TABLE OF CONTENT
TOPICS PAGE
NO.
1. SOUND OPERATED LIGHT GADGET 1-4
1.1
Introduction 1
1.2 Circuit
Diagram 2
1.3 Working 3
1.4 Application 4
2. INTEGRATED CIRCUITS 5-12
2.1 IC 555 5
2.1.1 Pin Connection 6
2.1.2 Monostable Mode 6
2.2 IC 741 8
2.2.1 Internal
Circuitry 8
2.2.2 Circuit
Notation 9
2.2.3 Operation 9
2.2.4 Non-Inverting
Amp. 10
2.2.5 Inverting
Amp. 11
2.2.6 Voltage
Comparator 12
2.2.7
Application 12
3. CONDENSER MICROPHONE 13-14
4. TRANSFORMER 15-17
4.1 Introduction 15
4.2 E.M.F. Equation 16
5. THYRISTORS 18-22
5.1 Silicon Controlled Rectifier 18
5.1.1 SCR Basics 18
5.1.2 Types of SCR 18
5.1.3 SCR’s Applications 19
5.2 Triac 20
5.2.1 Triac Structure 21
5.3 Diac 22
5.3.1 Diac structure 22
6. BIPOLAR JUNCTION TRANSISTOR 23
–24
6.1 History 23
6.2 Structure 23
6.3 Basic Operation 24
7.
DIODES 25-29
7.1 Introduction 25
7.2 Application 26
7.3 Power Diode 26
7.3.1 Characteristics Curve 27
7.4 Zener Diode 27
7.4.1 Characteristics Curve 28
8. RESISTORS 30-33
8.1 Introduction 30
8.2 Potentiometer 31
8.3
Light Dependent Resistor 31
8.3.1 Structure 32
8.3.2 Application 33
9. CAPACITORS 33-35
9.1 Introduction 33
9.2 Electrolytic Capacitor 35
10. FUSE 35
11. PUSH-PULL SWITCH 36
12. ESTIMATING & COSTING 37
13. BIBLIOGRAPHY 38
SOUND OPERATED LIGHT GADGET
INTRODUCTION
It
is a kind of smart gadget whose operation is based upon light and sound. It
reacts if any sound is produced and remains ON until it stops receiving sound
variations for a minute. It is specially designed in such a way that it
operates only in dark when there is no light.
Just
imagine a dark room which lights up at the sound of footsteps or a room that
flicks off when no one is in the room. If an intruder enters in a room at the
midnight the lights will suddenly switch on. As you enter the room it lights up
automatically by even a low intensity sound variations.
The
gadget uses IC555 to adjust that time duration by which the light will remain
on if no sound variation is sensed by the microphone. The circuit comprises of
an operational amplifier by which the sensitivity of the microphone can be
adjusted according to our need. If sensitivity is high the light will turn on
even by clicking of key in lock and if the sensitivity is low then a high sound
variation is needed to turn on the light.
Now
a days where energy saving is main concern in every domestic or commercial
areas. This gadget proves to be very useful in minimizing the wastage of
electricity by using it when required and turns off the light when not in use.
Employing this gadget in a locality alone can save energy up to 5 unit/day. Now
think how much energy it can save if this gadget is used on a large scale in
every house and commercial areas. Also this gadget is not too expensive to be
afforded and this can be used by a common people.
WORKING
It’s a switching circuit which gets activated when it receives a sound signal and gets deactivated after a specified time period. The major component used in this circuit is operational amplifier, timer IC 555, thyristors, sensitivity controller and microphone.
The circuit
consists of a step down transformer which converts 220V AC into 9V AC. The
output from transformer is then rectified and filtered by half wave rectifier
and capacitor filter. The filtered output is then provided to inverting
terminal of operational amplifier through 10kΩ resistor. Here operational
amplifier act as comparator circuit.
Comparator is a
circuit that is used to compare two voltages and provide an output indicating
the relationship between two voltages. In this case the comparator is used to
compare a changing voltage to set a set dc reference voltage. The non-
inverting terminal of the operational amplifier is connected to the sensitivity
controller. It actually varies the voltage across non-inverting terminal and
set the reference voltage. It’s the reference voltage that determines the
sensitivity of the circuit.
A high sensitivity
condenser microphone is used to pick up audio signals. The microphone receives
the sound signal and converts it into electrical voltage. The operational
amplifier is operated with a supply of 12V. When the signal voltage across
inverting terminal (pin no2) is greater than the reference voltage, the pin 2 gets
high and outputs a low. and output of
operational amplifier at terminal 6 is high. If signal voltage is low the pin
no2 is low and output at pin no 6 is low.
The zener diode
used is to regulate the voltage. The regulated output is given to the base of
NPN transistor (SL 100). The transistor T1 conducts to trigger the timer (Analog
Linear)IC 555. It can be used as
monostable multivibrator, astable multivibrator and in bistable multivibrator
mode. In this circuit timer IC is used to operate in monostable multivibrator
mode. In monostable multivibrator mode the timer IC 555 generates the pulse of
definite time. In the monostable mode, the 555 timer acts as a “one-shot” pulse
generator. The pulse begins when the 555 timer receives a signal at the trigger
input that falls below a third of the voltage supply. The width of the output
pulse is determined by the time constant of an RC network, which consists of a capacitor (C2) and a
varistor (VR2). The output pulse ends when the charge on the C equals 2/3 of
the supply voltage. The output pulse width can be lengthened or shortened to
the need of the specific application by adjusting the values of R and C.
The output pulse width of time t,
which is the time it takes to charge C to 2/3 of the supply voltage, is given
by T=RC In(3) @1.1RC
Where t is in seconds, R is in ohms and C is in farads. See RC circuit for an explanation of this effect.
The reset pin of IC 555 is at high
level when there is no light. The circuit uses light dependent resistor (LDR).
When light falls on light dependent resistor, its resistance decreases and
potential across resistor R1 switches transistor T2 on. In the dark, the
voltage across R1is insufficient to turn on and the potential at pin 4 of IC
555 is high.
The base of transistor (T2) can be
grounded by the switch S1. The varistor (VR2) connected to the IC 555 is used
to vary the charging time of capacitor C2 and hence the time for which pin 3 of
IC 555 is high. Pin 3 is connected to an OR gate formed by diodes D2 and D3.
The gate of triac TR2 is connected to the OR gate through a 750 Ω resistor.
Switch S2 is a bypass switch and when it is pressed it ensures that the gate of
TR2 is triggers and is permanently on. Thus switch S2 overrides microphone
light dependent resistor (LDR) and timer.
