JP2007287964A - Driving apparatus for light emitting element, light emitting apparatus, and driving method of same light emitting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving apparatus for light emitting elements which can keep the brightness of the light emitting elements equal to a predetermined value, and a light emitting apparatus having the mounted driving apparatus, and further, a driving method of the light emitting apparatus. <P>SOLUTION: In the driving apparatus for light emitting elements, a timing controlling portion 4 so feeds predetermined timing signals to a pulse generating portion 6 that the pulse generating portion 6 generates pulse signals thereby. Since there may be the cases that these pulse signals include distortions, the timing controlling portion 4 forces a sampling portion 7 to sample the voltage values of a point A at the timings of avoiding these distortions. Then, the voltage values sampled by the sampling portion 7 are inputted to an operating portion 3. The operating portion 3 performs predetermined operations based on those voltage values, and outputs to a driving-voltage/current feeding portion 2 such feedback signals as to make the brightness of the group of light emitting elements 15 constant. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a driving device for driving a light emitting element, a light emitting device equipped with the driving device, and a driving method thereof.

  In a control device that controls the light intensity of a plurality of LEDs (Light Emitting Diodes) to be constant, a method of driving by PWM (Pulse Width Modulation) is generally used (see, for example, Patent Document 1). It is known that PWM has an affinity with a digital circuit and has good linearity accuracy.

In the LED control method described in Patent Document 1, the amplifier in the current adjustment circuit (104) is configured such that the pulse voltage generated by the input node (106) and the current value of the LED array (102) are caused by resistance (R20, etc.). The voltage generated by the conversion is compared. That is, in response to the PWM control signal from the input node (106) and the emitter current (the converted voltage) of the current adjustment element (Q2), the current adjustment circuit (104) causes the base current of the element (Q2). Is controlled to adjust the collector current of the element (Q2), that is, the current of the LED array (102).
Japanese Patent Laying-Open No. 2004-253804 (paragraph [0016], FIGS. 1, 2 and the like)

  In recent years, it has become necessary to sample measured values such as current and voltage with high accuracy in a short time with an increase in the number of bits handled and an increase in processing speed. For example, if the waveform of the voltage generated at the resistor (sense resistor) end has waveform distortion such as overshoot, undershoot, or ringing, the measured value (voltage due to the sense resistor, etc.) is accurately sampled. Can not do it. In this case, it is difficult to increase the S / N ratio even if a filter is used.

  In addition, when a sufficient sampling time for obtaining a stable measurement value is shorter than the PWM on-time, an accurate measurement value cannot be obtained.

  Thus, if the measured value cannot be obtained accurately, it becomes difficult to maintain the current applied to the light emitting element at a predetermined value, and it becomes difficult to obtain a desired luminance.

  In view of the circumstances as described above, an object of the present invention is to provide a light emitting element driving device capable of maintaining the luminance of a light emitting element at a predetermined value, a light emitting device equipped with the driving device, and a driving method thereof. It is in.

  In order to achieve the above object, a driving device for a light emitting element according to the present invention includes a drive signal generating means for generating a drive signal for driving the light emitting element, and the light emitting element when the light emitting element is driven by the drive signal. A measuring means for measuring a signal corresponding to a driving current value, a driving voltage value, or a luminance of the light emitting element, a sampling means for sampling the measured measuring signal, and a waveform of the measuring signal. And at least control means for controlling the timing of the sampling.

  In the present invention, since the timing of sampling is controlled according to the waveform of the measurement signal, it is possible to select and sample the waveform of the desired measurement signal. Thereby, the measurement signal is sampled with high accuracy, and the luminance of the light emitting element can be maintained at a predetermined value.

  The control means may dynamically analyze the waveform according to the waveform of the measurement signal and control the sampling timing, or the control means may recognize the waveform of the measurement signal in advance as in the next invention. In addition, the sampling timing may be controlled.

  In the present invention, the drive signal generating means generates a pulse signal as a drive signal, and the control means controls the rising timing and falling timing of the pulse signal. Thereby, since the control means can recognize the rising timing and falling timing of the drive signal, the control means can recognize the timing of the measurement signal. Therefore, the control means can reliably control the sampling timing according to the waveform of the measurement signal.

