EP1701589B1 - Circuit et procédé pour surveiller la température d'une diode électroluminescente - Google Patents

Circuit et procédé pour surveiller la température d'une diode électroluminescente Download PDF

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Publication number
EP1701589B1
EP1701589B1 EP05005054A EP05005054A EP1701589B1 EP 1701589 B1 EP1701589 B1 EP 1701589B1 EP 05005054 A EP05005054 A EP 05005054A EP 05005054 A EP05005054 A EP 05005054A EP 1701589 B1 EP1701589 B1 EP 1701589B1
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EP
European Patent Office
Prior art keywords
light emitting
emitting diode
dependency
forward voltage
temperature
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EP05005054A
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German (de)
English (en)
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EP1701589A1 (fr
Inventor
Gunnar Klinghult
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Sony Mobile Communications AB
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Sony Ericsson Mobile Communications AB
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Priority to EP05005054A priority Critical patent/EP1701589B1/fr
Priority to DE602005009317T priority patent/DE602005009317D1/de
Priority to AT05005054T priority patent/ATE406783T1/de
Priority to PCT/EP2006/001102 priority patent/WO2006094590A1/fr
Publication of EP1701589A1 publication Critical patent/EP1701589A1/fr
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/20—Controlling the colour of the light
    • H05B45/22—Controlling the colour of the light using optical feedback
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/10—Controlling the intensity of the light
    • H05B45/12—Controlling the intensity of the light using optical feedback
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
    • H05B45/56—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits involving measures to prevent abnormal temperature of the LEDs
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/37—Converter circuits
    • H05B45/3725—Switched mode power supply [SMPS]
    • H05B45/38—Switched mode power supply [SMPS] using boost topology

Definitions

  • the invention relates to an electronic circuit and method for monitoring a temperature of a light emitting diode that is driven in a constant-current mode.
  • light emitting diodes are used for lightening applications, e. g. as flash lights, background lights for displays or for lightening keys, etc..
  • light emitting diodes are small size, low power consumption, high reliability and low heat generation in comparison to ordinary incandescent lamps.
  • white light emitting diodes are used.
  • Fig. 6 shows a solution according to the prior art frequently integrated into mobile phones.
  • a light emitting diode 62 is driven by a drive circuit 61.
  • the drive circuit 61 is connected to both a power supply 63 and the light emitting diode 62 and provides a constant current to the light emitting diode.
  • the current supplied to the light emitting diode 62 is maintained constant to guarantee a constant brightness of the light emitting diode 62 during operation.
  • a thermistor 64 is located as close as possible to the light emitting diode 62.
  • the thermistor 64 is a resistant whose resistance changes proportional to the temperature of the thermistor.
  • the thermistor is a temperature sensor. Therefore, the thermistor 64 is adapted to measure the temperature in an area surrounding the thermistor 64 and thus the temperature of the light emitting diode 62.
  • the thermistor 64 is connected to a microprocessor 65 for controlling the thermistor 64. Based on an output of the thermistor 64 the microprocessor 65 calculates a current temperature of the light emitting diode 62.
  • the thermistor 64 cannot exactly measure the temperature of the light emitting diode 62, since a sensing point of the thermistor 64 is not integrated into the light emitting diode 62. As it takes some time for the heat generated by the light emitting diode 62 to spread to the sensing point of the thermistor 64, a time delay with respect to the temperature measured by the thermistor 64 is inevitable.
  • the thermistor is an additional element that has to be integrated to the mobile electronic equipment and has to be provided with energy.
  • both energy and space are usually very limited.
  • EP-A-1 044 858 discloses a method for determining correction factors to compensate for a drift in LED luminosity due to temperature shifts, whereby the actual compensation factors are determined by measuring the forward voltage at a constant current, but different temperatures and LED luminosity.
  • Unites States Patent Application Publication [ US 2004/052076 A1 ] discloses controlled lighting methods and apparatus, whereby the light source is outputting radiation at a calibrated intensity that substantially corresponds in a predetermined manner to a control signal coming from a variety of sensors that generate one or more signals in response to some stimulus like temperature or infrared light.
  • United States Patent [ US-B1-6 807 202 ] discloses a process for stabilizing the optical output power of light-emitting diodes and laser modes.
  • a circuit for a light emitting diode or a laser diode is provided such that the changes in electrical behavior caused by the temperature lead to a temperature-independence of its optical output power.
  • US-A-6 144 165 discloses an organic electroluminescent device to form a light-emitting diode (LED), which supplies a photocurrent, which is an indication of the quantity of incident light. Said photocurrent is measured and its value is used to calculate the correct forward voltage to be set in order to obtain the desired display luminosity in consideration of the ambient light level.
  • LED light-emitting diode
  • the above object is achieved by a method for monitoring a temperature of a light emitting diode that is driven in a constant-current mode, the method comprising the following steps:
  • the present invention bases on the principle that the forward voltage of a light emitting diode in a constant-current mode is approximately inverse proportional to the temperature of the light emitting diode.
