased.
It is device which is used to increase or decrease the alternating current
and alternating voltage. For the rectifier, it may be step down or step up.
Junction Diode :
It is made up of p-type and n-type semiconductor which conducts when the p
terminal of diode to connect to positive terminal of battery and n region is
connected to negative terminal of battery i.e. during forward biased and
does not conduct during reverse biased.
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