COMPONENTS USED IN ELECTRONICS
Components - Introduction
Basic components used in electronics can be split into three primary classes,
Passive components cannot generate an increase in power and consist of capacitors, resistors and
inductors. Resistors are able to convert electrical power into heat. Inductors convert electrical
energy into a magnetic force. Neither devices are able to increase the power in a circuit.
Active components are devices that provide gain in an electronic circuit eg. a transistor has a
low-power input from the base current but a high power output as collector current.
Digital devices provide a logic function and operate in two states only, on or off, similar to a
switch. There are many different types ranging from basic gates, counters, decoders etc to
microprocessors and memory devices.
A capacitor is used to store electric charge and functions much like a battery.
A capacitor is made up of two conductors (plates) seperated by an insulator called the dielectric.
Their are two classes of capacitor,
2. Non polarised
Polarised types can only be connected one way in a
circuit and are marked to show which lead is positive or
negative. Fig 1 shows a wound alluminium electrolytic
capacitor, the white bar and –ve sign one the right
identifying the negative terminal. Polarised capacitors
are generally electrolytic types.
Electrolytic capacitors are available in a wide range of
working voltages, care must be taken when selecting the
circuit application as they can explode if the rating is
Wound alluminium capacitors (fig 1) are mostly used in
power supply applications as filter (reservoir) capacitors
due to the large values and working voltages that can be
Operating voltages are generally specified as the DC
Working voltage since the majority of applications are in dc circuits.and can range between 6.3
to 400V and capacity 2.2µf to 68,000µf.
Another type of electrolytic capacitor is the Tantalum bead, these are miniature electrolytics
used for local filtering on printed circuit board
assemblies due to their small size and high
capacitance ranging between 2.2 to 47µf. with a dc
working voltage from 6.3 to 35V.
They are very stable and have a much smaller
leakage current than the aluminium capacitors.
Non Polarised Types
There are many types of non polarised capacitors which
are mostly used for small signal applications in electronic
circuits eg filtering, timing, coupling, de-coupling, at high
frequences etc. Types include ceramic, mica,
polycarbonate, polyester etc.
There are also variable capacitors made up of
two sets of metal plates seperated by air one
of which is fixed while the other can be
The most common use for this device is in
Most capacitors use written markings indicating their value, working voltage and tolerance.
Some manufacturers of ceramic capacitors use a three digit code, the first two digits correspond
to the value and the third digit is the multiplier giving the number of zeros to be added to give
the value in picofarads.
Value Multiplier (pf) Tolerance Voltage (DC)
Brown Green Brown Red Brown
1 5 0 ±2% 100V DC
150pF ±2% 100V DC
There are many types of resistor ranging from
miniature metal film used for small signal
eg. biasing in amplifiers, timing and level
shifting etc, to large wire wound types used in
power applications such as loads for test
simulation or current sensing.
Resistors are used extensively in electronics
basic function of controlling levels of current and voltage.
Variable resistors known as potentiometers
are made up of a stationary resistance and
a rotating contact. The resistance can be either
carbon track or wire wound and may also be linear
or non linear in their operation.
Used in applications where there is a need for human
interaction with continuous adjustment eg volume
and temperature setting and timing etc.
Ref Type Range PTOT Tol. Use
CR12 Carbon Film 1Ω - 4.7MΩ 0.125W 5% General Purpose
CR25 Carbon Film 0Ω - 10MΩ 0.25W 5% General Purpose
VR25 Metal Glaze 3.9MΩ - 10MΩ 0.25W 5% High Voltage
MR25 Metal Film 10Ω - 1MΩ 0.25W 1% Industrial Electronics
MF40 Metal Film 10Ω - 9MΩ 0.4W 1% Industrial Electronics
MSR25 Metal Film 1Ω - 10MΩ 0.6W 1% High power Industrial
ES3W Wire Wound 0R1 – 270R 3W 5% Flameproof applications
SQP5W Wire Wound R01 –100R 5W 5% Flameproof applications
HSA25 Wire Wound 0R1 – 1K 25W 5% Alum. Clad High power
HSA50 Wire Wound 0R05 – 1K 50W 5% Alum. Clad High power
Fixed carbon, metal oxide/film resistors are usually marked with coloured bands indicating their
value and tolerance. Two methods are in common use,
(1) four coloured bands and
(2) five coloured bands.
Potentiometers and wire wound types have their values printed on them.
Table 1. Example of Resistor Ranges
Value Multiplier Tolerance
Construction of a Carbon Track
Light Dependant Resistor (LDR)
Light dependant resistors use a semicaonductor*
material whose resistance varies according to the
amount of light falling on it. The resistance can
range from 1MΩ in darkness to 500Ω in full light.
LDR’s are used
* a material which is neither a conductor or insulator.
Voltage Dependant Resistor (VDR)
The resistance of a voltage dependant resistor falls
rapidly when the voltage across it exceeds a
particular value. Under normal operating conditions
the current flowing in a VDR is negligible, however
when the resistance falls the current will increade
considerably. VDR’s are used in protection circuits
for clamping noise spikes to a safe value.
The diode is the simplest form of semiconductor device used in electronics and is formed using a
single P-N junction.
The diode will pass electric current in one direction only ie. its resistance is low in the
conducting or ‘forward’ direction but very high in the opposing or ‘reverse’ direction. For a
diode to conduct its anode must be connected positive with respect to its cathode.
A diode which is reverse-biased will not pass a significant current, however if the reverse
voltage rating is exceeded the diode will break down. This voltage is called the maximum
reverse voltage (VRRM).
