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What is a resistor?: Outline of a Resistor

Outline of a Resistor

Resistor Map: Classifications

There is a broad range of resistors. In order to know the position of ROHM's resistors, we have attempted to classify not only based on the general materials used, but also in terms of the shape, integration level, and functions.

Classification by Function

This is the classification based on the functions of the resistors. The classification is made as fixed resistors and variable resistors, and, normally, the word "resistor" implies a fixed resistor.

Classification by Function

Variable Resistors:
Variable resistors are composed of a fixed resistor element and a slider which taps onto the main resistor element. This gives three connections to the component: the fixed resistor element, the main resistor element, and the slider. Because of this, the component acts as a variable potential divider for all three connections that are being used. If variable resistance is desired, It is possible to connect to the slider on one end.

Fixed Resistors:
The most widely used type of resistor is the fixed resistor. They are used in electronics circuits to set the conditions for a circuit. During the design phase their values are determined, which from then on. they should never need to be changed to "adjust" the circuit.

Most fixed resistors use thin film technology and are of the surface mount type. As these are used in their billions these days, this makes this form of resistor technology one of the most widely used.

Square-plate chip resistor
Chip network resitor

The figures above show the cross-sectional views of surface mounted type resistors.

Classification by Material Used

This is the classification based on the material used for making the resistors. Apart from the generally well-known metal glazed type, there are the following types of resistors according to this classification.

Classification by material used

Metal glazed resistors
These are made by sintering on alumina or other substrates mixtures of metal or metal oxide with glass.

Classification by Shape

Broadly, this is the classification of resistors into leaded type and surface mounted type.

Classification by shape
Square chip type The square chip type surface mounted resistors are the major products of ROHM resistors and were developed for the first time in the industry by ROHM.
Leadless type These are round chip resistors.
Radial type This is a form of leaded type resistors that are compatible with vertical tapings and applied only to the products to be packaged in tapes.
Axial type This is a form of leaded type resistors in which the leads come out straight from the body of the resistor in the axial direction on both sides of the resistor body.
Classification by shape

Classification Based on the Level of Integration
Composite resistors are products in which several resistors are integrated together in a single package.

Classification based on the level of integration

Composite resistors
These are resistors in which several resistors of the same or different resistance values are formed on a single substrate to form a single circuit.

Temperature sensitive resistors (reference)
These are resistors using the characteristics of a resistor by which its resistance value changes with temperature. Normally, these are used more as sensors than as resistors. Their applications include, apart from temperature sensing, temperature compensation circuits for the temperature drift of semiconductor devices.

