CN101430223B - LED instantaneous light flux test method and apparatus in PWM activation technology - Google Patents

LED instantaneous light flux test method and apparatus in PWM activation technology Download PDF

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Publication number
CN101430223B
CN101430223B CN2008102007531A CN200810200753A CN101430223B CN 101430223 B CN101430223 B CN 101430223B CN 2008102007531 A CN2008102007531 A CN 2008102007531A CN 200810200753 A CN200810200753 A CN 200810200753A CN 101430223 B CN101430223 B CN 101430223B
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China
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led
luminous flux
measured
signal
pwm pulse
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CN101430223A (en
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钱雯磊
王峰
李抒智
杨卫桥
王康平
马可军
李筠
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SHANGHAI RESEARCH CENTER OF ENGINEERING AND TECHNOLOGY FOR SOLID-STATE LIGHTING
University of Shanghai for Science and Technology
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SHANGHAI RESEARCH CENTER OF ENGINEERING AND TECHNOLOGY FOR SOLID-STATE LIGHTING
University of Shanghai for Science and Technology
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Priority to CN2008102007531A priority Critical patent/CN101430223B/en
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01JMEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRA-RED, VISIBLE OR ULTRA-VIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00Photometry, e.g. photographic exposure meter
    • G01J1/42Photometry, e.g. photographic exposure meter using electric radiation detectors
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01JMEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRA-RED, VISIBLE OR ULTRA-VIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00Photometry, e.g. photographic exposure meter
    • G01J1/42Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J2001/4247Photometry, e.g. photographic exposure meter using electric radiation detectors for testing lamps or other light sources
    • G01J2001/4252Photometry, e.g. photographic exposure meter using electric radiation detectors for testing lamps or other light sources for testing LED's

Abstract

The invention discloses a test method of instantaneous luminous flux of an LED based on a PWM drive technology and a device thereof, and belongs to the measurement field. The method comprises the following steps: measuring the luminous flux of the LED to be tested by an integrating sphere method, providing an acquisition system which consists of a signal acquisition part, a signal conversion part and a data processing part in addition to a conventional spectral analysis system and a conventional spectral analysis device, measuring the instantaneous luminous flux of the LED to be tested under the PWM pulse drive, and multiplying the duty ratio of a PWM pulse signal with the instantaneous luminous flux to obtain the average luminous flux of the LED to be tested under the PWM pulse drive. The method is based on the existing test equipment, does not deviate from the traditional test methods, does not cause new near-field absorption, can respond to instantaneous peak signals of the pulse drive, helps measure the instantaneous luminous flux of the LED under heat equilibrium condition, and can help realize the dynamic measurement when the pulse drive power changes. The method and the device can be widely used in the fields of performance tests and the calibration of various LEDs and/or PWM pulse drive devices.

Description

The method of testing and the device of the instantaneous luminous flux of LED under a kind of PWM Driving technique
Technical field
The invention belongs to fields of measurement, relate in particular to a kind of method of testing and device thereof that is used for light source luminescent intensity.
Background technology
LED (Light Emitting Diode, light emitting diode) as a kind of emerging light source device, in recent years, earth-shaking variation has all taken place in its chip structure, packing forms, type of drive and application, each big manufacturer, company and research institution, research to LED is in the ascendant, and its research emphasis is placed on the aspects such as luminous intensity, glow frequency (colourity), luminance purity (frequency spectrum) and luminescence efficiency of improving led light source more
The raising or the improvement of These parameters (the particularly index of optical property aspect), except having the much relations, providing the source with the luminous energy of LED with the structure of luminescent device self, material (or component) etc.---driving circuit (also claiming type of drive) also has extremely confidential relation.
Usually, the type of drive of LED mainly contains three kinds of constant voltage driving, constant-current driving and pulsed drive (referring to that mainly PWM drives).
Among the above-mentioned driving side, preceding two kinds is that stable state drives, and the voltage at LED two ends or the electric current that flows through LED do not change in time; The third is that transient state drives, and the driving voltage of LED or electric current all can change in time and change, and thus, its characteristics of luminescence also can drive difference to some extent with stable state.
The colourity of the light that LED sent can change along with the electric current by its luminescent device, still, in many application scenarios or purposes (as liquid crystal panel backlight, automobile instrument panel backlight etc.), all can not allow LED that the drift of any color takes place.
Because PWM (Pulse Width Modulation, width modulation) Driving technique can be by regulating driving pulse dutycycle (total amount of turn-on time) control LED brightness under full current drives, realize the specific (special) requirements that light modulation is not mixed colours, so extremely wide application prospect is arranged.
Since the PWM Driving technique has huge using value, just need carry out necessary correlative study to this type of drive.
Measuring the luminous flux of luminescent device, is one of important means that LED luminescent device or driving circuit performance index are estimated.
The luminous energy summation that luminophor sent in the unit interval is called luminous flux phi V, its scale visible light is to describe the important parameter of light source characteristic and the important indicator of evaluation light source performance to the visual stimulus degree of human eye.
Measure the total light flux Φ of general conventional light source, adopt relative measurement method and distribution photometry (or claiming the absolute method of measurement) usually.Its concrete grammar can number be SJ2355.6-1983 " method of testing of light emitting semiconductor device method of testing luminous flux " referring to industry standard, and its particular content is no longer narrated at this.
The day for announcing is on February 6th, 2008, Granted publication number a kind of for disclosing in the Chinese utility model patent of CN201016843Y " adopting the proving installation of the LED luminous flux of arrow beam of light standard sources ", it comprises integrating sphere, light source, the optical fiber of narrow clear aperature, micro spectral instrument and light source, power supply is connected with light source and the some bright light source, arrow beam of light standard sources (luminous flux standard and spectroscopic standard light source) is positioned over the integrating sphere inside surface, no any blocking in the ball, optical fiber by narrow clear aperature will be guided to the miniature multi-channel spectral instrument by photometry, carry out spectral power distribution and test also and then calculate luminous flux, realize precision measurement luminous flux.
