Resistor or Resistor is a passive electronic component consisting of two connecting contacts, often used to limit the current flowing in the circuit, adjust the signal level, used to divide the voltage, activate the Active electronic packages such as transistors, end contacts in power lines and in many other applications. Power resistors can dissipate a large amount of electric energy into thermal energy in motor controllers, in power distribution systems. Resistors often have a fixed impedance, little changed by temperature and operating voltage. Variable is a type of resistor that can change impedance as volume adjustment knobs. Sensors have variable resistance such as temperature, light, humidity, impact and chemical reactions.
What is resistance
Resistors are common components in electrical networks, electronic circuits, practical resistors can be made up of many separate components and have many different shapes, in addition electricity can be integrated. in IC circuits.
Resistors are classified based on resistance, impedance, etc. all are symbolized by manufacturers.
Resistor symbol - Resistor convention
Symbol of resistor in a Electrical circuit diagram varies according to the standards of each country. There are two common types as follows
When reading foreign documents. The values recorded on resistors are usually conceived to include 1 letter alternating with IEC 6006 standard digits. is used to facilitate reading and writing the values people separate decimal numbers with a letter. Example 8k2 means 8.2 kΩ. 1R2 means 1.2 Ω, and 18R means 18 Ω.
Resistor unit
Ohm (symbol: Ω) is the unit in the SI system of the resistor, named after Georg Simon Ohm . One ohm is equivalent to volt / ampere. The resistors have different values including milliohm (1 mΩ = 10−3 Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 106 Ω).
Principle of resistor operation
The characteristic of an ideal resistor is represented by Ohm's law as follows:
V = IR
Ohm's law states that: the voltage (V) passing through the resistor is directly proportional to the current (I) and that this is a resistance constant (R) (R).
Principle of resistor operation
For example: If a 300 Ohm resistor is connected to a 12V DC voltage, the current flowing through the resistor is 12/300 = 0.04 Amperes.
Actual resistances also have some inductance and capacitance that affects the relationship between voltage and current in the current AC circuit.
Color resistor board
In fact, in order to read the value of a resistor, in addition to the manufacturer printing its numerical value on the component, people also use a common convention to read the resistance value and the Other necessary parameters. The value is calculated into Ohm units (which can then be rewritten into lots or mazes for convenience).
Color resistor board
How to read the resistor
The resistor in the left position has the value calculated as follows:
R = 45 × 102 Ω = 4.5 KΩ
Because gold corresponds to 4, green corresponds to 5, and red corresponds to exponential value 2. The final color ring indicates that the error of the resistance may be within 5% for the metallic gold color.
The resistance in the middle position has the value calculated as follows:
R = 380 × 103 Ω = 380 KΩ
Because oranges correspond to 3, gray corresponds to 8, black corresponds to 0, and cam corresponds to exponential value 3. The last round indicates the error value of 2% for red.
The resistor in the right position has the value calculated as follows:
R = 527 × 104 Ω = 5270 KΩ
Because green corresponds to 5, red corresponds to 2, and purple corresponds to 7, gold corresponds to 4, and brown corresponds to 1% error. The final color ring indicates the change in the value of the resistor according to the temperature of 10 PPM / ° C.
Note: To avoid confusion while reading the value of resistors, for resistors with a total number of 5 or less color rings, it may not be confused because the vacant position without the color ring will be set. toward the right hand before reading the value. For high-precision resistors and additional parameters that vary with temperature, the thermal parameter color ring will be visible to a larger width and must be folded to the right before reading the value.
Since fixed resistors often have a tolerance of up to 20%, it is possible to convert around the nominal value to 20%. So it is not necessary to have all the values of 10, 11, 12, 13, ... On the other hand, ordinary circuits allow design errors. So just the values of 10, 15, 22, 33, 47, 68, 100, 150, 200, ... are enough.
Convention to read resistor on the principle diagram
Color resistor board
On the principle diagram, the resistor is represented by a long rectangle. On the body there are lines to distinguish the power of the resistor. How to read the following convention:
Two diagonal lines (//) = 0.125w
A diagonal line (/) = 0.25w
A horizontal line (-) = 0.5w
A vertical line (|) = 1.0w
Two vertical lines (||) = 2.0w
Two slashes (/) = 5.0w
Also (X) = 10.0w
Next to write resistance value. Many times do not record units. How to read the following convention:
From 1 hug to 999 hugs to record 1 to 999
From 1000 hugs to 999 000 hacks recorded is 1K to 999K
From 1 Mega and above, it is recorded as 1.0; 2.0; 3.0 ... 5.0 ... 10.0 ... 20,0 ...