Triac TR1 and diac SD32 are used for
brightness control when triac TR2 is on. Capacitor C1 is charged through
varistor VR3. When the charging voltage exceeds 35V, the triac TR1 is switched
on. The time required to charge capacitor C1 to 35V can be adjusted by varistor
VR3.
APPLICATIONS
1.
It is widely
used in home automation
·
It is effectively used in dark room to turn on the light when
someone is in the room and for turning off the light when no one is in the room.
·
It can be used at the stairs for lightning control which will work
by the sound of footsteps.
2.
It can be used at the subways and underpasses for light switching
and saving lots of electrical energy.
555
TIMER IC
The
555 Timer IC is an integrated circuit implementing a variety of timer and
multivibrator applications. The original name was the SE555 (metal can)/NE555
(plastic DIP) and the part was described as "The IC Time Machine". It
has been claimed that the 555 gets its name from the three 5 k ohm resistors
used in typical early implementations.
internal block
diagram
Depending
on the manufacturer, the standard 555 package includes over 20 transistors 2
diodes and 15 resistors on a silicon chip installed in an 8-pin mini
dual-in-line package (DIP-8).
The
555 has three operating modes:
- Monostable Mode-In this mode, the 555 functions as a "one-shot" generator. Applications include timers, missing pulse detection, bounce free switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation(PWM) etc.
- Astable Mode - Free running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc.
- Bistable Mode or Schmitt Trigger - The 555 can operate as a flip-flop if the DIS pin is not connected and no capacitor is used. Uses include bounce free latched switches, etc.
pinout diagram
PIN CONNECTIONS
PIN NAME PURPOSE
1
GND Ground,
low level (0 V)
2
TRIG Rises,
and interval starts, when this input falls below 1/3
Vcc
3 OUT This output is driven to Vcc
or GND.
4 RESET A timing interval may be
interrupted by driving this input to GND
5 CTRL "Control"
access to the internal voltage divider (by
default,
2/3 Vcc)
6 THR The
interval ends when the voltage at THR is greater than
at
CTRL.
7
DIS Open collector output; may discharge a
capacitor between
intervals.
8
V+, Vcc Positive supply voltage is
usually between 3V and 15 V.
MONO-STABLE MODE
In
the monostable mode, the 555 timer acts as a one short pulse generator. The pulse
begins when the 555 timer receives a signal at the trigger input that falls
below a third of the voltage supply. The width of the output pulse is
determined by the time constant of an RC network, which consists of a
capacitor(C) and a resistor(R). The output pulse ends when the charge on the C
equals 2/3 of the supply voltage. The output pulse width can be lengthened or
shortened to the need of the specific application by adjusting the values of R
and C.
The
output pulse width of time T, which is the time it takes to charge C to 2/3 of
the supply voltage, is given by
Where
T is in seconds, R is in ohms and C is in farads.
OPERATIONAL
AMPLIFIER
INTERNAL
CIRCUITRY FOR OP-AMP
An
Operational amplifier (op-amp) is a DC coupled high-gain electronic voltage
amplifier with a differential input and, usually, a single-ended output. An
op-amp produces an output voltage that is typically hundreds of thousands times
larger than the voltage difference between its input terminals.
Operational
amplifiers are important building blocks for a wide range of electronic
circuits. They had their origins in analog computers where they were used in
many linear, non-linear and frequency-dependent circuits. Their popularity in
circuit design largely stems from the fact the characteristics of the final
elements (such as their gain) are set by external components with little
dependence on temperature changes and manufacturing variations in the op-amp
itself.
Op-amps
are among the most widely used electronic devices today, being used in a vast
array of consumer, industrial, and scientific devices. Op-amps may be packaged
as components, or used as elements of more complex integrated circuits.
CIRCUIT NOTATION
Circuit
diagram symbol for an op-amp
The
circuit symbol for an op-amp is shown to the right, where:
* V_ : non-inverting input
* V_ : inverting input
* Vout :
output
* Vs_ :
positive power supply
* Vs_ :
negative power supply
The
power supply pins (Vs+ and Vs-) can be labeled in different ways. Despite
different labeling, the function remains the same - to provide additional power
for amplification of the signal. Often these pins are left out of the diagram
for clarity, and the power configuration is described or assumed from the
circuit.
OPERATION
The
amplifier's differential inputs consist of a V_ input and a V_ input, and
ideally the op-amp amplifies only the difference in voltage between the two,
which is called the differential input voltage. The output voltage of the
op-amp is given by the equation,
V(out) = (V+ - V_)Aol
where
V+ is the voltage at the non-inverting terminal, V_ is the voltage at the
inverting terminal and Aol is the open-loop gain of the amplifier.
The
magnitude of AOL is typically very largest-10,000 or more for integrated
circuit op-amps and therefore even a quite small difference between V+ and V_
drives the amplifier output nearly to the supply voltage. This is called
saturation of the amplifier. The magnitude of AOL is not well controlled by the
manufacturing process, and so it is impractical to use an operational amplifier
as a stand-alone differential amplifier . If predictable operation is desired,
negative feedback is used, by applying a portion of the output voltage to the
inverting input. The closed loop feedback greatly reduces the gain of the
amplifier. If negative feedback is used,the circuit's overall gain and other
parameters become determined more by the feedback network than by the op-amp
itself. If the feedback network is made of components with relatively constant,
stable values, the unpredictability and inconstancy of the op-amp's parameters
do not seriously affect the circuit's performance.
An operational amplifier works as
·
Non-Inverting Amplifier
·
Inverting Amplifier
NON-INVERTING AMPLIFIER
An op-amp
connected in the non-inverting amplifier configuration
In a non-inverting amplifier, the output voltage
changes in the same direction as the input voltage. The equation
for the gain of an op-amp is:
However,
in this circuit V– is a function of Vout
because of the negative feedback through the R1R2
network. R1 and R2 form a voltage divider, and as V–
is a high-impedance input, it does not load it appreciably. Consequently:
where
Substituting
this into the gain equation, we obtain:
Solving
for Vout:
If
AOL is very large, this simplifies to
.
INVERTING AMPLIFIER
An op-amp
connected in the inverting amplifier configuration
In an inverting amplifier, the output voltage
changes in an opposite direction to the input voltage.
As
for the non-inverting amplifier, we start with the gain equation of the op-amp:
This
time, V– is a function of both Vout and Vin
due to the voltage divider formed by Rf and Rin.
Again, the op-amp input does not apply an appreciable load, so:
Substituting
this into the gain equation and solving for Vout:
If
AOL is very large, this simplifies to
.