Open day is on February 6th, 2008, publication number is to disclose " a kind of LED light flux testing method " in the application of CN101118178A Chinese invention patent, it is fixed on LED with anchor clamps the bottom of reflector, the LED light emission direction points to the big opening of reflector, lumen meter closely is fixed on the big opening of reflector to accept light signal.Use the constant-current supply driving LED, the total light flux that LED sends is assembled the total light flux value was collected, measures and finally provide in the back by lumen meter reading by reflector.
It should be noted that above-mentioned industry standard or patent and patent application document,, do not see the method for testing that is applicable to the instantaneous luminous flux of LED under the PWM type of drive and the report of device as yet all at constant voltage driving or constant current drive mode.
In the world, IEC (International Electro Technical Commission, International Electrotechnical Commission) only stipulates, " to the measurement (flashing rate is at 113-512Hz) of flash of light LED; the rise time of optical sensor should be enough little; and should be able to read the peak value of pulse ", the not mentioned problem how accurately to measure.
In addition, the Blondel-Rey method of the Flash lamps and lanterns luminous intensity measurement that generally adopts in the present industry, can be used for the single duration is the flash pulse luminous intensity measurement of 1ms~3s.The computing formula of its efficient intensity Ie is:
I e = ∫ t 1 t 2 I ( t ) dt a + ( t 2 - t 1 ) , (formula 1-1)
A=0.2s wherein.In China's industry standard, t1 and t2 are chosen as 1/3 largest light intensity place, i.e. the light pulse duration is adopted the width between 1/3 peak value.
And it is found that in actual applications when the pulsed light sequence, the result of calculation of this method is unreasonable, so correction formula is arranged:
I e = ∫ t 1 ta I ( t ) dt + ∫ tb t 2 I ( t ) dt a + ( t 2 - t 1 ) , (formula 1-2)
The selection cotype 1-1 of a and t1, t2 in the formula.
Above-mentioned two kinds of methods all need to measure pulse waveform accurately, and are higher to the hardware circuit performance requirement, find the solution integral equation again, need by computing machine, so processing speed is slow, are not easy to realize; And work as the duration of pulse very in short-term, measurement result is also inaccurate.Especially the measurement of single flash operation pulse is under the thermal nonequilibrium condition at the LED device and carries out, and the condition of this and LED practical application greatly differs from each other, and its measurement result also is difficult to provide effective reference for the continuous working situation.
This shows, convert the method for luminous flux more as calculated to and be not suitable for the peak light flux measurement of pwm pulse driving LED by the light intensity of measuring flash pulse.
To sum up, existing standard or regulation can't satisfy the measurement demand of the instantaneous luminous flux of LED under the PWM type of drive, and the disappearance of dependence test method and testing tool is brought very big inconvenience to research work.
Summary of the invention
Technical matters to be solved by this invention provides the method for testing and the device of the instantaneous luminous flux of LED under a kind of PWM Driving technique, it is based on existing testing apparatus, do not cause that new near field absorbs, do not deviate from conventional test methodologies, and the instantaneous peak value signal that the energy response impulse drives, the instantaneous luminous flux of measurement LED under thermal equilibrium condition, and the kinetic measurement can realize the pulsed drive variable power time.
Technical scheme of the present invention is: the method for testing that the instantaneous luminous flux of LED under a kind of PWM Driving technique is provided, comprise and adopt the integrating sphere method that the luminous flux of LED to be measured is measured, it is characterized in that: on the basis of conventional spectroscopic analysis system device, one cover is set by the acquisition system that signals collecting part, conversion of signals part and data processing division are grouped into again, according to following step the luminous flux of LED to be measured is measured then:
(A) measure the preparatory stage:
(a1) adopt conventional method that the integrating sphere luminous flux is calibrated;
(a2) in the linear working range of LED to be measured, choose at least 5 drive current points, it is luminous to adopt the constant current source mode to drive LED to be measured, collects the luminous flux numerical value [Φ of one group of correspondence 0];
(a3) probe and the annex of acquisition system signals collecting part are put into integrating sphere;
(a4) adopt the drive current point identical with step (a2), it is luminous to adopt the constant current source mode to drive LED to be measured, obtains the photoelectricity flow valuve [I] of one group of correspondence by acquisition system;
(a5) be horizontal ordinate with photoelectricity flow valuve [I], luminous flux numerical value [Φ corresponding with it 0] be ordinate, the variation relation curve of in rectangular coordinate system, draw luminous flux and photocurrent;
(a6) adopt least square fitting to obtain above-mentioned variation relation slope of a curve k;
(B) the actual measurement stage:
(b1) determine pwm pulse drive source duty of ratio Q;
(b2) under this dutycycle operational factor, adopt pwm pulse to drive LED to be measured, the peak light current value I of correspondence during to the pwm pulse peak point current by acquisition system LpMeasure;
(b3), determine that pwm pulse drives the instantaneous luminous flux phi of LED to be measured down according to following formula p:
φ p=k×I Lp
Wherein, Φ pFor pwm pulse drives the instantaneous luminous flux of LED to be measured down, k is the slope of luminous flux and photocurrent variations relation curve, I LpFor pwm pulse drives the peak light electric current of LED to be measured down;
(b4) calculate according to following formula, can obtain the average flux of LED to be measured:
φ avg=φ p×Q=k×I Lp×Q
Wherein, Φ AvgFor pwm pulse drives the average flux of LED to be measured down, Φ pFor pwm pulse drives the instantaneous luminous flux of LED to be measured down, Q is the dutycycle of pwm pulse signal, I LpFor pwm pulse drives the peak light electric current of LED to be measured down, k is the slope of luminous flux and photocurrent variations relation curve.
Further, described LED to be measured is arranged at the sphere center position of integrating sphere; Light/the electric transducer of described acquisition system signals collecting part is provided with over against LED to be measured, is used to receive the direct light that LED to be measured sends.
