BASIC ELECTRONIC COMPONENTS

1. RESISTOR:

Resistor is an electronic component whose function is to limit the flow of current sin
an electric circuit. It is measured in units called ohms. The symbol for ohm is
Ω(omega). They are available in different values, shapes and sizes.
Every material has some resistance. Some materials such as Rubber, Glass and air
have very high opposition to current to flow .These materials are called insulators.
Other materials such as Copper, Silver and Aluminum etc, has very low resistance,
they are called Conductors.
COLOUR CODING OF RESISTOR:
Colour Codes are used to identify the value of resistor. The numbers to the Colour are
identified in the following sequence which is remembered as BBROY GREAT
BRITAN VERY GOOD WIFE (BBROYGBVGW) and their assignment is listed in
following table.

Black Brown Red Orange Yellow Green Blue Violet Grey White
0 1 2 3 4 5 6 7 8 9

Table: Colour codes of resistor

First find the tolerance band, it will typically be gold ( 5%) and
sometimes silver (10%).
Starting from the other end, identify the first band - write down the
number associated with that color
Now read the next color, so write down a its value next to the first value.
Now read the third or 'multiplier exponent' band and write down that as
the number of zeros.
If the 'multiplier exponent' band is Gold move the decimal point one to
the left. If the 'multiplier exponent' band is Silver move the decimal
point two places to the left. If the resistor has one more band past the
tolerance
 band it is a quality band.

Read the number as the '% Failure rate per 1000 hour' This is rated
assuming full wattage being applied to the resistors. (To get better failure
rates, resistors are typically specified to have twice the needed wattage
dissipation that the circuit produces). Some resistors use this band for
temco information. 1% resistors have three bands to read digits to the
left of the multiplier. They have a different temperature coefficient in
order to provide the 1% tolerance. At 1% the temperature coefficient
starts to become an important factor. at +/-200 ppm a change in
temperature of 25 Deg C causes a value change of up to 1%

Table: Procedure to find the value of resistor using colour codes

2. CAPACITOR

A capacitor (originally known as a condenser) is a passive two-terminal electrical

component used to store energy electrostatically in an electric field. By contrast,
batteries store energy via chemical reactions. The forms of practical capacitors vary
widely, but all contain at least two electrical conductors separated by a dielectric
(insulator); for example, one common construction consists of metal foils separated
by a thin layer of insulating film. Capacitors are widely used as parts of electrical
circuits in many common electrical devices.
Capacitors are also very commonly used. A lot have their values printed on them,
some are marked with 3-digit codes, and a few are color coded. The same
resources listed above for resistors can also help you identify capacitor values.
They are typically marked with an “C” on a circuit board.

Symbol:
COLOUR CODING OF CAPACITORS

An electrical device capable of storing electrical energy. In general, a capacitor consists

of two metal plates insulated from each other by a dielectric. The capacitance of a
capacitor depends primarily upon its shape and size and upon the relative permittivity εr
of the medium between the plates. In vacuum, in air, and in most gases, εr ranges from
one to several hundred.

One classification of capacitors comes from the physical state of their dielectrics, which
may be gas (or vacuum), liquid, solid, or a combination of these. Each of these
classifications may be subdivided according to the specific dielectric used. Capacitors
may be further classified by their ability to be used in alternating-current (ac) or direct-
current (dc) circuits with various current levels.

Capacitor Identification Codes: There are no international agreements in place to

standardize capacitor identification. Most plastic film types (Figure1) have printed
values and are normally in microfarads or if the symbol is n, Nanofarads. Working
svoltage is easily identified. Tolerances are upper case letters: M = 20%, K = 10%, J
= 5%, H = 2.5% and F = ± 1pF.
 Figure 1: Plastic Film Types

A more difficult scheme is shown in Figure 2 where K is used for indicating Picofarads.
The unit is picofarads and the third number is a multiplier. A capacitor coded 474K63
means 47 × 10000 pF which is equivalent to 470000 pF or 0.47 microfarads. K indicates
10% tolerance. 50, 63 and 100 are working volts.
 Figure 2: Picofarads Representation

Ceramic disk capacitors have many marking schemes. Capacitance, tolerance, working
voltage and temperature coefficient may be found which is as shown in figure 3.
Capacitance values are given as number without any identification as to units. (uF, nF,
pF) Whole numbers usually indicate pF and decimal numbers such as 0.1 or 0.47 are
microfarads. Odd looking numbers such as 473 is the previously explained system and
means 47nf
Figure3: Ceramic Disk Capacitor
Figure shows some other miscellaneous schemes.

