Resistor

A resistor is a passive two-terminal electrical component for realization of an ohmic resistance in the electrical and electronic circuits. Resistors are used, for example to

• To limit the electric current to reasonable values
• Divide the voltage in a circuit
• Electrical energy into heat energy to convert.

• 7.1 Temperature Dependent Resistors
• 7.2 photoresistors
• 7.3 Voltage Dependent Resistors
• 7.4 Pressure and strain- dependent resistors

Main Applications

• Setting a certain electric current at a given electric voltage ( resistor)
• Setting a specific electrical voltage at a given electric current ( load resistor, shunt resistor )
• Parts of an electrical voltage in a certain ratio ( voltage divider ). To at least two or more resistors are connected in series (series connection).
• Parts of an electric current in a given ratio ( power divider ). For this purpose, at least two or more resistors connected in parallel (parallel connection).
• Generating a defined level, in case that a terminal of an electrical component (e.g., IC) is not connected or is connected via an electrical open circuit with the rest of the circuit (for example, pull-up or pull-down resistor )
• Generating a defined level for setting of operating points of active components, such as transistors or operational amplifiers
• Conversion of electrical energy into heat energy as incandescent lamps, soldering irons or heaters
• Use as backup

General

A linear resistor ( this includes all resistors whose resistance value depends on no other parameters ) provides an electrical current proportional to the applied electric voltage and vice versa one. It thus serves as a current - to-voltage converter or a voltage -to-current converters, and can not only limit the current such as an electrical fuse.

Parameters

Next to the resistance value of the following additional values ​​are indicative of a resistance:

• Tolerance of the resistance value ( Anliefertoleranz )
• Maximum power dissipation
• Maximum surface or film temperature
• Temperature coefficient ( TC value, specified in the form TKxxx with xxx = ppm per Kelvin)
• Dielectric strength
• Long-term stability (drift ) at maximum rated power dissipation over the life
• Parasitic inductance ( low-inductance resistors)
• Parasitic capacitance
• Current noise ( the current noise increases not only with the resistance, but also material-and voltage-dependent (microvolts / V) )
• Pulse load capacity ( short-time overload )

Classification

Electrical resistors as a component can be grouped according to various criteria, for example:

• Design
• Performance
• Resistance material

Another classification is according to the use of ( from top to bottom sinking requirements for accuracy and long term stability ):

• Precision resistance (<0.1%, in analog circuits with operational amplifiers )
• Measuring resistance (<0.5%, see also shunt)
• Voltage divider, variable resistor (fixed or variable in the form of a potentiometer or resistor trimming )
• Load resistance, series resistance, general applications in electronic circuits (1-5%, mass-produced goods ), terminator (see Dummy Load )
• Pullup-/Pulldown-Widerstand, digital circuits (> 10 %, often as a resistor array )

Designs and materials

The most common resistance design is the cylindrical ceramic support with axial lead wires. This leads, for example, through holes in printed circuit boards and soldered to the circuit connections arranged there. A ceramic substrate is coated with the resistive material which gets its desired resistance value either by its composition, layer thickness or by notches ( coiling ). The maximum power dissipation is 0.1 W and 5 W.

The axial design with a square cross-section ( see photo, first from top) is usually chosen for wire resistors and is filled with quartz sand. These resistors are designed for higher power losses.

A special design is the meander. To find this form is in power and high-power resistors. The advantage of this construction is that it can accommodate a large conductor length in a small area. Also the production of bending or milling machines is relatively simple. Good to see the meandering for example, fan heaters and manganin ceramic resistors ( see links).

As all components of electrical and SMD versions of resistors are manufactured. The common chip types are small square with, for example, 1 mm × 2 mm × 0.5 mm edge length, which at the two smallest areas metallizations as contacts. These are connected by soldering directly to a circuit board ( surface mount).

The various materials of the resistive layers are selected according to the desired precision (tolerance ) and the temperature stability. Coal layers have a negative temperature coefficient and are very inaccurate. Metal Film Resistors can be produced with very low temperature coefficient with highest accuracies and depending on the alloy. Metals have a positive temperature coefficient in general. Metal Film Resistors are manufactured as fuse resistors - these cause congestion at a safe interruption of current flow.