  The “pulse signal” here is, for example, a rectangular wave, a triangular wave, or a trapezoidal wave, but is not limited thereto, and may be any signal as long as the signal waveform rises and falls repeatedly. The “pulse signal” here does not necessarily have a final signal value that has fallen to zero.

  In the present invention, the control means controls to sample a portion where the measurement signal is stable. The “stable part” means a part where the measurement signal has a substantially constant value.

  In the present invention, the control means performs control so that the sampling is not performed when the period of the stable portion of the measurement signal is shorter than the minimum sampling period by the sampling means. In the present invention, meaningless sampling is not performed, so that efficient processing is possible.

  In the present invention, the control means further controls the number of samplings. For example, the control means may set the number of samplings to be small if the time required for the desired signal waveform in the measurement signal is short, or if the time required for the desired signal waveform is long, adjust accordingly. A large number of samplings can be set. That is, the control means can obtain an accurate measurement value by appropriately changing the number of times of sampling.

  In the present invention, the control means further variably controls the sampling period of the sampling. Thereby, for example, if the time for which the desired signal waveform of the measurement signal continues is short, the control means may set the sampling period to be short accordingly, and if the time for which the desired signal waveform continues is long, Accordingly, the sampling period can be set longer. That is, the control means can obtain an accurate measurement value by appropriately changing the sampling period.

  The “sampling period” is a concept different from the “minimum sampling period” defined in advance in the circuit design of the driving device for the issuing element, and is a period in which sampling is performed by the sampling unit. The control unit is variable. It is a “sampling period” in the sense that it can be controlled to

  In the present invention, the drive signal generated by the drive signal generator is a PWM signal.

  In the present invention, the light emitting element driving device further includes voltage / current control means for controlling a current or voltage supplied to the light emitting element based on a sample value of the measurement signal by the sampling means.

  “Based on” “based on the sample value of the measurement signal by the sampling means” means that the voltage / current control means performs various processing such as averaging process, median value extraction process, mode value extraction process, etc. This means performing arithmetic processing.

  In the present invention, the measuring means is a photosensor that measures the luminance. Thereby, since the luminance is directly monitored, a more accurate measurement value for maintaining the luminance at a predetermined value can be obtained.

  The light emitting device according to the present invention is applied to the light emitting element when the light emitting element is driven by the drive signal, and a drive signal generating means for generating a drive signal for driving the light emitting element. A measuring means for measuring a signal corresponding to a driving current value, a driving voltage value, or a luminance of the light emitting element; a sampling means for sampling the measured measuring signal; and at least the sampling according to a waveform of the measuring signal And control means for controlling the timing.

  The light-emitting device according to the present invention is a device further including a “light-emitting element” in each component of the above-described light-emitting element driving device.

  The driving method of the light emitting element driving device according to the present invention includes a step of generating a driving signal for driving the light emitting element, and a driving current applied to the light emitting element when the light emitting element is driven by the driving signal. Measuring a signal according to a value, a driving voltage value, or a luminance of the light emitting element, controlling a timing when sampling the measurement signal according to a waveform of the measured measurement signal, Sampling the measurement signal at a controlled timing.

  As described above, according to the present invention, the luminance of the light emitting element can be reliably maintained at a predetermined value.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a light emitting device according to an embodiment of the present invention.

  The light emitting device 100 includes, for example, a plurality of light emitting elements (hereinafter sometimes referred to as a light emitting element group 15) and a light emitting element driving device 10.

  The light emitting elements are, for example, LEDs, and these LEDs are connected in series. As the light emitting element, an EL (Electro-Luminescence) element may be used instead of the LED. In the case of an EL element, it may be either organic or inorganic. In FIG. 1, the number of LEDs is four, for example, but may be three or less, and may be five or more, and the number is not limited. The light emitting element group 15 is used as a backlight of a display, for example. When the light-emitting element is used as a backlight, a light-emitting element that emits white, red, green, or blue is used. Alternatively, a plurality of light-emitting elements arranged in combination may be used. The light-emitting device is not limited to the backlight, and may be any light-emitting device that maintains the luminance of the light-emitting element at a desired value.

  The light emitting element driving device 10 includes a drive voltage / current supply unit 2 that supplies current or voltage to the light emitting element group 15.

  The drive voltage / current supply unit 2 takes in power supplied from, for example, a primary power supply and supplies a constant current or voltage to the light emitting element group 15. For example, a switching regulator is used as the drive voltage / current supply unit 2.