Ref Type VRRM IF Case Use
BAT42 schottky 30V 200mA glass General purpose signal
BAT85 schottky 30V 200mA glass High speed signal
BAT41 schottky 100V 150mA glass General purpose signal
1N4000 silicon 50 – 1000V 1A DO41 Rectifier
1N5400 silicon 100 – 1000V 3A DO27 Rectifier
BYX99 silicon 300V 15A stud Power rectifier
BYX97 silicon 1200V 47A stud High power rectifier
Diode types range from small signal glass and
general purpose ceramic to high current stud mounted. Applications include power supply
rectifiers, protection and detector circuits for radio
Markings and Package Styles
Diodes are identified using an alphanumeric code
and the cathode is identified by a bar. Package
styles range from miniature glass bead to large metal
stud. Stud mounted styles print the diode symbol
orientated to identify the polarity.
conventional current flow
Cathode -Anode +
Silicon Diode Characteristics
Table 1. Example of Diode Data
Fig 2. Biasing a Zener Diode
Fig. 1 Stud Diode
If the reverse bias of a rectifier diode is increased beyond its VRRM and breakdown occurs then
the diode will suffer permanent damage. The zener diode is design to be used in the reverse bias
or breakdown region but must have a resistor placed in series to limit the diode current IZ.
Zener diodes are manufactured with defined breakdown voltages which remain almost constant
over a wide range of reverse current making them useful as a voltage reference in comparator
circuits and stabilized power supplies to maintain a steady output.
Ref Range PTOT Case Use
BZX55 2V7 – 33V 400mW DO35 General purpose
BZX85 4V7 – 39V 1.3W DO35 General purpose
BZT03C 7V5 – 43V 3.25W SOD-64 Hermetically sealed
1N5300B 3V3 – 200V 5W DO41 High power
Markings and Packaging
Zener diodes are marked and packaged in the same way as ordinary diodes but include the zener
voltage as part of the identification number, ie BZX85C4V7 for a BZX85 range 4.7 volt zener
diode. Since they operate in the reverse bias mode the cathode polarity is made positive with
respect to the anode.
Anode - Cathode +
conventional current flow
Fig. 3 Characteristics and Symbol for Zener Diode
Table 2. Example of Zener Diode Data
The bridge rectifier is a special device made up of four diodes in one package and is used to
convert a.c. waveforms to d.c. They are used in power supplies where a dc voltage is required
from an ac supply usually the secondary winding of a mains transformer but can also be used
direct on-line to the a.c. mains supply.
Markings and Package Styles
Generally they are four terminal devices with the two ac inputs marked ~ and the dc outputs
marked + and -. the manufacturers type number is also printed on the device.
Package styles range from pcb mounted dual-in-line to chasiss mounted with crimp or screw
termination depending on current rating.
Ref VRRM IF Case Use
WO2-8 200V -800V 1.5A plastic Miniature pcb mounting
2KBP08 800V 2A plastic Miniature in-line
KBU4J 600V 4A plastic Miniature in-line
KBU8K 800V 8A plastic Miniature in-line
KBPC608 800V 6A plastic Miniature pcb mounting
KBPC2506 600V 25A Metal clad High power rectifier
KBPC3506 600V 35A Metal clad High power rectifier
Table 3. Example of Bridge Rectifier Data
Fig 4. Examples of Bridge Rectifier
LIGHT-EMITTING DIODES (LED)
Light-emitting diodes give off light when a current
passes through them in the forward direction and must be
connect the correct way round to work. An LED is a
transducer which is used to change electrical energy into
light energy, available colours are red, yellow, green,
blue and white.
The LED has a forward volt drop of approx 2 volts and a
current of about 25mA therefore a resistor connected in series is required to limit the forward
Anode + Cathode -
conventional current flow
Fig 4. Biasing the LED
=Value of current limit resistor,
Fig 5. Examples of LED and Seven segment LED display
Inductors store electrical energy in the form of a magnetic field and are made up of a winding
placed, usually, on an iron core. The specification for an inductor includes the value of
inductance, the current rating and the tolerance.
Typical applications include chokes, filters on supply rails and power supplies, tuned circuits for
radio and television.
Most inductors use either the colour code as applied to capacitors with the inductance expressed
in microhenries or have their value and rating written on them
Fig 1. Examples of Inductors
Capacitors Working Voltage The maximum operating voltage
V DC. to be applied.
Resistors Power Rating The maximum power that can be
mW dissipated in the device. Must
also maintain device at 20˚C.
Tolerance Minimum to maximum range the
± 1%, 2%, 5% device value can be, taken about
the nominal value.
Diodes Maximum Reverse Voltage Reverse Breakdown voltage
(VRRM), 100 – 1000V
Power Rating The maximum power that can be
mW, W dissipated in the device. Must
also maintain device at 20˚C.
Forward Current The maximum operating current
(IF), mA, A. allowed to flow through device.
Forward Volt Drop The voltage lost across the
(VF), 0.6V device during conduction.
Semiconductor materials are the basis from which diodes, transistors thyristors, triacs and
integrated circuits are made. A semiconductor material is one that is neither a conductor or
The operation of semiconductor devices depends on effects that occur at the boundary or
‘junction’ between p- and n- type materials.
Course Work – Passive Components
To ensure an understanding of common terms and parameters used with passive components.
1. What is a passive component, give two examples.
2. Capacitors are split into two categories ‘Polarised and Non-polarised’,
what should we consider when using polarised types and why.
3. Polarised capacitors are known as ______________ capacitors.
4. Give an example of a common use for palarised capacitors.
5. Give two examples of typical values, markings and types of capacitor.
6. Name three styles of resistor.
7. Describe the make up of a potentiometer and its uses.
8. Give two examples of typical values, markings and types of resistor including its
tolerance. Provide the maximum and minimum values for your examples.
9. How is an inductor formed?
10. What are the typical uses for an inductor?
Components_Passive Section Test