A
resistor is often inserted between the non-inverting input and ground, reducing
the input offset voltage due to
different voltage drops due to bias current, and may reduce
distortion in some op-amps.
A
DC-blocking capacitor may be inserted
in series with the input resistor when a frequency response down to DC is
not needed and any DC voltage on the input is unwanted. That is, the capacitive
component of the input impedance inserts a DC zero and a low-frequency pole
that gives the circuit a band pass or high-pass characteristic
OP-AMP
VOLTAGE COMPARATOR
An
operational amplifier (op-amp) has a well balanced difference input and a very
high gain. This parallels the characteristics of comparators and can be
substituted in applications with low-performance requirements.
In
theory, a standard op-amp operating in open-loop configuration (without
negative feedback) may be used as a low-performance comparator. When the
non-inverting input (V+) is at a higher voltage than the inverting input (V-),
the high gain of the op-amp causes the output to saturate at the highest
positive voltage it can output. When the non-inverting input (V+) drops below
the inverting input (V-), the output saturates at the most negative voltage it
can output. The op-amp's output voltage is limited by the supply voltage. An
op-amp operating in a linear mode with negative feedback, using a balanced,
split-voltage power supply, (powered by ± VS) its transfer function is
typically written as: Vout = Ao(V1 − V2). However, this equation may not be
applicable to a comparator circuit which is non-linear and operates open-loop
(no negative feedback).
APPLICATIONS
·
Audio
and video frequency pre-amplifiers and buffers
·
Voltage
comparators
·
Differential
amplifiers
·
Differentiators
and integrators
·
Filters
(signal processing)
·
Precision
rectifiers
·
Precision
peak detectors
·
Voltage
and current regulators
·
Analog
calculators
·
Analog-to-digital
converters
·
Digital-to-analog
converter
·
Voltage
clamps
·
Oscillators
and waveform generators
CONDENSER
MICROPHONE
Electronic
symbol
The
condenser microphone, invented at Bell Labs in 1916 by E. C. Wente is also
called a capacitor microphone or electrostatic microphone. Here, the diaphragm
acts as one plate of a capacitor, and the vibrations produce changes in the
distance between the plates. There are two types, depending on the method of
extracting the audio signal from the transducer: DC-biased and radio frequency
(RF) or high frequency (HF) condenser microphones. With a DC-biased microphone,
the plates are biased with a fixed charge (Q). The voltage maintained across
the capacitor plates changes with the vibrations in the air, according to the
capacitance equation (C = Q / V), where Q = charge in coulombs, C = capacitance
in farads and V = potential difference in volts. The capacitance of the plates
is inversely proportional to the distance between them for a parallel-plate
capacitor. The assembly of fixed and movable plates is called an
"element" or "capsule."
A
nearly constant charge is maintained on the capacitor. As the capacitance changes,
the charge across the capacitor does change very slightly, but at audible
frequencies it is sensibly constant. The capacitance of the capsule (around 5
to 100 pF) and the value of the bias resistor (100 MWto tens of GW) form a filter that is high-pass
for the audio signal, and low-pass for the bias voltage. Note that the time
constant of an RC circuit equals the product of the resistance and capacitance.
Within
the time-frame of the capacitance change (as much as 50 ms at 20 Hz audio
signal), the charge is practically constant and the voltage across the
capacitor changes instantaneously to reflect the change in capacitance. The
voltage across the capacitor varies above and below the bias voltage. The
voltage difference between the bias and the capacitor is seen across the series
resistor. The voltage across the resistor is amplified for performance or
recording.
RF
condenser microphones use a comparatively low RF voltage, generated by a
low-noise oscillator. The oscillator may either be amplitude modulated by the
capacitance changes produced by the sound waves moving the capsule diaphragm,
or the capsule may be part of a resonant circuit that modulates the frequency
of the oscillator signal. Demodulation yields a low-noise audio frequency
signal with very low source impedance. The absence of a high bias voltage
permits the use of a diaphragm with looser tension, which may be used to
achieve wider frequency response due to higher compliance. The RF biasing
process results in a lower electrical impedance capsule, a useful by-product of
which is that RF condenser microphones can be operated in damp weather
conditions that could create problems in DC-biased microphones with
contaminated insulating surfaces.
Condenser
microphone internal diagram
Condenser
microphones span the range from telephone transmitters through inexpensive
karaoke microphones to high-fidelity recording microphones. They generally
produce a high-quality audio signal and are now the popular choice in
laboratory and studio recording applications. The inherent suitability of this
technology is due to the very small mass that must be moved by the incident
sound wave, unlike other microphone types that require the sound wave to do
more work. They require a power source, provided either via microphone outputs
as phantom power or from a small battery. Power is necessary for establishing
the capacitor plate voltage, and is also needed to power the microphone
electronics (impedance conversion in the case of electrets and DC-polarized
microphones, demodulation or detection in the case of RF/HF microphones).
Condenser microphones are also available with two diaphragms that can be
electrically connected to provide a range of polar patterns, such as cardioids,
omnidirectional, and figure-eight.
TRANSFORMERS
A
transformer is a device that transfers electrical
energy
from one circuit to another
through inductively
coupled
conductors—the transformer's coils. A varying current in the first or
primary winding creates a
varying magnetic
flux
in the transformer's core and thus a varying magnetic field through the secondary winding. This varying
magnetic field induces a varying electromotive
force (EMF)
or "voltage" in the
secondary winding. This effect is called mutual induction.
The transformers are electrical devices that change power via coupling.
The primary winding is connected to the power source and the other windings are
known as secondary windings. There is a core with one winding of wire placed
close to one or more windings, which can couple two or more alternating-current
circuits together by employing the induction between the windings. If the
secondary voltage wire is less than the primary wire, the transformer is called
a step down transformer. If the secondary wiring is of higher voltage, the
transformer is a step-up transformer, which increases voltage input.
A step-down transformer, as evidenced by the high turn count of
the primary winding and the low turn count of the secondary this transformer
converts high-voltage, low-current power into low-voltage, high-current power.
The larger-gauge wire used in the secondary winding is necessary due to the
increase in current. The primary winding, which doesn't have to conduct as much
current, may be made of smaller-gauge wire.
EMF EQUATION OF
TRANSFORMER
Let the applied
voltage V1 applied to the primary of a transformer, With secondary
open-circuited, be sinusoidal (or sine wave). Then the Current I1, due to
applied voltage V1, will also be a sine wave. The mmf N1I1 and core flux Ø will
follow the variations of I1 closely. That is
the flux is in
time phase with the current I1 and varies sinusoidally.
