Hello, I am Rose. Weilcome to the new post today. Today I will introduce resistor to you. Resistor is one of the three main passive components of electronics, along with inductors and capacitors; from an energy standpoint, resistance is an energy-consuming component that turns electrical energy into heat.

Ⅰ. The Basic Principle of Resistor

Resistor is one of the three main passive components of electronics, along with inductors and capacitors; from an energy standpoint, resistance is an energy-consuming component that turns electrical energy into heat.

A fourth basic passive device, the Memristor, appeared a few years ago, and it showed the relationship between magnetic flux and charge.

Typically, Ohm's law is used to determine resistance. How much current will be generated when a constant voltage is applied to the resistance? It may also be defined by Joule's law, which states that when a current runs through the resistance, how much heat will be generated per unit time.

Equivalent model of actual resistance

Similarly, the actual resistance is not ideal; there is some lead inductance and inter-electrode capacitance, and these variables cannot be overlooked when the frequency of the application is high.

Frequency characteristics of a thin film resistor

The resistor in the previous illustration has excellent high frequency characteristics. The electrode capacitance is only 0.03pF, the lead inductance is only 0.002nH, and the resistance of 75 may exceed 30GHz. The vast majority of chip resistors we use are thick film resistors, which have poor performance. The inter-electrode capacitance is a few pF, and the lead inductance is many nH. The majority of them are limited to a few hundred MHz or a few GHz of frequency.

Standard resistance table

The resistance values of resistors are generally standard. The standard resistance values of resistors with varying accuracy (tolerance) are shown in the diagram above, which are normally multiplied by a multiple of 10 or split by a multiple of 10 to obtain all resistance values.

How do you recall the resistance table above? In truth, it's rather simple; just keep the following three factors in mind:

Precision resistors are grouped into various precision series. E12 series has a 10% accuracy, E24 series has 2% and 5% accuracy, E96 series has 1% accuracy, and E192 series has 0.1 percent, 0.25 percent, and 0.5 percent accuracy.

The number in the series name denotes that there are various standard resistance values in the series, usually a multiple of six. The E12 series, for example, has 12 resistance levels, while the E192 series has 192 resistance values.

Each series' resistance value is roughly a geometric sequence, with a common ratio of ten to one and a base of ten. The E12 series, for example, has a common ratio of 10 to the 12th power, whereas the E96 series has a common ratio of 10 to the 96th power.

Those who are curious can count according to the table above and determine whether the rules are correct. Furthermore, 2 percent accuracy equates to 48 resistance values in the E48 series, according to IEC requirements. Those who are curious can figure out what the values are. Vishay may not be able to create the series shown in the table above.

Resistance Marking

Typically, chip resistors of 5% and 1% are used the most. Resistor packages with a resistance value greater than 0603 are usually marked.

E24 series (5%)

For resistance values greater than ten, there are normally three digits: the first two reflect the resistance value's base, while the last digit shows the number of powers multiplied by ten. For example, the number 100 stands for 10 instead of 100, while the number 472 stands for 4.7k. When the number is less than ten, the decimal point is commonly indicated by the letter R, as in 2R2, which equals 2.2.

E96 series (1%)

Two numerals and a letter are commonly used to symbolize it. The resistance value of the E96 series is represented by the two numbers. The letter symbolizes the number of times multiplied by 10, with Y denoting -1, X denoting 0, A denoting 1, B denoting 2, C denoting 3, and so on. For example, 47C represents multiplied by 10 to the power of 3, which is 30.1k when tallied from the table's 47 resistance values.

Furthermore, the resistance mark for the axial lead package is a circle of color circles, with the precise meaning illustrated in the following diagram:

Resistance color ring code

The first two or three rings indicate numbers, the next ring represents the multiplier, and the resistance is multiplied by the preceding number, in that order, from left to right. The tolerance of the resistance is shown by the following ring, and the temperature coefficient of the resistance is represented by the last ring.

Ⅱ. Process and Structure of Resistor

There are many different types of resistors, which can be classified into two groups based on whether or not the resistance can be changed:

Fixed resistance

Variable resistance

2.1 Fixed resistor

The resistance value of fixed resistance is fixed and unchanging, as the name implies. The resistors we use most of the time are fixed values. It's possible to classify it broadly into different packages.

2.1.1 Axial Leaded Resistor

The two external electrodes are normally axial wires at both ends of the cylinder, which can be further separated into several varieties depending on different materials and procedures.

Wire Wound Resistor

Winding a nickel-chromium alloy wire on an alumina ceramic substrate and controlling the resistance size one by one is known as wire-wound resistance. Precision resistors with a tolerance of 0.005 percent can be manufactured from wire-wound resistors, and the temperature coefficient is very low. The disadvantage is that wire-wound resistors have a high parasitic inductance and can't be employed at high frequencies. The wire-wound resistor's volume can be increased significantly, and then an external radiator can be utilized as a high-power resistor.

