CN103293183B - Method for extracting heat capacity and thermal time constant of LED system - Google Patents

Abstract

The invention discloses a novel method and theory for extracting heat capacity and a heat time constant of an LED system, which comprises the following steps: 1) measuring an LED junction temperature curve; 2) reading the time corresponding to the temperature rising to 63.2% of the maximum steady-state temperature in the curve, and recording the time as the thermal time constant tau of the LED device_jc(ii) a 3) Reading the maximum junction temperature and the initial junction temperature in the curve, subtracting the maximum junction temperature and the initial junction temperature from each other, and dividing the difference by the thermal power input by the LED to obtain the thermal resistance R of the LED device_jc(ii) a 4) Dividing the extracted thermal time constant by the extracted thermal resistance to obtain the heat capacity C of the LED device_jc. The invention provides a method and theory for simply and conveniently extracting the integral heat capacity and the integral heat time constant of an LED device. The method can extract the thermal resistance, the thermal capacity and the thermal time constant of the whole device at one time, simplifies the extraction process of the thermal resistance and the thermal capacity of the LED device, and also innovatively provides the extraction process of the thermal time constant of the LED device.

Description

A kind of method extracting LED information display system thermal capacitance and thermal time constant

Technical field

The present invention relates to the parameter extracting method in the design of a kind of LED illumination System and a set of dynamic junction temperature theoretical formula, particularly relate to a kind of novel extraction LED information display system thermal capacitance and the method for thermal time constant and theoretical formula, belong to technical field of LED illumination.

Background technology

The prediction of device performance and the preparation of device are played vital effect by the prediction of the thermal resistance of LED component, thermal capacitance and thermal time constant.Therefore, an important topic during the extraction of the thermal parameter of LED component is current LED illumination System field.Although, current researchers have been proposed for several method, but are not mostly widely recognized as due to its relatively low precision of prediction.At present, being most recognized and use structure function method in numerous methods, the method separates the thermal resistance within LED component and thermal capacitance by the integration on LED heat-transfer path and differential structrue function.

Technological deficiency and deficiency: integration and differential structrue function method process are complicated, and can not disposably draw the overall thermal resistance of device and overall thermal capacitance, the thermal time constant of whole device can not be given.Integration and differential structrue function method are only applicable to predict LED component inner. layers or the thermal resistance of each material and thermal capacitance.And can not disposably provide the thermal resistance of whole device, thermal capacitance and thermal time constant.

Summary of the invention

The technical problem to be solved is to provide disposable extracts LED component entirety thermal capacitance and the method for LED component overall thermal time constant, it is provided that method need simple and feasible, and possess high accuracy.

For solving above-mentioned technical problem, the present invention provides a kind of novel extraction LED information display system thermal capacitance and the method for thermal time constant and a set of theoretical formula, and its feature comprises the following steps:

1) measuring LED component and work in the junction temperature temperature rising curve under firm power, after junction temperature reaches the highest steady temperature, remove the electrical power of LED component, junction temperature temperature starts nature and declines, and now measures junction temperature temperature nature decline curve；

2) reading temperature in this curve and rise to LED component institute's time spent during the 63.2% of the highest steady temperature, this time is designated as the overall thermal timeconstantτ of LED component_jc；

3) maximum steady state junction temperature and initial junction temperature in curve is read, the thermal power that both input divided by LED after subtracting each other again, obtain overall thermal resistance R of LED component_jc；

4) by step 2) in the thermal time constant extracted divided by step 3) in the thermal resistance extracted, obtain overall thermal capacitance C of LED component_jc。

Step 1) in, constant LED sump temperature T_c, supply LED constant electric power P_d, the junction temperature of LED component starts nature and rises.Junction temperature temperature nature ascent stage, the Dynamic Thermal formula of the LED component thermal model of invention:

$\frac{T_j-T_c}{R_{jc}}+c_{jc}\frac{d(T_j-T_c)}{dt}=P_{heat},$

The junction temperature of LED component is at the formula of natural ascent stage:

$T_j=R_{jc}{P}_{heat}(1-e^{-\frac{t}{c_{jc}{R}_{jc}}})+T_c,$

Wherein, time t > 0, T_jFor the junction temperature temperature of LED component, T_cFor the sump temperature of LED component, C_jcFor the overall thermal capacitance of LED component, R_jcFor the overall thermal resistance of LED component, P_heatThe thermal power produced for LED component, wherein, P_heat=k_h*P_d, k_hCoefficient of heat transfer for device.

