Basically all materials have resistive properties but some materials such as copper , silver , gold and metal materials generally have resistance is very small . These materials deliver the electrical current well , so called conductors . The opposite of materials conductive , ie materials such as rubber , glass , carbon has a resistance greater resist the flow of electrons so called insulators .
Resistors are the basic components of electronics are always used in every electronic circuit because it could serve as a regulator or to limit the amount of current flowing in a circuit . With resistors , electric current can be distributed according to need . in accordance with his name is resistive resistor and generally made of carbon . Unit resistance of a resistor is called Ohmatau denoted by symbol Ω ( Omega ) .
In the electronic circuit , the resistor is denoted by the letter " R " . Judging from the material , there are several types of resistors in the market between Other : Carbon Resistor , Wirewound , and metalfilm . There are also resistors that can altered resistance value include: Potentiometer , Rheostat and Trimmer ( trimpot ) . In addition there is also a resistor that changes its resistance when exposed to light called LDR(Light Dependent Resistor) And resistors resistance value will increase in size when exposed to temperatures panasyang name PTC (Positive Thermal Coefficient) and resistor resistance value will small increase when exposed to hot temperatures whose name NTC (Negative Thermal Coefficient).
For the type of carbon and metalfilm resistors are commonly used color codes to guide the value of the resistance (resistance) of the resistor. This resistor has a tube-like shape with two legs on the left and right. In the body there is a circle to form a ring color code, the code is great to know without having to measure the resistance with an ohmmeter. The color code is the manufacturing standards issued by EIA (Electronic Industries Association) as shown in Table 1.1.
Table 1.1 value on the ring resistor color
The amount of resistance of a resistor is read from the position of the front ring ring towards tolerance . Usually this tolerance ring position on the resistor body most corner too wide or more prominent , while the position of the first ring slightly inward. Thus the user is instantly know how the tolerance of the resistor . If we had been able to determine where the first ring next is read the resistance value .
Number of circular rings in accordance with generally large resistor tolerance . Usually the resistor with a tolerance of 5 % , 10 % or 20 % have 3 rings ( not including the tolerance ring ) . But resistors with a tolerance of 1 % or 2 % ( small tolerance ) has 4 rings ( not including the tolerance ring ) . The first ring and so on successively showed large unit value , and the last ring is pengalinya factor .
For example, a resistor with a ring of yellow , violet , red and gold . Gold ring is a ring of tolerance . Thus the sequence is the resistor color ring , the first ring is yellow , violet and second ring to the three red rings . The fourth ring is a gold -colored ring tolerance . From table 1.1 tolerance is unknown if the gold-colored ring , this means the resistor has a tolerance of 5 % . Resistance value is calculated in accordance with the order of the color . The first is to determine the unit value of the resistor . Because this resistor resistor 5 % ( which usually has three rings in addition to the tolerance ring ) , then the value of the units is determined by the first ring and the second ring . Still from table 1.1 , note the yellow ring and ring value = 4 violet value = 7 . So the first and second ring or yellow and violet respectively , the value of the unit is 47 . The third ring is a multiplier factor , and if the color red ring means pengalinya factor is 100 . So with this in mind the resistor value is the value of the multiplier unit x or 47 x 100 = 4700 Ohm = 4.7 K Ohm ( on the electronic circuit board typically in 4K7 Ohm ) and the tolerance is + 5 % . Meaning of tolerance itself is a minimum limit and maximum resistance value that is owned by the resistor . So the actual value of the resistor 4.7 k Ohm + 5 % is :
4700 x 5 % = 235
Thus ,
Rmaksimum = 4700 + 235 = 4935 Ohm
Rminimum = 4700 - 235 = 4465 Ohm
If the above resistor is measured by using an ohmmeter and its value is in the range of maximum and minimum values (4465 s / d 4935) was still meets the standard resistor. This tolerance value is given by the manufacturer of resistors to anticipate the characteristics of materials that are not the same between the resistor with another resistor so that the electronics designer can estimate the tolerance factor in its design. The smaller the tolerance value, the better the quality the resistor. So that the market value of the resistor that has a 1% tolerance (eg resistor metalfilm) is much more expensive than the resistor has a tolerance of 5% (carbon resistor)
Another specification to consider in choosing a resistor on the draft resistance is a major addition to its huge wattage or the maximum power that can be detained by the resistor. Because the resistor works in aliri electric current, the power dissipation will occur in the form of heat:
The larger the physical size of a resistor , can demonstrate the greater ability of the resistor power dissipation . Generally available in the market size of 1/8 , 1/4 , 1/2 , 1 , 2 , 5 , 10 and 20 watts . Resistor which has a maximum power dissipation of 5 , 10 and 20 watts generally elongated rectangular -shaped beam is white , but some are cylindrical and usually for large size resistor resistance value printed directly on his body is not shaped rings of color , for example 100Ω5W or 1KΩ10W . Seen from the function , the resistor can be divided into :
1 . Fixed Resistors ( Fixed Resistors )
Ie resistor whose value can not be changed , so it is always fixed ( constant ) . This resistor is usually made from nikelin or carbon . Serve as a voltage divider , regulate or limit the current in a circuit as well as zoom in and out voltage .
2 . Variable resistor ( variable resistor )
Ie resistor whose value can change with the shift or rotate the toggle on the device , so that the value of the resistor can be set according to the needs . Serves as a volume control ( adjust the size of the stream ) , tone control on the sound system , the level of tone control ( bass / treble ) as well as serve as a voltage divider current and voltage .
3 . NTC and PTC resistors .
NTC ( Negative Temperature Coefficient ) , the resistor whose value will become smaller when exposed to hot temperatures . While the PTC ( Positive Temperature Coefficient ) , the resistor whose value will increase if the temperature being cold .
4 . resistor LDR
LDR ( Light Dependent Resistor ) is a type of resistor that changes its resistance due to the influence of light . When exposed to light dark detainees greater value , whereas when exposed to bright light into the smaller value .
2 . CIRCUIT RESISTOR
In practice the designer sometimes requires resistors with a certain value . However, the value of the resistor is not in the shop , even the factory itself does not produce it . Solution to get a resistor with a resistance value that is unique can be done by assembling a few resistors to obtain the required resistance value . There are two ways to weave resistors , namely :
1 . Serial ways
2 . Parallel way
The series resistor in series will result in greater total resistance value .
Below is an example of resistors arranged in series .
Series resistor in the circuit applies the formula:
While the series resistor in parallel will result in replacement for the smaller resistance value.
Below is an example of resistors arranged in parallel.
On a parallel resistor circuit applies the formula:
3. Standard resistor values
Not all resistance values are available in the market. Table 1.2 is a sample table of standard resistor value in the market. Data on the resistor on the market can be obtained from the Data Sheet issued by the manufacturer of resistors.
Table 1.2 Value standard resistor
Below are some formulas (Ohm's Law) that is often used in the calculation of electronics:
Where: V = voltage with units of Volt I = current in Amperes unit
R = resistance with Ohm unit
P = power to the unit Watt
Unit conversion:
1 Ohm = 1 Ω
1 K Ohm = 1 K Ω
1 M Ohm = 1 M Ω
1 K Ω = 1.000 Ω
1 M Ω = 1.000 Ω K
1 M Ω Ω = 1,000,000
(M = Mega (106), K = Kilo (103))
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