Research Of LED Thermal Resistance Measurement Theory And Arithmetic Based On Transient Response

With the improvement of luminous efficiency, LED has been applied inmore and more areas. One of the biggest problems that limit the performanceparameter of LED’s further development is that, the higher power will increase thejunction temperature, which raises demand of better heat dissipation potential of thedevice. Thermal resistance and thermal capacity are often used to measure the heatdissipation capability, but ordinary test method can only get the whole thermalresistance of the device. Actually, testers concern more about the thermal resistanceand thermal capacity of each layer inside the device. The issue of this paper is theresearch of thermal resistance measurement theory and arithmetic based on transientresponse. The purpose of the research is to calculate the thermal resistance andthermal capacity without damaging the device. The main research contents are listedbelow:1. Thermal resistance measurement theory based on transient response. The basictheories in thermology and electricity are analyzed first. Three methods of heattransfer, convection, radiation, and thermal conduction, are introduced. As theconcept of thermal resistance network is analogous to resistance network, thus theequivalent circuit model of thermal analysis is also presented. Further more, thenetwork function in electricity is defined based on the incentives image function andresponse image function. At last, an n-stage FOSTER network model is analyzedusing zero state response voltage function. Theoretical analysis has proved thatvoltage response function in electricity and transient temperature response function inthermology has the same expression.2. Research on demodulation arithmetic based on transient thermal response. Thewhole process of the transient resistance measurement is introduced first: thetemperature response function can be calculated from the measured voltage curve, andafter deconvoluted with weighing function, the time constant spectrum is determined;The FOSTER network function is the result of discretization of time constantspectrum. After network function transform, CAUER network function represents thethermal resistance and thermal capacity of real physical structure. The key concepts inthe transient thermal resistance theory are also analyzed and derived, includingjunction temperature and thermal resistance, RC network and time constant, two kinds of structure functions and the time constant spectrum. As the demodulation theory oftransient thermal response is rather complex, two key steps are analyzed separately:deconvolution arithmetic and network model transfer arithmetic. The main theoreticalformulas are derived, and possible improvement is raised aiming on the problem ofnumerical computation.3. Verify the demodulation arithmetic through simulation. First, the equivalent circuitmethod is used: A three-stage resistance and capacity network model is establishedusing the given parameters. Based on the voltage response function of the model, thearithmetic in the previous text is used to calculate the resistance and capacity, and theresults are compared to original data. Second, the sampling data of T3Ster is used asthe original data. The AD sampling result, which is acquired from T3Ster, is used tocalculate the time constant spectrum, network function and thermal resistancefunction model. The outcome of the theoretical calculation is compared to the resultsfrom T3Ster. The two simulations above have all proved the rationality and reliabilityof thermal resistance measurement arithmetic based on transient thermal response.