Step 1) in, after LED junction temperature rises to steady temperature, remove LED power supply, LED junction temperature starts nature and declines, the natural cooling formula of the LED component of invention:

$C_{jc}\frac{d(T_j-T_c)}{dt}+\frac{T_j-T_c}{R_{jc}}=0,$

LED component is at the junction temperature hygrometric formula in natural cooling stage:

$T_j\left(t\right)=\[T_{jss}-T_c\]e^{-\frac{t}{C_{jc}{R}_{jc}}}+T_c,$

Wherein, time t > 0, T_jT () is the junction temperature temperature of LED component, T_cFor the sump temperature of LED component, C_jcFor the overall thermal capacitance of LED component, R_jcFor the overall thermal resistance of LED component, T_jssThe maximum junction temperature temperature reached when firm power drives by LED component.

Step 2) in, extract the inventive method of the overall thermal time constant of LED component: utilize the junction temperature temperature rising curve of LED component, reading temperature and rise to institute's time spent 63.2% time of the highest steady temperature from initial temperature, this time is designated as the overall thermal timeconstantτ of LED component_jc。

Step 3) in, extract the inventive method of the thermal resistance of LED component: utilize LED junction temperature ascending curve, find out its initial temperature and the highest steady temperature, the highest steady temperature is deducted initial temperature, subtract each other result again divided by thermal power P produced by LED component_heat, division result is thermal resistance R of LED component_jc:

Wherein, T_jssFor the highest steady temperature of LED, T_cSump temperature for LED component.

Step 4) in, extract the inventive method of the thermal capacitance of LED component: by step 2) middle thermal time constant τ extracted_jcDivided by step 3) middle thermal resistance R extracted_Jc,Result is overall thermal capacitance C of LED component_jc:

$C_{jc}=\frac{{\mathrm{\τ}}_{jc}}{R_{jc}}.$

The beneficial effect that the present invention is reached:

The present invention gives a kind of extraction LED component entirety thermal capacitance easy and simple to handle and the method for LED component overall thermal time constant, have also been invented a set of analysis LED component Dynamic Thermal behavior and extract the theoretical formula of LED component thermal parameters.This inventive method can disposably draw the thermal resistance of whole device, thermal capacitance and thermal time constant, simplifies the extraction process of LED component thermal resistance and thermal capacitance, also the extraction process proposing LED component thermal time constant of novelty.The theoretical formula of invention is accurate, and the parametric results that invented party puts extraction is accurate.

Accompanying drawing explanation

Fig. 1 is the Dynamic Thermal equivalent model of LED component；

In figure, P_heatThermal power produced by LED component, C_jcFor LED component entirety thermal capacitance, R_jcFor LED component overall thermal resistance, T_jFor the junction temperature of LED component, T_cFor LED component sump temperature.

Detailed description of the invention

The invention will be further described below in conjunction with the accompanying drawings.Following example are only used for clearly illustrating technical scheme, and can not limit the scope of the invention with this.

(1) the extraction way of LED component thermal capacitance and thermal time constant and step:

1) constant LED sump temperature, supplies LED mono-firm power.Then measurement LED is under firm power, the natural uphill process of junction temperature, when junction temperature rises to the highest steady temperature, stops powering to LED, and now junction temperature is by natural cooling, measures the natural cooling process of LED junction temperature.

2) in temperature rising curve, read maximum junction temperature and initial junction temperature, both subtract each other after again divided by the thermal power of input, just obtained the thermal resistance of LED component.The thermal resistance obtained can be used for the extraction that LED heat holds.

3), after obtaining thermal resistance, then from junction temperature ascending curve, the thermal time constant of LED component is extracted.According to the meaning of time constant, junction temperature rises to time point corresponding during the 63.2% of maximum junction temperature, is designated as the thermal time constant of LED component.

4) by the thermal time constant extracted divided by the thermal resistance extracted, the thermal capacitance of LED component has just been obtained.

Generally speaking, the curve risen according to a junction temperature temperature measured or junction temperature nature decline curve, the method just can extract the thermal resistance of LED component, thermal capacitance and thermal time constant.

