This document provides an overview of electronic devices and circuits. It discusses semiconductors like silicon and germanium and how they are doped to create p-type and n-type materials. The junction diode is described as the simplest electronic device, formed by joining p-type and n-type silicon. Diode applications in rectifiers and clipping/clamping circuits are explained. The document also covers LEDs and provides the junction diode current equation.

1. • Electronics Devices and Circuits: Junction Diode,
Applications: rectifiers, Clipping and Clamping Circuits, LEDs
• Electronics devices are basically semiconductor (Si or Ge)
based devices.
• Semiconductors are of two types namely: Intrinsic (pure Si)
and Extrinsic (Doped with trivalent or pentavalent impurity
for making P – type and n-type semiconductor respectively)
• For practical applications intrinsic semiconductor is not used
as its conductivity can be regulated by temperature, which is
not practically possible.
• Hence, for practical applications p-type and n-type
semiconductors are used as their conductivity can be
controlled by doping level.
Unit - III

2. • Electronic circuits contain Electronic devices
• Electronic devices are mostly Non-linear as the relation
between voltage and current is not a straight line passing
through origin. Also, they don’t follow ohm’s law
• Electronic devices are mostly Unilateral as their behavior
is not same if we reverse them
• Electronics circuits can be categorized in two major parts
viz. (a) Analog Electronics and (b) Digital Electronics
• The basic building blocks of Analog electronics circuits
are diode, transistor etc which in turn are used to
construct logic gates and other digital electronics devices.
Electronic Devices & Circuits

3. • Junction Diode or p-n junction diode is the simplest
element of Electronics circuit.
• It is fabricated by doping trivalent impurity (on half
part) and pentavalent impurity (on another half part)
of the single silicon wafer.
• Two different pieces of silicon one with trivalent
doping and another with pentavalent doping cannot
be joined together to form a p-n junction diode as
inter-atomic space will be much higher and electrons
and holes movement will not be possible.
Junction Diode

4. • I = Io[e^(Ve/ηkBT) - 1]
• Where Io is the reverse saturation current at
temperature T K
• V is the applied voltage
• e is electronic charge in coulomb
• kB is Boltzmann constant = 1.38* 10^-23 J/K
• T is temperature in K
• η is a constant depending on Diode material (1
for Ge and 2 for Si)
Junction Diode Current equation

5. • I = Io[e^(Ve/ηkBT) - 1] = Io[e^(V/ηVT) - 1]
• Where VT = 0.026 V for at room temperature
• This equation is valid for both forward bias as
well as reverse bias
• For forward bias the exponential term is much
higher than unity and 1 is neglected such that the
relation becomes exponential one
• For reverse bias exponential term becomes
negligible as compared to 1 and I is simply –IO i.e.
constant value equal to reverse saturation current
Junction Diode Current equation

6. • Piecewise Linear Diode Model:
• AS per piecewise linear model Diode is treated as
on/off switch in forward and reverse bias region
respectively.
• In reverse bias it will act as a open switch and no
current flows across it.
• In forward bias it will act as a close switch and a
small voltage (knee voltage) drops across it.
• This model is used for studying diode applications
in rectifier and clipping/clamping circuits.
Diode Model for applications

7. • Rectifier is a circuit which converts AC to DC
• Rectifiers are of two types:
(a) Half wave rectifier
(b) Full wave rectifier
• Full wave rectifiers are again of two types
(i) Full wave Centre tap rectifier
(ii) Full wave Bridge rectifier
We will study them one by one
Diode applications: Rectifiers

8. • The half wave rectifier rectifies only one half (either positive half
or negative half) of the AC waveform to DC
• In this only one diode is used. For the half cycle of the AC wave it
is in the forward bias region and acts as short circuit, applying the
source voltage to the load.
• In the another half cycle of the AC wave it is in the reverse bias
region and acts as open circuit, applying zero voltage across the
load
Half wave Rectifier

9. • Peak Inverse Voltage (PIV): Same as maximum
of the transformer secondary output = Vmax
• Average output voltage (Vdc): Vmax/π
• RMS of output voltage (Vrms): Vmax/2
• Ripple factor (ϒ): defined as (ac
component)/(dc component) = 1.21; where ac
component = √((rms)^2 – (dc)^2)
• Form factor: defined as ratio of rms value and
dc value = π/2 = 1.57
Performance parameters for Half wave Rectifier

10. • In this rectifier a special type of transformer known as “Centre
Tap Transformer” is used and two diodes are connected on the
two extreme ends of the transformer as shown in circuit.
• It is clear that in one half of the AC wave diode D1 acts as short
circuit and another diode D2 acts as open circuit. In the other
half of the AC wave diode D1 acts as open circuit and another
diode D2 acts as short circuit. Such that a positive voltage
appears always across the load.
Full wave Centre Tap Rectifier

11. • In this rectifier a normal transformer is used and four diodes are
connected in bridge like structure as shown in the circuit.
• In this rectifier for one half of the AC wave diode pair D1 and D3
are forward biased and diode pair D2 and D4 are in reverse bias
simultaneously such that the transformer output voltage appears
across the load.
• In the another half of the AC wave the earlier forward bias diode
pair D1 and D3 are now reverse biased and earlier reverse biased
diode pair D2 and D4 are now in forward bias such that the
transformer output voltage appears across the load in the same
polarity as the first half cycle.
• Hence, the voltage across the load always appears in the same
polarity.
Full wave Bridge Rectifier

12. Full wave Bridge Rectifier
The output of full wave bridge rectifier is
same as centre-tap rectifier. But, the cost
of normal transformer used here is less
than the centre tap transformer. Also, the
PIV ratings of the diodes used here is just
half as compared to the PIV rating of
diodes used for centre tap method.