The emfs induced in primary and secondary windings of a
transformer are given as follows
E1
= 4.44 f N1 Ømax volts
E2
= 4.44 f N2 Ømax volts
Where Ømax is the maximum value of flux is webers, f is the
supply frequency in Hz, N1 is the number of turns on primary winding and N2 is
the number of turns on secondary winding.
In an ideal transformer, the voltage drops in primary and
secondary windings are negligible and, therefore E1 will be approximately equal
and opposite to voltage impressed across primary, V1 and terminal voltage V2
will be approximately equal to E2.
So voltage ratio, v2/v1 = E2/E1 = 4.44fN2 max / 4.44fN1 max
= N2/N1
Voltage Transformation Ratio. The ratio of secondary voltage to
primary voltage is known as the voltage transformation ratio and is designated
by letter K.
i.e. Voltage transformation ratio, K = V2/V1 = E2/E1 = N2/N1
Current Ratio. The ratio of secondary current to primary current
is known as current ratio and is reciprocal of voltage transformation ratio in
an ideal transformer.
Transformer on No Load. When the primary of a transformer is
connected to the source of an ac supply and the secondary is open circuited,
the transformer is said to be on no load. The
TRANSFORMER
ON NO LOAD
Alternating applied voltage will cause flow of an alternating
current I0 in the primary winding, which will create alternating flux Ø.
No-load current I0, also known as excitation or exciting current, has two
components the magnetizing component I’m and the energy component I.e. Im is
used to create the flux in the core and i.e. is used to overcome the hysteresis
and eddy current losses occurring in the core in addition to small amount of
copper losses occurring in the primary only (no copper loss occurs in the
secondary, because it carries no current, being open circuited.)
TRANSFORMER
ON LOAD
The transformer is said to be loaded, when its secondary circuit
is completed through an impedance or load. The magnitude and phase of secondary
current (i.e. current flowing through secondary) I2 with respect to secondary
terminals depends upon the characteristic of the load i.e. current I2 will be
in phase, lag behind and lead the terminal voltage V+2+ respectively when the
load is non-inductive, inductive and capacitive. The net flux passing through
the core remains almost constant from no-load to full load irrespective of load
conditions and so core losses remain almost constant from no-load to full load.
Vector diagram for an ideal transformer supplying inductive load
THYRISTORS
SCR
silicon
controlled rectifiers (SCR) find many uses in electronics, and in particular
for power control. Thyristors or silicon controlled rectifiers; SCRs are known
as workhorse of high power electronics.
SCR are able to
switch large levels of power are accordingly they used in a wide variety of
different applications. SCR even finds uses in low power electronics where they
are used in many circuits from light dimmers to power supply over voltage
protection.
The term SCR or
silicon controlled rectifier is often used synonymously with that of thyristors
the SCR or silicon controlled rectifier is actually a trade name used by
General Electric for a thyristors.
SCR basics
The SCR is a
device that has a number of unusual characteristics. The thyristor device has
three terminals: Anode, cathode and gate. The gate is the control terminal
while the main current flows between the anode and cathode.
The SCR is a
"one way device". Therefore when the device is used with AC, it will
only conduct for a maximum of half the cycle.
In operation,
the SCR will not conduct initially. It requires a certain level of current to
flow in the gate to "fire" the thyristor. Once fired, the thyristor
will remain in conduction until the voltage across the anode and cathode is
removed - this obviously happens at the end of the half cycle over which the
thyristor conducts. The next half cycle will be blocked as a result of the
rectifier action. It will then require current in the gate circuit to fire the
thyristor again.
SCR symbol
The SCR symbol used for circuit diagrams or circuit
seeks to emphasis its rectifier characteristics while also showing the control
gate. As a result the thyristor symbol shows the traditional diode symbol with
a control gate entering near the junction.
Thyristor symbol for circuit diagrams and schematics
TYPES OF SCR
There are a
number of different types thyristor - these are variants of the basic thyristor
component, but they offer different capabilities that can be used in various
instances and may be useful for certain circuits.
- Reverse conducting thyristor, RCT: Although thyristors normally block current in the reverse direction, there is a form of thyristor called a reverse conducting thyristor. This has an integrated reverse diode to provide conduction in the reverse direction, although there is no control in this direction.
- Within a reverse conducting thyristor, the thyristor itself and the diode do not conduct at the same time. This means that they do not produce heat simultaneously. As a result they can be integrated and cooled together.
The reverse
conducting thyristor can be used where a reverse or freewheel diode would
otherwise be needed. Reverse conducting thyristors are often used in frequency
changers and inverters.
- Gate Assisted Turn-Off Thyristor, GATT: The GATT is used in circumstances where a fast turn-off is needed. To assist in this process a negative gate voltage can sometimes be applied. In addition to reducing the anode cathode voltage. This reverse gate voltage helps in draining the minority carriers stored on the n-type base region and it ensures that the gate-cathode junction is not forward biased.
The structure of
the GATT is similar to that of the standard thyristor, except that the narrow
cathode strips are often used to enable the gate to have more control because
it is closer to the centre of the cathode.
- Gate Turn-Off Thyristors, GTO: The gate turn-off thyristor is sometimes also referred to as the gate turn off switch. This device is unusual in the thyristor family because it can be turned off by simply applying a negative voltage to the gate - there is no requirement to remove the anode cathode voltage. See further page in this series more fully describing the GTO.
- Asymmetric Thyristor: The asymmetric thyristor is used in circuits where the thyristor does not see a reverse voltage and therefore the rectifier capability is not needed. As a result it is possible to make the second junction, often referred to as J2 (see page on Thyristor structure) can be made much thinner. The resulting n-base region provides a reduced Von as well as improved turn on time and turn off time.
THYRISTORS APPLICATIONS
Thyristors, SCRs
are used in many areas of electronics where they find uses in a variety of
different applications. Some of the more common applications for thyristors are
outlined below:
- AC power control (including lights, motors, etc).
- Overvoltage protection crowbar for power supplies.
- AC power switching.
- Control elements in phase angle triggered controllers.
- Within photographic flash lights where they act as the switch to discharge a stored voltage through the flash lamp, and then cut it off at the required time.
Thyristors are
able to switch high voltages and withstand reverse voltages making them ideal
for switching applications, especially within AC scenarios.
TRIAC
Various models of TRAIC
The triac is a three terminal
semiconductor device for controlling current. It is effectively a development
of the SCR, but unlike the SCR which is only able to conduct in one direction,
the triac is a bidirectional device. As such the triac is an ideal device to
use for AC switching applications because it can control the current flow over
both halves of an alternating cycle. A thyristor is only able to control them
over one half of a cycle. During the remaining half no conduction occurs and
accordingly only half the waveform can be utilized.
