Passive Electronic Components - Resistors.

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Passive Components Resistors

• CEC

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Contents

• Introduction.
• Electronic Component Classifications.
• Passive Components.
• Resistors and Variants.
• Fixed and Variable Resistors.
• Identifying Resistors.
• Memristors.
• Zero Ohm Resistors.

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Electronic Components
Electronic Components

Passive Components
Active Components
Resistors, Inductors, Capacitors
Diodes, Transistors, FETs etc.
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Electronic Components

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Comparison
Passive Components Active Components
Resistors, Capacitors, Inductors. Incapable of Amplification, but can attenuate signals. No need of external power supply. Can store energy. Cannot provide gain. Utilize power or energy in the circuit. Diodes, Transistors, FETs, Thyristors, Integrated Circuits. Capable of Amplification. Derive parameters required for amplification from an external power supply. Provide gain. Can deliver power or energy to the circuit.
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Passive Components

• Resistors, Capacitors and Inductors.
• Resistors pure resistive component, attenuation
  is frequency independent.
• Capacitors and Inductors contain reactive
  components, frequency dependent attenuation.
• Fixed and Variable Components available in the
  market.

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Passive Components

Resistors
Capacitors
Inductors
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Resistors

• Implement Ohms Law, oppose current flow.
• Specifications
• Resistance Value
• measured in Ohms (O).
• - values colour coded or printed.
• Power Rating expressed in Watts.
• Tolerance expressed as percentage.
• Temperature Coefficient of Resistance
• drift in resistance with temperature.

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Colour Coding of Resistors

• Colour coding for small size resistors.
• Resistance value, Multiplier and Tolerance
  normally colour coded.
• Can be 4 bands, 5 bands or 6 bands.
• May fade with prolonged heating/ deteriorate with
  age.
• Possibility of reading errors.
• Difficult if vision defects.

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Resistor Colour Coding

Value
Value
No Colour - 20 Tolerance.
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Colour Coding - 6 Band

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Example 1

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Example 2

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Resistor Colour Codes

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A tip to remember..

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Resistors with values printed

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Letter Coding of Resistors

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Standard Resistor Values

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Tolerance

• Allowed variation of resistance value from the
  nominal value.
• Expressed as a percentage ().
• 100 O 10 means values can vary between 90 O
  and 110 O.

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Power Rating

• How much power the resistor can safely tolerate.
• Size of the resistor depends on power rating
  also.
• Current flow heats up the resistor.
• Heat produced in excess can damage the resistor.
• Expressed in Watts (W).
• Power dissipation P I2R, I Current through
  the resistor R.

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Wattage Rating and Resistor Size

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Resistors

Resistors
Fixed Resistors
Variable Resistors
Carbon Composition
Carbon
Metal Film
Light Dependent
Carbon Film
Wirewound
Cermet Film
Temperature Dependent
Wirewound
Voltage Dependent
Surface Mount
Semiconductor
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Resistor Symbols

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Carbon Composition Resistor

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Carbon Composition Resistors

• Resistive material finely powdered carbon or
  graphite and an insulating material like ceramic.
• Resin to bind the mixture.
• Tinned copper wires at both ends.
• Few ohms to up to 22 MO.
• Power rated ?W, ¼W, ½W, IW and 2W.
• Tolerance 5 to 20.
• Small size but increases with wattage rating,
  rugged.

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Carbon Film Resistors

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Carbon Film Resistors

• Deposit carbon film over insulating core.
• Helical groove cut to adjust resistance value.
• Contact caps at both ends.
• Tinned copper lead wires.
• Power rating ?W, ¼W, ½W.
• Tolerance up to 5.
• More precise.
• Better stability against temperature and
  humidity.
• Low power applications.

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Metal Film Resistors

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Metal Film Resistors

• More accurate, low temperature coefficient, good
  stability.
• Tolerance 0.05.
• Nichrome as resistive material.
• Resistive material sputtered over a ceramic core.
• Helical grooves on film for desired value.
• Protective coating prevents moisture and
  mechanical stress.

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Cermet Film Resistors

• Thick film resistors.
• Thicker conducting paste used.
• Cermet Ceramic Metal.
• Low noise, good thermal stability.

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Wirewound Resistors

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Wirewound Resistors

• Metal resistance wire wound over ceramic/
  plastic/porcelain core.
• Ends soldered/welded to two caps or rings at the
  ends.
• Protective enamel coating.
• 1O to 100 KO, tolerance 5.
• Wattage rating 3 W to 200 W.
• Can withstand up to 450C.
• Large size, higher cost, poor high frequency
  performance.

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Surface Mount Resistors

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Some Resistor Types

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Variable Resistors

Variable Resistors
Resistance value varied using a sliding contact
with rotating shaft .
Three terminals. For volume, brightness control.
Potentiometers
Rheostats
Presets
Carbon
Wirewound
Metal film
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Potentiometers

Carbon
Wirewound
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Potentiometer Variants

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Potentiometer Construction

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Potentiometers

• Linear and non-linear/logarithmic.
• Linear type
• wire wound over a former of uniform
• width.
• - as potential dividers.
• Nonlinear
• - wire wound over a former of nonuniform
• width.
• - as volume/brightness/contrast controls.

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Rheostat
Variable End
Wiper
Resistance Winding
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Rheostat

• Wirewound variable resistance for current
  control.
• Resistance wire wound over insulating ceramic
  core.
• Wiper slides over the winding.
• In high power applications for speed control,
  light intensity control etc.

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Presets
Use a screw driver to vary

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Presets

• Used when frequent variation is not
  required/initial setting undisturbed.
• Metallic wiper moved over carbonised or
  metallised ceramic.
• Use a small screw driver for resistance
  variation.
• For presetting line frequency/frame frequency in
  a TV receiver.

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Membrane Potentiometer

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Parameter Dependent Resistors

• Two terminals.
• LDR resistance varies with incident light
  intensity.
• Thermistor resistance varies with temperature.
• Varistor voltage dependent resistance.

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Parameter Dependent Resistors
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Memristors

• Fourth passive element.
• Developed in 1971 by Professor Leon Chua.
• Junction of doped and undoped TiO2 between
  platinum electrodes.
• Retains previous resistance value when voltage
  turned off.
• Resistance depends on polarity, magnitude and
  length.

Symbol

TiO2 resistive material
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Zero Ohm Resistors

• Used to connect traces on a printed circuit
  board, like a jumper.
• Allows traces on the same side of a PCB to cross.
• Packaged like cylindrical resistors or surface
  mount resistors.
• Resistance approximately zero (maximum 1050 mO)
  .
• Obtained with 5 or 1 tolerances.

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Zero Ohm Resistors

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Uses of Resistors

• Current Limiting/Circuit Protection.
• As Potential Dividers.
• Current Shunts.
• As Controls.
• Pull Up and Pull Down.
• Sensing, eg LDR, Thermistor etc.
• Resistive Fuses.

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Conceptual Symmetries of Four Passive Elements

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References

• Syllabus prescribed text books.
• K A Nawas and T A Suhail, Basics of Electronics
  Engineering, Rajath Publishers, Second Edition,
  2016.

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Thank You