Diode and their applications

Assignment
To be submitted on 24/09/2021.
NO EXTENSION !!!

1. ZENER DIODE AND Zener Diode as Voltage

Regulator
2. Resistance of diode: Forward and reverse
resistances
3. Comparison of Rectifiers
4. How varactor diode is used in RF applications
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
amplitude modulation detectors (envelope detectors) of radio signals. Rectifiers are most commonly made
using solid state diodes but other type of components can be used when very high voltages or currents
are involved. When only a single 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 simply one of usage. The
term rectifier describes a diode that is being used to convert AC to DC. Most rectifier circuits contain a
number of diodes in a specific arrangement to more efficiently convert AC power to DC power than is
possible with only a single diode.
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 only 50% efficient
if used for power transfer. Half-wave
rectification can be achieved with a single
Output DC voltage of a half wave rectifier,
diode in a single phase supply as shown in given a sinusoidal input
figure 6.20, or with three diodes in a three-
phase supply.
Centre-tap full wave rectifier
CLIPPER AND CLAMPER CIRCUITS
 Clipper
 A clipper is a type of diode network that has the ability to “clip off” a
portion of the input signal without distorting the remaining part of the
alternating waveform.
 The half-wave rectifier is an example of the simplest form of diode
clipper—one resistor and a diode.
 Depending on the orientation of the diode, the positive or negative
region of the input signal is “clipped” off.
 There are two general categories of clippers: series and parallel.
 Series clipper:- A series clipper and its response for two types of
alternating waveforms are provided.

Series clipper circuit Response of clipper circuit

CLIPPER AND CLAMPER CIRCUITS
 Key points
1. The first step is to find out in which interval of the input signal the
diode is in forward-bias.
2. The direction of the diode suggests that the signal vi must be
positive to turn it on. The dc supply further requires the voltage vi to
be greater than v volts to turn the diode on.The negative region of
the input signal turns the diode into the OFF state. Therefore, in the
negative region the diode is an open circuit.

Series clipper with a dc supply

CLIPPER AND CLAMPER CIRCUITS
3. Determine the applied voltage (transition voltage) that will cause a change
in state for the diode. For the ideal diode the transition between states will
occur at that point on the characteristics where vd = 0 V and id = 0 A.
Applying this condition, it is recognized that the level of vi that will cause a
transition in state is:
vi = V
For an input voltage greater than V volts, the diode is in the short-circuit
state, while for input voltage less than V volts it is in the open-circuit or OFF
state (as it is reverse-biased).

Determining the transition level

of the input signal Determining vo in the clipper circuit
CLIPPER AND CLAMPER CIRCUITS
4. Be continually aware of the defined terminals
and polarity of vo. When the diode is in the
short-circuit state, the output voltage vo can
be determined by applying KVL in the clock-
wise direction:

5. It can be helpful to sketch the input signal

above the output and determine the output
at instantaneous values of the input. It is
then possible to sketch the output voltage
from the resulting data points of vo.

Determining levels of vo
CLIPPER AND CLAMPER CIRCUITS

For Vm > V, the diode is in the

short-circuit state and vo = Vm – V.
At vi = V, the diode changes state
and vi = – Vm, vo = 0 V. The
complete curve for vo can be
sketched.

Determining vo when vi Vm

Sketch for vo
CLIPPER AND CLAMPER CIRCUITS
 Parallel clipper:- Input vi is
applied for the output vo. The
analysis of parallel configuration
is very similar to the series
configuration.