There are three terminals on a
triac. These are the Gate and two other terminals. These other triac terminals
are often referred to as an "Anode" or "Main Terminal".
Symbol of Triac
On the triac, the gate that acts as
the trigger to turn the device on. The current then flows between the two
anodes or main terminals. These are usually designated Anode 1 and Anode 2 or
Main Terminal 1 and Main Terminal 2 (MT1 and MT2).
It can be imagined from the circuit
symbol that the triac consists of two thyristors back to back. The operation of
the triac can be looked on in this fashion, although the actual operation at
the semiconductor level is rather complicated. When the voltage on the MT1 is
positive with regard to MT2 and a positive gate voltage is applied, one of the
SCRs conducts. When the voltage is reversed and a negative voltage is applied
to the gate, the other SCR conducts. This is provided that there is sufficient
voltage across the device to enable a minimum holding current to flow.
Equivalent
circuit of a Triac
TRIAC
STRUCTURE
The structure of a triac may be
considered as a p-n-p-n structure and the triac may be considered to consist of
two conventional SCRs fabricated in an inverse parallel configuration.
In operation, when terminal A2 is
positive with respect to A1, then a positive gate voltage will give rise to a
current that will trigger the part of the triac consisting of p1 n1 p2 n2 and
it will have an identical characteristic to an SCR. When terminal A2 is
negative with respect to A1 a negative current will trigger the part of the
triac consisting of p2 n1 p1 n3. In this way conduction on the triac occurs
over both halves an alternating cycle.
The structure of a Triac
DIAC
A
diac is a full-wave or bi-directional semiconductor switch that can be turned
on in both forward and reverse polarities. Indeed the name diac means diode AC
switch. The diac is widely
used to assist even triggering of a triac when used in AC switches. Diacs are
mainly used in dimmer applications and also in starter circuits for florescent
lamps.
Symbol of diac
CIRCUIT SYMBOL FOR THE DIAC
Typically the diac is placed in
series with the gate of a triac. Diacs are often used in conjunction with
triacs because these devices do not fire symmetrically as a result of slight
differences between the two halves of the device. This results in harmonics
being generated and the less symmetrical the device fires, the greater the
level of harmonics produced. It is generally undesirable to have high levels of
harmonics in a power system.
To help in overcoming this problem,
a diac is often placed in series with the gate. This device helps make the
switching more even for both halves of the cycle. This results from the fact
that the diac switching characteristic is far more even than that of the triac.
Since the diac prevents any gate current flowing until the trigger voltage has
reached a certain voltage in either direction, this makes the firing point of
the triac more even in both directions.
DIAC
STRUCTURE
The diac can be fabricated as either
a two layer or a five layer structure. In the three layer structure the switching
occurs when the junction that is reverse biased experiences reverse breakdown.
A five layer diac structure is also available. This does not act in quite the
same manner, although it produces an I-V curve that is very similar to the
three layer diac. It can be considered as two break-over diodes connected back
to back.
The structure of a diac
BIPOLAR JUNCTION TRANSISTOR
The bipolar junction transistor is
the cornerstone of much of today's semiconductor electronics industry. This
form of transistor has been in existence for many years and is still very
widely used in electronic circuits. The bipolar transistor is very versatile
and finds applications in many applications and at a wide range of frequencies.
HISTORY
The bipolar
transistor dates back to the middle of the twentieth century when three
scientists named Bardeen, Brattain, and Shockley working at Bell Laboratories
in the USA discovered it. They had been researching an idea for a semiconductor
field effect device, but they had been unable to make it work. They had not
succeeded in making this idea work and as a result they decided to follow other
lines of research and in doing this they developed the bipolar transistor..
Today the semiconductor
industry is enormous and vast quantities of money are being invested in new
semiconductor device developments
STRUCTURE
The bipolar
transistor can be made from a variety of types of semiconductor. The original
devices were made from germanium, but silicon is widely used today.
In essence a
transistor consists of an area of either p type of n type semiconductor
sandwiched between regions of oppositely doped silicon. As such devices can be
either a p-n-p or an n-p-n configuration.
There are three
connections, namely the emitter, base, and the collector. The base is the one
in the centre and it is bounded by the emitter and collector. Of the two outer
two the collector is often made larger as this is where most of the heat is
dissipated.
The base derives its name from the first point
contact transistors where the centre connection also formed the mechanical
"base" for the structure. It is essential that this region should be
as thin if high levels of current gain are to be achieved. Often it may only be
about 1 um across.
The emitter is
where the current carriers are "emitted", and the collector is where
they are "collected".
BASIC OPERATION
The transistor
can be considered as two p-n junctions that are placed back to back. In
operation, the base emitter junction is forward biased and the base collector
junction is reverse biased. When a current flows through the base emitter
junction, a current also flows in the collector circuit. This is larger and
proportional to the one in the base circuit. In order to explain the way in
which this happens, the example of an n-p-n transistor is taken. The same
principles are used for the p-n-p transistor except that the current carrier is
holes rather than electrons and the voltages are reversed.
Operation of a bipolar junction
transistor
The emitter in
the n-p-n device is made of n-type material and here the majority carriers are
electrons. When the base emitter junction is forward biased the electrons move
from the n-type region towards the p-type region and the holes move towards the
n-type region. When they reach each other they combine enabling a current to
flow across the junction. When the junction is reverse biased the holes and
electrons move away from one another resulting in a depletion region between
the two areas and no current flows.
When a current
flows between the base and emitter, electrons leave the emitter and flow into
the base. Normally the electrons would combine when they reach this area.
However the doping level in this region is very low and the base is also very
thin. This means the most of the electrons are able to travel across this
region without recombining with the holes. As a result the electrons migrate
towards the collector, because they are attracted by the positive potential. In
this way they are able to flow across what is effectively a reverse biased
junction, and current flows in the collector circuit.
It is found that
the collector current is significantly higher than the base current, and
because the proportion of electrons combining with holes remains the same the
collector current is always proportional to the base current. In other words
varying the base current varies the collector current.
The ratio of the
base to collector current is given the Greek symbol B. Typically the ratio B
may be between 50 and 500 for a small signal transistor. This means that the
collector current will be between 50 and 500 times that flowing in the base.
For high power transistors the value of B is likely to be smaller, with figures
of 20 not being unusual.
DIODES
A
diode is a two-terminal electronic component that conducts electric current in
only one direction. This is a crystalline piece of semiconductor material connected to two electrical
terminals.
