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)
Types of Resistors
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
ii.Photo resistor LDR
iv.Surface mount SMD
a)Fixed resistors: The values of the resistors are fixed and can not be changed.
i. Carbon composition resistor:
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
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
This resistor will have thick conducting material.
- metal oxide resistors:
- These have very low noise and are used at high voltage levels.
- cermet oxide resistorThese are very stable and they may be in square and rectangular shape
- Fusible resistorsThese 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:
The conducting material is very thin
- carbon film resistorsThese have negligible noise so widely used in electronic circuit
- Metal 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.
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 potentiometer
Rheostat other name is tapped resistor. These are used to control the current level.
- 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
These will have additional screw and by moving that screw by screwdriver we can change the value of resistance
2. Nonlinear resistors:
The flow of current changes with a change in temperature or the applied voltage.
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.
Types of thermistors:
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)
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.
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.
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.
|R or Y||0.01|
|S or X||0.1|
|B or H||10|
Also, look in the examples of reading EIA-96 SMD Resistor Codes for importance the use of table (2)
Examples of EIA-96 SMD Resistor Codes
01F = 10M
01E = 1MΩ
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:
Note: these calculations are applicable only to that resistors which are with color bands.