Carbon Composition Resistor

Carbon composite resistors are made up mostly of carbon powder and a binder that is sintered into a cylindrical resistor body. The resistance value is determined by the concentration of carbon powder. At both ends, tinned copper leads are added before being packaged. Carbon composite resistors are the cheapest because they use simple technology and have easy access to raw materials. Carbon composite resistors, on the other hand, have poor performance, a huge tolerance (which means they can't be utilized as precision resistors), poor temperature characteristics, and high noise. The withstand voltage performance of carbon composite resistors is better. Because the interior can be thought of as a carbon rod, it will not burn down due to breakdown.

Carbon Film Resistor

Carbon film resistors are mostly made by directly coating a layer of carbon mixture film on a ceramic rod; the thickness of the carbon film and the carbon concentration in it can control the size of the resistance; it can also be processed on the carbon film to control the resistance more precisely. Finally, the metal lead is attached, and the resin encapsulation is formed, with the spiral groove increasing in size as the resistance increases. The procedure for making carbon film resistors is a little more sophisticated, and precise resistors can be manufactured, but the temperature characteristics are still poor due to the carbon quality.

Metal Film Resistor

Metal film resistors use vacuum deposition technology to generate a layer of nickel-chromium alloy coating on a ceramic rod, and then process spiral grooves in the coating to accurately regulate the resistance, similar to carbon film resistors. Metal film resistors can be described as resistors with superior performance and precision. They are available in the E192 series, which has good temperature properties, reduced noise, and increased stability.

Metal Oxide Film Resistor

The metal oxide film is primarily generated by producing a layer of tin oxide film on the ceramic rod, similar to the metal film resistor construction. A layer of antimony oxide film can be placed to the tin oxide film and then treated on the oxide film to boost resistance. To carefully adjust the resistance, spiral grooves are used. Metal oxide film resistors' major advantage is its strong temperature resistance.

2.1.2 Chip resistor

Metal Foil Resistor

The metal foil resistor is manufactured by vacuum melting a nickel-chromium alloy, then rolling it into a metal foil, bonding it to an alumina ceramic substrate, and finally controlling the shape of the metal foil via a photolithography technique to regulate the resistance. Metal foil resistance is the best-performing resistance that can currently be adjusted.

Thick Film Resistor

In thick film resistors, a layer of silver palladium electrodes is pasted on the ceramic substrate, and then a layer of ruthenium dioxide is printed as the resistor between the electrodes. A thick film resistor's resistive film is typically thicker, around 100 microns. The process flow is depicted in the diagram below.

Thick film resistors are the most commonly used resistors today. They are inexpensive and have tolerances of 5% and 1% respectively. The majority of items use 5% and 1% chip thick film resistors.

Thin Film Resistor

Thin-film resistors are made by vacuum depositing a chromium nickel film on an alumina ceramic substrate, which is usually only 0.1um thick, or one-thousandth the thickness of a thick-film resistor, and then photolithographically etching the film into a certain shape. In previous entries on capacitance and inductance, the thin film method was addressed several times. The photolithography method is extremely precise and capable of producing complicated shapes. As a result, thin film capacitor performance may be precisely regulated.

2.2  Variable Resistor

The term " Variable Resistor" refers to the ability to modify the resistance value. There are two types: one that can be manually altered, and the other where the resistance value can be changed based on other physical factors.

2.2.1 Rheostat

You should have used sliding rheostats for experiments when you were in middle school. The little light bulb can be brightened or darkened by using the sliding rheostat. The sliding rheostat is an adjustable resistor that works on the same concept as the sliding rheostat.

Three types of adjustable resistors are commonly used:

Potentiometer

This three-port device is a potentiometer or voltage divider. The center tap divides the potentiometer into two resistors, and the resistance values of the two resistors can be altered through the middle tap, as can the divided voltage.

The rheostat is a potentiometer in disguise. The only difference is that the rheostat only requires two ports, whereas the resistor is simply a resistor that can be adjusted precisely.

Trimmer

Although the trimmer is a potentiometer, it does not require frequent adjustments. When the device leaves the factory, for example, it can be altered. It normally necessitates the use of specialized instruments, such as a screwdriver, to make the necessary adjustments.

2.2.2 Sensitive resistor

A sort of sensitive component is a sensitive resistor. The majority of these resistors are quite sensitive to certain environmental factors. The resistance value will alter in response to changes in physical conditions. Photoresistors, humidity-sensitive resistors, and magneto-sensitive resistors are examples of sensors that can be employed. Resistance, for example. Protection devices should be thermistors and varistors, which are more widely utilized in circuit design.