The oblique sphere center position that is arranged at integrating sphere of described LED to be measured.
Further, the oblique sphere center position that is arranged at integrating sphere up or down of described LED to be measured.
Particularly, described pwm pulse drives the instantaneous luminous flux phi of LED to be measured down p, for pwm pulse drives the luminous flux that LED to be measured down exports when the Maximum Peak Impulse Current, it equals the slope k of luminous flux and photocurrent variations relation curve and the peak light electric current I of the following LED to be measured of pwm pulse driving LpProduct
Described pwm pulse drives the average flux Φ of LED to be measured down Avg, equal pwm pulse and drive the instantaneous luminous flux phi of LED to be measured down pProduct with the dutycycle Q of pwm pulse signal.
Perhaps, pwm pulse drives the average flux Φ of LED to be measured down Avg, the corresponding with it peak light electric current I of acquisition system photodetector when equaling slope k, the pwm pulse peak point current of luminous flux and photocurrent variations relation curve LpAnd the product of the dutycycle Q of pwm pulse signal.
In described acquisition system, its signals collecting is partly finished the conversion of light signal to electric signal; Its conversion of signals part becomes simulating signal behind the A/D unscented transformation can and finish data for the digital signal of Computer Processing and send task; Its data processing section is realized corresponding computing and Presentation Function, and provides a personal-machine mutual friendly operation interface.
The pwm pulse drive signal response frequency scope of described acquisition system is 50Hz~200Hz; The response speed of the light/electric transducer of described acquisition system signals collecting part is the ns level.
The pwm pulse drive signal response frequency scope of described acquisition system is 50Hz~200Hz; The response speed of the light/electric transducer of described acquisition system signals collecting part is the ns level.
Described drive current point uniformly-spaced or unequal interval be distributed in the linear working range of LED to be measured.
Further, described drive current point is 7~11, and described each drive current point equally spaced is distributed in the linear working range of LED to be measured.
The present invention also provides the proving installation of the instantaneous luminous flux of LED under a kind of PWM Driving technique, comprise the conventional spectral analysis device that is made of integrating sphere, spectroscopic analysis system controller and PC, LED to be measured and its driving power, it is characterized in that: the sphere center position at integrating sphere is provided with LED to be measured; The two ends of LED to be measured are connected with the output terminal of PWM driving power; On the basis of conventional spectral analysis device, be provided with again that a cover is connected with a data processing unit successively by a signal gathering unit, signal conversion unit at least and the acquisition system that constitutes; Described signal gathering unit is finished the conversion of light signal to electric signal; Described signal conversion unit becomes simulating signal behind the A/D unscented transformation can and finish data for the digital signal of Computer Processing and send task; Described data processing unit is realized corresponding computing and Presentation Function, and a friendly operation interface that people/machine is mutual is provided.
Further, the oblique sphere center position that is positioned over integrating sphere up or down of described LED to be measured.
Light/the electric transducer of described acquisition system signal gathering unit is provided with over against LED to be measured.
Concrete, described signal gathering unit is light/electrical signal conversion circuit, it comprises light/electric transducer, first resistance, second resistance, first electric capacity and second electric capacity at least, wherein, the positive pole of light/electric transducer is connected with an end and the earth terminal of first resistance, first electric capacity, second electric capacity respectively; The negative pole of light/electric transducer is connected with the other end and the power end of first resistance, first electric capacity, is connected through the other end of second resistance with second electric capacity simultaneously; The two ends of second electric capacity, the signal output part of formation signal gathering unit.
Described signal conversion unit comprises signal amplification circuit, A/D change-over circuit and the RS232 level shifter interface circuit that connects successively at least.
Described signal amplification circuit comprises the 3rd to the 8th resistance, the 3rd to the 5th electric capacity and first, second discharge circuit at least, wherein, the 3rd, the 4th resistance is serially connected in respectively between the positive and negative input end of the signal input part of signal amplification circuit and first discharge circuit; The 5th resistance and the 3rd electric capacity are connected in parallel between the negative input end and output terminal of first discharge circuit; The 6th resistance string is connected between the negative input end of the output terminal of first discharge circuit and second discharge circuit; The 7th resistance and the 4th electric capacity are connected in parallel between the negative input end and output terminal of second discharge circuit; The 8th resistance string is connected between the signal output part of the output terminal of second discharge circuit and signal amplification circuit; The 5th electric capacity is connected in parallel between the output and ground of second discharge circuit.
Described RS232 level shifter interface circuit comprises single-chip microcomputer, the 6th to the 11 electric capacity and the attachment plug of RS232 port at least, and wherein, corresponding connection is distinguished with C1+, C1-, C2+, the C2-pin of single-chip microcomputer successively in the two ends of the 6th, the 7th electric capacity; The T1IN of single-chip microcomputer, R1OUT, T2IN and R2OUT pin are distinguished corresponding the connection with TX, RX, RTS and the CTS function terminal of A/D change-over circuit successively; The T1OUT of single-chip microcomputer, R2IN, R2IN and T2OUT pin, successively with XRX, the XRTX of A/D change-over circuit, XTS and XCTS function terminal corresponding connection respectively, the while is distinguished corresponding the connection with 2,7,3 of RS232 port attachment plug with 8 pins successively; The the 8th and the 11 electric capacity is attempted by between power end and the earth terminal; The the 9th and the tenth electric capacity, corresponding connection between the V+ of single-chip microcomputer, V-pin and earth terminal respectively successively.
Described data processing unit is a PC.
Compared with the prior art, advantage of the present invention is:
1. based on existing method of testing and equipment, do not cause that new near field absorbs, not opposing with conventional test methodologies;
2. the instantaneous peak value signal that can response impulse drives can be measured the instantaneous luminous flux of LED under thermal equilibrium condition, and the kinetic measurement can realize the pulsed drive variable power time.