Resistors usually are denoted by 4 color rings, exact resistors , then denoted by 5 color rings.
How to read 4-color resistor values
How to read 4-color resistor values
Round 4 is the last ring always yellow or silver, this is the ring of the resistance of the resistor, when reading the numerical value, we ignore this circle.
Opposite the last round is round 1, followed by round 2, number 3
Rounds 1 and 2 are dozens and units
Round 3 is a multiple of base 10.
Value = (round 1) (round 2) x 10 (caps 3)
It is possible to calculate round 3 as the number of zero "0" added
The color of the emulsion is only in the wrong number or round 3, if the 3rd round is the emulsion, the exponent of base 10 is a negative number.
How to read resistor values 5 color rings: ( exact resistor )
How to read resistor values 5 color rings: ( exact resistor )
Round 5 is the last round, which is the wrong round, and 5 color rings, the color has many colors, so it is difficult for us to determine where is the last round, but the last round always has a gap. a little further.
Opposite the last round is round 1
Similarly, reading the numerical value becomes 4 color rings but here round 4 is a multiple of base 10, round 1, number 2, number 3 are hundreds, tens and units.
Value = (round 1) (round 2) (round 3) x 10 (exponential round 4)
It is possible to calculate round 4 as the number of zero "0" added
Diagram of resistive connection
Power consumption resistance
At all times, Power P (watt) consumed by an impedance resistor R (Ohm) is calculated by the formula:
P = I2R = IV = V2 / v
With V (volts) is the voltage on the resistor and I (amps) is the current flowing through it.
Use Ohm's law. The electricity is dissipated into a thermistor.
Power resistors are usually rated according to the maximum dissipation power, in solid state electrical systems, the power resistors are rated at 1/10, 1/8 and 1/4 watt. The normally consumed resistor is lower than the rated value written on the resistor.
The characteristics are not ideal on resistors
In fact, the resistor contains a series of inductance and a small amount of capacitance in parallel. Features are very important for applications that need to operate at high frequencies. In a low noise amplifier, resistive noise characteristics can still occur.
The temperature coefficient on the resistor can also be applied to applications that require high accuracy.
The inductance, excessive noise and temperature coefficient on the resistor depend on the technology that makes it.
These types of resistors have a fixed value
Resistors are made of lead
Through component holes often have "directed" (pronounced lēdz) leaving the "shaft" body, that is, on a parallel line that matches the longest axis of a part. Others have come out of their bodies "radically" instead. Other components can be SMT (surface mount technology), while high resistivity may have one of their leads designed into the radiator.
Resist carbon compound
The carbon compound resistor consists of a resistive tube with a lead wire or metal plate embedded inside. The outer shell is protected by paint or plastic. At the beginning of the 20th century, the resistor was not covered with an insulating shell, the wires were wrapped around the two ends and welded again, and then the barcode was painted with the value of electricity. return.
Physical principle of resistor
The electrical conductivity, or electrical resistance, of many materials can be explained by quantum mechanics . All materials are made up of a network of atomic . Atoms contain electrons , having energy attached to atomic nuclei receives discrete values on fixed levels. These levels can be grouped into two groups: lead region and valence band often have lower energy than the conduction band. Electrons with energies in the conduction band can move easily between the network of atoms.
When there is voltage between two ends of the material, a electric field is set up, pulling electrons in the conduction band moving through the [Coulomb force], creating [ ]electric. Strong or weak current depends on the number of electrons in the conduction band.
Electrons are generally arranged in atoms from low to high energy levels, so most are in the valence band. The number of electrons in the conduction band depends on the material and the conditions that stimulate the energy (temperature, of electromagnetic radiation from the environment). By the nature of the energy levels of the electron, there are six main types of materials:
MATERIAL | POWER RETURN, Ρ (ΩM) |
Superconducting | 0 |
Metal | 10-8 |
Semiconductor | strong change |
Electrolyte | strong change |
Insulated | 1016 |
Superinsulators | ∞ |
This theory does not explain the electrical conductivity for all materials. Materials such as superconductors have other conductive mechanisms, but are not mentioned here because this material has no resistance.
Metal resistors
In the metal there is always electron in the conduction zone. In fact, there is no gap between the conduction band and the valence band, and the two regions can be considered one for metal.