  The light emitting element driving device 10 further includes a current amount control element 8, a sense resistor 9, a pulse generation unit 6, a sampling unit 7, and an overall operation control unit 5 that controls the entire light emitting element driving device 10.

  The current amount control element 8 is connected to the current output side of the light emitting element group 15, and, for example, an FET (Field Effect Transistor) is used. The current amount control element 8 is not limited to the FET but may be a bipolar transistor.

  The sense resistor 9 has one end connected to the source of the current amount control element 8 and the other end grounded. Thereby, the current value at the point A, that is, the current flowing through the light emitting element group 15 is converted into a voltage value. That is, the sense resistor 9 measures the voltage value that is a signal corresponding to the drive current value of the light emitting element 15. This voltage value (measurement signal) is sampled by the sampling unit 7 at a predetermined timing. In addition, when the light emitting element 15 is a voltage drive type light emitting element, the drive voltage value itself becomes a voltage value to be measured.

  The pulse generator 6 outputs a control signal for controlling the current amount of the current amount control element 8 to the gate of the current amount control element 8. The pulse generator 6 and the current amount control element 8 constitute a “drive signal generating means” of the light emitting element group 15. Examples of the control signal generated by the pulse generator 6 include a pulse signal by PWM, PDM (Pulse Density Modulation), or the like. In the case of PWM, the time average voltage is changed by changing the duty ratio of the pulse, and thereby the luminance of the light emitting element is variable.

  Since the relationship between the drive current and the luminance is nonlinear, the LED has a characteristic that the luminance does not become 50% even if the drive current is 50%, for example. Therefore, in order to obtain 50% luminance, it is a general method to set the current flowing time to 50%, that is, to perform PWM driving with a duty ratio of 50%. Thereby, the luminance can be reduced to 50%.

  The overall operation control unit 5 includes a timing control unit 4 and a calculation unit 3. The timing controller 4 supplies a timing signal for generating a pulse to the pulse generator 6. The overall operation control unit 5 sets what pulse the pulse generation unit 6 generates. That is, the pulse interval, pulse width, pulse size, etc. are set. Further, the timing control unit 4 supplies the sampling unit 7 with a timing signal for starting sampling. The calculation unit 3 performs a predetermined calculation based on the voltage value sampled by the sampling unit 7 and outputs a feedback signal indicating how to change the current or voltage applied to the light emitting element group 15 as a drive voltage / current. Output to the supply unit 2. That is, the overall operation control unit 5 monitors the voltage value at the measured point A and controls the drive voltage / current supply unit 2 so that the voltage value is constant. The calculation unit 3 and the drive voltage / current supply unit 2 constitute a “voltage / current control unit”.

  The operation of the light emitting element driving apparatus 10 configured as described above will be described. FIG. 2 is a diagram illustrating examples of various signals for explaining the operation.

  When the timing controller 4 supplies a predetermined timing signal to the pulse generator, the pulse generator 6 generates a pulse signal 16 having various pulse widths as shown in FIG. 2A, for example. The pulses a, b, and c are not necessarily generated in such a temporal order. In order to make the explanation of the operation easy to understand, only three types of pulses having different pulse widths are shown. The current amount control element 8 emits a current corresponding to the voltage of this pulse signal. Thereby, the light emitting element group 15 emits light with luminance according to the amount of current.

  Here, FIG. 2B shows a voltage value generated at the point A, and naturally occurs in synchronization with the pulse of FIG. For example, at the timing corresponding to the rise and fall of the pulse a shown in FIG. 2A, the voltage waveform 17 in FIG. 2B has distortion such as overshoot and undershoot. Such distortion is difficult to remove.

  FIG. 2C shows the sampling pulse supplied from the timing control unit 4. The timing control unit 4 outputs a sampling pulse (sets the signal 18 to ON) when the voltage waveform 17 is not distorted, that is, during a period in which the voltage value 17 is substantially constant. To do. The sampling unit 7 samples the voltage value 17 at this timing. In this example, in the case of the pulse a, sampling is performed twice, and in the case of the pulse b, sampling is performed once. In the case of the pulse c, since the period during which the voltage value 17 is constant is shorter than the minimum sampling period t shown in FIG. 2C, sampling is not performed in this case.