(2) model during LED component thermal capacitance and thermal time constant are extracted and formula:

1) hot dynamic equivalent model such as Fig. 1: wherein P of LED component_heatThe thermal power produced for LED component, C_jcFor LED component thermal capacitance, R_jcFor LED component thermal resistance, T_jFor the junction temperature of LED component, T_cFor LED component sump temperature.

2) thermal capacitance of LED component and thermal time constant extract formula and the process of extraction:

After LED powers on, thermal power produced by electrical power can flow through the parallel branch of Fig. 1.Analysis chart 1, obtaining Dynamic Thermal formula is:

$\frac{T_j-T_c}{R_{jc}}+C_{jc}\frac{d(T_j-T_c)}{dt}=P_{heat},$ Wherein t > 0 (1)

Obtain the dynamic junction temperature expression formula of LED component junction temperature ascent stage further:

$T_j=R_{jc}{P}_{heat}(1-e^{-\frac{t}{C_{jc}{R}_{jc}}})+T_c,$ Wherein t > 0 (2)

In formula (2), when the time, t tended to infinite, junction temperature arrives steady-state value T_jss, namely maximum.Utilize this maximum, just can represent the expression formula of LED component thermal resistance:

Wherein T_jssMaximum for the junction temperature of LED.

After junction temperature reaches maximum, the constant electric power on LED is removed, now LED start nature make but, analysis chart 1, obtain LED natural cooling formula:

$C_{jc}\frac{d(T_j-T_c)}{dt}+\frac{T_j-T_c}{R_{jc}}=0---\left(4\right)$

Obtain LED component junction temperature hygrometric formula in the natural cooling stage further:

$T_j\left(t\right)=\[T_{jss}-T_c\]e^{-\frac{t}{C_{jc}{R}_{jc}}}+T_c---\left(5\right)$

Thermal time constant τ of LED component_jcExpression formula: τ_jc=C_jcR_jc(6)

According to the physical significance of time constant, in measuring LED temperature ascending curve, reading the time point that temperature rises to the 63.2% of maximum temperature, this time point is the thermal time constant of LED.

Thermal time constant τ of the LED component that recycling finds_jcThermal resistance R divided by LED component_jc, just have found the thermal capacitance of LED component, expression formula is:

$C_{jc}=\frac{{\mathrm{\τ}}_{jc}}{R_{jc}}---\left(7\right)$

Embodiment 1

Below to extract thermal time constant and the thermal capacitance of Philip-LuxeonLED, as a example by LED type number is LXHL-PW01, this method is described and extracts result.

The output power of this LED is 1 watt, drain pan initial temperature T_cIt it is 30 DEG C.After LED junction temperature rises to steady temperature, removing output power, LED junction temperature starts nature and declines.The LED junction temperature ascending curve measured and natural decline curve.From the curve measured, maximum steady state temperature T can be read_jssIt it is 41 DEG C.

So, the thermal resistance of this LED is:Wherein P_heat=k_h*P_d, k_hFor the coefficient of heat transfer of device, for this device, coefficient of heat transfer k_h=0.87, P_dOutput power for LED.

The LED junction temperature measured rises and natural decline curve, according to the method for the extraction thermal time constant that this patent provides, reads temperature and rises to the time point corresponding to 63.2% of maximum temperature.This LEDs has been spent 0.3 second and has just been risen to the 63.2% of peak, therefore, thermal time constant τ of this LED_jcBe 0.3 second, i.e. τ_jc=C_jcR_jc=0.3s.

At present, thermal resistance and thermal time constant it are extracted the most respectively.The thermal capacitance extracting method now provided according to this patent, can calculate thermal capacitance C_jcValue:

At present, the thermal resistance of this device, thermal capacitance and thermal time constant it are extracted the most respectively.These three parameter is now updated to junction temperature temperature rise and naturally decline in formula (2) and (5), verifies the correctness of institute's extracting parameter and formula.

The curve calculated according to formula (8), it can be seen that the curve of calculating and the curve of measurement have reached preferably to coincide.Demonstrate effectiveness and the accuracy of this method, model and theoretical formula.

The above is only the preferred embodiment of the present invention; it should be pointed out that, for those skilled in the art, on the premise of without departing from the technology of the present invention principle; can also make some improvement and deformation, these improve and deformation also should be regarded as protection scope of the present invention.