  • the forward voltage of the light emitting diode is directly related to the current temperature status of said light emitting diode, there is no time delay between a temperature variation of the light emitting diode and a variation of the forward voltage.
  • the inventive method provides a very quick, easy and reliable way to monitor a temperature of a light emitting diode.
  • the step of detecting a dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode comprises the steps of
  • the forward voltage of a light emitting diode is approximately inverse proportional to the temperature of the light emitting diode, normally it is sufficient to measure the actual forward voltage of the light emitting diode in said constant-current mode at at least two different temperatures to calculate a linearised dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode.
  • calibration to a certain individual light emitting diode can be performed in a very easy way by only two measurements.
  • heating of the light emitting diode preferably is performed by the light emitting diode itself by simply using said light emitting diode in a constant-current mode.
  • the step of detecting a dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode comprises the steps of
  • heating of the light emitting diode preferably is performed by the light emitting diode itself by simply using said light emitting diode in a constant-current mode.
  • said heat might be provided by a separate heater.
  • the temperature curve inclination for a certain identified type of light emitting diode is known.
  • Said temperature curve inclination for a certain type of light emitting diode might be determined and provided by manufacturers of light emitting diodes, for example.
  • the linearised dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode is calculated by adjusting the position of the known temperature curve inclination for the identified type of light emitting diode in a temperature / forward voltage diagram according to the measured actual forward voltage at said known temperature. Since the above described calibration requires one measurement step, only, it is very quick and cheap.
  • heating of the light emitting diode preferably is performed by the light emitting diode itself by simply using said light emitting diode in a constant-current mode.
  • said heat might be provided by a separate heater.
  • the step of measuring the actual forward voltage of the light emitting diode in said constant-current mode is performed by supplying a current that is at least 10%, preferably at least 20%, more preferably at least 40 % and most preferably at least 60 % lower than nominal current of the light emitting diode to the light emitting diode.
  • the general dependency between the forward voltage of the light emitting diode in said constant-current mode at nominal current can be calculated by using the above calibration process and general characteristics of the light emitting diodes with ease.
  • the method further comprises the step of storing said calculated linearised dependency and / or said generated dependency table as a stored dependency, wherein said stored dependency further is used as detected general dependency for calculating the actual temperature of the light emitting diode.
  • the calibration process has to be performed only once for an individual light emitting diode.
  • the above embodiment bases on the principal that light emitting diodes are light sensitive elements. Therefore, light emitting diodes can be used as light sensors when not connected to a voltage source. Consequently, in an open-circuit mode, a light emitting diode generates a small voltage proportional to the light intensity irradiating the light emitting diode.
  • the light emitting diode can be used as an ambient light sensor, e. g. for adjusting the intensity of light emitted by the light emitting diode in a very easy way. This can be performed e. g. when the light emitting diode is not in use or between two flash pulses of the light emitting diode.
  • the step of detecting a light dependency between the forward voltage of the light emitting diode in said open-circuit mode and ambient light irradiating the light emitting diode comprises the steps of
  • the method further comprises the step of storing said calculated linearised light dependency and / or said generated light dependency table as a stored light dependency, wherein said stored light dependency further is used as detected light dependency for calculating the amount of ambient light actually hitting the light emitting diode.
  • a computer program product directly loadable into the internal memory of a digital computer, comprising software code portions for performing the steps of one of the claims 1 to 8 when said product is run on a computer.
  • an electric circuit for monitoring a temperature of a light emitting diode in a constant-current mode comprising
  • the inventive electric circuit calculates the actual temperature of the light emitting diode by using the stored general dependency and the measured actual forward voltage, the temperature of the light emitting diode is monitored with high velocity, accuracy and reliability. Furthermore, as no additional elements such as thermistors are necessary to sense the temperature of the light emitting diode, the inventive electric circuit has a very easy and compact structure.
  • the electric circuit further comprises a calibrator, said calibrator being adapted to control the voltage sensor in a way that the voltage sensor sequentially measures the actual forward voltage of the light emitting diode in said constant-current mode at different temperatures, to calculate a linearised dependency and / or a dependency table between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode by using the measured actual forward voltages at said different temperatures and to store said calculated linearised dependency and / or said generated dependency table as said dependency in said storage.
  • a calibrator being adapted to control the voltage sensor in a way that the voltage sensor sequentially measures the actual forward voltage of the light emitting diode in said constant-current mode at different temperatures, to calculate a linearised dependency and / or a dependency table between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode by using the measured actual forward voltages at said different temperatures and to store said calculated linearised dependency and / or said generated dependency table as said
  • calibration of the inventive electric circuit for monitoring a temperature of a light emitting diode to an individual light emitting diode can be performed with ease.
  • Dependent on the requirements and on accuracy either a linearised dependency by using at least two measured actual forward voltages of the light emitting diode in said constant-current mode at different temperatures or a detailed dependency table can be used. Since, said linearised dependency and /or said dependency table are stored in said storage, quick access to said dependency is guaranteed during the operation of the inventive electric circuit.