The
most common function of a diode is to allow an electric current to pass in one
direction (called the diode's forward direction) while blocking current in the
opposite direction (the reverse direction).This unidirectional behavior is
called rectification, and is used to convert alternating current to direct
current, and to extract modulation from radio signals in radio receivers.
However,
diodes can have more complicated behavior than this simple on-off action. This
is due to their complex non-linear electrical characteristics, which can be
tailored by varying the construction of their P-N junction. These are exploited
in special purpose diodes that perform many different functions. For example,
specialized diodes are used to regulate voltage (Zener diodes, to electronically
tune radio and TV receivers (varactor diodes), to generate radio
frequency oscillations(tunnel diodes), and to produce light (light
emitting diodes ). Tunnel diodes exhibit negative resistance, which makes them
useful in some types of circuits.
Diodes
were the first semiconductor electronic devices. The discovery of crystals'
rectifying abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor diodes,
called cat's whisker diodes, developed around 1906, were made of mineral
crystals such as galena. Today most diodes are made of silicon, but other semiconductors
such as germanium are sometimes used.
Typical diode
packages in same alignment as diode symbol. Thin bar depicts the cathode
A
modern semiconductor diode is made of a crystal of semiconductor like silicon
that has impurities added to it to create a region on one side that contains
negative charge carriers (electrons), called n-type semiconductor and a region
on the other side that contains positive charge carriers called p-type
semiconductor. The diode's terminals are attached to each of these regions. The
boundary within the crystal between these two regions, called a PN junction, is
where the action of the diode takes place. The crystal conducts conventional
current in a direction from the p-type side (called the anode) to the n-type
side (called the cathode), but not in the opposite direction. Another type of
semiconductor diode, the Schottky diode, is formed from the contact between a
metal and a semiconductor rather than by a p-n junction.
APPLICATIONS
Radio
demodulation
The
first use for the diode was the demodulation of amplitude modulated(AM) radio
broadcasts.
Power
conversion
Rectifiers
are constructed from diodes, where they are used to convert alternating current
(AC) electricity into direct current (DC). Automotive alternators are a common
example, where the diode, which rectifies the AC into DC, provides better
performance than the commutator of earlier dynamo. Similarly, diodes are also
used in Cockcroft-Walton voltage multipliers to convert AC into higher DC voltages.
Logic
gates
Diodes
can be combined with other components to construct AND and OR logic gates. This
is referred to as diode logic.
Ionizing
radiation detectors
In
addition to light, mentioned above, semiconductor diodes are sensitive to more
energetic radiation. Semiconductor detectors for high energy particles are used
in large numbers. Because of energy loss fluctuations, accurate measurement of
the energy deposited is of less use.
Temperature
measurements
A
diode can be used as a temperature measuring device, since the forward voltage
drop across the diode depends on temperature, as in a Silicon band-gap
temperature sensor Kelvins. Typically, silicon diodes have approximately 2
mV/EsC temperature coefficient at room temperature.
Current
steering
Diodes
will prevent currents in unintended directions. Other uses for semiconductor
diodes include sensing temperature, and computing analog logarithms
POWER DIODE
A
power diode is a
crystalline semiconductor device used
mainly to convert alternating current (AC) to direct current (DC), a
process known as rectification. Found in the power supply circuits of
virtually all modern-day electrical and electronic equipment, a power diode's
function is akin to a mechanical one-way valve. It conducts electric current with minimal
resistance in one direction, known as its forward direction, while preventing
current from flowing in the opposite direction. Typically capable of passing as
much as several hundred amps forward, power diodes have much larger P-N
junctions and hence higher forward current carrying capacity than their smaller
signal diode relatives used in consumer electronics to regulate and reduce
current. This makes power diodes better suited for applications where larger
currents and higher voltages are involved.
Manufacturers
generally produce a range of power diodes suitable for particular uses. They
are rated according to the maximum current they can carry in the forward
direction and the maximum reverse voltage they can withstand. Due to
resistance, a small drop in voltage occurs when passing an electric current
through a power diode in the forward direction. Conversely, a power diode can
only withstand a certain amount of voltage flowing in the reverse direction
before it breaks down and ceases functioning.
CHARACTERISTICS
CURVE
Power
diodes are made primarily of silicon, though small quantities of other
materials, such as boron, gallium arsenide, germanium or phosphorous are also used. A single
power diode can be used to convert AC to DC, but this produces what is known as
half-wave varying DC. More commonly, two or three or more diodes are connected
in circuit to produce full-wave varying DC. The most important of these is the
bridge rectifier, in which four connected diodes convert both positive and
negative sections of an AC wave into DC, thus producing full-wave
rectification.
ZENER DIODE
Zener diodes are PN junction devices
that are designed to operate in the reverse-breakdown region. The breakdown
voltage (Vz) of Zener diodes is set by carefully controlling the doping level
during manufacture. This breakdown phenomenon is referred to as the Zener
voltage or the Zener effect.
Symbol of Zener Diode
The
Zener effect functions as follows. When reverse voltage is applied to the PN
junction of a diode, there is a rapid avalanche breakdown. This causes the
current to reverse direction. The change in current direction accelerates
valence electrons within the applied electric field, enough to free them. These
free valence electrons collide with and free other electrons, building the
avalanche. While this process is taking place, the current changes rapidly.
Changes in current are based on changes in voltage, and even a tiny voltage
change can have a massive effect on the current. In practical application, the
avalanche breakdown depends upon the applied electric field. Changing the
thickness of the layer to which the voltage is applied forms Zener diodes.
Typical Zener diodes break down at voltages from about 4 volts to several
hundred volts.
CHARACTERISTICS
CURVE
Functionally,
Zener diodes are used as regulators, limiters and to control output switching.
When used as regulators, the constant reverse voltage of Zener diodes allows
for the regulation of output voltage against both variations in the input
voltage from an unregulated power supply and from variations in the load
resistance. The current traveling through Zener diodes changes to keep the
voltage within the threshold of Zener action and the maximum power it can
dissipate. Zener regulators tend to most efficiently function when
constant voltage is applied, especially when used in conjunction with regulated
power supplies, and for limiter applications.
Zener
limiters are constructed with two opposing zener diodes. Each individual
diode can limit one side of a sinusoidal waveform to Zener voltage while
keeping the other side near zero. When the two opposing Zener diodes are
paired, the waveform is limited to Zener voltage on both polarities.
Zener
diodes are also used to control output switching. In this application, Zener
diodes switch the output between voltages. This is determined by the
changes in input voltage through the diode. The output circuit amounts to a
Zener regulator that switches from one Zener voltage to the other on transition
through the Zener diode.
