Passive Components – Resistors

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Resistors: These are the electric components which are use to oppose the flow of current. Generally, Resistors are made by the ceramic rod and over that rod, aluminum is coated. For every resistor will have the different colors. So depending on the colors, the value of resistors are calculated. So that value gives the how much current it can resists. When the current flow through the resistance it absorbs that electrical energy and it dissipates in the form of heat.

Formula: R= V/I   ( R – resistance,  V- Voltage, I – current )

The power which is dissipated is given as P= VI   (P – power, V- voltage, I –current)

Units: Ohms

Types of Resistors

1.Linear

a.Fixed resistor

i .Carbon composition resistor

ii.Wire wound resistor

iii.Thick film resistor

  • Fusible resistor
  • Cermet film resistor
  • Metal oxide resistor

iv. Thin film resistor

  • Carbon film resistor
  • Metal film resistor

b. Variable resistor

i.potentiometer

ii.rheostrat

iii.trimmer

2. Non-Linear

i.thermistor

ii.Photo resistor LDR

iii.Varistor resistor

iv.Surface mount SMD

1. Linear:

a)Fixed resistors:  The values of the resistors are fixed and can not be changed.

Symbolic representation:

Image result for fixed resistor symbol

i. Carbon composition resistor:

Related image

These are very cheap and occupies less place.Its range from  1 ohm to 25 mega ohms. Power rating will be ¼ th watt to 5 watts. These are less stable and makes noise compared to other resistors.

ii. Wire wound resistor

Image result for wire wound resistor

Wound wire is known as resistor wire and it is made of Tungsten, manganin, Nichrome or nickel or a nickel-chromium alloy. the Enamel coating is made of porcelain, Bakelite, press bond paper or ceramic clay material.

Its range from 0.1 ohms to 100 K ohms and power is 2 watts to 100 watts.These are costly and use in the industries.

iii. Thick film resistors

Related image

This resistor will have thick conducting material.

  • metal oxide resistors:
  • Image result for metal oxide resistorsThese have very low noise and are used at high voltage levels.
  • cermet oxide resistorImage result for cermet oxide resistorThese are very stable and they may be in square and rectangular shape
  • Fusible resistorsImage result for fusible resistorThese are same as wire wound resistor that is when the power is increased the resistor will be fused.so it is called fused resistors. Its resistance range is less than 10 ohms. Used in the TV sets.

    iv. Thin film resistors:

     

    Image result for thin film resistors

    The conducting material is very thin

  • carbon film resistorsRelated imageThese have negligible noise so widely used in electronic circuit
  • Metal film resistorsImage result for thin film resistorsThese are same as carbon film resistors but instead of carbon, we use the metal.

    b.Variable resistors:The value of the resistors can be changed through the dial, knob, screw or manually.

    i. Potentiometer

    Image result for potentiometer

    Potentiometer used for the controlling the voltage level. It is of 3 terminals two are constant connections ad other one is the slider.By moving the slider we can the change the value of a resistor. The range of them varies up to 10 mega ohms.

    Types of the potentiometerImage result for types of potentiometer

    ii. Rheostats

     

    Image result for rheostat

  • Symbolic representation

    Image result for symbol rheostat

    Rheostat other name is tapped resistor. These are used to control the current level.

     

    Image result for rheostat diagram

  • And in this, there is wire wound rheostat and its range is from 1 ohm to 150 Ohm and power is 3 to 200 watts.

    iii.Trimmer Potential meter

Image result for trimmer potentiometer

These will have additional screw and by moving that screw by screwdriver we can change the value of resistance

2. Nonlinear resistors:

Image result for non linear resistor

The flow of current changes with a change in temperature or the applied voltage.

i. Thermister:

The flow current changes with the change in temperature are known as the thermister. So thermister is the temperature sensitive device.

The resistance is inversely proportional to temperature so it is called as negative temperature coefficient.But there also positive temperature coefficients. So that type of thermistors made up of the pid barium titanate semiconductor materials.

Symbolic representation:

Image result for thermistor symbol

Types of thermistors:

Image result for types of thermistor

 

ii. Varistors(VDR)

Image result for varistors

The flow of current changes with the change in the applied voltage is known as the Varistors.

iii.Photo Resistor or Photo Conductive Cell or LDR (Light Dependent Resistors)

Related image

Depending on the intensity of the light the resistance value changes. I.e, when the light falls on the LDR the flow electrons increases then the resistance of semiconductor material decreases. So LDR is the negative temperature coefficient.

Symbolic Representation:

Image result for ldr

iv.SMD

SMD stands for Surface Mounted Device. An SMD is any electronic component that is made to use with SMT or Surface Mount Technology. SMT was developed to meet the ongoing desire for printed circuit board manufacture to use smaller components and be faster, more efficient, and cheaper.

Image result for smd resistor

Calculation of  SMD Value

Examples of 3-Digit SMD Resistor Codes

250 = 25 x 100 = 25 x 1 = 25 Ω (This is only and only 25Ω not 250 Ω)

Examples of 4-Digit SMD Resistor Codes

2500 = 250 x 100 = 250 x 1 = 250 Ω (This is only and only 250Ω not 2500 Ω)

 

Below is the table (1) to shows the multiplier values of different Letters using in the EIA-96 coding system for SMD Resistor Codes.

Table (1)

Letters

Multipliers

Z 0.001
R or Y 0.01
S or X 0.1
A 1
B or H 10
C 100
D 1000
E 10000
F 100000

Also, look in the examples of reading EIA-96 SMD Resistor Codes for importance the use of table (2)

Table (2)…

Table (2)

Code Value Code Value Code Value Code Value
01 100 25 178 49 316 73 562
02 102 26 182 50 324 74 576
03 105 27 187 51 332 75 590
04 107 28 191 52 340 76 604
05 110 29 196 53 348 77 619
06 113 30 200 54 357 78 634
07 115 31 205 55 365 79 649
08 118 32 210 56 374 80 665
09 121 33 215 57 383 81 681
10 124 34 221 58 392 82 698
11 127 35 226 59 402 83 715
12 130 36 232 60 412 84 732
13 133 37 237 61 422 85 750
14 137 38 243 62 432 86 768
15 140 39 249 63 442 87 787
16 143 40 255 64 453 88 806
17 147 41 261 65 464 89 825
18 150 42 267 66 475 90 845
19 154 43 274 67 487 91 866
20 158 44 280 68 499 92 887
21 162 45 287 69 511 93 909
22 165 46 294 70 523 94 931
23 169 47 301 71 536 95 953
24 174 48 309 72 549 96 976

Examples of EIA-96 SMD Resistor Codes

01F =     10M

01E =     1MΩ

01C=     10kΩ

01B =   1kΩ

01A =   100Ω

01X =   10Ω

01Y =   1Ω

66X = 475 x 0.1 = 47.5 …→ (in table (2), 66 = 475 and in table (1), X = 0.1. so 475 x 0.1 = 47.1Ω)

Calculation of resistors:

Image result for calculation of resistors color code

Note: these calculations are applicable only to that resistors which are with color bands.

 

 

 

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