  • said calibration has to be performed only once for an individual light emitting diode.
  • the electric circuit further comprises a calibrator, said calibrator being adapted to control the voltage sensor in a way that the voltage sensor measures the actual forward voltage of the light emitting diode in said constant-current mode at a known temperature, to identify a type of the light emitting diode, to calculate a linearised dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode by using the measured actual forward voltage at said known temperature and a predefined temperature curve inclination for the identified type of light emitting diode and to store said calculated linearised dependency as said dependency in said storage.
  • a calibrator being adapted to control the voltage sensor in a way that the voltage sensor measures the actual forward voltage of the light emitting diode in said constant-current mode at a known temperature, to identify a type of the light emitting diode, to calculate a linearised dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode by using the measured actual forward
  • the calibrator is further adapted to control the driver circuit in a way that a current that is at least 10%, preferably at least 20%, more preferably at least 40% and most preferably at least 60% lower than nominal current of the light emitting diode is supplied to the light emitting diode in said constant-current mode during operation of said calibrator.
  • the calibrator of the inventive electric circuit is a adapted to control the driver circuit in a way that a current that is lower than nominal current of the light emitting diode is supplied to the light emitting diode in said constant-current mode during the operation of said calibrator, it is ensured that the light emitting diode is not damaged during calibration.
  • the corresponding linearised dependency and / or dependency table for the light emitting diode at nominal current can easily be calculated by using the measurement results of the calibrator.
  • the driver circuit of the inventive electric circuit is further adapted to run the light emitting diode in an open-circuit mode, it is possible to use the light emitting diode as an ambient light sensor.
  • the inventive electric circuit can be further used to adjust e. g. the intensity of light emitted by the light emitting diode.
  • said calibrator is further adapted to control the voltage sensor in a way that the voltage sensor sequentially measures the actual forward voltage of the light emitting diode in said open-circuit mode at different intensities of ambient light irradiating the light emitting diode, to calculate a linearised light dependency and / or generate a light dependency table between the forward voltage of the light emitting diode in said open-circuit mode and the intensity of ambient light irradiating the light emitting diode by using said measured actual forward voltage at said different intensities of ambient light and to store said calculated linearised light dependency and / or said generated light dependency table as said light dependency in said storage.
  • the circuit is comprised in a portable radio communication equipment.
  • the inventive electric circuit Since the inventive electric circuit has a very compact and reliable structure, it is adapted to be implemented into a portable electronic equipment and especially a portable radio communication equipment like a mobile phone. In this respect, monitoring of the temperature of light emitting diodes used in a portable electronic equipment is very important, since said equipments frequently have a rather complex structure that is heat sensitive and prevents air circulation. Thus, these equipments are prone to heat accumulation.
  • the term 'portable radio communication equipment' which herein after is referred to as a mobile radio terminal, includes all equipments such as mobile telephones, pagers, communicators, i. e. electronic organisers, smart phones or the like.
  • Fig. 1A shows a flow diagram of a preferred embodiment of the inventive method for monitoring a temperature of a light emitting diode.
  • a general dependency between a forward voltage of a light emitting diode in a constant-current mode and a temperature of the light emitting diode is detected. This step will be explained in more detail by reference to Figs. 1B and 1C , respectively.
  • step S12 said light emitting diode is driven in said constant-current mode during ordinary operation of the light emitting diode to produce light.
  • the actual forward voltage of a light emitting diode in said constant-current mode is measured in step S13.
  • This measurement preferably is performed continuously. Alternatively a regular measurement at a predefined or variable time interval might be performed.
  • the actual temperature of the light emitting diode is continuously or regularly calculated in step S14 by using the detected general dependency and the measured actual forward voltage.
  • the calculation step S14 preferably is closely linked to the measurement step S13.
  • the steps S12 to S14 are repeated as long as the light emitting diode is in a constant-current mode.
  • step S11 of detecting a general dependency between a forward voltage of a light emitting diode in a constant-current mode and a temperature of the light emitting diode are explained by reference to Figs. 1B and 1C , respectively.
  • a constant current that is at least 10 %, preferably at least 20 % , more preferably at least 40 % and most preferably at least 60 % lower than nominal current of the light emitting diode is supplied to the light emitting diode.
  • the reason is that the risk of damaging the light emitting diode during calibration of the light emitting diode because of too high temperatures is significantly reduced by providing a lower current.
  • the light emitting diode is driven in a constant-current mode.
  • step S112 the light emitting diode is sequentially heated to a plurality of different temperatures by driving the light emitting diode in said constant-current mode. Since the light emitting diode generates heat during the production of light the light emitting diode is heated.
  • an external heater might be used to heat the light emitting diode.
  • step S113 the actual forward voltage of the light emitting diode that is driven in said constant-current mode is measured at said different temperatures.
  • an actual forward voltage of the respective light emitting diode for a respective temperature is obtained.