Figure 4: Miscellaneous Schemes.

3.INDUCTORS

An inductor, also called a coil or reactor, is a passive two-terminal electrical

component which resists changes in electric current passing through it. It consists
of a conductor such as a wire, usually wound into a coil. When a current flows
through it, energy is stored in a magnetic field in the coil. When the current
flowing through an inductor changes, the time- varying magnetic field induces a
voltage in the conductor, according to Faraday‟s law of electromagnetic
induction, which by Lenz's law opposes the change in current that created it.
Inductors, also called coils, can be a bit harder to figure out their values. If they are
color coded, the resources listed for resistors can help, otherwise a good meter that
can measure inductance will be needed. They are typically marked with an “L” on
a circuit board.
 COLOUR CODING OF INDUCTORS

Inductor is just coil wound which provides more reactance for high frequencies and
low reactance for low frequencies.
Molded inductors follow the same scheme except the units are usually micro
henries. A brown-black-red inductor is most likely a 1000 uH. Sometimes a silver or
gold band is used as a decimal point. So a red-gold-violet inductor would be a 2.7 uH.
Also expect to see a wide silver or gold band before the first value band and a thin
tolerance band at the end. The typical Colour codes and their values are shown in
Figure

1000uH (1millihenry), 2%

6.8 uH, 5%

Figure : Typical inductors colour coding and their values.

5.BREAD BOARDS:

This is the platform (or chasis) on which any circuit can be ringed up to provide
 inter connections between electronics components and devices.
The advantage of bread board is, the components can be connected (or)
disconnected easily. It has holes both horizontally and vertically as shown in the
figure.
The horizontal holes at the top and bottom are having internal shorts where as in the
remaining part vertical holes are shorted internally.

PCB (PRINTED CIRCUIT BOARD ):

A printed circuit board (PCB) mechanically supports and electrically connects

electronic components using conductive tracks, pads and other features etched
from copper sheets laminated onto a non-conductive substrate. Components (e.g.
capacitors, resistors or active devices) are generally soldered on the PCB.
6.DIODE:

A popular semiconductor device called a diode is made by combining P & N type

semiconductor materials. The doped regions meet to form a P-N junction. Diodes
are unidirectional devices that allow current to flow through them in one direction
only.
The schematic symbol for a semiconductor diode is shown in fig-1. The P-side of
the diode is called the anode (A), while the N-side of the diode is called the cathode
(K).

Figure : symbol of P-N diode.

Diode specifications:

Breakdown voltage rating VBR

The Breakdown voltage rating VBR is the voltage at which avalanche occurs. This
rating can be designed by any of the following: Peak Inverse Voltage (PIV); Peak
Reverse Voltage (PRV); Break down voltage rating VBR
Average forward – current rating, IF

This important rating indicates the maximum allowable average current that the
diode can handle safely, the average forward current rating is usually designated as
IF Maximum reverse current, IR1N4007 silicon diode specifies a typical IR of 0.05
A for a diode junction.
Temperature TJ of 250C and a reverse voltage VR of
100 V. The maximum rating of a diode should never be
exceeded.
Testing of diode:

Using an ohmmeter to check a diode: when using an ohm meter, check the
resistance of the diode in one direction , then reverse the meter leads and measure
the resistance of the diode in the other direction. If the diode is good it should
measure a very high resistance in one direction, and a low resistance in the other
direction. For a silicon diode the ratio of reverse resistance RR , to forward
resistance RF should be very large, such as 1000:1 or more.
Note: If the diode is shorted it will measure a low resistance in both the directions. If
the diode is open, it will measure a high resistance in both the directions.
Using a DMM to check a diode: Most digital multimeters provide a special range for
testing the diodes. This range is called the diode range. This is the only range setting
on the DMM that can provide the proper amount of forward bias for the diode being
tested. It is important to note that when the digital multimeter forward biases the
diode being tested, the digital display will indicate the forward voltage dropped
across the diode rather that the forward resistance, RF.
A good silicon diode tested with the

Identification:
 7.BIPOLAR JUNCTION TRANSISTOR (BJT):

A transistor has three doped regions there are two types of transistors one is npn and
other is pnp. Notice that for both types, the base is narrow region sandwiched
between the larger collector and moderate emitter regions.
In npn transistors, the majority current carriers are free electrons in the emitter and
collector, while the majority current carriers are holes in the base. The opposite is
true in the pnp transistor where the majority current carriers are holes in the emitter
and collector, and the majority current carriers are free electrons in the base.
1. Emitter 2. Base 3. Collector

Schematic symbols for transistors (a) npn transistor (b) pnp transistor.

