Terminology & Glossary

Derating Curve:

The curve that expresses the relation between the ambient temperature and the maximum value of continuously loadable power at its temperature, which is generally expressed as a percentage.

Dielectric Withstanding Voltage:

The rated voltage that can be applied to a designated point between the resistive element and the outer coating, or the resistive element and the mounting surface, without causing dielectric breakdown.

Maximum Overload Voltage:

The maximum value of voltage capable of being applied to resistors for a short period of time in the overload test. Typically the applied voltage in the short time overload test is 2.5 times larger than the rated voltage. However, it should not exceed the maximum overload voltage.

Maximum Working Voltage:

The maximum value of DC voltage or AC voltage (rms) capable of being applied continuously to resistors or element. However, the maximum value of the applicable voltage is the rated voltage at the critical resistance value or lower.

Power Rating:

Power ratings are based on physical size, allowable change in resistance over life, thermal conductivity of materials, insulating and resistive materials, and ambient operating conditions. For best results, employ the largest physical size resistors at less than their maximum rated temperature and power.

Rated Ambient Temperature:

The maximum ambient temperature at which resistors are capable of being used continuously with the prescribed rated power. The rated ambient temperature refers to the temperature around the resistors inside the equipment, not to the air temperature outside the equipment.

Rated Power:

The maximum amount of power that can be continuously loaded to a resistor at a rated ambient temperature. Network and array products have both rated power per package as well as per element.

Rated Voltage:

The maximum value of DC voltage or AC voltage (rms) capable of being applied continuously to resistors at the rated ambient temperature.

Resistor Tolerance:

Resistor tolerance is expressed as the deviation from nominal value in percent and is measured at 25 °C only with no appreciable power applied. A resistor's value will also change with applied voltage (VCR) and temperature (TCR). For networks, absolute resistor tolerance refers to the overall tolerance of the network. Ratio tolerance refers to the relationship of each resistor to the others in the package.

Temperature Coefficient of Resistance (TCR):

TCR is expressed as the change in resistance in ppm (0.0001 %) with each degree Celsius of change in temperature. TCR is typically referenced at +25 °C and changes as the temperature increases (or decreases). A resistor with a TCR of 100 ppm/°C will change 0.1 % over a 10 °C change and 1 % over a 100 °C change. In the context of a resistor network, the TCR value is called the absolute TCR in that it defines the TCR of a specific resistor element. The term TCR tracking refers to the difference in TCR between each specific resistor in a network.

MELF Resistor - Alias & Acronym :

Melf is the abbreviation of "Metal Electrode Leadless Face" and is a cylindrically shaped resistor designed for surface mounting.
Acronym: Leadless Resistor; Cylindrical Resistor; Metal Electrode Leadless Face device; Surface Mounted Leadless Component

General Information of MELF Resistors

Direct MELF Offers Designer a Greater Choice:

Direct Electronics is now offering the complete range of MELF products, comprising DIN-0411, DIN-0309, DIN-0207, DIN-0204 and DIN-0102. These high stability, close-tolerance MELF resistors have a footprint very close to comparable chip resistors but maintain their tolerance and deliver higher stability over a wider temperature range. Download Entire MELF Resistor Catalogue in PDF file (579KB).

Where applications require even tighter tolerance, Direct offer Ultra Precision range in the RJM package, with values from 0.1Ω ~ 22MΩ, tolerance from ±5% down to as low as ±0.05% and TC from ±50ppm/°C to ±5ppm/°C.

For high pulse load and high-frequency applications, Direct Electonics offer specialised MELF resistor. The high pulse load resistors are metal glaze film RGM, available in values from 50KΩ ~ 22MΩ and ±0.5% precision tolerance, for 0.125 W ~ 3W applications.

High-frequency RFM resistors are available for RF microwave applications where impedance change due to the parasitic inductance of regular resistors is not acceptable.

Chip Resistor Alternatives:

In very low resistance values, between 0.1Ω and 475Ω, not usually offered by conventional chip resistors, these are available in RJM72P 0102, RJM73P 0204, RJM74P 0207 and standard RJM18M 0411 MELF precision packages.

All MELF-type resistors are available on blister tape for automated placement and maintain their high stability, high precision characteristics when exposed to soldering temperatures and operating stresses including moisture, vibration, humidity and temperature variation within the specified range.

This makes them suitable for a wide range of applications, from laboratory and prototyping work to installation in hostile environments such as airframe or under-bonnet areas, exposed parts of vehicles, or other places where electronic sensing and controls must be installed.

MELF Design Notes and Product Catalogue Download: