Terms and Definitions

Nominal resistance

Designed resistance value usually indicated on the resistor.

Power rating(Rated power)

Maximum allowable power at rated ambient temperature or rated terminal part temperature. For our chip resistor arrays and networks, the rated power per package may be specified in addition to the rated power per element.

Rated ambient temperature

Maximum ambient temperature at which the rated power may be applied continuously. Note that the rated ambient temperature refers to the temperature around the resistor mounted inside the equipment, not to the temperature outside the equipment.

Rated terminal part temperature

Maximum terminal part temperature of the surface mount resistor at which the rated power may be applied continuously. It includes temperature rise due to self-heating.

Derating curve

Shows the relation of the maximum power that can be applied continuously to ambient or terminal part temperatures. It is generally expressed in percentage.
Click here for details on the derating curve based on the terminal part temperature.

Rated voltage

Maximum DC voltage or AC voltage (rms) that can be applied continuously at the rated ambient temperature or rated terminal temperature. The value is calculated by the following formula using the rated power and nominal resistance. Rated voltage shall not exceed the maximum working voltage.

Critical resistance value (Boundary resistance)

Maximum nominal resistance value at which the rated power can be applied without exceeding the maximum working voltage. The rated voltage is equal to maximum working voltage at the critical resistance value.

Maximum working voltage

Maximum DC or AC voltage (rms) that can be applied continuously to a resistor or resistive element.
However, the rated voltage becomes the maximum applicable voltage when the resistance is below the critical value.
The maximum operating voltage and rated voltage are the DC voltages calculated based on the power rating. In the case of AC, the peak voltage should be √ 2 times the maximum working voltage due to the assumed sine wave. Please inquire us for the applicable peak voltage when not having a sine wave or when the resistance is above the critical value.

Overload voltage

Maximum value of the voltage that can be applied for 5 seconds in a short-time overload test (line 4 in the figure below.) Overload voltage shall be 2.5 times of rated voltage. However, the voltage should not exceed the maximum overload voltage.

Maximum overload voltage

Maximum value of overload voltage (line 5 in the figure below).

Dielectric withstanding voltage

AC voltage (rms) that can be applied to a designated spot between the electrode and the outer coating for one minute, in the voltage proof test (JIS C5201-1 4.7).

Temperature Coefficient of Resistance(T.C.R.)

Relative variation of resistance between two given temperatures when temperature is changed by 1K, which is given by the following formula.

R ：Resistance value（Ω）at T°C
R₀：Resistance value（Ω）at T₀°C
T ：Measured test temperature（°C）
T₀：Measured reference temperature（°C）

Temperature rise

Unless defined otherwise, temperature rise is the difference between the highest temperature observed on the resistor surface and the ambient temperature when power is applied to the resistor. The surface location with the highest observed temperature is often called the Surface hot spot.

Thermal resistance

Thermal resistance can be derived by dividing the temperature difference between two given points by the applied power.