  • the actual temperature of the light emitting diode might be measured by any suitable temperature sensor.
  • step S114 a linearised dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode is calculated by using the measured actual forward voltage at said different temperatures.
  • a linearised dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode is calculated by using the measured actual forward voltage at said different temperatures.
  • only two pairs of measured actual forward voltage and temperature values have to be provided for calculating said linearised dependency in order to obtain a good estimate.
  • the reason is that the forward voltage of a light emitting diode is approximately inverse proportional to the temperature of the light emitting diode.
  • a dependency table between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode can be generated in step S115 by using said measured actual forward voltages at said different temperatures.
  • steps S114 and S115 can be performed alternatively or complementary.
  • a constant current that is at least 10%, preferably at least 20%, more preferably at least 40 % and most preferably at least 60% lower than nominal current of the light emitting diode is supplied to the light emitting diode.
  • step 112' the light emitting diode is heated to a known temperature.
  • step S113' the actual forward voltage of the light emitting diode in said constant-current mode at said known temperature is measured.
  • step S114' a type of the light emitting diode currently used is identified. This can either be performed automatically by measuring certain component characteristics of the light emitting diode or based on a manual user input. Step S114' might be performed either before, in parallel or after steps S111', S112' and S113'.
  • step S115' a linearised dependency between the forward voltage of the light emitting diode in said constant-current mode and the temperature of the light emitting diode is calculated by using the measured actual forward voltage at said known temperature and a predefined temperature curve inclination for the identified type of light emitting diode.
  • step S 117 S 117' as detected general dependency for calculating the actual temperature of the light emitting diode in step S 14.
  • steps S11 and S111 to S 117 and S111' to S 117' have to be performed only once for calibrating the general dependency for an individual light emitting diode or a type of light emitting diodes.
  • the reason is that the dependency of the forward voltage of a light emitting diode in a constant-current mode and the temperature spreads between different individual light emitting diodes of different types.
  • the dependency of the forward voltage of a light emitting diode in a constant-current mode and the temperature might even spread between different individual light emitting diodes of the same types. This is accounted for by the calibration methods explained by reference to Figs. 1B and 1C , respectively.
  • the inventive method provides a very quick, easy and reliable way to monitor a temperature of a light emitting diode.
  • a general light dependency between a forward voltage of a light emitting diode in an open-circuit mode and ambient light irradiating the light emitting diode is detected. This detection will be further explained by reference to Fig. 2B .
  • step S22 said light emitting diode is driven in said open-circuit mode.
  • step S23 the actual forward voltage of the light emitting diode in said open-circuit mode is measured.
  • the steps S22 to S24 are repeated as long as the light emitting diode is driven in said open-circuit mode and as long as a sensing of ambient light irradiating the light emitting diode is required.
  • step S21 of detecting a general light dependency between a forward voltage of a light emitting diode in an open-circuit mode and ambient light irradiating the light emitting diode is further explained by reference to Fig. 2B .
  • a first step S211 said light emitting diode is driven in said open-circuit mode. Thus, no external voltage is applied to the light emitting diode.
  • the light emitting diode is sequentially irradiated with different intensities of ambient light in step S212.
  • the intensity of the irradiating light is known (either due to external measurement or due to a detailed knowledge of the light source).
  • step S213 the actual forward voltage of the light emitting diode driven in said open-circuit mode is measured at different intensities of ambient light.
  • the steps S212 and S213 are repeated until sufficient numbers of pairs of measured actual forward voltages and corresponding intensities of irradiating ambient light are provided.
  • a linearised light dependency is calculated and / or a light dependency table is generated.
  • Both the linearised light dependency and the light dependency table relate to the dependency between the forward voltage of the light emitting diode in said open-circuit mode and the intensities of ambient light irradiating the light emitting diode. Both are provided by using said measured actual forward voltages at said different intensities of ambient light. While for the calculation of the linearised light dependency only two pairs of measured actual forward voltage and corresponding intensity of irradiating ambient light are necessary, the accuracy can be increased by using a higher number of pairs in a light dependency table.
  • both said calculated linearised light dependency and / or said generated light dependency table are stored as a stored light dependency in step S215.
  • step S216 is used in step S216 as detected general light dependency for calculating the amount of ambient light actually hitting the light emitting diode.
  • the calibration method described with reference to Fig. 2B above has to be performed only once for an individual diode or type of diodes.
  • the light emitting diode can be used as an ambient light sensor, e. g. for adjusting the intensity of light emitted by the light emitting diode in a constant-current mode in a very easy way. This can be performed e. g. when the light emitting diode is not in use or between two flash pulses of the light emitting diode.
  • Fig. 3 is a diagram showing the general dependency between the forward voltage of three light emitting diodes D1, D2 and D3 in a constant-current mode and the temperature of the light emitting diodes D1, D2 and D3.
