Power ratings are normally specified at +25oC and must be reduced as the resistor temperature increases, see the derating curve above. A derating chart is often used, with derating starting at 70oC. Since parameters are application dependent, power de-rating curves or charts should be considered general rather than absolute, and only used as a guideline. The safest designs use the largest physical size operating at conservative temperatures and power ratings.
|
|
Wire Wound Temperature |
Metal Film Temperature |
| 100% | 70oC | 70oC |
| 80% | 110oC | 85oC |
| 60% | 150oC | 100oC |
| 40% | 190oC | 120oC |
| 20% | 240oC | 140oC |
| 10% | 260oC | 145oC |
As these are average guide-lines, they may change with other IC packages.
Resistor Network Manufacturers, Resistor Manufacturers, Potentiometer Manufacturers
There are a number of possible IC packages, this is a guide, always check the data sheet for the device being used. Note the chart above starts to derate at 25C, but only because below 25C the device is being operated at 120% of rated wattage. With any derating curve, this graph applies to still air and it applies to a Fixed Film Resistor Network in a DIP package.
Note the curve shown above relates to MIL-PRF-83401 [Resistor Networks]. The Power Rating for this series is given at an ambient temperature of 700C, so for temperatures below that value the device may be operated above the maximum power rating [above 100 percent]. So at 250C the resistor network may operate at 125% of maximum power.
Derating guidelines for other components; Guideline for Derating Electronic Components
Resistor Network Package Styles, SIP Package Style. Resistor Network Schematics
Key Words: Resistor, Component Derating, reliability, Sizing, Derate, Burned, Network, Curve, Rated Temp, Temperature, Guide, Burning, Guideline, Example, Class, Design.