 PTC resistor 

A PTC resistor is a resistor with a positive temperature coefficient. There are usually two types: one is a ceramic material known as CPTC, which is appropriate for high voltage and high current applications, and the other is a polymer material known as PPTC, which is suitable for low voltage and low current applications.

Ceramic PTC is a polycrystalline ceramic that is formed by sintering a mixture of different components such as barium carbonate and titanium dioxide. The temperature coefficient of the PTC is highly nonlinear. When the temperature rises above a specific point, the resistance rises dramatically, equating to an open circuit, which can be used to protect against short-circuits and over-currents.

In addition, there is a negative temperature coefficient resistance, which will not be discussed in depth.

Varistor

Metal oxide varistors, referred to as Metal Oxide Varistor (MOV), are varistors whose resistance material is a blend of zinc oxide particles and ceramic particles fused together. MOVs have the property that when the voltage surpasses a particular threshold, the resistance reduces quickly and a high current can pass through, allowing them to be utilized for surge and overvoltage protection.

Using a method identical to that of MLCC, the zinc oxide ceramic is transformed into a multilayer varistor, or MLV. The MLV package is tiny, usually chip-shaped, and has a substantially lower rated voltage and current capability than the MOV package. It's ideal for DC applications with low voltages.

Ⅲ. Application and Selection of Resistor

Manufacturers of resistors include Yageo, Panasonic, Rohm, Vishay, and Fenghua Hi-Tech from China.

3.1 Application of resistor

Resistors will not be used on any circuit boards. Capacitors and resistors are the most commonly utilized components on any circuit board. Pull-up and pull-down resistors, feedback resistors, and other components Let's take a look at how limited the level is.

Thermal effect

When current travels through a resistor, heat is generated, according to Joule's law. Electric blankets, electric fire barrels, and electric kettles are just a few examples of how the thermal effect of resistance can be used.

The operating temperature requirements for some outdoor electronic equipment, particularly for those SOC coupled with high-performance CPU, are highly tight, and most of them can only meet commercial-level applications.It's possible that it won't be able to turn on the machine. For pre-heating, a high-power resistor is usually used. The device is switched on and then off when the temperature rises. The entire thing is a waste of time because the device's own work generates heat, which can keep the temperature stable.

As a hardware engineer, I frequently visit the environmental laboratory to track down issues. You must travel to an environmental laboratory to put up a test environment in order to duplicate a high temperature problem. Only a few critical incubators are available, and you must book an appointment. It is frequently too difficult to line up.So I constructed my own simple positional artifact, a DC power socket for resistance welding cement, and then plugged in several power adapters to control the temperature. Then put it on a specific chip for a few minutes; no problem; then switch to another; the problem reappears; the problem is centered on a certain chip; and the high temperature problem is situated at its own workstation.

Zero ohm resistor

Jumper resistance is another name for zero ohm resistance. It is frequently used in circuit design to debug convenience or compatible designs. For example, in the pre-research design, it is common to divide the power supply into various circuits with zero-ohm resistors in order to verify the functioning current of each set of power supplies of the chip during debugging.

The most typical issue when utilizing a zero-ohm resistor is determining how to compute power consumption and determining whether the selected resistor fits the criteria. You'll need to get the required parameters from the resistance specification at this point. The resistance value of the RC0402 zero ohm resistance does not exceed 50m, and the rated current does not exceed 1A, as shown in the diagram below. This can be used to determine whether the resistance matches the design requirement. In most cases, a current need of less than 1A can be met using a 0402 zero-ohm resistance.

Current-limiting

A set of tens of milliamps of power is occasionally required in the circuit, although its voltage is not employed elsewhere. Because the current is too little, it is not appropriate to use a single DCDC or LDO at this time. The voltage regulator circuit might be employed at this point.

Differential pressure

ADC sampling circuits, DCDC output voltage feedback, level conversion, and other voltage division circuits are examples.

Matching resistor

PCB routing for high-speed signals must take into account the transmission line model to provide impedance matching and prevent signal reflections from compromising signal integrity. To eliminate reflections, impedance matching ensures that the load impedance is equivalent to the transmission line's characteristic impedance. The most popular and easiest method is source terminal series matching, which involves connecting a resistor in series with the signal source terminal.Because the sum of the source's resistance and internal resistance equals the transmission line's characteristic impedance, even if the load terminal is not matched, the signal reflected back will be reflected by the source terminal signal. Consider it once more.

There are also non-linear sensitive resistors that can be utilized as sensors, protective circuits, and other applications.

3.2 Selection of resistor

Simply put, the selection is based on extracting essential parameters from the device specification to see if it satisfies the application's needs.

3.2.1 Resistor with a fixed value

In the diagram below, the key parameters of popular types of resistors are compared. Thick film and metal film resistors should account for the majority of shipments.

