42 Facts About Foil resistors

In electronic circuits, Foil resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.

Variable Foil resistors can be used to adjust circuit elements, or as sensing devices for heat, light, humidity, force, or chemical activity.

Electrical function of a resistor is specified by its resistance: common commercial Foil resistors are manufactured over a range of more than nine orders of magnitude.

Since Foil resistors are specified and manufactured over a very large range of values, the derived units of milliohm, kilohm, and megohm are in common usage.

Total resistance of Foil resistors connected in series is the sum of their individual resistance values.

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Total resistance of Foil resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual Foil resistors.

Some complex networks of Foil resistors cannot be resolved in this manner, requiring more sophisticated circuit analysis.

Power Foil resistors are required to dissipate substantial amounts of power and are typically used in power supplies, power conversion circuits, and power amplifiers; this designation is loosely applied to Foil resistors with power ratings of 1 watt or greater.

Practical Foil resistors have a series inductance and a small parallel capacitance; these specifications can be important in high-frequency applications.

Practical Foil resistors are specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications.

Carbon composition Foil resistors consist of a solid cylindrical resistive element with embedded wire leads or metal end caps to which the lead wires are attached.

Early 20th-century carbon composition Foil resistors had uninsulated bodies; the lead wires were wrapped around the ends of the resistance element rod and soldered.

Resistive element in carbon composition Foil resistors is made from a mixture of finely powdered carbon and an insulating material, usually ceramic.

Carbon composition Foil resistors were commonly used in the 1960s and earlier, but are not popular for general use now as other types have better specifications, such as tolerance, voltage dependence, and stress.

Carbon composition Foil resistors have higher capability to withstand overload relative to the component's size.

Special carbon film Foil resistors are used in applications requiring high pulse stability.

Carbon composition Foil resistors can be printed directly onto printed circuit board substrates as part of the PCB manufacturing process.

Thick film Foil resistors became popular during the 1970s, and most SMD Foil resistors today are of this type.

Thin film Foil resistors are made by sputtering the resistive material onto an insulating substrate.

Thick film Foil resistors are manufactured using screen and stencil printing processes.

Metal film Foil resistors are usually coated with nickel chromium, but might be coated with any of the cermet materials listed above for thin film Foil resistors.

Metal film Foil resistors possess good noise characteristics and low non-linearity due to a low voltage coefficient.

Metal-oxide film Foil resistors are made of metal oxides which results in a higher operating temperature and greater stability and reliability than metal film.

Wirewound Foil resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core.

Wirewound Foil resistors are coils they have more undesirable inductance than other types of resistor.

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Applications of wirewound Foil resistors are similar to those of composition Foil resistors with the exception of high frequency applications.

The high frequency response of wirewound Foil resistors is substantially worse than that of a composition resistor.

Since their introduction in the 1960s, foil resistors have had the best precision and stability of any resistor available.

The TCR of foil resistors is extremely low, and has been further improved over the years.

Such industrial grade Foil resistors can be as large as a refrigerator; some designs can handle over 500 amperes of current, with a range of resistances extending lower than 0.

Some wirewound power Foil resistors have a tapping point that can slide along the resistance element, allowing a larger or smaller part of the resistance to be used.

Standard-tolerance surface-mount technology Foil resistors are marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten .

Many precision Foil resistors, including surface mount and axial-lead types, are marked with a four-digit code.

Thick-film and carbon composition Foil resistors generate more excess noise than other types at low frequencies.

Wire-wound and thin-film Foil resistors are often used for their better noise characteristics.

Thin film surface mount Foil resistors typically have lower noise and better thermal stability than thick film surface mount Foil resistors.

Low-power thin-film Foil resistors can be damaged by long-term high-voltage stress, even below maximum specified voltage and below maximum power rating.

Carbon film and composition Foil resistors can fail if running close to their maximum dissipation.

Surface mount Foil resistors have been known to fail due to the ingress of sulfur into the internal makeup of the resistor.

Sulfur resistant and anti-corrosive Foil resistors are sold into automotive, industrial, and military applications.

The voltage dropped across large value Foil resistors can be exceeded before the power dissipation reaches its limiting value.

Since the maximum voltage specified for commonly encountered Foil resistors is a few hundred volts, this is a problem only in applications where these voltages are encountered.