Microsoft PowerPoint - a2_circuit elements-diode []
Diode
MOSFETMOSFET
BJT
2
Diode
The basic operation of a diodep The basic structure of atoms The
properties of insulators conductorsThe properties of insulators,
conductors, and semiconductors Covalent bonding The properties of p
and n type materialsp p p yp The forward and reverse biasing of a
p-n junctionjunction The application of diode
3
Introduction
The basic function of a diode is to restrict current flowThe basic
function of a diode is to restrict current flow to one
direction.
Forward bias Reverse Bias
Bohr model of an atom
As seen in this model, electrons circle the nucleus. Atomic
structure of a material determines it’s ability to conduct orit s
ability to conduct or insulate.
5
Conductors, Insulators, and Semiconductors
The ability of a material to conduct current isThe ability of a
material to conduct current is based on its atomic structure.
The orbit paths of the electrons surroundingThe orbit paths of the
electrons surrounding the nucleus are called shells.
Each shell has a defined number of electrons itEach shell has a
defined number of electrons it will hold. This is a fact of nature
and can be determined by the formula, 2n2.
The less complete a shell is filled to capacity the
The outer shell is called the valence shell.
The less complete a shell is filled to capacity the more conductive
the material is.
6
Conductors, Insulators, and Semiconductors
The valence shell determines the ability of material to conduct
current.
A Copper atom has only 1 electron in it’ l i Thi k it
A Silicon atom has 4 electrons in it’s it’s valence ring. This
makes it a good conductor. It takes 2n2
electrons or in this case 32 electrons to fill the valence
shell
valence ring. This makes it a semiconductor. It takes 2n2 electrons
or in this case or 18 electrons to fill
to fill the valence shell. the valence shell.
7
Covalent BondingCovalent Bonding
Covalent bonding is a bonding of two or more atoms by the
interaction of their valence electrons.
8
Covalent Bonding
Certain atoms will combine in this way to form a crystal structure
Silicon and Germanium atoms combine in this
g
structure. Silicon and Germanium atoms combine in this way in their
intrinsic or pure state.
9
The process of creating N and P type
Other atoms with 5 electrons such Other atoms with 3 electrons such
as
The process of creating N and P type materials is called
doping.
as Antimony are added to Silicon to increase the free
electrons.
Boron are added to Silicon to create a deficiency of electrons or
hole charges.
N-type P-type
The Depletion Region
p region n region p region n regionp g g p g g
With the formation of the p and n materials combination
This creates the depletion region and has a barrier
of electrons and holes at the junction takes place.
region and has a barrier potential. This potential cannot be
measured with a
lt t b t it ill
11
Forward and Reverse Bias
Voltage source or bias connections Voltage source or bias
connections are
to the p material and + to the n
Forward Bias Reverse Bias
g are + to the p material and – to the n material
Bias must be greater than 3 V for
– to the p material and + to the n material
Bias must be less than the break down Bias must be greater than .3
V for Germanium or .7 V for Silicon diodes.
voltage.
12
The depletion region widens.
Ideal Diode Characteristic Curve
In this characteristicIn this characteristic curve we do not
consider the voltage drop or the resistive properties. Current flow
proportionallyflow proportionally increases with voltage.
13
Practical Diode Characteristic Curve
In most cases we consider only the f d bi ltforward bias voltage
drop of a diode. Once this voltage is g overcome the current
increases proportionally withproportionally with voltage.This drop
is particularly important p y p to consider in low voltage
applications.
15
Complex Characteristic Curve of a Di dDiode
The voltage drop is not the only loss of a diode. In some cases we
must take into account other factorsaccount other factors such as
the resistive effects as well as reverse breakdown.
16
Diode Packagesg
Diodes come in a variety of sizes and shapes. The design and
structure is determined by what type of circuit they will be used
in.
17
Typical diode packages and terminal identification. A is anode and
K is cathode.a ode a d s cat ode
18
19
22
clipperpp
27
Figure 3.37 The clamped capacitor with a load resistance R.
The clamped capacitor with a load resistance Rresistance R
30
32
Zener Diode
The basic function of zener diode is to maintain a specific p
voltage across it’s terminals within given limits of line or load
change. Typically it is used for providing a stable reference
voltage for use in power supplies and otherreference voltage for
use in power supplies and other equipment.
This particular zener circuit will work to maintain 10 V across the
load
33
This particular zener circuit will work to maintain 10 V across the
load.
Zener Diodes A zener diode is much like a normal diode. The
exception being is that it is placed in the circuit in reverse bias
andbeing is that it is placed in the circuit in reverse bias and
operates in reverse breakdown. This typical characteristic curve
illustrates the operating range for a zener. Note that it’s forward
characteristics are just like a normal diode.