In order for a transistor to function properly as an amplifier, the emitter-base

junction must be forward biased and the collector base junctions must be reverse
biased.
Transistor lead Identification:

There are three leads in a Transistor called collector, emitter and base. When a
transistor is to be connected in a circuit it is necessary to identify the leads of
transistor before connecting in a circuit. The identification of the leads of transistor
varies with manufacturer. There are three systems in general.
When the lead of a transistor is in the same plane and unevenly as in above fig., they
are identified by the position and spacing of leads. The central lead is the base lead.
The collector lead is identified by the large spacing existing between it and the base
lead. The remaining is the emitter.
When the leads of a transistor are in the same plane but evenly spaced, the central

lead is the base, the lead identified by dot is the collector and the remaining lead is
the emitter.

When the leads of a transistor are spaced around the circumference of a circle, the
three leads are generally in E-B-C order clockwise from a notch.

SPECIFICATIONS:

In all cases, the maximum ratings are given for collector-base voltage, collector
emitter voltage, emitter base voltage, collector current and power dissipation.
Power dissipation rating Pd (Max):

The product of VCE and IC gives the power dissipation, Pd of the transistor. The
product of VCE x IC must not exceed the maximum power dissipation rating, Pd
(Max) of the transistor is nearly 1Watt.
Derating factor:

Manufacturers usually supply derating factors for determining the power dissipation

rating at any temperature above 25 0C. The derating factor is specified in Watt/0C.

For example if a transistor has a derating factor of 2 mW/0C, then for each 10oC rise
in junction temperature the power rating of the transistor is reduced by 2 mW.
Breakdown voltage ratings;

A data sheet lists the breakdown voltage ratings for the emitter- base, collector-base,
and collector-emitter junctions. Exceeding these voltage ratings can destroy the
transistor.
BVCBO is 60V, BVCEO is 40V and BVEBO is 6V.

Testing of BJTs:

Checking a transistor with an ohmmeter:

To check the base-emitter junction of an npn transistor, first connect the ohmmeter
and then reverse the ohmmeter leads. The resistance indicated by the ohmmeter
should be low since
 the base emitter junction is forward biased. The resistance indicated by the
ohmmeter should read high because the base emitter junction is reverse biased. For a
good pn junction made of silicon the ration RR/RF should be equal to or greater than
1000:1.
To check the collector-base junction, repeat the process described for the base-
emitter junction.
Shorted and open junctions:

A low resistance across the junction in both directions implies that the emitter-base
or collector-base junctions are shorted. If the ohmmeter indicates a high resistance in
both directions, then the junctions are open. In both cases the transistor is defective
and must be replace.
Checking a transistor with a Digital Multimeter (DMM):

Insert the transistor in the provided slots, position the knob of DMM in hFE mode
and check the hFE value.
Applications:

• Amplifiers.

• Oscillators.

• Switches.

8.FIELD EFFECT TRANSISTORS (FETS):

The field effect transistor (FET) is a three terminal device similar to the bipolar
junction transistor. The FET, however, is a unipolar device, which depends on only
one type of charge carriers; either electrons or holes. There are basically two types
of FETs. The junction field effect transistor, abbreviated JFET, and the metal oxide
semiconductor field effect transistor, abbreviated MOSFET.
A junction field effect Transistor is a three terminal semiconductor device in which
current conduction is by one type of carriers i.e., electrons or holes.
There are two basic types of FET‟s

2. Junction field effect transistor (JFET)

3. Metal oxide field effect transistor (MOSFET)

Schematic symbol of JFET

 Specifications:

i. A.C. drain resistance (rd): Drain resistance has a large value, ranging from
10kΩto 1MΩ
ii. Transconductance (gm): It is expressed in mA/V

iii. Amplification factor (µ): It is product of A.C drain resistance and transconductance.

