CN103293183A - Novel method for extracting heat capacity and thermal time constant of light-emitting diode (LED) system - Google Patents

Abstract

The invention discloses a novel method and a theory for extracting heat capacity and thermal time constant of a light-emitting diode (LED) system. The method comprises the following steps: 1) measuring a temperature curve of the LED junction temperature; 2) reading the corresponding time when the temperature is raised to 63.2 percent of the highest steady state temperature in the curve, and recording the time as the thermal time constant tau jc of the LED device; 3) reading the highest junction temperature and initial junction temperature in the curve, subtracting the two temperatures, dividing the thermal power input by the LED to obtain the thermal resistance Rjc of the LED device; and 4) dividing the extracted thermal resistance by the extracted thermal time constant to obtain the heat capacity Cjc of the LED device. The invention provides a simple and convenient method and theory for extracting the overall heat capacity and the overall thermal time constant of the LED device. According to the method, the thermal resistance, heat capacity and thermal time constant of the whole device can be extracted at one time, the process for extracting the thermal resistance and heat capacity of the LED device is simplified, and the process for extracting the thermal time constant of the LED device is innovatively provided.

Description

The method of a kind of novel extraction LED system's thermal capacitance and thermal time constant

Technical field

The present invention relates to parameter extracting method and the dynamic junction temperature theoretical formula of a cover in a kind of LED illumination system layout, relate in particular to method and the theoretical formula of a kind of novel extraction LED system's thermal capacitance and thermal time constant, belong to the LED lighting technical field.

Background technology

The prediction of the thermal resistance of LED device, thermal capacitance and thermal time constant is played crucial effects to prediction and the preparation of devices of device performance.Therefore, the extraction of the thermal parameter of LED device is an important topic in the present LED field of illumination systems.Though researchers have proposed several method at present, mostly extensively do not approved owing to its lower precision of prediction.At present, approved in numerous methods and what use is the structure function method that the method is separated thermal resistance and the thermal capacitance of LED device inside with the differential structrue function by the integration on the LED heat-transfer path most.

Technological deficiency and deficiency: integration and differential structrue function method process complexity, and can not disposablely draw overall thermal resistance and the whole thermal capacitance of device, can not provide the thermal time constant of entire device.Integration and differential structrue function method only are applicable to thermal resistance and the thermal capacitance of prediction LED each layer of device inside or each material.And can not disposablely provide thermal resistance, thermal capacitance and the thermal time constant of entire device.

Summary of the invention

Technical matters to be solved by this invention provides the method for the whole thermal capacitance of disposable extraction LED device and LED device overall thermal time constant, and the method that provides needs simple and feasible, and possesses high precision.

For solving the problems of the technologies described above, the invention provides method and a cover theoretical formula of a kind of novel extraction LED system's thermal capacitance and thermal time constant, its feature may further comprise the steps:

1) measure the LED device and work in junction temperature temperature rising curve under the firm power, treat that junction temperature reaches the highest steady temperature after, remove the electric power of LED device, the junction temperature temperature begins nature and descends, and measures junction temperature temperature nature decline curve this moment;

2) read that temperature rises to 63.2% o'clock LED device institute's time spent of high steady temperature in this curve, this time is designated as the overall thermal timeconstant of LED device _Jc

3) read maximum steady state junction temperature and initial junction temperature in the curve, again divided by the thermal power of LED input, obtain the overall thermal resistance R of LED device after both subtract each other _Jc

4) with step 2) in the thermal time constant extracted divided by the thermal resistance of extracting in the step 3), obtain the whole thermal capacitance C of LED device _Jc

In the step 1), constant LED sump temperature T _c, supply with the constant electrical power P of LED _d, the junction temperature of LED device begins nature and rises.Junction temperature temperature nature ascent stage, the dynamic hot formula of the LED device thermal model of invention:

$\frac{T_j-T_c}{R_{\mathrm{jc}}}+C_{\mathrm{jc}}\frac{d(T_j-T_c)}{\mathrm{dt}}{P}_{\mathrm{heat}},$

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

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

Wherein, time t〉0, T _jBe the junction temperature temperature of LED device, T _cBe the sump temperature of LED device, C _JcBe the whole thermal capacitance of LED device, R _JcBe the overall thermal resistance of LED device, P _HeatBe the thermal power of LED device generation, wherein, P _Heat=k _h* P _d, k _hCoefficient of heat transfer for device.

In the step 1), after the LED junction temperature rises to steady temperature, remove the LED power supply, the LED junction temperature begins nature and descends, the formula of cooling naturally of the LED device of invention:

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

The LED device is at the junction temperature hygrometric formula of natural cooling stage:

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

Wherein, time t〉0, T _j(t) be the junction temperature temperature of LED device, T _cBe the sump temperature of LED device, C _JcBe the whole thermal capacitance of LED device, R _JcBe the overall thermal resistance of LED device, T _JssThe maximum junction temperature temperature that when firm power drives, reaches for the LED device.