For very high values ​​of resistance and high voltage metal oxide film resistors are manufactured. They are particularly stable to the migration processes occur at high voltages.

Very small, heavy-duty resistors (eg, shunts and braking resistors for high energy absorption ) of metal foil ( manganin ) are manufactured. If these resistors for current measurements (shunts ), they often have so-called Kelvin connections, that is, two additional ports to avoid the measurement error due to the voltage drop at the contact.

Electrical resistors are available as electronic components in different versions, which differ, for example, the type and shape of the resistive material:

• Film resistors: Carbon film resistor
• Metal film resistor
• Metal oxide film resistor
• Cermet (also thick-film ) resistance
• Photo resistor ( LDR short, light-dependent resistance, for example, a cadmium sulfide layer)

• Braking resistor (short-term high loads )
• Shunt resistor ( plate or film, also in the form of a plurality of parallel rods, often with Kelvin contacting)

• Coal bulk resistance
• Carbon ceramic mass resistance
• Metal-ceramic mass resistance
• Thermistor ( NTC ) and PTC ( PTC ) resistors
• Varistor ( VDR short, voltage-dependent resistor )

Furthermore, one knows

• Suitable for high-frequency designs such as the Möbius resistor. These designs are inductance, uncoiled, there are also coaxial designs. Applications include termination resistors.
• For high voltages suitable designs ( great length, usually made of metal ).
• The use of resistance material to heat or defrost.

In a monolithic integrated circuit ( monocrystalline silicon base material ) is a very limited choice of resistance materials. Here each one especially Wired Mechanical transistor is used as resistance for each resistor replacement needed often, as "real" resistors in the layout need more space. If real resistors in the circuit are required, one usually uses polymorphic silicon.

Fixed Resistors

Graduation of the resistance values

The nominal values ​​of resistors are graded according to geometric consequences. In this case, the same number of each decade of different n, the factor Q = 10 ( 1 / n) of graduated values. International valid are those with n = 3.2 a (a is an integer) graded E- series. Depending on tolerance resistors can with values ​​from the E12 (10%), E24 ( 5%), E48 ( 2%) or E96 series ( 1% ) are produced. The percentage figures represent minimum accuracies of the respective row.

For example, the values ​​of the number of E12 = {10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 }. The values ​​are chosen so that there are overlapping ranges of tolerance. As a side effect of a minimum number of storage values ​​is achieved.

Anders and simpler terms: The E- series feature as many resistors per decade (eg 100-1 kOhm ) are present. E12 for example, has twelve resistors whose distance is geometrically ( almost) equally distributed. Previously, the E12 series was only common but nowadays there are more accurate and stable resistors.

Today it is possible to produce and process parameters to be controlled so that arise without readjustment resistors to the desired values ​​of the E96 series or any other series with a conventional tolerance of 1 %, which can be sold all resistors in high stability.

Sizes of leaded resistors

In the printed circuit board assembly, through hole resistors in the industry today (2009) are rarely used. They are still very common in the non-professional area, since the processing is very simple and unlike the PCB assembly with some very small SMD components requires very little soldering experience.

Designs and sizes of SMD resistors

SMD resistors are miniature resistors for direct soldering on the circuit board surface. Due to small dimensions, they enable the construction of compact devices.

In addition, this design has been in the RF technology significant advantages over wired components, since the resulting by resistance coils and inductors connecting wires omitted or be greatly reduced.

SMD resistors are available in round ( MELF ) and cuboidal shape. SMD MELF Resistors ( MICRO- MELF 0102 MINI- MELF 0204 MELF 0207 ) are found in professional applications in the industrial and automotive electronics, where high power dissipation, ambient temperature, pulse loads and a small change in resistance over time ( drift) are required. They are available as thin-film or metal film, metal glaze and carbon film resistors. Your sizes are padkompatibel to the chip designs listed below:

• MICRO- MELF 0102 is compatible with chip 0805

• MINI- MELF 0204 is compatible with chip 1206

• MELF 0207 is compatible with the chip - design 2512

The majority of SMD resistors used are cuboidal ( chip resistors ); they are offered as a thin and thick film resistors. The following remarks refer to this design.