Description of drawings
Fig. 1 is a method of testing process flow diagram of the present invention;
Fig. 2 is that hardware system of the present invention constitutes synoptic diagram;
Fig. 3 is the acquisition system electrical block diagram;
Fig. 4 is a signal gathering unit embodiment circuit diagram;
Fig. 5 is a signal conversion unit signal amplification circuit embodiment circuit diagram;
Fig. 6 is a signal conversion unit RS232 level shifter interface circuit embodiments circuit diagram;
Fig. 7 is the workflow diagram of data processing unit;
Fig. 8 is constant-current driving LED detector photocurrent and luminous flux corresponding relation curve map;
Fig. 9 is the graph of a relation of pwm pulse driving LED average flux and dutycycle.
1 is integrating sphere among the figure, 2 is the spectroscopic analysis system controller, and 3 is PC, and 4 is the luminous flux probe of spectral analysis device, 5 is LED to be measured, 6 is baffle plate, and 7 is the light/electric transducer of acquisition system, and 8 is the PWM driving power, 9 is acquisition system, A is a signal gathering unit, and B is a signal conversion unit, and C is a data processing unit.
Embodiment
The present invention will be further described below in conjunction with drawings and Examples.
Among Fig. 1, provided the testing process of this method of testing.
From the aforesaid background technology of the application as can be known, because the pulse drive mode of LED is compared with the stable state type of drive, exist and leak the problem of adopting aspects such as phenomenon in frequency difference and unit interval, measure so existing two kinds of measuring methods all can not be directly used in the photoelectric parameter of pulsed drive LED.
But for the limitation of stable state driving LED measuring method in the measurement of pwm pulse driving LED, if can improve the response speed of light/electric transducer, be that dt is enough little at interval, suitably adjust the definition of measurement of correlation parameter again, be aided with certain measurement and data processing method, also can satisfy the needs of the instantaneous luminous flux test of pulsed drive LED.
Pulsed drive LED is under the constant situation of drive current peak value, if change dutycycle, the electric power of input will change, and " the instantaneous peak value luminous flux " that obtain this moment is only relevant with the drive current peak value, does not reflect the variation of dutycycle.So can embody the difference of signal dutyfactor under the constant situation of peak value with " average flux under the pwm pulse driving " one side, also can be convenient on the other hand make comparisons with traditional " luminous flux ".
Because the pulse width of pulse current is generally decided by the mean flow rate that will export.For square wave, the product of peak inrush current and dutycycle is the average current of LED; The brightness of exporting when peak inrush current and the product of dutycycle are exactly its average output brightness.Similarly, we can obtain following notion:
The luminous flux that LED exported when peak inrush current under pwm pulse drove is called the instantaneous luminous flux of LED under the pwm pulse driving; The product of it and pulse signal dutycycle is the average flux of LED under pwm pulse drives;
According to above-mentioned notion and analysis, can obtain the measuring method that the application proposes, it comprises the following steps: at least
1) on the basis of conventional spectroscopic analysis system device, the acquisition system that a cover is grouped into by signals collecting part, conversion of signals part and data processing division is set again;
2) adopt conventional method that the integrating sphere luminous flux is calibrated;
3) in the linear working range of LED to be measured, choose at least 5 drive current points, it is luminous to adopt the constant current source mode to drive LED to be measured, collects the luminous flux numerical value [Φ of one group of correspondence 0];
4) probe and the annex of acquisition system signals collecting part are put into integrating sphere;
5) adopt the drive current point identical with step 3), it is luminous to adopt the constant current source mode to drive LED to be measured, obtains the photoelectricity flow valuve [I] of one group of correspondence by acquisition system;
6) be horizontal ordinate with photoelectricity flow valuve [I], luminous flux numerical value [Φ corresponding with it 0] be ordinate, the variation relation curve of in rectangular coordinate system, draw luminous flux and photocurrent;
7) adopt least square fitting to obtain above-mentioned variation relation slope of a curve k;
8) determine pwm pulse drive source duty of ratio Q;
9) under this dutycycle operational factor, adopt pwm pulse to drive LED to be measured, the peak light current value I of correspondence during to the pwm pulse peak point current by acquisition system LpMeasure;
10) slope k and the pwm pulse with luminous flux and photocurrent variations relation curve drives the peak light electric current I of LED to be measured down LpMultiply each other, obtain pwm pulse and drive the instantaneous luminous flux phi p of LED to be measured down;
11) the instantaneous luminous flux phi p of LED to be measured and the dutycycle Q of pwm pulse signal under the pwm pulse driving are multiplied each other, obtain pwm pulse and drive the average flux Φ avg of LED to be measured down.
Particularly, pwm pulse drives the instantaneous luminous flux phi of LED to be measured down p,, equal the slope k of luminous flux and photocurrent variations relation curve and the peak light electric current I of the following LED to be measured of pwm pulse driving for pwm pulse drives the luminous flux that LED to be measured down exports when the Maximum Peak Impulse Current LpProduct.
Pwm pulse drives the average flux Φ of LED to be measured down Avg, equal pwm pulse and drive the instantaneous luminous flux phi of LED to be measured down pProduct with the dutycycle Q of pwm pulse signal.
Perhaps, pwm pulse drives the average flux Φ of LED to be measured down Avg, the corresponding with it peak light electric current I of acquisition system photodetector when equaling slope k, the pwm pulse peak point current of luminous flux and photocurrent variations relation curve LpAnd the product of the dutycycle Q of pwm pulse signal.
The actual measurement formula, the oblique sphere center position that is arranged at integrating sphere up or down of LED to be measured, the light/electric transducer of acquisition system signals collecting part is provided with over against LED to be measured, is used to receive the direct light that LED to be measured sends.
When measuring LED with integrating sphere, LED device to be measured obliquely or oblique placement down can make LED reach best mixed light effect, that is minimum test error; So adopt oblique upwards 45 ° the plan of establishment in the technical program.
In acquisition system, signals collecting is partly finished the conversion of light signal to electric signal; Conversion of signals part becomes simulating signal behind the A/D unscented transformation can and finish data for the digital signal of Computer Processing and send task; Data processing section is realized corresponding computing and Presentation Function, and provides a personal-machine mutual friendly operation interface.