3.2.2 Thermistor

The major purpose of PTC in the circuit is overcurrent protection, comparable to that of a fuse. The distinction is that the fuse is only used once, whereas the PTC can be used again. Changing the fuse is often unacceptably inconvenient and has a negative impact on the customer experience. PTC is also a safety device that is often UL1439 certified.

The resistance temperature properties of PTC are shown in the diagram above. When there is an overcurrent, the PTC heats up, and the temperature quickly rises. The PTC's impedance rises quickly, generating an open circuit. The current declines after the open circuit, the heating drops, the temperature drops, and the PTC returns to low impedance. As a result, PTC is ideal for short-term overcurrent.

Holding current

Consider the design working current, which must not exceed the PTC holding current, while selecting a PTC. The PTC can sustain a low impedance state at this time. As the operating temperature rises, the PTC's holding current decreases. As a result, during the operating temperature, this is an important issue to consider.

Action current

The operational current, or the current at which the PTC enters a high-impedance state and initiates a protective circuit.

Rated voltage

That is, if the PTC's maximum withstand voltage exceeds the rated voltage, the PTC may be broken down and short-circuited, resulting in burnout. As a result, the design must account for the fact that the PTC's operational voltage cannot exceed its rated voltage under varied conditions.

The PTC circuit will tolerate the entire power supply voltage if it loses protection. When choosing a PTC, make sure the rated voltage is higher than the power supply voltage. Typically, derating to 80% is used, which means the power supply voltage is 12V and a PTC with a withstand voltage of 15V or more is used.

Surge protection should be considered at the power input port. The maximum surge current must be considered at this time, multiplied by the resistance of the PTC, resulting in the surge voltage that the PTC carries, which cannot exceed the PTC's rated voltage.

Rated current

That is, the maximum short-circuit current that the PTC can withstand at the rated voltage. The PTC will be damaged if the short-circuit current exceeds the rated current.

DC Resistor

Because of the PTC DC resistance, there will be a DC voltage drop in the PTC. To meet the criteria, pay attention to the power supply voltage after the voltage drop when designing.

The rated voltage and current of a PTC are substantially lower than those of a fuse, and the DC impedance of a PTC is usually roughly double that of a fuse. When PTC is protected, it is in a high resistance state, resulting in milliamperes of leakage current, and the fuse is a fusing device that closes off the current channel, resulting in virtually no leakage current.

3.2.3 Varistor

Varistors have features that are similar to Zener diodes and TVS. They're clamping devices that primarily safeguard circuits from transient overvoltages like surges.

There are two basic factors when choosing a protective device: one is that it cannot operate or is damaged under normal working settings; the other is that it can protect the circuit under abnormal conditions within the design range, i.e. the protective ability.

Rated working voltage

The highest continuous working voltage at which the MOV can sustain a high impedance state is referred to as the rated operating voltage. MOV can be classified as AC or DC depending on the application. The devices used in the two instances have distinct specifications. In general, MOVs designed for DC purposes cannot be used in AC applications.

Consider AC rated voltage, namely Vrms or Vm(ac) in AC situations, for the rated working voltage of MOV. The device in the above illustration can operate normally in AC at a voltage of 130V. The MOV may operate or be damaged above this voltage, causing the circuit to fail.

It is primarily used to protect MOVs against transitory high voltage; nevertheless, persistent high voltage can destroy MOVs.

Clamp voltage

The MOV is a clamping device. The impedance will drop when it comes into contact with transitory high voltage. The transitory high voltage will be suppressed by a big current, but it will not drop to zero; instead, it will remain at a reasonably high voltage, usually 2 times the rated operating voltage. up to three times When choosing MOV, keep in mind that the clamping voltage must not exceed the covered device's maximum withstand voltage. When it surpasses, multi-level protection is required, such as the addition of a high-power resistor in the rear stage for decoupling, the addition of a TVS, and the use of the low clamp of the TVS. The bit voltage lowers the residual voltage even more.

Maximum pulse current

A large inrush current is generated when lightning strikes or inductive loads are switched on, for example. The MOV must discharge the inrush current in addition to clamping the high voltage.

The amount of energy that the MOV bears over time determines whether or not it can sustain the surge current. The MOV will overheat and burn if the energy is too high. The waveform and quantity of surges influence the energy magnitude. The 8/20us waveform can be used to assess the device's surge capability in general. A single 3500A 8/20us surge pulse, two consecutive 3000A 8/20us surge pulses, and 20 consecutive 750A 8/20us surge pulses make up the MOV in the above figure.

Furthermore, because MOV has a high parasitic capacitance, it cannot be employed on high-speed signal lines. MOV has a slower response time than TVS, and it may not function for some quick pulses, such as ESD. These are also important variables to consider.