SMD components are available in various sizes, including

• 2512, 2010, 1218, 1210, 1206, 0805, 0603, 0402, 0201, 01005

In this case, enter the larger designs ( from 0402 ) the first two digits are the length and the last two the width of the component, in units of about 1/100 inch ( = 0.254 mm ) and 0.250 mm at. For example, a resistor 0805 having a length of 2 mm and a width of 1.25 mm. For types 0201 and smaller, this assignment is no longer correct.

Details: Chip Design, Surface Mounted Device

The height is slightly greater than 0.635 mm for many series ( 1/40 inch = 25 mil, which is a standard thickness of the starting material used alumina ceramic substrates ), but are generally not larger than the width of the device (because otherwise more difficult assembly, danger of tipping).

For the different designs different maximum power dissipation and maximum voltages are permitted:

Information on resistors

Resistors in round design for electronic circuits or can not be printed with numbers often. In order to identify their values ​​, color codes are used. At present, even smaller but flat SMD resistors, the parameters are applied by printing or laser engraving.

Alphanumeric labeling

For compact alphanumeric labeling of resistance values ​​, the letter " R " may be used as the decimal separator:

In the same way, the SI prefixes can be used as the decimal separator. The value of the prefix represents an extra multiplier is:

This presentation is mainly used in circuit diagrams.

Information on SMD resistors

The label is dependent on the E- series and the size of the components.

The larger the E line, the lower the tolerances of the components: E3 = 20 % = 20% E6, E12 = 10%, E24 = 5% = 2 % E48, E96 = 1% E192 = 0 5%

SMD Resistors 0402 and have less space reasons generally do not print.

Resistances of 0603 and larger are usually identified as follows (there are also series of manufacturers, in which the resistors are not marked at all, and this is especially true for 0603 ):

SMD resistors tolerance class > = 5% are generally identified by three digits. The first two digits indicate the resistance value, the third the power of ten, which is multiplied by the value of the first two digits, in simple terms: the number of appended zeros.

• 472 = 47 × 102 = 47 × 100 = 4700 Ω = 4.7 kOhm
• 104 = 10 × 104 = 10 × 10 000 = 100 000 = 100 k Ω
• 101 = 10 × 101 = 10 × 10 = 100 Ω
• Substituted for values ​​below 10 Ω ' R' represents the decimal point: 1R0 = 1.0 Ω

SMD resistors tolerance class <5% have an imprint with four digits if evidence sufficient space is available (generally from 0805 or 1206). In this case, enter the first three digits of the resistance value of the fourth power of ten, which is multiplied by the value of the first three digits, in simple terms: the number of appended zeros.

Resistors 0603 and 1% tolerance are either not or marked with three characters. Wherein a resistance value from the E24 series, or the coarser components, such as those marked with 5% tolerance (see above), but in addition, the average number is underlined. For resistors from a finer E- series (eg E96 ) rich two digits of the resistance value is not sufficient. For this purpose, the resistance value is encoded by a ( continuously counted ) two-digit number, the exponent but by a letter to distinguish this code secure than those of the other Labelling can.

Related articles on SMD resistors: Metal Electrode Faces, chip design

Color coding on resistors

The resistor color coding or color coding for resistors is a color marking for the electrical values ​​of resistors. As electronic components, these are often very small and beyond cylindrical, so it is difficult to print readable numbers on it. As a replacement one therefore has devised a system to indicate the resistance value with a tolerance by rotating colored rings.

There are color-coded with three, four, five or six rings. In three or four rings, the first two rings give a two digit value from 10 Ω to 99 Ω (see table below), and the third ring is a multiplier on ( power of ten from 10-2 to 109 ) with which to multiply the value is. Thus, 1080 different resistance values ​​can be expressed. The fourth ring, if present, is in the tolerance range. If it is missing, the tolerance is ± 20%. In five or six rings, the first three rings indicate the value ( 100-999 Ω ), the fourth ring is the multiplier, and the fifth ring, the tolerance class. If a sixth ring present, it indicates the temperature coefficient ( stability).