RESISTORS
A resistor is a component of an
electrical circuit that resists the flow of electrical current. A resistor has
two terminals across which electricity must pass, and is designed to drop the
voltage of the current as it flows from one terminal to the next. A resistor is
primarily used to create and maintain a known safe current within an electrical
component.
Resistance is measured in ohms, after Ohm's law. This rule states that electrical resistance is equal
to the drop in voltage across the terminals of the resistor divided by the
current being applied to the resistor. A high ohm rating indicates a high
resistance to current. This rating can be written in a number of different ways
depending on the ohm rating. For example, 81R represents 81 ohms, while 81K
represents 81,000 ohms.
The amount of resistance offered by
a resistor is determined by its physical construction. A carbon composition resistor has resistive carbon packed into a
ceramic cylinder, while a carbon film resistor consists of a similar ceramic
tube, but has conductive carbon film wrapped around the outside. Metal film or
metal oxide resistors are made much the same way, but with metal instead of
carbon. A wire wound resistor, made with metal wire wrapped around clay,
plastic, or fiberglass tubing, offers resistance at higher power levels. For
applications that must withstand high temperatures, materials such as Cermet, a
ceramic-metal composite, or tantalum, a rare metal, are used to build a resistor that can endure
heat
A resistor is coated with paint or
enamel, or covered in molded plastic to protect it. Because resistors are often
too small to be written on, a standardized color-coding system is used to
identify them. The first three colors represent ohm value, and a fourth
indicates the tolerance, or how close by percentage the resistor is to its ohm
value. This is important for two reasons: the nature of resistor construction
is imprecise, and if used above its maximum current, the value of the resistor
can alter or the unit itself can burn up.
Every resistor falls into one of two
categories: fixed or variable. A fixed
resistor has a predetermined amount of
resistance to current, while a variable resistor can be adjusted to give
different levels of resistance. Variable resistors are also called potentiometers and are commonly used as volume controls on audio devices.
A rheostat is a variable resistor made specifically for use with high
currents. There are also metal-oxide Varistors, which change their resistance in response to a rise in
voltage; Thermistors, which either raise or lower resistance when temperature
rises or drops; and light-sensitive resistors.
POTENTIOMETER
A
potentiometer is a manually adjustable resistor. The way this device works is
relatively simple. One terminal of the potentiometer
is connected to a power source. Another is hooked up to ground (a point with no
voltage or resistance and which serves as a neutral reference point), while the
third terminal runs across a strip of resistive material. This resistive strip
generally has a low resistance at one end; its resistance gradually increases
to a maximum resistance at the other end. The third terminal serves as the
connection between the power source and ground, and is usually interfaced to
the user by means of a knob or lever. The user can adjust the position of the
third terminal along the resistive strip in order to manually increase or
decrease resistance. By controlling resistance, a potentiometer can determine how much current
flow through a circuit. When used to regulate current, the potentiometer is limited by the maximum
resistivity of the strip
The power of this simple device is
not to be underestimated. In most analog devices, a potentiometer is what
establishes the levels of output. In a loud speaker, for example, a
potentiometer directly adjusts volume; in a television monitor, it controls brightness.
A potentiometer can also be used to
control the potential difference, or voltage, across a circuit. The setup
involved in utilizing a potentiometer for this purpose is a little bit more
complicated. It involves two circuits: the first circuit consists of a cell and
a resistor. At one end, the cell is connected in series to the second circuit,
and at the other end it is connected to a potentiometer in parallel with the
second circuit. The potentiometer in this arrangement drops the voltage by an
amount equal to the ratio between the resistance allowed by the position of the
third terminal and the highest possible resistivity of the strip. In other
words, if the knob controlling the resistance is positioned at the exact
halfway point on the resistive strip, then the output voltage will drop by
exactly fifty percent, no matter how high the potentiometer's input voltage.
Unlike with current regulation, voltage regulation is not limited by the
maximum resistivity of the strip.
LIGHT DEPENDENT RESISTOR (LDR)
The light dependent resistor, LDR,
is known by many names including the photo resistor, photo resistor,
photoconductor, photoconductive cell, or simply the photocell. These devices
have been seen in early forms since the nineteenth century when photoconductivity
in selenium was discovered by Smith in 1873. Since then many variants of
photoconductive devices have been made.
Other light dependent resistors, or
photo resistors have been made using materials including cadmium sulphide, lead
sulphide, and the more commonly used semiconductor materials including
germanium, silicon and gallium arsenide.
The photo resistor, or light
dependent resistor, LDR, finds many uses as a low cost photo sensitive element
and was used for many years in photographic light meters as well as in other
applications such as flame, smoke and burglar detectors, card readers and
lighting controls for street lamps.
STRUCTURE
Although there are many ways in
which light dependent resistors, or photo resistors can be manufactured, there
are naturally a few more common methods that are seen. Essentially the LDR or
photo resistor consists of a resistive material sensitive to light that is
exposed to light. The photo resistive element comprises section of the material
with contacts at either end. Although many of the materials used for light
dependent resistors are semiconductors, when used as a photo resistor, they are
used only as a resistive element and there are no pn junctions. Accordingly the
device is purely passive.
A typical structure for a light
dependent or photo resistor uses an active semiconductor layer that is
deposited on an insulating substrate. The semiconductor is normally lightly
doped to enable it to have the required level of conductivity. Contacts are
then placed either side of the exposed area.
In many instances the area between
the contacts is in the form of a zig zag, or interdigital pattern. This
maximizes the exposed area and by keeping the distance between the contacts
small it enhances the gain.
It is also possible to use a
polycrystalline semiconductor that is deposited onto a substrate such as
ceramic. This makes for a very low cost light dependent resistor. In order to
ensure that the resistance of the light dependent area of the device is the
major component of the resistance, all other spurious resistances must be
minimized. A major contributor could be the resistance between the contact and
the semiconductor. To reduce this component of resistance, the region around
the metal contact is heavily doped to increase its conductivity.
APPLICATIONS
The photo resistor, or light
dependent resistor, LDR, finds many uses as a low cost photo sensitive element
and was used for many years in photographic light meters as well as in other
applications such as flame, smoke and burglar detectors, card readers and
lighting controls for street lamps.
CAPACITORS
A capacitor, also called a storage cell, secondary cell or condenser,
is a passive electronic component that is capable of storing an electric
charge. It is also a filter, blocking direct current (DC) and allowing
alternating current (AC) to pass. A capacitor is composed of two conductive
surfaces called electrodes, separated by an insulator, which is called a dielectric. Unlike some capacitors, a ceramic capacitor is not polarized, which means the two
electrodes are not positive and negatively charged; and it uses layers of metal
and ceramic as dielectrics.