Step 2) in, extract the inventive method of the overall thermal time constant of LED device: the junction temperature temperature rising curve that utilizes the LED device, read temperature and rise to 63.2% o'clock institute's time spent of high steady temperature from initial temperature, this time is designated as the overall thermal timeconstant of LED device _Jc

In the step 3), extract the inventive method of the thermal resistance of LED device: utilize LED junction temperature upcurve, find out its initial temperature and the highest steady temperature, the highest steady temperature is deducted initial temperature, subtract each other the thermal power P that the result produces divided by the LED device again _Heat, the phase division result is the thermal resistance R of LED device _Jc:

Wherein, T _JssBe the highest steady temperature of LED, T _cSump temperature for the LED device.

In the step 4), extract the inventive method of the thermal capacitance of LED device: with step 2) the middle thermal time constant τ that extracts _JcDivided by the thermal resistance R that extracts in the step 3) _Jc, the result is the whole thermal capacitance C of LED device _Jc:

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

The beneficial effect that the present invention reaches:

The present invention has provided a kind of whole thermal capacitance of extraction LED device easy and simple to handle and the method for LED device overall thermal time constant, has also invented a cover and has analyzed the thermal behavior of LED device dynamic and the theoretical formula of extracting LED device thermal parameters.This inventive method can disposablely draw thermal resistance, thermal capacitance and the thermal time constant of entire device, has simplified the leaching process of LED device thermal resistance and thermal capacitance, also the proposition of novelty the leaching process of LED device thermal time constant.The theoretical formula of invention is accurate, and the parameter result that extraction is put in invention side is accurate.

Description of drawings

Fig. 1 is the dynamic hot equivalent model of LED device;

Among the figure, P _HeatBe the thermal power that the LED device produces, C _JcBe the whole thermal capacitance of LED device, R _JcBe LED device overall thermal resistance, T _jBe the junction temperature of LED device, T _cBe LED device sump temperature.

Embodiment

Below in conjunction with accompanying drawing the present invention is further described.Following examples only are used for technical scheme of the present invention more clearly is described, and can not limit protection scope of the present invention with this.

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

1) constant LED sump temperature is supplied with LED one firm power.Measure LED then under firm power, the natural uphill process of junction temperature when junction temperature rises to the highest steady temperature, stops the power supply to LED, and this moment, junction temperature will be cooled off naturally, measured the natural cooling process of LED junction temperature.

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

3) obtain after the thermal resistance, from the junction temperature upcurve, extract the thermal time constant of LED device again.According to the meaning of time constant, junction temperature rises to 63.2% o'clock corresponding time point of maximum junction temperature, is designated as the thermal time constant of LED device.

4) with the thermal resistance of the thermal time constant of extracting divided by extraction, just obtained the thermal capacitance of LED device.

Generally speaking, according to curve or junction temperature nature decline curve that the junction temperature temperature of a measurement rises, the method just can extract thermal resistance, thermal capacitance and the thermal time constant of LED device.

(2) model and the formula in LED device thermal capacitance and the thermal time constant leaching process:

1) dynamically equivalent model such as Fig. 1 of the heat of LED device: P wherein _HeatBe the thermal power that the LED device produces, C _JcBe LED device thermal capacitance, R _JcBe LED device thermal resistance, T _jBe the junction temperature of LED device, T _cBe LED device sump temperature.

2) thermal capacitance of LED device and thermal time constant are extracted formula and leaching process:

After LED powered on, the thermal power that electric power produces can flow through the parallel branch of Fig. 1.Analysis chart 1 obtains dynamic hot formula and is:

$\frac{T_j-T_c}{R_{\mathrm{jc}}}+C_{\mathrm{jc}}\frac{d(T_j-T_c)}{\mathrm{dt}}=P_{\mathrm{heat}},$ T wherein〉0(1)

Further obtain the dynamic junction temperature expression formula of LED device junction temperature ascent stage:

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

In formula (2), when time t was tending towards infinite, junction temperature arrived steady-state value T _Jss, maximal value just.Utilize this maximal value, just can express the expression formula of LED device thermal resistance:

(3), T wherein _JssMaximal value for the junction temperature of LED.

After junction temperature reaches maximal value, the constant electric power on the LED is removed, this moment, LED began the nature order but, and analysis chart 1 obtains the formula that LED cools off naturally:

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

Further obtain the junction temperature hygrometric formula of LED device in natural cooling stage:

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

The thermal time constant τ of LED device _JcExpression formula: τ _Jc=C _JcR _Jc(6)

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

The thermal time constant τ of the LED device that recycling finds _JcThermal resistance R divided by the LED device _Jc, just found out the thermal capacitance of LED device, expression formula is:

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

Embodiment 1

To extract thermal time constant and the thermal capacitance of Philip-Luxeon LED, the LED model is that LXHL-PW01 is example below, this method is described and extracts the result.

The output power of this LED is 1 watt, drain pan initial temperature T _cBe 30 ° of C.After the LED junction temperature rises to steady temperature, remove output power, the LED junction temperature begins nature and descends.From the curve of measuring, can read the maximum steady state temperature T _JssBe 41 ° of C.