Features of Resistors

Fixed resistors Features
Chip resistor This is a surface mounted type resistor which incorporates electrodes suitable for PCB surface mounting. Chip resistors are the most standard resistors today. A little less than 90% of fixed resistors produced are square-shaped chip resistors.
Carbon film resistor This type of resistors incorporates a solid ceramic core coated with carbon film that has electric resistant properties. Carbon film resistors have been most popular for low-power applications from a safety point of view, considering their heat radiation and fire retardation.
Metal film resistor Unlike carbon film resistors, this type of resistors incorporates a stable ceramic core coated with metal, such as Ni-Cr. Metal film resistors excel carbon film resistors in temperature characteristics, current-noise suppression level, linearity, and accuracy. On the other hand, however, metal film resistors are more expensive than carbon film resistors.
Metal oxide film resistor Unlike metal film resistors, this type of resistors incorporates a stable ceramic core coated with metal oxide, such as tin oxide. The metal oxide film does not burn, thus withstanding a few watts. Although metal oxide film resistors do not burn, utmost attention is required when mounting metal oxide film resistors because they radiate heat.
Wire-wound resistor This type of resistors incorporates a coil of thin metal wire on a ceramic bobbin. Wire-wound resistors are not so much affected by temperature. Furthermore, their noise generation is comparatively low. Their frequency characteristics are, however, poor. Therefore, they are not suitable for high-frequency circuits. Other types of resistors have been replacing wire-wound resistors applied to existing applications, due to difficulty in the production of high-quality wire-wound resistors. Wire-wound resistors for power applications and those for high-precision applications are available.
Solid resistor This type of resistors incorporates a solid mixture of carbon powder and resin. Solid resistors are sturdy but not highly precise. Therefore carbon film resistors have been gradually replacing solid resistors applied to existing applications. High-resistance solid resistors withstanding high voltages are, however, available. They are mainly applied to power supply circuits and others where high stress is imposed.
Network resistor A resistor network is a composite component package consisting of multiple resistors. Electronic circuits are now employing an increasing number of network resistors for the elimination the number of parts, a reduction in labor cost, and high-density mounting needs. The characteristics of the multiple resistors are the same as those of thick film resistors.
Variable resistor Features
Thick film variable resistor This type of variable resistors incorporates thick film that has electric resistant properties. The temperature coefficient of a thick film resistor is smaller than that of a carbon film variable resistor. Thick film resistors in a wide variety of models that are different in shape from one another are available (e.g., a multi-turn model). Thick film resistors are indispensable to the fine-tuning of analog circuits.
Carbon film variable resistor This type of variable resistors incorporates carbon film that has electric resistant properties. They are inexpensive but do not have good performance characteristics. No temperature coefficient is specified for carbon variable resistors, because the temperature coefficient of a carbon variable resistor varies with the resistance.
Metal film variable resistor This type of variable resistors incorporates metal film that has electric resistant properties, such as Ni-Cr film. Metal film variable resistors excel carbon film variable resistors in temperature characteristics and resistance stability but they are more expensive than carbon film variable resistors.

Characteristics of Resistors

Nominal Resistance Nominal resistance is established by the IEC (International Electrotechnical Commission) and expressed by E-series nominal standard resistance values. An E-series nominal standard resistance value is determined on the basis of an initial value of 1, a common radio of 10, and the series number n (6, 12, 24, and so forth). The rules are intended for regularizing the tolerance of each resistance value. The E6-, E12-, E24-series, et cetera are available according to the series number n, which is variable. For example, E12-series nominal standard resistance values are 1.0, 1.2, 1.5, 1.8Ω, and so forth and the tolerance of each nominal standard resistance value is ±100Ω. Such progression sequence values are not only applied to resistance values but also the electrostatic capacitance values of capacitors.
Operating Temperature Range The operating temperature range of each resistor refers to the range of ambient temperatures where the resistor can be used in continuous operation.
Rated Power The rated power of each resistor refers to the maximum permissible power applied to the resistor in continual operation at specified ambient temperature. Usually, the type of resistor as a load is determined according to the power consumption of the resistor. For example, a square chip resistor is provided with a maximum power of 1 W in most cases. If the ambient temperature exceeds 70°C, a decrease in power supply to the load is necessary.
Resistance Tolerance The resistance tolerance of each resistor refers to the maximum permissible dispersion of the nominal resistance of the resistor. This value is expressed by the code F, G, J, K, or M, which refers to a permissible tolerance of ±1%, ±2%,±5%, ±10%, and ±20% respectively.
Resistance Range The resistance range refers to the available range of resistors that can replace other manufacturers' series or types of resistors as equivalent ones. Resistors in a resistance range between 1Ω and 1MΩ are usually available. Sometimes a resistor with a resistance of 1Ω or less or 1MΩ or more is required. Be aware that resistors in a usual resistance range may not replace some special series or types of other manufacturers' resistors.
Rated Voltage The rated voltage of each resistor refers to the maximum value of DC or the maximum root-mean-square value of AC that can be continuously imposed to the resistor at specified ambient temperature. The rated voltage value is calculated from the rated power and nominal resistance on condition that the rated voltage does not exceed the maximum operating voltage of the resistor. The withstand voltage of a usual resistor refers to this value.
Maximum Operating Voltage The maximum operating voltage of each resistor refers to the maximum value of DC or the maximum root-mean-square value of AC that can be imposed on the resistor.

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