When DC voltage is applied to a
ceramic capacitor, the electric charge is stored in the electrodes. Storage
capacity is small, and is measured in units called Farads (F). Most capacitors
are so small, that their capacity is measured in microfarad (10-6),
nanofarad (10-9), or picofarad (10-12) units. New super
capacitors have been designed which actually hold enough charge to be measured
in full Farad units.
The first ceramic capacitor design
was in the 1930s, when it was used as a component in radio receivers and other vacuum
tube equipment. Capacitors are now a
vital component in numerous electronic applications, including automobile,
computers, entertainment equipment, and power supplies. They also are helpful
in maintaining voltage levels in power lines, improving electrical system
efficiency and reducing energy loss.
The original ceramic capacitor
design was disc-shaped, and with the exception of monolithic ceramic
capacitors, that is still the predominate design. Ceramic capacitors use
materials like titanium acid barium as the dielectric. They are not constructed in a coil, like
some other capacitors, so they can be used in high frequency applications and
in circuits which bypass high frequency signals to ground.
A monolithic ceramic capacitor is
made up of thin dielectric layers interwoven with staggered metal-film
electrodes. Once the leads are attached, the unit is pressed into a monolithic,
or solid and uniform shape. The small size and high capacity of monolithic
capacitors has helped to make possible the miniaturization, digitalization and
high frequency in electronic equipment.
A multilayer ceramic capacitor uses
two non-polarized electrodes separated by multiple alternating layers of metal
and ceramic as the dielectric. These are found in high frequency power
converters and in filters in switching power supplies and DC to DC converters.
Computers, data processors, telecommunications, industrial controls and
instrumentation equipment also use multilayer ceramic capacitors.
Ceramic capacitors are classified as
Type I, Type II or Type III. The Type I ceramic capacitor generally has a
dielectric made from a mixture of metal oxides and titanates. They have high
insulation resistance and lower frequency losses and maintain a stable capacity
even when voltage varies. These are used in resonant
Type II capacitors have dielectrics
made from zirconates and titanates, such as barium, calcium and strontium. They have somewhat higher losses of frequency and less
insulation resistance than Type I capacitors, but can still maintain high
capacity levels. These are popular for use in coupling, blocking and filtering.
One disadvantage of Type II capacitors is that they can lose capacity with age.
Type III ceramic capacitors are general use capacitors that are adequate in
applications which do not require high insulation resistance and capacity
stability.
ALUMINUM
ELECTROLYTIC CAPACITORS
Aluminum electrolytic capacitors use
an electrolytic process to form the dielectric. Wet electrolytic capacitors
have a moist electrolyte. Dry or solid electrolytic capacitors do not. There
are two basic configurations or form factors for aluminum electrolytic
capacitors: leaded and surface mount. There are also several different mounting
styles. Leaded capacitors have leads for connections to circuits. They use through hole
technology (THT) to mounts component on a printed
circuit board (PCB) by inserting component leads through holes in the board and
then soldering the leads in place on the opposite side of the board. Surface
mount capacitors or chip capacitors do not have leads or use THT. Instead, SMT
capacitors have a flat surface that is soldered to a flat pad on the face of
the PCB. Mounting styles for aluminum electrolytic capacitors may also use
bolts, brackets, and poles.
Aluminum electrolytic capacitors
differ in terms of capacitance type, product features, and package
specifications. Fixed capacitors have a nonadjustable capacitance value. With variable capacitors,
specific capacitance values can be set via an adjustment mechanism, typically a
potentiometer. In terms of features, some aluminum electrolytic capacitors are
polarized or self-healing. Polarized capacitors can be safely operated with
only one direct current (DC) polarity. Self-healing capacitors can withstand
high-pulsed voltages without breaking the dielectric. Aluminum electrolytic
capacitors that meet military standards or comply with Restriction of Hazardous
Substances (RoHS) are also available. With regard to packaging, leaded aluminum
electrolytic capacitors may use axial leads, radial leads, flying
leads, tab leads, screw leads,
gull-wing leads, or J-leads. SMT capacitors are also commonly available.
Selecting aluminum electrolytic
capacitors requires an analysis of performance specifications and packing methods.
Performance specifications include capacitance range, capacitance tolerance, DC
rated voltage range (WVDC), leakage current, equivalent series resistance (ESR)
and operating temperature. There are three basic packing methods for aluminum
electrolytic capacitors: tape reel, tray or
ail, and shipping tube or stick magazine. Aluminum electrolytic capacitors that
are packed in tape reel assemblies include a carrier tape with embossed
cavities for storing individual components. Electronic components that are
packed in trays (rails) fit matrices of uniformly-spaced pockets. Capacitors
that are packed in shipping tubes use stick magazines that are made of rigid
polyvinylchloride (PVC) and extruded in industry-standard sizes.
FUSE
In electronics
and electrical engineering a fuse is a type of sacrificial over
current protection device. Its essential component is a metal wire
or strip that melts when too much current flows, which interrupts the circuit in which it is
connected. Short circuit, overload or
device failure is often the reason for excessive current.
A fuse
interrupts excessive current (blows) so that further damage by overheating or fire is
prevented. Wiring regulations often define a maximum fuse current rating for
particular circuits. Over current protection devices are essential in
electrical systems to limit threats to human life and property damage. Fuses
are selected to allow passage of normal current and of excessive current only
for short periods.
FUSE
PUSH SWITCH
A Push Switch
or Push to make switch, allows
electricity to flow between its two contacts when held in. When the button is
released, the circuit is broken. So it is called a non-latching switch.
ESTIMATING AND
COSTING
S.NO COMPONENTS QTY COST
(RS)
1 IC 741 1 5
IC 555 1 5
2 Condenser Microphone 1 10
3 Transformer 1 35
4 Transistor (SL 100) 2 20
5 Diode 3 2
6 Zener Diode 2 2
7 Triac 2 20
8 Diac 1 10
9 Variable Resistor 2 20
10 Potentiometer 1 15
11 Light Dependent Resistor 1 10
12 Resistor 20
13 Capacitors 3 20
14 Lamp 1 10
15 Push Pull Switch 3 30
16 Printed Circuit Board 1 50
17 Soldering Iron 1 80
18 Solder Wire & Flux (20 gm) 40
19 Connecting Wire (1 mtr) 5
20 Fuse 1 1
TOTAL COST=Rs.410
BIBLIOGRAPHY
BOOKS REFFERED
Applied Electronics by R.S. SEDHA
Industrial Electronics and Control
by BISWANATH PAUL
Electronics Project by EFY
WEBSITE VISITED
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