  In the pulses a, b, and c, the period during which distortion occurs is recognized by the overall operation control unit 5 in advance by circuit design. Therefore, the timing control unit 4 can generate the sampling pulse while avoiding the period in which the distortion occurs. Further, since the overall operation control unit 5 recognizes what pulse signal 16 the pulse generation unit 6 generates as described above, what is the waveform of the voltage waveform 17 at the point A? Further, the generation timing of the voltage waveform 17 can be recognized. Therefore, the timing control unit 4 can reliably control the sampling timing according to the waveform of the pulse signal generated by the pulse generation unit 6, for example, the pulse width shown in FIGS. Become.

  The voltage value sampled by the sampling unit 7 is input to the calculation unit 3. The calculation unit 3 performs a predetermined calculation based on the voltage value, and outputs a feedback signal that makes the luminance of the light emitting element group 15 constant to the drive voltage / current supply unit 2. Specifically, the overall operation control unit 5 compares the sampled voltage value 17 with a desired reference voltage value, and drives the drive voltage so that the deviation signal obtained by the comparison becomes a predetermined value or zero. Control the current supply unit 2 This can be freely realized by an analog circuit or a digital circuit.

  In addition, the overall operation control unit 5 uses which voltage value of the sampled voltage values should be calculated by the calculation unit 3, what algorithm should be calculated, or sampled as described above When the voltage value and the reference voltage value are compared, various settings such as how much the reference voltage value is set can be performed.

  As described above, in the light emitting element driving device 10 according to the present embodiment, the sampling timing is controlled according to the voltage waveform 17, so that the desired voltage waveform 17 can be selected and sampled. Thereby, the voltage value is sampled with high accuracy, and the luminance of the light emitting element group 15 can be maintained at a predetermined value. In particular, as shown in FIG. 2, the luminance of the light-emitting element group 15 is reliably increased by sampling during a period when the voltage value 17 is stable, that is, a period when the voltage value 17 is substantially constant. It can be maintained at a predetermined value.

  In the present embodiment, when the pulse signal 16 by the pulse generator 6 is zero (the ON time of the current amount control element 8 is zero) or extremely short like the pulse c, meaningless sampling is not performed. The calculation unit 3 enables efficient processing.

  In the present embodiment, the overall operation control unit 5 sets the number of samplings to be small according to the duration of the desired waveform of the voltage waveform 17 at point A, and sets the duration of the desired waveform. If it is long, the number of samplings is set accordingly. As described above, the overall operation control unit 5 can obtain an accurate voltage value by appropriately changing the number of times of sampling. The desired waveform is, for example, a waveform in which the voltage value 17 is substantially constant without distortion as described above.

  In the present embodiment, not only the timing and number of times of sampling, but also the overall operation control unit 5 may variably control the sampling period. Thereby, for example, if the time during which the desired waveform of the voltage waveform 17 at point A continues is short, the overall operation control unit 5 may shorten the sampling period accordingly, and the desired waveform will continue. If the time is long, the sampling period can be lengthened accordingly. That is, the overall operation control unit 5 can obtain an accurate voltage value 17 by appropriately changing the sampling period.

  Here, the “sampling period” is a concept different from the “minimum sampling period t”, and is a period in which sampling is performed by the sampling unit 7, and can be variably controlled by the overall operation control unit 5. It is a “sampling period” in the sense that it can be done. The minimum sampling period t is a value determined in advance by circuit design.

  In the present embodiment, measurement errors due to complicated filters (low-pass filter, band-pass filter, etc.) (not shown) used after sampling by the sampling unit 7 can be reduced. In addition, the configuration of the filter used after the sampling can be simplified.

  FIG. 3 is a block diagram showing a configuration of a light emitting device according to another embodiment of the present invention. In the following description, the same elements and functions of the light emitting device 100 and the light emitting element driving device 10 according to the embodiment shown in FIG. 1 and the like will not be described or will be mainly described. To do.