The pwm pulse drive signal response frequency scope of acquisition system is 50Hz~200Hz, and the response speed of the light/electric transducer of acquisition system signals collecting part is the ns level.
Drive current point is chosen more than 5 at least, according to applicant's experiment, think that 7~11 are advisable, and each drive current point is distributed in equally spaced in the linear working range of LED to be measured.
Adopt said method, the pwm pulse that can obtain drives the instantaneous luminous flux phi of LED down pDrive the average flux Φ of LED down with pwm pulse Avg
The object of putting in the integrating sphere more or less can bring certain influence to accuracy of measurement, and the socket as LED in the ball uses can absorb a part of luminous flux, causes the absorption errors of marching into the arena.It can not be avoided fully, can only reduce as far as possible.So,, also can bring the near field to absorb if after in integrating sphere, putting into light/electric transducer and lead and support.
Yet as can be known by the flow process of measuring method, under constant-current driving, step 3) obtains the corresponding relation of a group " LED drive current<-〉 LED luminous flux ", step 5) obtains the corresponding relation of a group " acquisition system photocurrent<-〉 LED drive current ", both are in conjunction with the corresponding relation that can get " acquisition system photocurrent<-〉 LED luminous flux ", luminous flux system is by the conventional test methodologies gained herein, and the acquisition system photocurrent is produced by LED direct light energy, do not introduce the near field absorption effect in the corresponding relation, so the test macro that increases in the ball brings extra test error can for original luminous flux test macro.
Among Fig. 2, this proving installation comprises conventional spectral analysis device, LED5 to be measured and its driving power 8, at the sphere center position of integrating sphere LED to be measured is set, and the two ends of LED to be measured are connected with the output terminal of PWM driving power; The wall of integrating sphere 1 is provided with the luminous flux probe 4 of spectral analysis device, between LED to be measured and luminous flux probe, is provided with baffle plate 6.
Conventional spectral analysis device is made of integrating sphere 1, spectroscopic analysis system controller 2 and PC 3, and the minimum sampling interval of the signal of this system is 0.1s, can be used for measuring stable state and drives the luminous flux of LED down.
On the basis of conventional spectral analysis device, be provided with that a cover is connected with a data processing unit successively by a signal gathering unit, signal conversion unit at least and the acquisition system 9 that constitutes, the light/electric transducer 7 of acquisition system signal gathering unit is provided with over against LED to be measured again.
The electrical block diagram of acquisition system is seen shown in Figure 3.
Signal gathering unit in the acquisition system is finished the conversion of light signal to electric signal; Signal conversion unit becomes simulating signal behind the A/D unscented transformation can and finish data for the digital signal of Computer Processing and send task; Data processing unit is realized corresponding computing and Presentation Function, and a friendly operation interface that people/machine is mutual is provided.
Signal gathering unit is light/electrical signal conversion circuit.
The pwm pulse drive signal response frequency scope of acquisition system is 50Hz~200Hz, and the response speed of the light/electric transducer of acquisition system signals collecting part is the ns level.
For satisfying the needs of frequency acquisition, the sampling interval of acquisition processing system is 0.0001s (sample frequency 10KHz), at first guarantee to gather the peak pulse signal on hardware, the data processing method that adopts Fig. 1 to propose can be leaked the situation of adopting from effective data of eradicating on the principle.
During measurement, tested led light source places the integrating sphere centre of sphere, and wherein LED 45 ° of placements obliquely can at utmost reduce the measuring error brought because of the LED non-uniform light, and acquisition system light/electric transducer is placed over against LED, is used to receive the LED direct light.
Suppose that the luminous flux of pulsed drive LED when peak point current drives is Φ, integrating sphere inwall light reflectivity is ρ, and the integrating sphere radius is R, instrument luminous flux probe illumination is E, the distance of acquisition system light/electric transducer and light source is r, and direct projection illumination is E ' on the sensor, and the photocurrent of generation is I.
Analyze light/electric transducer one end earlier: because sensor and led light source is very little apart from r, and select light/electric transducer that photosensitive area is little, receiving angle is narrow for use, can at utmost suppress interference of stray light like this, can be similar to the illuminance of thinking on light/electric transducer when computational analysis is the direct light part of light source, and the luminous energy of integrating sphere diffuse reflection part can be ignored.Moreover, because the singularity of led light source is maximum in theory even exiting surface is accomplished, also have only sphere (2 π r half 2) be subjected to the direct light photograph, suppose that the direct light energy even is distributed on the hemisphere face, has:
E ′ = φ 2 π · r 2 , (formula 2)
In the range of linearity of light/electric transducer, photocurrent is directly proportional with illuminance, so have:
E ' ∝ I, (formula 3)
With formula 3 substitution formulas 2,
φ=2 π r 2E ∝ I, (formula 4)
Consider the instrument luminous flux end of popping one's head in again, associative multiplication bulb separation measuring principle has:
E = r 2 2 R 2 · ρ 1 - ρ · E ′ ∝ I , (formula 5)
Can see by the aforementioned calculation process, ignore under the prerequisite of some complex effects factors choosing approximate condition, if keep r constant in the test process, then in the peak point current part of pulsed drive LED, the peak light flux of LED is directly proportional with the peak light electric current and (can adjusts according to the light source characteristics before test apart from r, it is non-adjustable to begin the test back, otherwise the linear relationship of above-mentioned theory analysis is no longer set up).This shows that if can obtain the pulse drive signal dutycycle, the average flux and the transformational relation of peak light flux that provides by preamble can obtain average flux by the value of measurement peak light electric current again.
In other words, the luminous flux that LED exported when peak inrush current under pwm pulse drove is called the instantaneous luminous flux of LED under the pwm pulse driving; The product of it and pulse signal dutycycle is the average flux of LED under pwm pulse drives.