The atomic network of metal is, in fact, imperfect: the chipped areas in the network scatter the electrons, causing obstruction to the movement of electrons (resistors). As the temperature increases, the atoms fluctuate stronger and are more likely to collide with electrons, causing the resistance to increase.
The longer the conductor is, the greater the number of collisions of electrons on the path, causing the conductor resistance to increase.
Semiconductor resistors - Insulation resistors
In semiconductors and insulating substances, atoms interact with each other, causing the energy gap between the conduction band and the large valence band; Most electron is not located in the conduction band. In order to have enough electrons, it is necessary to provide more energy for electrons to jump onto the conduction band, for example [photovoltaic or photonic heat. A large voltage signal can only produce weak current because there is little [[]] electronic electricity; therefore semiconductors and insulators have a high resistivity.
In semiconductor , when the temperature is increased, electrons can receive thermal heat to jump onto the conduction band. This thermal effect is stronger than the barrier effect due to network vibration, causing the resistance to decrease as the temperature increases. Similarly, it is possible to project light, or , electromagnetic radiation in general, to some semiconductors, to transfer energy to electrons (after absorption [ nbsp] photon) jumps onto the conduction band and increases the electrical conductivity, like in the CCD of the camera or the solar battery .
It is possible to change the conductivity of semiconductors by adding a specially chosen impurity to produce errors in the free electron lattice (n-type semiconductor) or lack of electrons is called electron hole (p-type semiconductor). Impurity concentrations determine the number of free holes or electrons in the material, thereby determining the electrical conductivity of the material.
Superconducting resistor
Resistors of a conductive substance decrease gradually as the temperature is lowered. In the regular leads, such as copper or silver, this reduction is limited by impurities and other defects. Even near the absolute zero , a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops suddenly to zero when the material is cooled down to its critical temperature. An current runs in a loop of superconductors can last indefinitely without power.
In 1986, researchers discovered that some cuprate - perovskite ceramics materials had a higher temperature than many important materials, and in the year 1987 has a substance manufactured with a critical temperature above 90K (-183.15 ° C). Such a high switching temperature is theoretically impossible for a super common guide, so the researchers named high-temperature conductors . boiling liquid at 77K (-196.15 ° C) , enabling many experiments and applications that are less practical at lower temperatures. In conventional superconductors, electrons are held together in pairs by an intermediate attraction by phonon grid. The best available models of silks High temperature conductors are still slightly crude. There is a hypothesis that pairs of electrons in high-temperature superconductors are mediated by short-range spin waves [paramagnons].
Plasma resistors
Lightning is an example of plasma phenomenon at Earth's surface. Typically, lightning has an index of up to 30,000 amperes and 100 million volts , emit light, radio , X-rays and even gamma ray . The temperature of plasma in lightning can reach 28,000K (27,726,85 ° C) and electronic density can exceed 10 24 m - 3.
Plasma is very good electrical wire and electric potential plays an important role. Potentials like it exist on average in space between charged particles, independent of sentences how it can be measured, called potential plasma , or spatial potential. If an electrode is inserted into a plasma, its potential is often significant. below the potential in plasma, due to what is called a Debye cover . Good electrical conductivity of plasma makes their electric field very small. This leads to the Important concept of quasineutrality, which states that negative charge density is approximately equal to the positive charge density
Distinguishing this relationship provides a means to calculate the electric field from density:
It can produce a plasma that is not quasineutral. An electron beam, for example, has a negative cost only. The density of neutral neutral plasma must be very low, or it must be very small. Otherwise, push the electrostatic force to dissipate it.
In plasma physics , Debye screening preventing electrical fields from directly affecting plasma over a large distance, ie larger than Debye length. However, the existence of charged particles causes plasma to produce, and is affected by from the field. This can and does not cause extremely complex behavior, such as generations of dual-layer plasma, an object that separates more than a few dozen Debye lengths. Plasma dynamics interact with outside and self Creating from the field is studied in the sectors of from hydrodynamics.