  • Said diagram can be generated either by measuring a forward voltage value for each temperature value or by calculating a linearised dependency between the forward voltage of the light emitting diodes D1, D2, D3 in said constant-current mode and the temperature of the light emitting diodes D1, D2 and D3 by using two pairs of forward voltage T D11 , T D12 ; T D21 , T D22 ; and T D31 , T D32 , respectively.
  • D1, D2 and D3 either can characterise different types of diodes or different individual light emitting diodes of one type.
  • Fig. 3 the dependency described with respect to Fig. 3 is not limited to single light emitting diodes but is also applicable to several light emitting diodes connected in parallel or in series. In this case, the average temperature of the diodes would be monitored.
  • Fig. 4 a preferred embodiment of an electronic circuit for monitoring a temperature of a light emitting diode according to the present invention is described. Said electronic circuit is adapted to perform the above-described inventive method of monitoring the temperature of a light emitting diode.
  • the electronic circuit 1 is connected to a power supply 8 (in the present case a battery) and a light emitting diode 2 whose temperature has to be monitored.
  • a power supply 8 in the present case a battery
  • a light emitting diode 2 is a conventional diode for white light.
  • said diode 2 could be a laser diode or a colour diode, for example. It is obvious that said light emitting diode 2 can be a single diode or several light emitting diodes connected in parallel or in series.
  • the electronic circuit 1 comprises a driver circuit 3, a storage 4, a voltage sensor 5, a calculator 6 and a calibrator 7.
  • the driver circuit 3 is adapted to supply a predefined constant current to the light emitting diode 2 to run the light emitting diode 2 in a constant-current mode.
  • the driver circuit contains a voltage step-up converter to ensure that a constant current is applied to the diode 2 by correspondingly adapting the voltage applied to the diode 2.
  • the driver circuit 3 is adapted to run the light emitting diode 2 in an open-circuit mode and thus not to apply external voltage to the light emitting diode 2.
  • the light emitting diode 2 can be driven either in the open-circuit mode or in the constant-current mode.
  • the storage 4 stores a general dependency between a forward voltage of the light emitting diode 2 in said constant-current mode and the temperature of the light emitting diode 2.
  • the storage 4 further stores a general light dependency between the forward voltage of the light emitting diode 2 in an open-circuit mode and ambient light irradiating the light emitting diode 2.
  • the storage 4 is an EPROM and thus a non-volatile memory. Alternatively any other non-volatile memory might be used.
  • the voltage sensor 5 is adapted to measure an actual forward voltage of said light emitting diode 2, wherein said diode 2 is driven either in the constant-current mode or in the open-circuit mode.
  • the voltage sensor 5 uses a differential amplifier for measuring the actual forward voltage and comprises an A/D converter to digitise the measured value.
  • the calculator 6 is a microprocessor adapted to calculate the actual temperature of the light emitting diode 2 by using the detected general dependency and the measured actual forward voltage when the diode is driven in said constant-current mode. Moreover, in the present example, the calculator 6 is adapted to calculate an amount of ambient light actually irradiating the light emitting diode 2 by using the general light dependency and the measured actual forward voltage.
  • the calibrator 7 is adapted to control the voltage sensor 5 in a way that the voltage sensor 5 sequentially measures the actual forward voltage of the light emitting diode 2 in said constant-current mode at different temperatures.
  • the calibrator 7 is further adapted to control the driver circuit in a way that a current that is at least 10 % , preferably at least 20 % , more preferably at least 40% and most preferably at least 60% lower than nominal current of the light emitting diode 2 is supplied to the light emitting diode 2 in said constant-current mode during the operation of said calibrator 7.
  • the different temperatures of the light emitting diode 2 are achieved by a self-heating effect of the light emitting diode 2, due to the operation of the light emitting diode 2.
  • the light emitting diode 2 might be heated by using an external heater not shown in the figure.
  • the temperature of the light emitting diode 2 is measured by using an external temperature sensor (not shown in Fig. 4 ).
  • the calibrator 7 Based on the corrected actual forward voltages at said different temperatures, the calibrator 7 automatically calculates a dependency table between the forward voltage of the light emitting diode 2 in said constant-current mode and the temperature of the light emitting diode 2.
  • a dependency table is shown in Fig. 5A .
  • Fig. 5A the upper line indicates the measured actual forward voltage of said light emitting diode, and the lower line indicates the corresponding temperature value.
  • the calibrator 7 can calculate a linearised dependency as shown in Fig. 3 by simply using two pairs of voltage / temperature values for the light emitting diode 2.
  • said calibrator 7 is adapted to control the voltage sensor 5 in a way that the voltage sensor 5 measures the actual forward voltage of the light emitting diode 2 in said constant-current mode only at one known temperature.
  • the calibrator 7 automatically identifies a type of the light emitting diode 2 by measuring component characteristics of the light emitting diode 2.
  • said light emitting diode might be identified based on a manual user input.
  • a linearised dependency between the forward voltage of the light emitting diode 2 in said constant-current mode and the temperature of the light emitting diode 2 automatically is calculated by said calibrator 7 by using the measured actual forward voltage at said known temperature and a predefined temperature curve inclination for the identified type of light emitting diode 2.