This group corresponding relation is prerequisite with the relative measurement.To guarantee all the time in the measuring process that the relative position of light source and each detector is constant.By formula 5 as seen, scale-up factor is all relevant with r and R, and the variation of any one value all can make scale-up factor change the i.e. change of corresponding relation.
Among Fig. 3, acquisition system is connected successively with a data processing unit C by a signal gathering unit A, signal conversion unit B at least and constitutes.
Signal gathering unit in the acquisition system is finished the conversion of light signal to electric signal; Signal conversion unit becomes simulating signal behind the A/D unscented transformation can and finish data for the digital signal of Computer Processing and send task; Data processing unit is realized corresponding computing and Presentation Function, and a friendly operation interface that people/machine is mutual is provided.
Described signal gathering unit is light/electrical signal conversion circuit, and described signal conversion unit comprises signal amplification circuit, A/D change-over circuit and the RS232 level shifter interface circuit that connects successively at least, and described data processing unit is a PC.
Among Fig. 4, signal gathering unit comprises light/electric transducer D2, first resistance R 1, second resistance R 2, first capacitor C 1 and second capacitor C 2 at least, wherein, the positive pole of light/electric transducer is connected with an end and the earth terminal of first resistance, first electric capacity, second electric capacity respectively; The other end of the negative pole of light/electric transducer and first resistance, first electric capacity and power end V CCConnect, be connected through the other end of second resistance simultaneously with second electric capacity; The two ends of second electric capacity, the signal output part of formation signal gathering unit.
The effect of entire circuit is with the current signal converting voltage signal, and exports after filtering.
Among Fig. 5, signal amplification circuit comprises the 3rd to the 8th resistance R 3~R8, the 3rd to the 5th capacitor C 3~C5 and first, second discharge circuit AR1, AR2 at least, wherein, the 3rd, the 4th resistance is serially connected in respectively between the positive and negative input end of signal input part Vref, the Vin of signal amplification circuit and first discharge circuit; The 5th resistance and the 3rd electric capacity are connected in parallel between the negative input end and output terminal of first discharge circuit; The 6th resistance string is connected between the negative input end of the output terminal of first discharge circuit and second discharge circuit; The 7th resistance and the 4th electric capacity are connected in parallel between the negative input end and output terminal of second discharge circuit; The 8th resistance string is connected between the signal output part Vout of the output terminal of second discharge circuit and signal amplification circuit; The 5th electric capacity is connected in parallel between the output and ground of second discharge circuit.
Signalization amplifying circuit purpose is the driving force that increases Chip Microcomputer A/D.
Among Fig. 6, RS232 level shifter interface circuit comprises single-chip microcomputer U1, the 6th to the 11 capacitor C 6~C11 and RS232 port attachment plug DB9 at least, wherein, the two ends of the 6th, the 7th electric capacity, successively with C1+, the C1 of single-chip microcomputer-, the corresponding connection respectively of C2+, C2-pin; The T1IN of single-chip microcomputer, R1OUT, T2IN and R2OUT pin are distinguished corresponding the connection with TX, RX, RTS and the CTS function terminal of A/D change-over circuit successively; The T1OUT of single-chip microcomputer, R2IN, R2IN and T2OUT pin, successively with XRX, the XRTX of A/D change-over circuit, XTS and XCTS function terminal corresponding connection respectively, the while is distinguished corresponding the connection with 2,7,3 of RS232 port attachment plug with 8 pins successively; The the 8th and the 11 electric capacity is attempted by between power end and the earth terminal; The the 9th and the tenth electric capacity, corresponding connection between the V+ of single-chip microcomputer, V-pin and earth terminal respectively successively.
RS232 level shifter interface circuit is changed Transistor-Transistor Logic level and computing machine 232 serial ports level.
Single-chip microcomputer U1 can select SP3223, the MAX3223 series RS-232 transceiver integrated circuit chip of Sipex or IMI company for use, and all the other elements do not have specific (special) requirements.
During real work, signal conversion unit carries out according to following order:
1) response PC begins the request of image data;
2) start A/D, the pulse signal in acquired signal source also carries out analog to digital conversion;
3) an image data bag is sent to PC by the RS232 serial ports.
Among Fig. 7, provided the workflow of data processing unit in the acquisition system, its task is:
1) start and stop of control single chip computer;
2) packet that single-chip microcomputer is sent is removed the byte of shaking hands that increases in the communication, carries out denoising, calculates the impulse level amplitude and the dutycycle of pulse signal;
3) utilize the primary light pulse signal of graphical user interface displays LED, treated pulse signal, the value of the interior instantaneous luminous flux of acquisition time section and the average duty ratio of the interior light pulse of acquisition time section;
4) store all image data for consulting.
Thus, the workflow that has determined data processing unit in the acquisition system is as shown in Figure 7:
At first, the program creation serial equipment object of PC; Carry out the serial ports initialization, and the attribute of configuration serial ports object;
Then, whether the serial ports physical equipment connected carry out a logic determines, connect as the serial ports physical equipment, then send the communication handshake, wait for the generation of serial ports incident, in case satisfy condition, then call instroallback () call back function, receive the serial communication data;
At last, carry out a task such as demonstration of real-time processing, file storage and the figure of data.
The workflow that the A/D change-over circuit that is not described in detail in above-mentioned Fig. 3~7, the RS232 interface of PC and the realization of employing computer program are shown in Figure 7 etc. is prior art, those skilled in the art is after understanding and understanded technical scheme of the present invention and invention intention, need not through performing creative labour, can realize the technical program, reach the corresponding techniques effect, so its concrete principle of work and line connecting relation are no longer narrated at this.
Embodiment:
Adopt the PMS-50 of Hangzhou Everfine Photo-E-Info Co., Ltd. (enhancement mode) ultraviolet-visible-near-infrared spectrum analytic system+0.3m integrating sphere, test according to industry standard SJ2355.6-1983 " integrating sphere measuring light flux calibrating method ", its detailed process is as follows:
Preparatory stage is provided with by the described method and apparatus annexation of Fig. 1, Fig. 2, selects a large power white light LED chip in the experiment for use, passes to steady current.Electric current increases to 400mA from 20mA, obtains the variation relation curve of light/electric transducer photocurrent and luminous flux, as shown in Figure 8.