Resistance of conductor
The resistance R of the conductor is directly proportional to the resistivity and wire length, inversely proportional to the section of the wire
Inside:
L IS THE LENGTH OF THE CONDUCT, MEASURE BY METER
S IS A DISCOUNT (CUTTING SIZE), MEASURE BY M2
Ρ (GREEK: ROOM) IS THE POWER RETURN TO (OR CALLS THE PRIVATE POWER OR THE POWER OFF), IT IS A POSSIBLE MEASURE RESISTANCE OF ELECTRIC LINE OF MATERIALS. ELECTRIC RESPONSIBILITY OF A ELECTRIC CONDUCTOR OF A 1M2 LONG CONDITIONER WITH 1MM2 DISCHARGE, IT FEATURES FOR CONDUCTOR MATERIALS.
Additional note: There are two reasons why a small conductor with a cross section tends to increase impedance. The first is that electronic has the same negative charge, pushing each other, so that in a small space the resistance will increase. The second reason is that electrons "collide" with each other, producing "scattering" phenomena and so they are deflected. (See page 27 of [Industrial] Industrial Electronics written by D. J. Shanefield, Noyes, Boston, 2001 publisher with English for more discussion.)
Loss of resistance
When current with intensity I runs through a resistor R, the power is converted to thermal heat loss with capacity
Inside:
P IS CAPACITY, MEASUREED BY W
I AM THE ELECTRIC LINE, MEASURE BY A
R IS POWER ON, MEASURE BY Ω
This effect is useful in some applications such as electric filament lamps or electrical heating devices, but it is undesirable in power transmission. Common methods for reducing power loss are: using better conductive materials, or materials with larger cross-sections or using high voltages. Superconducting wires are used in a number of special applications, but it is difficult to be popular because of the high cost and the technology is still underdeveloped.
Differential impedance
When resistors can be dependent on voltage and current, differential impedance or resistance increments are defined as curves of the graph two axes VI at a specific point, so:
This quantity is sometimes simply called a resistor, although these two definitions are only equivalent to devices such as ideal resistors. If the V-I graph is not a uniform variation (ie there are convex or concave points), the differential impedance will be negative for certain values of voltage and amperage. This attribute is commonly known as "negative impedance", although more accurately it is called negative differential impedance, since the absolute value of the V / I resistance is still a positive number.
The resistance is temperature dependent
The resistance of the metal increases when heated. The temperature coefficient (Alpha) of the resistor is the amount of resistance increase of a conductor with a 1-ohm resistor when the temperature rises by 1 degree C (the phase factor is recorded in the table)
MATERIAL | POWER RETURN AT 20OC Ω MM2 / M | RESISTANCE ELECTRIC TEMPERATURE FACTOR |
Copper | 0,0175=1/54 | 0,004 (IEC 60909-0) |
Aluminum | 0,033=1/34 | 0,0037 (IEC 60909-0) |
Iron | 0,13 – 0,18 | 0,0048 |
The silver | 0,016 | 0,0038 |
The resistance of a typical semiconductor decreases with exponent with increasing temperature
Electromagnetic units in SI
NAME | SYMBOL | DIMENSIONAL | GAUGE VOLUME |
ampere (basic unit of SI) | A | A | Electric |
Coulomb | C | A·s | Electricity, Electricity |
von | V | J/C = kg·m2·s−3·A−1 | Voltage, Voltage |
om | Ω | V/A = kg·m2·s−3·A−2 | Resistor, Impedance, Resistance |
om m | Ω·m | kg·m3·s−3·A−2 | Resistivity |
fara | F | C/V = kg−1·m−2·A2·s4 | Capacitance |
fara/m | F/m | kg−1·m−3·A2·s4 | Dielectric |
Inverse fara | 1/F hay F−1 | kg·m2·A−2·s−4 | Elastance?? |
siemen | S | Ω−1= kg−1·m−2·s3·A2 | Conductivity, conductivity, charge |
siemen/m | S/m | kg−1·m−3·s3·A2 | Conductivity |
weber | Wb | V·s = kg·m2·s−2·A−1 | Phase |
tesla | T | Wb/m2= kg·s−2·A−1 | Magnetic flux density |
ampe/m | A/m | A·m−1 | Inductive |
ampe trên weber | A/Wb | kg−1·m−2·s2·A2 | Words back |
henry | H | V·s/A = kg·m2·s−2·A−2 | Feelings |
henry/m | H/m | kg·m·s−2·A−2 | Magnetism |
(Non-dimensional) | – | – | Words |
Resistors In alternating current
For alternating current, Pure resistance is a property of conductors, it depends on the material and the size of the wire, the atoms of the wire prevent the transfer. dynamics of free electrons, that is, preventing current. The elements made of materials with common resistances are also called resistors. [2]. In electrical circuits only pure resistance, at the maximum time of the voltage, the current is also maximum. When the voltage is zero, the current in the circuit is also zero. Voltage and current in phase. All formulas for DC circuits can be used for AC circuits with only pure resistors, but alternating current values are taken according to the effective values. In engineering, especially electronic engineering, people apply the different properties of the three main types of resistance: Net resistance, resistance, and resistance ] to design combinational circuits.
