[Source: High-tech LED " LED Good Products" magazine September issue ] LED solid light source has the advantages of high efficiency, long life, flexible application, no pollution, etc., has been widely used in the field of lighting. However, most of the electrical energy consumed by LEDs is converted into thermal energy, which causes the chip temperature to rise significantly, and temperature has an important influence on LED performance, including color temperature change, efficiency degradation, life reduction and reliability. Therefore, improving the thermal management performance of LEDs has become a key technical link in the design of high-power LED structures.
Commonly used LED thermal management analysis techniques include the use of thermal design software simulation and measurement using thermal resistance analysis equipment. The former is often used for thermal management design of LEDs; the latter focuses on thermal resistance measurement and analysis of actual samples to verify the actual effects and product quality of the design, and to improve the manufacturing process or to guide the secondary design.
Basic principle of thermal resistance
The heat dissipation of the LED is carried out in three ways: heat conduction, convection, and heat radiation. Inside the LED, heat conduction is the main heat dissipation path, and its thermal conductivity depends on the thermal impedance of the medium. Thermal impedance is determined by both thermal resistance and heat capacity. The definition of thermal resistance is:
　 Rth = Δt / p.
Where ΔT is the temperature difference, Rth is the thermal resistance, and P is the thermal power.
As shown in Fig. 1, the heat flow corresponds to the current, and the potential corresponds to the temperature, the thermal resistance corresponds to the resistance, and the heat capacity corresponds to the capacitance. For any thermal medium, it can be simplified as an RC parallel circuit:
When heat flows through the media unit, a temperature difference is formed at both ends. Similar to the circuit, the initial heat will accumulate in the heat capacity, and the temperature difference between the two ends will gradually increase until the heat balance is reached. The thermal resistance at this time is usually called the "steady-state thermal resistance". Before the device reaches thermal equilibrium, the junction temperature of the device changes continuously according to the heat capacity and the thermal resistance, and the corresponding thermal resistance also changes with time. The thermal resistance is called “transient thermal resistanceâ€. Measurement of transient thermal resistance is the basis for thermal resistance structure measurements.
>>>Unfinished , please refer to the September issue of Gaogong LED 's " LED Good Products" magazine.
Commonly used LED thermal management analysis techniques include the use of thermal design software simulation and measurement using thermal resistance analysis equipment. The former is often used for thermal management design of LEDs; the latter focuses on thermal resistance measurement and analysis of actual samples to verify the actual effects and product quality of the design, and to improve the manufacturing process or to guide the secondary design.
Basic principle of thermal resistance
The heat dissipation of the LED is carried out in three ways: heat conduction, convection, and heat radiation. Inside the LED, heat conduction is the main heat dissipation path, and its thermal conductivity depends on the thermal impedance of the medium. Thermal impedance is determined by both thermal resistance and heat capacity. The definition of thermal resistance is:
　 Rth = Δt / p.
Where ΔT is the temperature difference, Rth is the thermal resistance, and P is the thermal power.
As shown in Fig. 1, the heat flow corresponds to the current, and the potential corresponds to the temperature, the thermal resistance corresponds to the resistance, and the heat capacity corresponds to the capacitance. For any thermal medium, it can be simplified as an RC parallel circuit:
When heat flows through the media unit, a temperature difference is formed at both ends. Similar to the circuit, the initial heat will accumulate in the heat capacity, and the temperature difference between the two ends will gradually increase until the heat balance is reached. The thermal resistance at this time is usually called the "steady-state thermal resistance". Before the device reaches thermal equilibrium, the junction temperature of the device changes continuously according to the heat capacity and the thermal resistance, and the corresponding thermal resistance also changes with time. The thermal resistance is called “transient thermal resistanceâ€. Measurement of transient thermal resistance is the basis for thermal resistance structure measurements.
>>>Unfinished , please refer to the September issue of Gaogong LED 's " LED Good Products" magazine.
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