COMPONENTS USED IN ELECTRONICSPASSIVE TYPES

Components - Introduction

Basic components used in electronics can be split into three primary classes,

1. Passive2. Active3. Digital

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.

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Passive Components

The Capacitor

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,

1. Polarised2. Non polarised

Polarised Types

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 exceeded.

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 achieved.

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 2.2f to 68,000f.

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 47f. 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.

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Fig 1

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 oftwo sets of metal plates seperated by air oneof which is fixed while the other can be rotated.

The most common use for this device is in radio tuning.

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Capacitor markings

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)BlackBrownRedOrangeYellowGreenBlueVioletGreyWhite

0123456789

SilverGoldBlackBrownRedOrangeYellowGreenBlue

0.010.11101001000100001000001000000

RedGoldSilverNone

2% 5% 10% 20%

BrownRedYellow

100 V200 V400 V

Brown Green Brown Red Brown

1 5 0 ±2% 100V DC

150pF ±2% 100V DC

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1st and 2nd significant figures

RESISTORS

There are many types of resistor ranging from miniature metal film used for small signal applications 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 with a basic function of controlling levels of current and voltage.

Variable resistors known as potentiometersare 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. UseCR12 Carbon Film 1 - 4.7M 0.125W 5% General PurposeCR25 Carbon Film 0 - 10M 0.25W 5% General PurposeVR25 Metal Glaze 3.9M - 10M 0.25W 5% High VoltageMR25 Metal Film 10 - 1M 0.25W 1% Industrial ElectronicsMF40 Metal Film 10 - 9M 0.4W 1% Industrial ElectronicsMSR25 Metal Film 1 - 10M 0.6W 1% High power IndustrialES3W Wire Wound 0R1 – 270R 3W 5% Flameproof applicationsSQP5W Wire Wound R01 –100R 5W 5% Flameproof applicationsHSA25 Wire Wound 0R1 – 1K 25W 5% Alum. Clad High powerHSA50 Wire Wound 0R05 – 1K 50W 5% Alum. Clad High power

Resistor markingsFixed 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.

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Table 1. Example of Resistor Ranges

Value Multiplier ToleranceBlackBrownRedOrangeYellowGreenBlueVioletGreyWhite

0123456789

SilverGoldBlackBrownRedOrangeYellowGreenBlue

0.010.11101001000100001000001000000

RedGoldSilverNone

2% 5% 10% 20%

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1st and 2nd significant figures

1st, 2nd and 3rd significant figures

Control shaft

Sliding contact(wipe

r)

Slider

Connection Connection

Carbon track

Construction of a Carbon Track Potentiometer

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 1M in darkness to 500 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.

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RECTIFIER DIODES

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 UseBAT42 schottky 30V 200mA glass General purpose signalBAT85 schottky 30V 200mA glass High speed signalBAT41 schottky 100V 150mA glass General purpose signal1N4000 silicon 50 – 1000V 1A DO41 Rectifier1N5400 silicon 100 – 1000V 3A DO27 RectifierBYX99 silicon 300V 15A stud Power rectifierBYX97 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 tuning.

Markings and Package StylesDiodes 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.

Zener Diodes

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+ Holes

- Electrons

NP

conventional current flow

Cathode -Anode +

+V

If(mA)

-Ir(μA)

Forwardbias

-V0.6V

Silicon Diode Characteristics

Table 1. Example of Diode Data

+

-

R

IL

VLZ RL

IZI

Vi

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 UseBZX55 2V7 – 33V 400mW DO35 General purposeBZX85 4V7 – 39V 1.3W DO35 General purposeBZT03C 7V5 – 43V 3.25W SOD-64 Hermetically sealed1N5300B 3V3 – 200V 5W DO41 High power

Markings and PackagingZener 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.

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Zener Diode

Anode - Cathode +

conventional current flow

-V

forward bias

+V0.6V

-Ir (mA)

+If (mA)

Breakdown current

zenerbreakdown voltage

Fig. 3 Characteristics and Symbol for Zener Diode

Table 2. Example of Zener Diode Data

BRIDGE RECTIFIER

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 StylesGenerally 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 UseWO2-8 200V -800V 1.5A plastic Miniature pcb mounting2KBP08 800V 2A plastic Miniature in-lineKBU4J 600V 4A plastic Miniature in-lineKBU8K 800V 8A plastic Miniature in-lineKBPC608 800V 6A plastic Miniature pcb mountingKBPC2506 600V 25A Metal clad High power rectifierKBPC3506 600V 35A Metal clad High power rectifier

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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 current.

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Anode +

Cathode -

conventional current flow

+

-

Fig 4. Biasing the LED

RLIM

Vi

Vf

If

F

fiLIM I

VVR

Value of current limit resistor,

Fig 5. Examples of LED and Seven segment LED display

INDUCTORS

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.

Inductor markingsMost 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

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Fig 1. Examples of Inductors

RELATED CIRCUIT SYMBOLS

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Potentiometer

PresetPotentiometer

VariableResistor

FixedResistor

Fixed Inductor(ferrite-core)

ElectrolyicCapacitor

Fixed Inductor(iron-core)

Variable Inductor(air-core)

Fixed Inductor(air-core)

Diode LEDZener Diode

LDR VDR

V

FixedCapacitor

VariableCapacitor

ElectrolyticCapacitor

PresetCapacitor

USEFUL PARAMETERS

Capacitors Working Voltage The maximum operating voltageV DC. to be applied.

Resistors Power Rating The maximum power that can bemW 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 bemW, 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.

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SEMICONDUCTORS

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 insulator.

The operation of semiconductor devices depends on effects that occur at the boundary or ‘junction’ between p- and n- type materials.

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junction

+ Holes

- Electrons

n-typep-type

p-n junction

Course Work – Passive Components

ObjectiveTo ensure an understanding of common terms and parameters used with passive components.

General1. What is a passive component, give two examples.

Capacitors

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.

Resistors

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.

Inductors

9. How is an inductor formed?

10. What are the typical uses for an inductor?

Components_Passive Section Test