  The light emitting element driving device 20 includes a photosensor 11 that detects the luminance of the light emitting element group 15. As the photosensor, for example, a photodiode or the like is used. The photosensor 11 converts the light intensity into an electric signal, and the sampling unit samples the voltage value at a predetermined timing. Similar to the light emitting element driving device 10 described above, the timing control unit 4 of the overall operation control unit 5 controls the sampling timing. The overall operation control unit 5 monitors the voltage value, that is, the luminance, and outputs a feedback signal to the drive voltage / current supply unit so that the luminance becomes a predetermined value. Also in the present embodiment, the overall operation control unit 5 may select and sample a desired waveform from the output voltage values of the photosensor.

  In the light emitting element driving apparatus 10, the overall operation control unit 5 maintains the brightness constant by keeping the current value of the light emitting element group 15 constant. However, when a semiconductor is used for the light-emitting element, the luminance may change due to a temperature change. For such a problem, the overall operation control unit 5 according to the present embodiment can directly monitor the luminance of the light emitting element group 15, and thus a more accurate voltage value for maintaining the luminance constant. Can be obtained.

  FIG. 4 is a perspective view showing a part of the LED backlight device. When the light emitting element is an LED, the light emitting device 100 is mounted on such an LED backlight device 50. The LED backlight device 50 is configured by arranging a plurality of LED groups 15 on the back side of the optical sheet 51. A reflecting plate 52 is provided around the LED group 15.

It is a block diagram which shows the structure of the light-emitting device which concerns on one embodiment of this invention. It is a figure which shows the example of the various signals for demonstrating operation | movement of the drive device for light emitting elements. It is a block diagram which shows the structure of the drive device for light emitting elements which concerns on other embodiment of this invention. It is a perspective view which shows a part of LED backlight apparatus carrying the said drive device for light emitting elements.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Drive voltage / current supply part 3 ... Operation part 4 ... Timing control part 5 ... Whole operation control part 6 ... Pulse generation part 7 ... Sampling part 8 ... Current amount control element 9 ... Sense resistance 10, 20 ... Drive for light emitting element Device 11 ... Photosensor 15 ... Light emitting element group 100 ... Light emitting device

Claims (11)

Drive signal generating means for generating a drive signal for driving the light emitting element;
A measuring means for measuring a signal corresponding to a driving current value, a driving voltage value, or a luminance of the light emitting element applied to the light emitting element when the light emitting element is driven by the driving signal;
Sampling means for sampling the measurement signal measured by the measurement means;
And a control unit that controls at least the sampling timing according to the waveform of the measurement signal. The light-emitting element driving device according to claim 1,
The drive signal generating means generates a pulse signal as a drive signal,
The drive means for a light emitting element, wherein the control means controls a pulse rising timing and a falling timing of the pulse signal. The light-emitting element driving device according to claim 2,
The drive means for a light emitting element, wherein the control means controls to sample a portion where the measurement signal is stable. It is a drive device for light emitting elements according to claim 3,
The light emitting element driving device according to claim 1, wherein the control means performs control so that the sampling is not performed when a period of a stable portion of the measurement signal is shorter than a minimum sampling period by the sampling means. The light-emitting element driving device according to claim 1,
The drive means for a light emitting element, wherein the control means further controls the number of times of sampling. The light-emitting element driving device according to claim 1,
The control unit further variably controls a sampling period of the sampling. The light-emitting element driving device according to claim 2,
The drive signal for the light emitting element, wherein the drive signal by the drive signal generating means is a PWM signal. The light-emitting element driving device according to claim 1,
A drive device for a light emitting element, further comprising voltage / current control means for controlling a current or voltage supplied to the light emitting element based on a sample value of the measurement signal by the sampling means. The light-emitting element driving device according to claim 1,
The driving device for a light emitting element, wherein the measuring means is a photosensor that measures the luminance. A light emitting element;
Drive signal generating means for generating a drive signal for driving the light emitting element;
A measuring means for measuring a signal corresponding to a driving current value, a driving voltage value, or a luminance of the light emitting element applied to the light emitting element when the light emitting element is driven by the driving signal;
Sampling means for sampling the measured measurement signal;
And a control unit that controls at least the sampling timing according to the waveform of the measurement signal. Generating a drive signal for driving the light emitting element;
Measuring a signal corresponding to a drive current value, a drive voltage value, or a luminance of the light emitting element applied to the light emitting element when the light emitting element is driven by the drive signal;
Controlling the timing of sampling the measurement signal according to the waveform of the measured measurement signal;
Sampling the measurement signal at the controlled timing. A driving method for a light emitting element driving device.

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