Like this, the thermal resistance of this LED is:

P wherein _Heat=k _h* P _d, k _hBe 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 that returns measurement rises and natural decline curve, and the method for the extraction thermal time constant that provides according to this patent reads the 63.2% corresponding time point that temperature rises to maximum temperature.This LEDs has been spent 0.3 second and has just been risen to 63.2% of mxm., therefore, and the 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 have been extracted respectively.Now the thermal capacitance extracting method that provides according to this patent can calculate thermal capacitance C _JcValue:

At present, thermal resistance, thermal capacitance and the thermal time constant of this device have been extracted respectively.Now these three parameters are updated in the rising of junction temperature temperature and natural decline formula (2) and (5), verify the correctness of institute's extracting parameter and formula.

According to the curve that formula (8) calculates, that can see the curve of band round dot of calculating and measurement has reached desirable coincideing with leg-of-mutton curve.Validity and the accuracy of this method, model and theoretical formula have been proved.

The above only is preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the technology of the present invention principle; can also make some improvement and distortion, these improvement and distortion also should be considered as protection scope of the present invention.

Claims (7)

1. the method for novel extraction LED system's thermal capacitance and thermal time constant is characterized in that method is easy, the result is accurate, may further comprise the steps:

1) measure the LED device and work in junction temperature temperature rising curve under the firm power, treat that junction temperature reaches the highest steady temperature after, remove the power supply electric power of LED device, the junction temperature temperature begins nature and descends, and measures junction temperature temperature nature decline curve this moment;

2) read that temperature rises to 63.2% o'clock LED device institute's time spent of high steady temperature in this curve, this time is designated as the overall thermal timeconstant of LED device _Jc

3) read maximum steady state junction temperature and initial junction temperature in the curve, again divided by the thermal power of LED input, obtain the overall thermal resistance R of LED device after both subtract each other _Jc

4) with step 2) in the thermal time constant extracted divided by the thermal resistance of extracting in the step 3), obtain the whole thermal capacitance C of LED device _Jc

2. the method for novel extraction LED system's thermal capacitance according to claim 1 and thermal time constant is characterized in that,

In the step 1), the step that measurement LED device works in the junction temperature temperature rising curve under the firm power is:

The sump temperature T of constant LED device _c, supply with the constant electrical power P of LED _d, measure LED then under constant electric power, the natural uphill process of junction temperature.The step of measuring LED device junction temperature temperature decline curve is: after the LED junction temperature rises to steady temperature, remove the power supply electric power, the LED junction temperature begins nature and descends, and measurement can obtain LED junction temperature nature decline curve.

3. the method for novel extraction LED system's thermal capacitance according to claim 2 and thermal time constant is characterized in that, in the step 1), the constant electric power of LED drives down, and the dynamic hot formula that temperature nature ascent stage satisfies is:

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

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

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

Wherein, time t〉0, T _jBe the junction temperature temperature of LED device, T _cBe the sump temperature of LED device, C _JcBe the whole thermal capacitance of LED device, R _JcBe the overall thermal resistance of LED device, P _HeatBe the thermal power of LED device generation, wherein, P _Heat=k _h* P _d, k _hCoefficient of heat transfer for device.

4. according to the method for any described novel extraction LED system's thermal capacitance and thermal time constant in the claim 1 to 3, it is characterized in that in the step 1), after the LED electric power was removed, the formula of cooling naturally of LED was:

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

The LED device at the junction temperature hygrometric formula of natural cooling stage is:

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

Wherein, time t〉0, T _j(t) be the junction temperature temperature of LED device, T _cBe the sump temperature of LED device, C _JcBe the whole thermal capacitance of LED device, R _JcBe the overall thermal resistance of LED device, T _JssThe maximum junction temperature temperature that when firm power drives, reaches for the LED device.

5. the method for novel extraction LED system's thermal capacitance according to claim 1 and thermal time constant is characterized in that,

Step 2) in, definite step and the method for the overall thermal time constant of LED device are: by seek temperature rise to system 63.2% method of high steady temperature determine thermal time constant; Utilize the junction temperature temperature rising curve of LED device, read temperature and rise to 63.2% o'clock institute's time spent of maximum temperature from initial temperature, this time is designated as the overall thermal timeconstant of LED device _Jc

6. the method for novel extraction LED system's thermal capacitance according to claim 1 and thermal time constant is characterized in that,

In the step 3), definite step and the method for the thermal resistance of LED device are: utilize LED junction temperature upcurve, find out its initial temperature and the highest steady temperature, the highest steady temperature is deducted initial temperature, subtract each other the thermal power P that the result produces divided by the LED device again _Heat, the phase division result is the overall thermal resistance R of LED device _Jc, formula is:

Wherein, T _JssBe the highest steady temperature of LED, T _cSump temperature for the LED device.

7. the method for novel extraction LED system's thermal capacitance according to claim 1 and thermal time constant is characterized in that,

In the step 4), step and method that the thermal capacitance of LED device is determined are: with step 2) the middle thermal time constant τ that extracts _JcDivided by the thermal resistance R that extracts in the step 3) _Jc, the result is the whole thermal capacitance C of LED device _Jc, formula is:

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

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