Pinch off voltage:

The value Vp is the start of the interval VP to VDS max during which ID remain
constant. As VDS is increased from 0V to Vp called the pinch off voltage, ID
increases from 0 to the maximum drain current that can be attained without
destroying the JFET, the voltage IDSS. VGS(off):
Maximum drain current flows when VGS = 0 and minimum drain
current when VGS = VGS (off).
Testing:

In case of FET, drain to source should be a fixed resistance in either

direction. Gate to drain or gate to source should be an open circuit or a
very high resistance.

Applications:

Used in tuners of radio and TV

receivers Amplifiers and Voltage
variable resistor.

Specifications:

A typical MOSFET is the 3N200 made by BEL. It has two independent gates against
only one in a common MOSFET. Its specifications are drain to source voltage VDS=
0.2V to 20
V. Gate 1 to source voltage V G1S = 0.6 V to +3 V
 Gate 2 to source voltage V G2S = 0.6 V to +6 V Drain to gate 2 voltage VDG2
= +20V Drain current ID = 50 mA
Transistor dissipation PT = 330 mw Derating = 2.2 m2/0C

Testing:

1. In case of MOSFET, drain to source should be a fixed resistance in

either direction
2. Gate to drain or gate to source should be an open circuit or a very
high resistance (greater than FET).
s
The device under test in the given circuit is a depletion type N- channel JFET, with
the gate circuit kept open, the magnitude of the drain current is sufficient to make
the ID R2 drop large enough. So that the BJT is forward biased and driven into its
ON state. Therefore the lamp glows. The switch SW is now closed. The bias on the
FET gate then causes depletion of its channel.
This lowers the IDR2 drop to the point where conduction through the BJT output
circuit fails to keep the bulb glowing. All this will happen if the FET is in good
condition. On the other hand, a short circuited FET will deep the lamp On in either
position of switch SW, while an open FET will fail to switch the indicator lamp ON.
9. SCR

The basic structure and circuit symbol of SCR is shown below. It is a four layer three
terminal device in which the end P-layer acts as anode the end N-layer acts as cathode
and P-layer nearer to cathode acts as a gate. As leakage current in silicon is very small
compared to Germanium SCRs are made of silicon and not Germanium.
Identification:

When the leads of the SCR are in the same plane but evenly spaced the central lead is
the Gate, left side of the gate is Anode and the other is Cathode.
Specifications:

The following is a list of some important SCR specifications:

4. Latching Current (IL):

Latching current is the minimum current required to latch or trigger the device from
its OFF-state to its ON-state.
5. Holding Current (IH):

Holding current is the minimum value of current to hold the device in ON-state. For
turning the device OFF, the anode current should be lowered below IH by
increasing the external circuit resistance.
6. Gate Current (Ig):

Gate current is the current applied to the gate of the device for control purposes.
The minimum gate current is the minimum value of current required at the gate for
triggering the device the maximum gate current is the maximum value of current
applied to the device without damaging the gate. Move the gate current earlier is the
triggering of the device and vice versa.
Voltage safety factor (Vf) voltage safety factor Vf is a ratio which is related to the
PIV, the RMS value of the normal operating voltage.
Testing:
 The SCR should be switched on and voltage measured between anode and
cathode, which should be approximately volt and the voltage between gate
and cathode should be 0.7 volt.
 An ohmmeter can also be used to test SCR the gate –cathode of a thyristor
has a similar characteristic to a diode with the gate positive with respect to
the cathode,
 a low resistance (typically below 100Ω) should be indicated on the other
hand with the gate negative with respect to the cathode a high resistance
(greater than 100kΩ) will be indicated. A high resistance is indicated in
either direction for the anode to cathode connections.

10.UJT

Identification:

UJT is a three terminal semiconductor switching device. As it has only one PN

junction and three leads it is commonly called as uni- junction transistors.
The basic structure of UJT is as shown below.

Picture

Testing
:
 ak emitter current (Ip) = 2A
Specifi
 Continuous emitter current (IE) = 50mA
cations:
 Inter Base Voltage (VBB) = 35V
(For
UJT  Emitter Base Reverse Voltage (VEB2) = -30V
2N264  Power dissipation at 25°C = 300mW
6)

 P
e
 In case of UJT, emitter to base, (cont1) and emitter to base2 (confg2) should be
exhibit a typical diode characteristics except that the diode resistance in forward
and reverse cases is different for the two configurations.
 The resistance across base1 to base2 should be fixed resistance in either direction.