The reading direction is marked in two different ways: either the first ring is placed separately from the edge of the resistor body is a smaller distance than the last ring, or the last ring. Examination: The other direction of reading makes no value of its E series or can not be decoded ( eg last ring is silver or gold, which is not allowed for the first ring).

The color coding is in the DIN IEC 62, or set for resistors with an indication of the temperature coefficient according to DIN 41429 as follows:

High precision resistors (metal film resistors ) usually have five or six rings. In five rings indicate the first three values ​​, the multiplier and four ring ring five tolerance. A sixth ring indicates the temperature coefficient.

• The color rings yellow-purple -red- brown mean 47 102 Ω = 4.7 kOhm and a tolerance of ± 1%. As a result of the resistance of a possible tolerance range of 4.653 to 4.747 kOhm kOhm.
• A resistor with the five rings green-brown - brown - orange-blue has a nominal value of 511 103 Ω = 511 kOhm and has a tolerance of ± 0.25% up.

Parameter Dependent Resistors

Parameter-dependent resistors are referred to as non -linear resistors. An important feature is that the resistance value of one or more other physical parameters such as the voltage applied to the resistance, the temperature, pressure, light and the like more dependent. It is essential that in the non-linear resistors, the connection between the voltage and current through the resistance can not be described by the relationship at a constant ohmic resistance R.

Thermistors

Thermistors are resistors with a targeted pronounced temperature dependence. We distinguish:

• PTC resistors ( thermistors, positive temperature coefficient): the resistance increases with increasing temperature, is used as a temperature sensor, a self- resetting fuse, as self-regulating heater and controlling the demagnetization of picture tubes.
• NTC resistors ( thermistor, negative temperature coefficient ), the resistance value decreases with increasing temperature, is used, inter alia, as a temperature sensor and the current limit.

And the iron hydrogen resistor having PTC behavior. He was formerly used as a current stabilizer in the heating circuits of tube gear and works due to self-heating of an iron wire in hydrogen.

Photoresistors

A photoresistor, abbreviated LDR (light- Dependent Resistor ) changes its resistance under the action of light. When light strikes the photosensitive surface of the photo resistor, the resistance is reduced by the internal photoelectric effect.

Voltage Dependent Resistors

They are called varistors ( from "variable" and " Resistor " portmanteau formed ) and consist of metal oxides ( usually doped zinc oxide ). They reduce their resistance with increasing voltage, usually drastically from a critical threshold similar to a zener diode ( However, for both polarities ). They are used to limit the over voltage pulses ( threshold voltages of 5 volts and several kilovolts ), but not for voltage stabilization.

Abbreviations such as MOV ( metal oxide varistor ) or VDR (of English. Voltage dependent resistor) are derived from material and behavior.

Fritter contain coal meal and reduce their resistance by high- frequency currents.

Pressure and strain- dependent resistors

• Strain gauges are foil resistors, which are glued. They change their resistance depending on their strain or tension.
• Resistances of stacks of graphite discs reduce their resistance at pressure. You can endure high power losses and motor control (sewing ) were previously installed and operated with a pedal.
• The carbon microphones not designated as a resistance change their resistance value by the changing pressure of a sound receiving metal membrane on a charcoal meal filling.

Adjustable resistors

• An electrical component with the help of which any resistance value between two limits can be set, ie, potentiometer, also called in the jargon of Poti. It has three terminals, the simple part of the resistance and a third Grinders connector for tapping the adjusted resistance value. Potentiometers are suitable for frequent adjustment. Main applications are level setting or detecting a lateral or angular position.
• Trimming resistors / trimpots (low power) and variable resistors (large capacity) are only suitable for occasional adjustment.

Both forms are also available in electronic form (integrated circuit with resistor chain, electronic switching and EEPROM for storing the control value )

• Regularly continuously variable power resistors are called rheostat.

By sliding variable resistor (Fader )

Wire resistor with tap ( adjustable clamp)

Trimming resistors