HALF WAVE RECTIFIER
What is Rectifier?
A rectifier is an electrical device that converts alternating current
(AC) to direct current (DC), a process known as rectification.
Rectifiers have many uses including as components of power
supplies and as detectors of radio signals. Rectifiers may be
made of solid state diodes, vacuum tube diodes, mercury arc
valves, and other components
When only one diode is used to rectify AC (by blocking the
negative or positive portion of the waveform), the difference
between the term diode and the term rectifier is merely one of
usage, i.e., the term rectifier describes a diode that is being
used to convert AC to DC. Almost all rectifiers comprise a
number of diodes in a specific arrangement for more
efficiently converting AC to DC than is possible with only one
Rectifier is a device that can convert ac
voltage into dc voltage.
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
Half wave rectification
In half wave rectification, either the positive or
negative half of the AC wave is passed, while
the other half is blocked. Because only one
half of the input waveform reaches the output,
it is very inefficient if used for power transfer.
Half-wave rectification can be achieved with a
single diode in a one-phase supply, or with
three diodes in a three-phase supply.
The process of removing one half the input
signal to establish a dc level is aptly called half
Transformer-coupled Input Voltage
Transformer is used to
couple the ac input
voltage from the source
to the rectifier.
Advantages of using
Adjust the source n N sec N pri
voltage to be stepped
up or stepped down V(sec) nV( pri )
Prevent shock hazard in V p ( out ) V p (sec)0.7V
the secondary circuit
PIV V p (sec)
Operation of half wave rectifier
During the positive half cycle of the input voltage the polarity of
the voltage across the secondary forward biases the diode. As a
result a current IL flows through the load resistor, RL. The forward
biased diode offers a very low resistance and hence the voltage
drop across it is very small. Thus the voltage appearing across
the load is practically the same as the input voltage at every
During the negative half cycle of the input voltage the polarity of
the secondary voltage gets reversed. As a result, the diode is
reverse biased. Practically no current flows through the circuit
and almost no voltage is developed across the resistor. All input
voltage appears across the diode itself.
Operation of half-wave rectifier
Average Value of Output Voltage
V( avg )
Vavg Approximately 31.8% for a half wave
Operation of half-wave rectifier
V p ( out ) V p ( in ) 0.7V
The input voltage must overcome the barrier potential
(0.7V) before the diodes becomes forward-biased
Result: A half-wave output with a peak value that is
0.7V less than the peak value of the input
Power supply specification
The required output dc voltage.
The average and peak currents in the
The peak inverse value (PIV) of each
The ripple factor.
Analysis of Half-Wave Rectifier
Average & peak currents in the diode.
DC output voltage.
RMS current & voltage.
An aspect of most rectification is a loss from the peak
input voltage to the peak output voltage, caused by the
built-in voltage drop across the diodes (around 0.7 V
for ordinary silicon p-n-junction diodes and 0.3 V for
Schottky diodes). Half-wave rectification and full-wave
rectification using two separate secondaries will have
a peak voltage loss of one diode drop. Bridge
rectification will have a loss of two diode drops. This
may represent significant power loss in very low
voltage supplies. In addition, the diodes will not
conduct below this voltage, so the circuit is only
passing current through for a portion of each half-
cycle, causing short segments of zero voltage to
appear between each "hump".
Peak Inverse Voltage (PIV)
PIV V p (in )
PIV – maximum value of reverse voltage which occurs
at the peak of the input cycle when the diode is
PIV is equals to the peak value of the input voltage
Equation Laws And Formulae Used
Transformer Utilization Factor
Form Factor Peak Factor
Disadvantage of Half-Wave Rectifier
Half wave rectification involves a lot of wastage of
energy and hence it is not preferred.
A small current flows during reverse bias due to
minority charge carriers. As the output
across (RL) is negligible.
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.
The simplest rectifier circuit is nothing
more than a diode connected in series
with the ac input, as shown to the right.
Since a diode passes current in only one
direction, only half of the incoming ac
wave will reach the rectifier output. Thus,
this is a basic half-wave rectifier.
In half wave rectification, either the positive or negative half of the
AC wave is passed, while the other half is blocked. Because only
one half of the input waveform reaches the output, it is very
inefficient if used for power transfer. Half-wave rectification can be
achieved with a single diode in a one-phase supply, or with three
diodes in a three-phase supply.
Result: - The output waveform may be
observed in the waveform viewer