Analysis of the relationship between resistor operating temperature and power (2)

Functional relationship between resistor temperature rise and time

From the perspective of heating, resistors can be divided into active and passive parts. The active part is the direct heating part - the resistance wire, and the passive part is the heated part - the substrate, filler, protective layer, lead wire, etc. Under the rated power load, the heat generated by the active part is timely transferred to the passive part, so that the temperature of the two parts tends to balance, but the temperature gradually rises to a stable value to achieve normal operation. The passive part is regarded as a constant temperature heat storage, and the active part dissipates heat to the passive part, which is similar to the heat dissipation of the resistor to the surrounding environment under continuous load.

Continuous constant electric power, it can be DC or AC, but not pulsed. When the resistor is just subjected to electric power, the temperature of the resistor body is the same as the ambient temperature. At this time, most of the electric power is used to heat up the resistor body, and the heat dissipation power is very small. As the temperature of the resistor gradually rises, the heat dissipation power gradually increases. When the heat dissipation power is equal to the electric power, the resistor body no longer heats up, and a stable state is reached at this time.

As shown in the figure below: But when the resistor works under continuous power for a period of time and reaches thermal equilibrium, according to the law of conservation of energy: Qdt=Q₁dt+Q₂dt Where: Q represents the heat applied to the resistor by the power supply per unit time, Q₁ represents the heat released to the outside, and Q₂ represents the heat absorbed by the resistor body for every 1°C increase in temperature.