  • predefined temperature curve inclinations for different types of light emitting diodes 2 preferably are stored in the storage 4 of the electronic circuit 1.
  • said predefined temperature curve inclination might be input by a user.
  • Said calculated linearised dependency and / or said generated dependency table according to all embodiments is automatically stored by said calibrator 7 as a general dependency in said storage 4.
  • said calibrator 7 is further adapted to control the driver circuit in a way that the light emitting diode 2 is driven in an open-circuit mode. Thus, no external voltage is applied on the diode 2.
  • the calibrator 7 controls the voltage sensor 5 in a way that the voltage sensor 5 sequentially measures said actual forward voltage of the light emitting diode 2 in said open-circuit mode at different intensities of ambient light irradiating the light emitting diode 2.
  • a certain amount of ambient light has to be irradiated on the light emitting diode 2 in some way by using a light source not shown in the figures.
  • said calibrator 7 preferably is adapted to calculate a linearised light dependency similar to the dependency shown in Fig. 3 but with the light intensity at the horizontal axis (x-axis) and / or to generate a light dependency table relating to the dependency between the forward voltage of the light emitting diode 2 in said open-circuit mode and the intensity of ambient light irradiating the light emitting diode 2 by using said measured actual forward voltage at said different intensities of ambient light.
  • a light dependency table is shown in Fig. 5B .
  • the upper line indicates the measured actual forward voltage of said light emitting diode
  • the lower line indicates the illuminance irradiating the light emitting diode.
  • said calculated linearised light dependency and / or said generated light dependency table are automatically stored by said calibrator 7 as said general light dependency in said storage 4.
  • said calculator 6 uses said general dependency stored in said storage 4 to automatically calculate the actual temperature of a light emitting diode 2 in real time by using the actual forward voltage measured by said voltage sensor 5.
  • the inventive electric circuit 1 is adapted to reliably monitor a temperature of the light emitting diode with ease and high accuracy in real-time.
  • the calculator 6 uses said general light dependency stored in the storage 4 for calculating an amount of ambient light actually irradiating the light emitting diode 2 by using the actual forward voltage measured by said voltage sensor 5.
  • the inventive electronic circuit 1 is adapted to monitor ambient light irradiating the light emitting diode driven in an open-circuit mode.
  • the inventive electronic circuit 1 can be used for adjusting the light intensity of the light emitting diode 2, for example.
  • the light emitting diode usually is in an open-circuit mode when it is switched off or between two flash points when the light emitting diode is used as a flasher.
  • the inventive electric circuit provides a further benefit without any extra costs or additional elements.
  • All elements of the inventive electric circuit 1 can be integrated into a circuit necessary to drive the light emitting diode 2. Thus, no additional components are needed.
  • the inventive electric circuit 1 is ideally suited to be used in portable radio communications equipments such as mobile phones. In this respect it is an advantage that the inventive electric circuit measures the temperature of the light emitting diode without a time delay and thus in real-time.

Claims (15)

  1. Procédé pour surveiller la température d'une diode électroluminescente qui est attaquée dans un mode à courant constant, comprenant les étapes suivantes :
    - (S11) détecter une dépendance entre une tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente ;
    - (S13) mesurer la tension directe effective de la diode électroluminescente dans ledit mode à courant constant ;
    - (S14) calculer la température effective de la diode électroluminescente en utilisant la dépendance détectée et la tension directe effective mesurée ; et
    caractérisé en ce qu'il comprend en outre les étapes suivantes :
    - (S21) détecter une dépendance à la lumière entre la tension directe de la diode électroluminescente dans un mode à circuit ouvert et la lumière ambiante illuminant la diode électroluminescente ;
    - (S23) mesurer la tension directe effective de la diode électroluminescente dans ledit mode à circuit ouvert ; et
    - (S24) calculer la quantité de lumière ambiante illuminant effectivement la diode électroluminescente en utilisant la dépendance détectée à la lumière et la tension directe effective mesurée.
  2. Procédé selon la revendication 1, caractérisé en ce que l'étape (S11) de détection d'une dépendance entre la tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente comprend les étapes consistant à :
    - chauffer la diode électroluminescente à une première température ;
    - mesurer la tension directe effective de la diode électroluminescente dans ledit mode à courant constant à ladite première température ;
    - chauffer la diode électroluminescente à au moins une deuxième température différente de ladite première température ;
    - mesurer la tension directe effective de la diode électroluminescente dans ledit mode à courant constant à ladite au moins une deuxième température ; et
    - (S114) calculer une dépendance linéarisée entre la tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente en utilisant les tensions directes effectives mesurées auxdites différentes températures.