Claims (5)

1. the method extracting LED information display system thermal capacitance and thermal time constant, is characterized in that, comprises the following steps:

1) measuring LED component and work in the junction temperature temperature rising curve under firm power, after junction temperature reaches the highest steady temperature, remove the power supply electrical power of LED component, junction temperature temperature starts nature and declines, and now measures junction temperature temperature nature decline curve；

2) reading temperature in this curve and rise to LED component institute's time spent during the 63.2% of the highest steady temperature, this time is designated as the overall thermal timeconstantτ of LED component_jc；

3) maximum steady state junction temperature and initial junction temperature in curve is read, the thermal power that both input divided by LED after subtracting each other again, obtain overall thermal resistance R of LED component_jc；

4) by step 2) in the thermal time constant extracted divided by step 3) in the thermal resistance extracted, obtain overall thermal capacitance C of LED component_jc；

Step 1) in, measurement LED component works in the step of the junction temperature temperature rising curve under firm power and is:

Sump temperature T of constant LED component_c, supply LED constant electric power P_d, then measurement LED is under constant electric power, the natural uphill process of junction temperature；The step measuring LED component junction temperature temperature decline curve is: after LED junction temperature rises to steady temperature, remove power supply electrical power, and LED junction temperature starts nature and declines, and measures available LED junction temperature nature decline curve；

Step 1) in, under LED constant electric power drives, the Dynamic Thermal formula that temperature nature ascent stage meets is:

$\frac{T_j-T_c}{R_{jc}}+C_{jc}\frac{d(T_j-T_c)}{dt}=P_{heat},$

The junction temperature hygrometric formula of the LED component of temperature nature ascent stage is:

$T_j=R_{jc}{P}_{heat}(1-e^{-\frac{t}{C_{jc}{R}_{jc}}})+T_c,$

Wherein, time t > 0, T_jFor the junction temperature temperature of LED component, T_cFor the sump temperature of LED component, C_jcFor the overall thermal capacitance of LED component, R_jcFor the overall thermal resistance of LED component, P_heatThe thermal power produced for LED component, wherein, P_heat=k_h*P_d, k_hCoefficient of heat transfer for device.

Extraction LED information display system thermal capacitance the most according to claim 1 and the method for thermal time constant, is characterized in that, step 1) in, after LED electrical power is removed, the natural cooling formula of LED is:

$C_{jc}\frac{d(T_j-T_c)}{dt}+\frac{T_j-T_c}{R_{jc}}=0,$

The LED component junction temperature hygrometric formula in the natural cooling stage is:

$T_j\left(t\right)=\[T_{jss}-T_c\]e^{-\frac{t}{C_{jc}{R}_{jc}}}+T_c,$

Wherein, time t > 0, T_jT () is the junction temperature temperature of LED component, T_cFor the sump temperature of LED component, C_jcFor the overall thermal capacitance of LED component, R_jcFor the overall thermal resistance of LED component, T_jssThe maximum junction temperature temperature reached when firm power drives by LED component.

Extraction LED information display system thermal capacitance the most according to claim 1 and the method for thermal time constant, is characterized in that,

Step 2) in, determination step and the method for the overall thermal time constant of LED component be: by find temperature rise to the highest steady temperature of system 63.2% method determine thermal time constant；Utilizing the junction temperature temperature rising curve of LED component, read temperature and rise to institute's time spent 63.2% time of maximum temperature from initial temperature, this time is designated as the overall thermal timeconstantτ of LED component_jc。

Extraction LED information display system thermal capacitance the most according to claim 1 and the method for thermal time constant, is characterized in that,

Step 3) in, the determination step of the thermal resistance of LED component and method be: utilizes LED junction temperature ascending curve, finds out its initial temperature and the highest steady temperature, the highest steady temperature is deducted initial temperature, subtracts each other result again divided by thermal power P produced by LED component_heat, division result is overall thermal resistance R of LED component_jc, formula is:

Wherein, T_jssFor the highest steady temperature of LED, T_cSump temperature for LED component.

Extraction LED information display system thermal capacitance the most according to claim 1 and the method for thermal time constant, is characterized in that,

Step 4) in, step and method that the thermal capacitance of LED component determines be: by step 2) in thermal time constant τ extracted_jcDivided by step 3) middle thermal resistance R extracted_jc, result is overall thermal capacitance C of LED component_jc, formula is:

$C_{jc}=\frac{{\mathrm{\τ}}_{jc}}{R_{jc}}.$