How to calculate the temperature rise of power resistor? Detailed explanation of the calculation method of temperature rise of power resistor

In electronic circuit design and applications, powerresistanceIt is an important component that carries current and consumes power. Power resistors generate heat during operation, causing their temperature to rise. Excessive temperature rise may affect the performance and life of the resistor. Therefore, accurate calculation of the temperature rise of the power resistor is crucial to ensure the stable operation of electronic equipment. This article will systematically explain the calculation formula of power resistor temperature rise and related influencing factors to help engineers and technicians better understand and apply this key parameter.

1. Basic concept of temperature rise of power resistor

The temperature rise of a power resistor refers to the rise in temperature of the resistor relative to the ambient temperature when the resistor generates power through current. Usually represented by ΔT, the unit is degrees Celsius (℃). The amount of temperature rise depends on the power dissipated by the resistor and the heat dissipation conditions between the resistor and the environment.

2. Calculation formula for temperature rise of power resistor

The basic formula for calculating the temperature rise of a power resistor is:

ΔT = P × Rth

in:

ΔT: temperature rise, unit is °C;

P: The power consumed by the resistor, in watts (W);

Rth: thermal resistance, unit is ℃/W.

The formula states that temperature rise is equal to power multiplied by thermal resistance. Thermal resistance is a parameter that measures the heat dissipation ability of a power resistor. The smaller the value, the better the heat dissipation effect and the lower the temperature rise.

3. Power calculation method of power resistor

Power P can be calculated through Ohm's law and the power formula:

P = I² × R or P = V² / R

in:

I is the current, the unit is ampere (A);

V is voltage, unit is volt (V);

R is the resistance value in ohms (Ω).

According to the specific circuit conditions, choose the appropriate formula to calculate the resistor power.

4. Types and influencing factors of thermal resistance Rth

Thermal resistance Rth is a key parameter in temperature rise calculation, which usually includes the following:

1. Thermal resistance of the resistor itself (junction to case thermal resistance, Rth(jc))

2. Thermal resistance from case to radiator (Rth(cs))

3. Thermal resistance from heat sink to environment (Rth(sa))

The total thermal resistance is:

Rth = Rth(jc) + Rth(cs) + Rth(sa)

Thermal resistance is affected by the resistor material, construction, mounting method, and ambient temperature and air flow conditions.

5. Effect of ambient temperature on temperature rise

The actual operating temperature of the power resistor is:

T = T_ambient + ΔT

Where T_ambient is the ambient temperature. The higher the ambient temperature, the higher the operating temperature of the resistor, which may cause performance degradation or damage. Therefore, the temperature rise must be evaluated in conjunction with the ambient temperature when calculating the temperature rise.

6. Adjustment of temperature rise by heat dissipation conditions

The heat dissipation conditions directly affect the thermal resistance value, for example:

Natural air cooling and heat dissipation: large thermal resistance and high temperature rise;

Forced air cooling or water cooling: The thermal resistance is small and the temperature rise decreases;

Install a heat sink: effectively reduce thermal resistance and improve heat dissipation efficiency.

Properly designed heat dissipation solutions can help control temperature rise and extend the life of power resistors.

7. Practical application of power resistor temperature rise calculation

In actual design, engineers need to select appropriate power resistors and calculate the temperature rise based on load conditions and usage environment to ensure that the temperature does not exceed the rated temperature of the resistor. If necessary, reduce the temperature rise by installing a radiator or improving heat dissipation conditions to ensure the safety and stability of the circuit.

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The calculation of the temperature rise of the power resistor mainly depends on the power consumption and thermal resistance parameters. The temperature rise can be quickly estimated through the formula ΔT = P × Rth. Understanding and mastering the impact of factors such as power, resistance value, thermal resistance, and ambient temperature on temperature rise is crucial to designing efficient and reliable electronic equipment. Reasonable temperature rise calculation and heat dissipation design not only ensure the stable operation of the power resistor, but also extend its service life and improve the overall system performance. I hope this article can help readers fully understand the calculation method of power resistor temperature rise and provide valuable reference for engineering design.