  3. Procédé selon la revendication 1 ou 2, caractérisé en ce que l'étape (S11) de détection d'une dépendance entre la tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente comprend les étapes consistant à :
    - (S112) chauffer séquentiellement la diode électroluminescente à une pluralité de températures différentes et (S113) mesurer la tension directe effective de la diode électroluminescente dans ledit mode à courant constant auxdites différentes températures ; et
    - (S115) générer une table de dépendance entre la tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente en utilisant lesdites tensions directes effectives mesurées auxdites différentes températures.
  4. Procédé selon la revendication 1,
    caractérisé en ce que
    l'étape (S11) consistant à détecter une dépendance entre la tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente comprend les étapes consistant à :
    - (S112') chauffer la diode électroluminescente à une température connue ;
    - (S113') mesurer la tension directe effective de la diode électroluminescente dans ledit mode à courant constant à ladite température connue ;
    - (S114') identifier le type de la diode électroluminescente ; et
    - (S115') calculer une dépendance linéarisée entre la tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente en utilisant la tension directe effective mesurée à ladite température connue et une pente prédéfinie de la courbe de température pour le type identifié de diode électroluminescente.
  5. Procédé selon l'une des revendications 2, 3 et 4, caractérisé en ce que, lors de ladite étape (S11) de détection d'une dépendance entre la tension directe de la diode électroluminescente dans ledit mode à courant constant et la température de la diode électroluminescente, l'étape (S113 ; S113') consistant à mesurer la tension directe effective de la diode électroluminescente dans ledit mode à courant constant est effectuée en délivrant (S111 ; S111') à la diode électroluminescente un courant qui est inférieur d'au moins 10 %, et de préférence d'au moins 20 %, et mieux encore, d'au moins 40 % et de façon plus particulièrement préférable d'au moins 60 % au courant nominal de la diode électroluminescente.
  6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le procédé comprend en outre l'étape (S116 ; S116') consistant à mémoriser ladite dépendance linéarisée calculée et/ou ladite table de dépendance générée sous la forme d'une dépendance mémorisée, dans lequel ladite dépendance mémorisée est en outre utilisée (S117, S117') en tant que dépendance détectée pour calculer la température effective de la diode électroluminescente.
  7. Procédé selon la revendication 1, caractérisé en ce que
    l'étape (S21) consistant à détecter une dépendance à la lumière entre la tension directe de la diode électroluminescente dans ledit mode à circuit ouvert et la lumière ambiante illuminant la diode électroluminescente comprend les étapes consistant à :
    - (S212) illuminer séquentiellement la diode électroluminescente avec différentes intensités de lumière ambiante et mesurer (S213) la tension directe effective de la diode électroluminescente dans ledit mode à circuit ouvert à différentes intensités de la lumière ambiante ; et
    - (S214) calculer une dépendance à la lumière linéarisée et/ou générer une table de dépendance à la lumière entre la tension directe de la diode électroluminescente dans ledit mode à circuit ouvert et les intensités de la lumière ambiante illuminant la diode électroluminescente en utilisant lesdites tensions directes effectives mesurées auxdites différentes intensités de la lumière ambiante.
  8. Procédé selon la revendication 7, caractérisé en ce que
    le procédé comprend en outre l'étape (S215) consistant à mémoriser ladite dépendance à la lumière linéarisée calculée et/ou ladite table de dépendance à la lumière générée sous la forme d'une dépendance à la lumière mémorisée, dans lequel ladite dépendance à la lumière mémorisée est en outre utilisée (S216) en tant que dépendance à la lumière détectée pour calculer la quantité de lumière ambiante effectivement incidente sur la diode électroluminescente.
  9. Produit à base de programme informatique pouvant être directement chargé dans la mémoire interne d'un ordinateur numérique, comprenant des parties de codes logiciels permettant d'exécuter les étapes de l'une des revendications 1 à 9 lorsque ledit produit est exécuté sur un ordinateur.
  10. Circuit électrique (1) pour surveiller la température d'une diode électroluminescente (2) dans un mode à courant constant, comprenant :
    - un circuit d'attaque (3) pour délivrer un courant constant prédéfini à la diode électroluminescente (2) afin de faire fonctionner la diode électroluminescente (2) dans ledit mode à courant constant ;
    - une mémoire (4) pour mémoriser une dépendance entre une tension directe de la diode électroluminescente (2) dans ledit mode à courant constant et la température de la diode électroluminescente (2) ;
    - un capteur de tension (5) pour mesurer la tension directe effective de la diode électroluminescente (2) dans ledit mode à courant constant ;
    - un calculateur (6) pour calculer la température effective de la diode électroluminescente (2) en utilisant la dépendance mémorisée et la tension directe effective mesurée ; et
    caractérisé en ce que
    - ledit circuit d'attaque (3) est en outre apte à faire fonctionner la diode électroluminescente (2) dans un mode à circuit ouvert ;
    - ladite mémoire (4) mémorise en outre une dépendance à la lumière entre la tension directe de la diode électroluminescente (2) dans ledit mode à circuit ouvert et la lumière ambiante illuminant la diode électroluminescente (2) ;
    - ledit capteur de tension (5) est en outre apte à mesurer la tension directe effective de la diode électroluminescente (2) dans ledit mode à circuit ouvert ; et
    - ledit calculateur (6) est en outre apte à calculer la quantité de lumière ambiante illuminant effectivement la diode électroluminescente (2) en utilisant la dépendance à la lumière et la tension directe effective mesurée.
