Download HALF AND FULL WAVE RECTIFIERS

Adnan Menderes University
EE210 Circuit Theory-II
HALF AND FULL WAVE RECTIFIERS
A device is capable of converting a sinusoidal input waveform into a unidirectional waveform
with non-zero average component is called a rectifier.
Half-Wave Rectifier
Since diodes restrict the flow of current to one direction, they can be used to convert an AC
power supply, which switches polarity from + to - many times a second, into a straight DC
supply. The simplest rectifier uses one diode, like this:
Called a half-wave rectifier, this circuit takes an AC signal in and chops off anything that falls
below 0 Volts. (In addition, the input signal have a voltage drop of 0.2-0.3 V or 0.6-0.7 V
depends on the materials of diode that is Germanium or Silicon, respectively.)
Signal In:
Signal Out (Half-wave):
Summary of Main Characteristics:
 A practical half wave rectifier with a resistive load is shown above. During the positive
half cycle of the input the diode conducts and all the input voltage is dropped across RL.
During the negative half cycle the diode is reverse biased so the output voltage is zero.
 The filter is simply a capacitor connected from the rectifier output to ground. The
capacitor quickly charges at the beginning of a cycle and slowly discharges through RL
after the positive peak of the input voltage.


The variation in the capacitor voltage due to charging and discharging is called ripple
voltage. Generally, ripple is undesirable, thus the smaller the ripple, the better the
filtering action.
Ripple factor is an indication of the effectiveness of the filter and is defined as
Ripple factor = √
where Vrms =
𝑉𝑚
2
,
Vdc =
𝑉𝑚
π
(𝑉𝑟𝑚𝑠)2
(𝑉𝑑𝑐)2
−1
and Vm: is the maximum peak value in one half
of the signal

The ripple factor can be lowered by increasing the value of the filter capacitor or
increasing the load capacitance.
Full-Wave Rectifier
The half-wave rectifier chopped off half our signal. A full-wave rectifier flips the - half of the
signal up into the + range. When used in a power supply, the full-wave rectifier allows us to
convert almost all the incoming AC power to DC. A full-wave rectifier uses a diode bridge,
made of four diodes, like this:
Here's what the circuit looks like to the signal as it alternates:
Rectified output voltage/current waveforms
So, if we feed our AC signal into a full wave rectifier, we'll see both halves of the wave above
0 Volts. Since the signal passes through two diodes, the voltage out will be lower by two diode
drops (for example; 1.2 Volts).
AC Wave In:
AC Wave Out (Full-Wave Rectified):
If we're interested in using the full-wave rectifier as a DC power supply, we'll add a
smoothing capacitor to the output of the diode bridge.
Summary of Main Characteristics:




A full wave rectifier with a resistive load is shown above. During the positive and
negative half cycle of the input the diode conducts and all the input voltage is dropped
across RL.
The filter is simply a capacitor connected from the rectifier output to ground. The
capacitor quickly charges at the beginning of a cycle and slowly discharges through RL
after the positive peak of the input voltage.
The variation in the capacitor voltage due to charging and discharging is called ripple
voltage. Generally, ripple is undesirable, thus the smaller the ripple, the better the
filtering action.
Ripple factor is an indication of the effectiveness of the filter and is defined as
Ripple factor = √
where Vrms =
𝑉𝑚
√2
half of the signal
,
Vdc =2 x
𝑉𝑚
π
(𝑉𝑟𝑚𝑠)2
(𝑉𝑑𝑐)2
−1
and Vm: is the maximum peak value in one