13. • Only the PIV is different for the two types of full wave rectifiers.
Rest all the parameters are same.
• Peak Inverse Voltage (PIV) for Centre tap type: Twice of
maximum of the transformer secondary output between one
extreme and centre tap = 2Vmax
• Peak Inverse Voltage (PIV) for Bridge type: Same as maximum
of the transformer secondary output = Vmax
• Average output voltage (Vdc): 2Vmax/π
• RMS of output voltage (Vrms): Vmax/√2
• Ripple factor (ϒ): defined as (ac component)/(dc component) =
0.482; where ac component = √((rms)^2 – (dc)^2)
• Form factor: defined as ratio of rms value and dc value = π/2√2
= 1. 11
Performance parameters for Full wave Rectifier

14. • The clipper circuit is a circuit which clips (removes) some
portion of the applied waveform
• Clipping circuits are widely used in RADAR, digital and
other electronic systems.
• Simple clipping circuits can be configured using diodes
• The important types of clipping circuits are as follows:
1. Positive clipper: removes positive half of waveform
2. Negative clipper: removes negative half of waveform
3. Biased clipper: removes some portion of positive or
negative half (not completely the half portion)
4. Combination clipper: removes some part of positive half
as well as some part of negative half simultaneously
Diode applications: Clippers

15. Positive Clipper
As explained earlier the Positive Clipper
removes the positive half of waveform
completely and only the negative half of the
waveform is available in the output as
shown in the figure.

16. Negative Clipper
As explained earlier the Negative Clipper
removes the negative half of waveform
completely and only the positive half of the
waveform is available in the output as
shown in the figure.

17. Biased Clipper
The biased Clipper has a DC source in series with the Diode such
that the DC source will reverse bias the diode as shown in the
figure. Till the time AC voltage is lower than the DC source, the
diode will remain reverse biased and source voltage will appear
across the load. Once the AC source voltage is higher than the DC
source the diode will be forward biased (short) such that the DC
source voltage will appear across the load as shown in the figure.

18. Combination Clipper
The combination Clipper will have two parallel branches in which diode will be
connected in opposite direction and two different DC sources will be connected
in series with the Diodes as shown in the figure. In positive half cycle till the
time AC voltage is lower than the DC source V1, the diode D1 will remain
reverse biased and source voltage will appear across the load. Similarly, in
negative half cycle till the time AC voltage is lower than the DC source V2, the
diode D2 will remain reverse biased and source voltage will appear across the
load. Once the AC source voltage is higher than the DC source (either V1 or V2)
the corresponding diode will be forward biased (short) such that the DC source
voltage will appear across the load as shown in the figure.

19. • A clamper circuit is a circuit which introduces a DC level to an
applied AC signal.
• The effect of the clamper circuit is that the whole input
waveform clamps (shifts) up or down without any change in
the waveform.
• For constructing a clamper circuit, a capacitor of high
capacitance is chosen such that the time constant of the RC
circuit is high as compared to the time period of applied
voltage such that it will be assumed that capacitor will
maintain a fairly constant voltage once charged.
• The clamper circuits are of two types:
1. Positive peak clamper or clamp down circuit or Negative DC
restoring circuit
2. Negative peak clamper or clamp up circuit or Positive DC
restoring circuit
Diode Clamper

20. Positive peak clamper or clamp down circuit or
Negative DC restoring circuit
As discussed earlier, for constructing a clamper circuit, a capacitor of
high capacitance is chosen such that the time constant of the RC circuit
is high as compared to the time period of applied voltage such that it will
be assumed that capacitor will maintain a fairly constant voltage once
charged. The circuit diagram and output of the clamp down clamper is as
shown in the figure below.

21. Negative peak clamper or clamp up circuit or
Positive DC restoring circuit
As discussed earlier, for constructing a clamper circuit, a capacitor of
high capacitance is chosen such that the time constant of the RC circuit
is high as compared to the time period of applied voltage such that it will
be assumed that capacitor will maintain a fairly constant voltage once
charged. The circuit diagram and output of the clamp up clamper is as
shown in the figure below.

22. • LEDs are special purpose diodes, which emit light when
connected in forward bias.
• They are fabricated of different materials (like GaAs, GaP,
GaAsP etc) for emitting different color light.
• These materials have band gap energy (between
Valence and Conduction band) in the range of 1.5 – 3 eV,
and emits radiation of visible range by the
recombination of electrons and holes
• The use of LEDs as a light source is increasing very fastly
now a days as they are more efficient than tungsten
filament bulb as the energy is not converted to heat in
them.
Light emitting Diodes (LEDs)