Resistance
The impedance that the capacitor causes for alternating current. If the capacitor has capacitance C, sinusoidal alternating current has angular frequency ω, the resistance is valued: Zc = 1 / ω.C
If a capacitor is connected to a pure resistor into an alternating current, I is the common current for both serial elements. The voltage on the resistor is in phase with the current I, the voltage component on the capacitor Uc is slow after the current I is 900. Both components determine the voltage of the U source, the voltage is slow after an electric current at an angle (phase).
If the match is parallel, then the current exceeds the voltage by 90 degrees (1/4 cycle)
Resistance
Obstruction caused by a coil's inductance induced by alternating current. If ω is the angular frequency of the current, the inductance of the coil is valid: XL = Lω.
If a coil (inductance) is connected to a pure resistor into an alternating current (variable). Then the current flows through them the same but creates the Falling voltage and according to the Kinder Law: The sum of algebra of all the electromotive forces of the closed circuit is equal to all algebraic total the voltage falls on the resistor of that loop
If paralleling an inductor (with inductance) with a pure resistor into alternating current (variable). Then the source voltage is the same but the current on the pure resistor is the same phase on the coil (inductance), the current is slow after the voltage of 90 degrees (1/4 cycle). To determine the current we must add geometry (vector graph) of current in both branch circuits. This current is slow after one-angle voltage (phase).
Types of resistors
There are thousands of different types of resistors and are manufactured in many ways, because their specific characteristics are suitable for a number of application areas, such as high stability, high voltage, high current, etc. , or used as a general purpose resistor, where its own characteristics are less concerned.
Some common characteristics related to resistance are: temperature coefficient, voltage coefficient, noise, frequency response, power as well as the level of thermal resistance, physical size and reliability.
Types of resistors
Classification based on electrical conductivity of resistors
Linear resistance: A linear resistor is a type of resistor with constant impedance when increasing the voltage difference on it. Either the impedance or the current through the resistor does not change when the voltage (P.D) changes. The V-I characteristics of the resistor are like a straight line (linear).
Non-linear resistors (Non-Linear): These are the types of resistors in which the current flowing through it is not exactly proportional to the voltage difference on it. These types of resistors with non-linear V-I characteristics will not follow ohm's law.
Based on the value of the resistor
Resistors have a fixed value
Fixed value resistors are those resistors that have fixed resistivity values during production and cannot be changed during use.
Variable or potentiometer
or potentiometer are resistors whose resistivity values can be changed during use. These types of resistors usually contain an axis that can be rotated or moved by hand or a screw control slot to change its value in the middle of a fixed range. Example: 0 Kilo Ohms to 100 Kilo Ohms.
Based on the function of the resistor:
Precision resistor
The exact resistance is a resistor with a very low tolerance value, it is very accurate (close to its nominal value). All resistors go with a value, given as a percentage. Tolerance values tell us the actual parameters close to the nominal values.
Fusible Resistor (Melting resistor)
The molten resistor is a winding resistor designed to be easily destroyed when the power across the resistor exceeds the permitted level. In this way, a molten resistor serves the dual function. When the power is not exceeded, it acts as a current limit resistor. When the power exceeds the allowed level, it functions as a fuse, it melts, and opens the circuit to protect the components of the circuit from overflowing.
Thermistor (Thermal resistance)
A thermistor is a heat sensitive resistor whose electrical resistance value varies with changes in operating temperature. Due to the self-heating effect of the current in a thermal resistor, the device changes itself with the changes of the current.
The thermistor has two characteristic types, the Positive temperature coefficient (PTC), or the Negative temperature coefficient (NTC) negative temperature coefficient.
Photoresistors (Optical resistors)
Optical resistance is a resistor whose resistance value changes according to the light shining on its surface. In a dark environment, the resistor of a photoresistor is very high, maybe a few MΩ, depending on the efficiency of the specific impedance of the photoresistor used. When intense light hits the surface, the photoresistor's resistance decreases significantly, possibly as low as 400Ω