  11. Circuit électrique (1) selon la revendication 10,
    caractérisé en ce que le circuit électrique (1) comprend en outre
    un dispositif d'étalonnage (7), ledit dispositif d'étalonnage (7) étant apte
    à commander le capteur de tension (5) de telle manière que le capteur de tension (5) mesure séquentiellement la tension directe effective de la diode électroluminescente (2) dans ledit mode à courant constant à différentes températures,
    à calculer une dépendance linéarisée et/ou une table de dépendance entre la tension directe de la diode électroluminescente (2) dans ledit mode à courant constant et la température de la diode électroluminescente (2) en utilisant les tensions directes effectives mesurées auxdites différentes températures et,
    à mémoriser ladite dépendance linéarisée calculée et/ou ladite table de dépendance générée en tant que ladite dépendance dans ladite mémoire (4).
  12. Circuit électrique (1) selon la revendication 10, caractérisé en ce que le circuit électrique (1) comprend en outre
    un dispositif d'étalonnage (7), ledit dispositif d'étalonnage (7) étant apte
    à commander le capteur de tension (5) de manière que le capteur de tension (5) mesure la tension directe effective de la diode électroluminescente (2) dans ledit mode à courant constant à une température connue,
    à identifier le type de la diode électroluminescente (2),
    à calculer une dépendance linéarisée entre la tension directe de la diode électroluminescente (2) dans ledit mode à courant constant et la température de la diode électroluminescente (2) en utilisant une tension directe effective mesurée à ladite température connue et une pente prédéfinie de la courbe de température pour le type identifié de la diode électroluminescente (2), et
    à mémoriser ladite dépendance linéarisée calculée en tant que ladite dépendance dans ladite mémoire (4).
  13. Circuit électrique (1) selon l'une des revendications 10, 11 et 12, caractérisé en ce que
    le dispositif d'étalonnage (7) est en outre apte à commander le circuit d'attaque (3) de telle manière qu'un courant inférieur d'au moins 10 %, et de préférence d'au moins 20 %, et mieux encore, d'au moins 40 % et de façon plus particulièrement préférable d'au moins 60 % au courant nominal de la diode électroluminescente (2), soit délivré à la diode électroluminescente (2) dans ledit mode à courant constant pendant le fonctionnement dudit dispositif d'étalonnage (7).
  14. Circuit électrique (1) selon la revendication 10, caractérisé en ce que
    ledit dispositif d'étalonnage est en outre apte à commander le capteur de tension (5) de telle manière que le capteur de tension (5) mesure séquentiellement la tension directe effective de la diode électroluminescente (2) dans ledit mode à circuit ouvert à différentes intensités de la lumière ambiante illuminant ladite diode électroluminescente (2),
    à calculer une dépendance à la lumière linéarisée et/ou à générer une table de dépendance à la lumière entre la tension directe de la diode électroluminescente (2) dans ledit mode à circuit ouvert et l'intensité de la lumière ambiante illuminant la diode électroluminescente (2) en utilisant ladite tension directe effective mesurée auxdites différentes intensités de la lumière ambiante, et à mémoriser ladite dépendance à la lumière linéarisée calculée et/ou ladite table de dépendance à la lumière générée en tant que ladite dépendance à la lumière dans ladite mémoire (4).
  15. Circuit électrique (1) selon l'une des revendications 10 à 14, caractérisé en ce que le circuit est mis en place dans un équipement de communication radio portatif.
EP05005054A 2005-03-08 2005-03-08 Circuit et procédé pour surveiller la température d'une diode électroluminescente Not-in-force EP1701589B1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
EP05005054A EP1701589B1 (fr) 2005-03-08 2005-03-08 Circuit et procédé pour surveiller la température d'une diode électroluminescente
DE602005009317T DE602005009317D1 (de) 2005-03-08 2005-03-08 Schaltung und Verfahren zum Überwachen der Temperatur einer Leuchtdiode
AT05005054T ATE406783T1 (de) 2005-03-08 2005-03-08 Schaltung und verfahren zum überwachen der temperatur einer leuchtdiode
PCT/EP2006/001102 WO2006094590A1 (fr) 2005-03-08 2006-02-08 Circuit electrique et procede de surveillance de la temperature d'une diode electroluminescente

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP05005054A EP1701589B1 (fr) 2005-03-08 2005-03-08 Circuit et procédé pour surveiller la température d'une diode électroluminescente

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EP1701589A1 EP1701589A1 (fr) 2006-09-13
EP1701589B1 true EP1701589B1 (fr) 2008-08-27

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ATE406783T1 (de) 2008-09-15
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