Enter the ambient temperature, the rated/reference temperature (where the device is at 100% rating), and the maximum allowable temperature into the calculator to determine a simplified linear temperature derating factor for electronic components.
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Derating Factor Formula (Linear Temperature Derating)
The following formula is used to calculate a simplified linear temperature derating factor (the fraction of nominal rating that is allowable between a rated/reference temperature and a maximum allowable temperature):
DF = \frac{T_{max} - T_{ambient}}{T_{max} - T_{rated}}Variables:
- DF is the derating factor (unitless, typically between 0 and 1)
- T_max is the maximum allowable temperature (°C)
- T_ambient is the ambient temperature (°C)
- T_rated is the rated/reference temperature where the device is at 100% of its nominal capacity (°C)
To calculate the derating factor for linear derating, subtract the ambient temperature from the maximum allowable temperature and then divide by the temperature span between the maximum allowable temperature and the rated/reference temperature. In many datasheets, the rating is constant (DF = 1) at or below T_rated and derates down to DF = 0 at T_max.
What is a Derating Factor?
A derating factor is a coefficient used in engineering to reduce the nominal operating capacity of a device when it is subjected to certain conditions, such as elevated temperatures. It is a safety measure to prevent overloading electronic components when they operate in environments warmer than their optimal temperature range. The derating factor is used to calculate a safe operating capacity to enhance the longevity and reliability of electronic components.
How to Calculate Derating Factor?
The following steps outline how to calculate the Derating Factor.
- First, determine the maximum allowable temperature (T_max) of the device (often specified by the datasheet as a maximum ambient/case/junction temperature, depending on the part).
- Next, determine the rated/reference temperature (T_rated) where the device can operate at 100% of its nominal capacity (for example, many resistors are rated at 70°C ambient; many photovoltaic ratings reference 25°C cell temperature).
- Then, determine the ambient temperature (T_ambient) where the device will operate.
- Use the formula DF = (T_max – T_ambient) / (T_max – T_rated) to calculate the derating factor for linear derating between T_rated and T_max.
- Finally, apply the derating factor to the device’s nominal capacity to estimate a safe operating capacity under the given conditions (Safe capacity ≈ Nominal capacity × DF).
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem:
Use the following variables as an example problem to test your knowledge.
maximum allowable temperature (T_max) = 150°C
ambient temperature (T_ambient) = 35°C, rated/reference temperature (T_rated) = 25°C. Derating factor: DF = (150 − 35) / (150 − 25) = 115 / 125 = 0.92.
