Resistor is most common passive two terminal component used in electronics circuit . This device used in various circuits. Without resistor we can’t imagine any circuit . Resistor is very important device to make a circuit. Any simple to simple circuit we can see made using resistor.
The main function of resistor is limits the flow of current. It restricts and controls the power supply between other components. Controlling of supply through the path because it make disturbance in flow of electrons. The resistance of any resistor is noted by ohm (Ω), ohm (symbol of ohm is omega) is unit of measurement of resistance of any resistor. If a resistor has large value of resistance then it creates more disturbance to flow of electron . It means large value resistor have large resistance and small value resistor creates very little disturbance and it has small resistance.
There are mainely 6 types of fixed resistor:
Metal film: The metal film resistor construction is similar to the carbon film resistor except that the material used for constructing the film is different. This type of resistor uses a metal film. Metals such as nickel alloy may be used. In carbon film resistors, carbon is used to construct the film whereas in metal film resistors, tin and antimony or nickel chromium is used to construct the film. In metal film resistor, the desired resistance value can be achieved by either trimming the thickness of metal layer or by cutting the metal film in a helical manner along its length. This is generally done by using the lasers. Once the desired resistance value is obtained, the cutting of metal is stopped. The metal film resistors is very similar to the metal oxide film resistor in terms of visual appearance and performance. Resistance of metal film resistor depends on the thickness of metal film layer and width of helical metal film cut.
This resistor type is generally used in high power applications.. The more expensive varieties are wound on a ceramic former and they may be covered by a vitreous or silicone enamel. This resistor type is suited to high powers and exhibits a high level of reliability at high powers along with a comparatively low level of temperature coefficient, although this will depend on a number of factors including the former, wire used, etc.
Thin film: Thin film technology is used for most of the surface mount types of resistor. As these are used in their billions these days, this makes this form of resistor technology one of the most widely used.
Termination and mounting
Through-hole (Leaded resistor)
Through-hole resistors come with legs which easily entered through hole on the pcb board. Both terminals have legs of specific length which is used during connecting with other components using solder. This type of resistors are in axial size and take more space on circuit implementation. The size of an axial resistor is relative to its power rating. A common ½W resistor measures about 9.2mm across, while a smaller ¼W resistor is about 6.3mm long.
Surface mount (non leaded)
Surface mount resistor are mainly tiny size and rectangular shape in black colour. Terminal on its side with smaller, shiny, silver, with conductive edges. These resistors are intended to sit on top of PCBs, where they’re soldered onto mating landing pads. Because these resistors are so small, they’re usually set into place by a robot, and sent through an oven where solder melts and holds them in place. SMD resistors come in standardized sizes; usually either 0805 (0.8mm long by 0.5mm wide), 0603, or 0402. They’re great for mass circuit-board-production, or in designs where space is a precious commodity. They take a steady, precise hand to manually solder.
Surface Mount Resistors are printed with either a 3 or 4-digit numerical code which is similar to that used on the more common axial type resistors to denote their resistive value. Standard SMD resistors are marked with a three-digit code, in which the first two digits represent the first two numbers of the resistance value with the third digit being the multiplier, either x1, x10, x100 etc. For example
103 = 10 × 1,000 ohms = 10 kiloΩ
392 = 39 × 100 ohms = 3.9 kiloΩ
563 = 56 × 1,000 ohms = 56 kiloΩ
105 = 10 × 100,000 ohms = 1 MegaΩ
Surface mount resistors that have a value of less than 100Ω’s are usually written as: “390”, “470”, “560” with the final zero representing a 10 xo multiplier, which is equivalent to 1. For example:
390 = 39 × 1Ω = 39Ω or 39RΩ
470 = 47 × 1Ω = 47Ω or 47RΩ
Method of finding the value of through hole resistor
• Digit digit multiplier tolerance (for 4 band resistor )
• Digit digit digit multiplier tolerance (for 5 band resistor)
Yellow Violet Red = 4 7 2 = 4 7 x 102 = 4700Ω or 4.7or 4k7.
Green Grey Black Red Brown=6 8 0 2 = 680x102 =68000or 68kΩ
If A resistor colored Green-Red-Gold-Silver then its value is 5.2 Ω and tolerance of +/- 10%.
A resistor colored Brown-Green-Grey-Silver-Red would be 1.58 Ω with a tolerance of +/- 2%.
Colour Code Table of Resistor
A series circuit is a circuit in which resistors are arranged in a chain, so the current has only one path to take. The current is the same through each resistor. The total resistance of the circuit is found by simply adding up the resistance values of the individual resistors:
equivalent resistance of resistors in series : R = R1 + R2 + R3 + ....
series circuit is shown in the diagram above. The current flows through each resistor in turn. If the values of the three resistors are:
R1=8 Ω , R2= 8 Ω , R3=4Ω then total resistance = 8+8+4= 20 Ω
With a 10 V battery, by V = I R the total current in the circuit is:
I = V / R = 10 / 20 = 0.5 A. The current through each resistor would be 0.5 A
A parallel circuit is a circuit in which the resistors are arranged with their heads connected together, and their tails connected together. The current in a parallel circuit breaks up, with some flowing along each parallel branch and re-combining when the branches meet again. The voltage across each resistor in parallel is the same.
The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total:
equivalent resistance of resistors in parallel: 1 /R = 1 / R1 + 1 / R2 + 1 / R3 +....
A parallel circuit is shown in the diagram above. In this case the current supplied by the battery splits up, and the amount going through each resistor depends on the resistance. If the values of the three resistors are:
R1=8 Ω , R2= 8 Ω , R3=4Ω then total resistance =1/R=1/8+1/8+1/4
1/R=1/2, then R=2 Ω
With a 10 V battery, by V = I R the total current in the circuit is: I = V / R = 10 / 2 = 5 A.
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