34
Zener Diodes
Zeners are available• Zeners are available with voltage breakdowns
of 1.8 Vbreakdowns of 1.8 V to 200 V.
• This curve illustrates• This curve illustrates the minimum and
maximum ranges of g current operation that the zener can ff ti l i
t ieffectively maintain
it’s voltage.
Zener Diodes
As with most devices, zener diodes have given characteristics such
as temperature coefficients and
i h h b id d Th dpower ratings that have to be considered. The data
sheet provides this information.
36
37
RegulationRegulation
In this simple illustration of zener regulation circuit, the zener
diode will “adjust” it’s impedance based on varying inputdiode will
adjust it s impedance based on varying input voltages and loads
(RL) to be able to maintain it’s designated zener voltage. Zener
current will increase or decrease directly with voltage input
changes. The zener current will increase or decrease inversely with
varying loads. Again, the zener has a finite range of
operationfinite range of operation.
38
Zener Limitingg
Zener diodes can used for limiting just as normal diodesZener
diodes can used for limiting just as normal diodes. Recall in
previous chapter studies about limiters. The difference to consider
for a zener limiter is a it’s zener b kd h t i tibreakdown
characteristics.
39
Varactor Diodes
A varactor diode is best explained as a variable capacitorA
varactor diode is best explained as a variable capacitor. Think of
the depletion region a variable dielectric. The diode is placed in
reverse bias. The dielectric is “adjusted” by bias changes.
40
Varactor Diodes
The varactor diode can be useful in filter circuits as the
adjustable component.
41
Light Emitting Diodeg g
The light emitting diode (LED) emits photons asThe light-emitting
diode (LED) emits photons as visible light. It’s purpose is for
indication and other intelligible displays. Various impurities are
added g p y p during the doping process to vary the color
output.
42
44
Optical Diodesp The seven segment display is an example of LEDs use
for di l f d i l di itdisplay of decimal digits.
45
46
Other Diode Types - LDyp The laser diode (light amplification by
stimulated emission f di ti ) d h ti ( i l l ) li htof radiation)
produces a monochromatic (single color) light.
Laser diodes in conjunction with photodiodes are used to retrieve
data from compact discs. p
47
Optical Diodes - Photo Diodep
The photodiode is used to vary current by the amount ofThe
photodiode is used to vary current by the amount of light that
strikes it. It is placed in the circuit in reverse bias. As with
most diodes when in reverse bias, no current flows when in reverse
bias, but when light strikes the exposed junction through a tiny
window, reverse current increases proportional to light
intensityproportional to light intensity.
48
Optical Diodes - Solar Cellp
The solar cell operates on the same principleThe solar cell
operates on the same principle as the photo diode. The area of the
junction is larger and enough pairs are produced thatlarger, and
enough pairs are produced that significant energy can be taken from
the d idevice.
49
Other Diode Typesyp
The Schottky diode’s significant characteristic is it’sThe Schottky
diode’s significant characteristic is it s fast switching speed.
This is useful for high frequencies and digital applications. It is
not a typical diode in the g pp yp fact that it does not have a p-n
junction, instead it consists of a heavily doped n-material and
metal bound togethertogether.
50
Other Diode Typesyp
h i di d l d lThe pin diode is also used in mostly microwave
frequency applications. It’s variable forward series resistance
characteristic is used for attenuation,resistance characteristic is
used for attenuation, modulation, and switching. In reverse bias
exhibits a nearly constant capacitance.
51
Other Diode Typesyp
Th t l di d h ti i t It ill t llThe tunnel diode has negative
resistance. It will actually conduct well with low forward bias.
With further increases in bias it reaches the negative resistance
range where g g current will actually go down. This is achieved by
heavily doped p and n materials that creates a very thin depletion
regionregion.
52
Summary
Diodes, transistors, and integrated circuits are
P-materials are doped with trivalent impurities
, , g all made of semiconductor material.
N-materials are doped with pentavalent impurities
P and N type materials are joined together to form aP and N type
materials are joined together to form a PN junction.
A diode is nothing more than a PN junctionA diode is nothing more
than a PN junction.
At the junction a depletion region is formed. This creates barrier
which requires approximately .3 V for acreates barrier which
requires approximately .3 V for a Germanium and .7 V for Silicon
for conduction to take place.
53
Summaryy
A di d d t h f d bi d d d t
Wh d bi d di d l ith t d
A diode conducts when forward biased and does not conduct when
reverse biased
When reversed biased a diode can only withstand so much applied
voltage. The voltage at which avalanche current occurs is called
reverse breakdown voltage.
There are three ways of analyzing a diode. These There are three
ways of analyzing a diode. These are ideal, practical, and complex.
Typically we use a practical diode model.
54