Parallel clipper

Response of parallel clipper

CLIPPER AND CLAMPER CIRCUITS
 Break region
 There is a discontinuity at the voltage Vγ. Actually the transition
of a diode state is not exactly abrupt but gradual.
 Thus, a waveform, which is transmitted through the clipper
circuit, will not show an abrupt clipping. Instead, it will show a
gradual broken region, exhibiting the regions of un-attenuated
and attenuated transmission. Now, we will estimate the range of
this break region. The output current of a diode is given by:
at diode break point

 The incremental diode resistance r = dv/dI is given by:

 Again for meaningful clipping to be done, the applied signal

must vary from one side of the break point to a point well on the
other side.
CLIPPER AND CLAMPER CIRCUITS
Clamper
 A clamping network is one that will “clamp” a signal to a different dc
level. The network must have a capacitor, a diode, and a resistive
element, but it can also employ an independent dc supply to introduce an
additional shift.
 Before further probing into the clamper circuit one must have a basic
understanding of a transient RC circuit.
From the basic understanding of a series RC transient circuit applied
across a dc voltage EO, the instantaneous charge across the capacitor at
any time is given by

Q0=E0C where, C is the

capacitance of the capacitor.
We know that the time
constant τ = RC. The rise time
becomes smaller if we
decrease the time constant. Charging of a RC circuit
CLIPPER AND CLAMPER CIRCUITS
The discharge will occur quickly
if the time constant of the circuit is
decreased.
The magnitude of R and C must
be so chosen that the time
constant, τ = RC, is large enough
to ensure that the voltage across
the capacitor does not discharge
significantly during the interval the
diode is non-conducting.
Discharging of an RC circuit

 The clamping
circuit will clamp
the input signal to
the zero level.

Simple clamper circuit

CLIPPER AND CLAMPER CIRCUITS
 During the interval 0 –T/2 the network will appear, with the diode in the ON
state effectively “shorting out” the effect of the resistor R.
 The resulting RC time constant is so small that the capacitor will charge to V
volts very quickly. During this interval the output voltage is directly across the
short circuit and vo = 0 V.
 The diode will now be in the open-state condition. Applying KVL around the
input loop of figure will result in:

 The negative sign results from

the fact that the polarity of 2 V is
opposite to the polarity defined
for vo.
 For a clamping network the
total swing of the output is equal
to the total swing of the input.
State of the circuit in the negative half-cycle
 COMPARATORS
 The diode circuit which has been used in the
design of the clipping circuit can also be used for
the purpose of comparison, hence the name
comparator.
 The basic principle on which the comparator
works is the switching of the diodes.
 This action corresponds to the phase when the
diode conducts; and when it does, the comparator
circuit is used to compare the input arbitrary A diode comparator
voltage with the reference voltage.

Input signal with the threshold voltage Corresponding output waveform

 ADDITIONAL DIODE CIRCUITS
 Voltage Multiplier
 The voltage multiplier is a passive circuit, similar to the rectifier circuit
and gives an output which is approximately equal to a certain multiple of
the peak value of the peak input voltage.
 Here it is possible to obtain a dc voltage equal to the peak value of the
applied ac voltage.
 Peak Detector
 The half-wave rectifier circuit can be suitably manipulated to obtain the
peak detector circuit.
 The working principle depends on the charging and discharging of the
capacitor, and also on the conducting and non-conducting regions of the
diode. Its simple circuit consists of a diode kept in series with a resistor and
a load at the end.

Peak detector
Voltage doublers
 ADDITIONAL DIODE CIRCUITS
 Digital Circuits
 In various kinds of analog to digital converters, and in many digital circuits,
diodes are extensively brought to use.
Their primary domain of operation is switching, i.e., to keep a portion of a
large circuit in the ON state, selectively for a given interval of time.
 They, in coherent action with resistors, form many important logic families,
which are used in digital electronic circuits.

 Switching Regulators
 Power supplies with switching regulators offer great versatility, as the
design of power supplies employing this type of regulator can be lighter and
more compact.
 Another advantage of these power supplies is that the circuit can be
designed to give an output voltage that is higher than the unregulated voltage
or, has a different polarity.
 But there is also a disadvantage. The circuit becomes more complex
because of the control circuitry.
The structure of the converter can be of three types: buck, boost and
buck–boost.