As we can see from the figure, in light/electric transducer range of linearity, the output of the photocurrent of light/electric transducer is directly proportional with luminous flux, and the result is consistent with former theoretical analysis.
The actual measurement stage passes to the pulse square wave signal that the peak point current amplitude is 40mA to this chip, and dutycycle changes from 10%-95%.Utilize acquisition system to obtain the peak light electric current earlier, the change curve by Fig. 8 checks in the peak light flux again, and obtains the final pwm pulse driving average flux value of LED down by aforementioned formula 4, and measurement result as shown in Figure 9.Contrasted the luminous flux (with symbol ◆ expression) that obtains by traditional PMS-50 test macro among the figure and utilized acquisition system to convert again the average flux value (■ represents with symbol) that obtains.
The result is as follows for actual measurement numerical value:
Two kinds of method of testing light flux values relatively
The luminous flux difference that the light photocurrent conversion Calculation that signal duty PMS-50 records obtains
Than % flux lm luminous flux lm lm
95 7.4362 7.6346 0.1984
80 6.3418 6.5972 0.2554
50 4.0889 4.4361 0.3472
30 2.3583 2.7380 0.3797
9 0.7839 1.2325 0.4486
As we can see from the figure, the luminous flux that obtains at pwm pulse driving method of testing specially that the light flux ratio that adopts traditional measurement method to obtain adopts this paper to set up is little, its main cause be traditional testing tool do not have can the peak value of response parameter light/electric transducer, have aforesaid " leakage is adopted " phenomenon; Moreover along with the drive signal dutycycle becomes big, both luminous flux differences obviously reduce; This phenomenon shows that on measuring principle, there is not the situation of runing counter in two kinds of measuring methods, and changes to steady state value with measured signal and reaches unanimity.
The experiment proved that this method of testing is rationally feasible, the photoelectric parameter measurement of pwm pulse driving LED is had better guide significance.
Above embodiment only be used for explaining and illustrate of the present invention, rather than to the qualification of the invention scope of claim of the present invention.
Especially, the applicant thinks, concerning those skilled in the art, according to above technical scheme and embodiment, can associate being equal to of other at an easy rate and replace and/or distortion.Therefore, the present invention is not limited to above-mentioned specific embodiment, and it carries out detailed and/or exemplary explanation as just example to technical scheme of the present invention.
In the scope that does not deviate from aim of the present invention, those of ordinary skill in the art, can be according to technique scheme and/or specific embodiment, be equal to replacement by various, obtain having the technical scheme of identical or close technical functionality, but these technical schemes all should be included in the scope of claim of the present invention and the scope that is equal within.
The present invention can be widely used in performance test, the demarcation field of various LED luminescent devices and/or pwm pulse drive unit.

Claims (19)

1. the method for testing of the instantaneous luminous flux of LED under the PWM Driving technique comprises and adopts the integrating sphere method that the luminous flux of LED to be measured is measured, and it is characterized in that:
On the basis of conventional spectroscopic analysis system device, a cover is set again by the acquisition system that signals collecting part, conversion of signals part and data processing division are grouped into, according to following step the luminous flux of LED to be measured is measured then:
(A) measure the preparatory stage:
(a1) adopt conventional method that the integrating sphere luminous flux is calibrated;
(a2) in the linear working range of LED to be measured, choose at least 5 drive current points, it is luminous to adopt the constant current source mode to drive LED to be measured, collects the luminous flux numerical value [Φ of one group of correspondence 0];
(a3) probe and the annex of acquisition system signals collecting part are put into integrating sphere;
(a4) adopt the drive current point identical with step (a2), it is luminous to adopt the constant current source mode to drive LED to be measured, obtains the photoelectricity flow valuve [I] of one group of correspondence by acquisition system;
(a5) be horizontal ordinate with photoelectricity flow valuve [I], luminous flux numerical value [Φ corresponding with it 0] be ordinate, the variation relation curve of in rectangular coordinate system, draw luminous flux and photocurrent;
(a6) adopt least square fitting to obtain above-mentioned variation relation slope of a curve k;
(B) the actual measurement stage:
(b1) determine pwm pulse drive source duty of ratio Q;
(b2) under this dutycycle operational factor, adopt pwm pulse to drive LED to be measured, the peak light current value I of correspondence during to the pwm pulse peak point current by acquisition system LpMeasure;
(b3), determine that pwm pulse drives the instantaneous luminous flux phi of LED to be measured down according to following formula p:
φ p=k×I Lp
Wherein, Φ pFor pwm pulse drives the instantaneous luminous flux of LED to be measured down, k is the slope of luminous flux and photocurrent variations relation curve, I LpFor pwm pulse drives the peak light electric current of LED to be measured down;
(b4) calculate according to following formula, can obtain the average flux of LED to be measured:
φ avg=φ p×Q=k×I Lp×Q
Wherein, Φ AvgFor pwm pulse drives the average flux of LED to be measured down, Φ pFor pwm pulse drives the instantaneous luminous flux of LED to be measured down, Q is the dutycycle of pwm pulse signal, I LpFor pwm pulse drives the peak light electric current of LED to be measured down, k is the slope of luminous flux and photocurrent variations relation curve.
2. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 1, it is characterized in that described LED to be measured is arranged at the sphere center position of integrating sphere; Light/the electric transducer of described acquisition system signals collecting part is provided with over against LED to be measured, is used to receive the direct light that LED to be measured sends.
3. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 2, it is characterized in that the oblique sphere center position that is arranged at integrating sphere of described LED to be measured.
4. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 3, it is characterized in that the oblique sphere center position that is arranged at integrating sphere up or down of described LED to be measured.
5. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 1, it is characterized in that described pwm pulse drives the instantaneous luminous flux phi of LED to be measured down p, for pwm pulse drives the luminous flux that LED to be measured down exports when the Maximum Peak Impulse Current, it equals the slope k of luminous flux and photocurrent variations relation curve and the peak light electric current I of the following LED to be measured of pwm pulse driving LpProduct.
6. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 1, it is characterized in that described pwm pulse drives the average flux Φ of LED to be measured down Avg, equal pwm pulse and drive the instantaneous luminous flux phi of LED to be measured down pProduct with the dutycycle Q of pwm pulse signal; The corresponding with it peak light electric current I of acquisition system photodetector when perhaps, equaling slope k, the pwm pulse peak point current of luminous flux and photocurrent variations relation curve LpAnd the product of the dutycycle Q of pwm pulse signal.
7. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 1, it is characterized in that in described acquisition system its signals collecting is partly finished the conversion of light signal to electric signal; Its conversion of signals part becomes simulating signal behind the A/D unscented transformation can and finish data for the digital signal of Computer Processing and send task; Its data processing section is realized corresponding computing and Presentation Function, and provides a personal-machine mutual friendly operation interface.
8. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 1, it is characterized in that the pwm pulse drive signal response frequency scope of described acquisition system is 50Hz~200Hz; The response speed of the light/electric transducer of described acquisition system signals collecting part is the ns level.
9. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 1, it is characterized in that described drive current point uniformly-spaced or unequal interval be distributed in the linear working range of LED to be measured.
10. according to the method for testing of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 9, it is characterized in that described drive current point is 7~11, described each drive current point equally spaced is distributed in the linear working range of LED to be measured.
11. the proving installation of the instantaneous luminous flux of LED comprises the conventional spectral analysis device that is made of integrating sphere, spectroscopic analysis system controller and PC, LED to be measured and its driving power under the PWM Driving technique, it is characterized in that:
Sphere center position at integrating sphere is provided with LED to be measured;
The two ends of LED to be measured are connected with the output terminal of PWM driving power;
On the basis of conventional spectral analysis device, be provided with again that a cover is connected with a data processing unit successively by a signal gathering unit, signal conversion unit at least and the acquisition system that constitutes;
Described signal gathering unit is finished the conversion of light signal to electric signal;
Described signal conversion unit becomes simulating signal behind the A/D unscented transformation can and finish data for the digital signal of Computer Processing and send task;
Described data processing unit is realized corresponding computing and Presentation Function, and a friendly operation interface that people/machine is mutual is provided.
12. the proving installation according to the instantaneous luminous flux of LED under the described PWM Driving technique of claim 11 is characterized in that the oblique sphere center position that is positioned over integrating sphere up or down of described LED to be measured.
13. the proving installation according to the instantaneous luminous flux of LED under the described PWM Driving technique of claim 11 is characterized in that the light/electric transducer of described acquisition system signal gathering unit is provided with over against LED to be measured.
14., it is characterized in that described signal gathering unit is light/electrical signal conversion circuit according to the proving installation of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 11.
15. according to the proving installation of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 14, it is characterized in that described signal gathering unit comprises light/electric transducer, first resistance, second resistance, first electric capacity and second electric capacity at least, wherein,
The positive pole of light/electric transducer is connected with an end and the earth terminal of first resistance, first electric capacity, second electric capacity respectively;
The negative pole of light/electric transducer is connected with the other end and the power end of first resistance, first electric capacity, is connected through the other end of second resistance with second electric capacity simultaneously;
The two ends of second electric capacity, the signal output part of formation signal gathering unit.
16., it is characterized in that described signal conversion unit comprises signal amplification circuit, A/D change-over circuit and the RS232 level shifter interface circuit that connects successively at least according to the proving installation of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 11.
17. according to the proving installation of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 16, it is characterized in that described signal amplification circuit comprises the 3rd to the 8th resistance, the 3rd to the 5th electric capacity and first, second discharge circuit at least, wherein,
Three, the 4th resistance is serially connected in respectively between the positive and negative input end of the signal input part of signal amplification circuit and first discharge circuit;
The 5th resistance and the 3rd electric capacity are connected in parallel between the negative input end and output terminal of first discharge circuit;
The 6th resistance string is connected between the negative input end of the output terminal of first discharge circuit and second discharge circuit;
The 7th resistance and the 4th electric capacity are connected in parallel between the negative input end and output terminal of second discharge circuit;
The 8th resistance string is connected between the signal output part of the output terminal of second discharge circuit and signal amplification circuit;
The 5th electric capacity is connected in parallel between the output and ground of second discharge circuit.
18. according to the proving installation of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 16, it is characterized in that described RS232 level shifter interface circuit comprises single-chip microcomputer, the 6th to the 11 electric capacity and the attachment plug of RS232 port at least, wherein,
Six, corresponding connection is distinguished with C1+, C1-, C2+, the C2-pin of single-chip microcomputer successively in the two ends of the 7th electric capacity;
The T1IN of single-chip microcomputer, R1OUT, T2IN and R2OUT pin are distinguished corresponding the connection with TX, RX, RTS and the CTS function terminal of A/D change-over circuit successively;
The T1OUT of single-chip microcomputer, R2IN, R2IN and T2OUT pin, successively with XRX, the XRTX of A/D change-over circuit, XTS and XCTS function terminal corresponding connection respectively, the while is distinguished corresponding the connection with 2,7,3 of RS232 port attachment plug with 8 pins successively;
The the 8th and the 11 electric capacity is attempted by between power end and the earth terminal;
The the 9th and the tenth electric capacity, corresponding connection between the V+ of single-chip microcomputer, V-pin and earth terminal respectively successively.
19., it is characterized in that described data processing unit is a PC according to the proving installation of the instantaneous luminous flux of LED under the described PWM Driving technique of claim 11.
CN2008102007531A 2008-09-28 2008-09-28 LED instantaneous light flux test method and apparatus in PWM activation technology Expired - Fee Related CN101430223B (en)

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