JP2012080017A - Light-emitting element driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element driving circuit which makes it possible to gradually change a luminance value in a predetermined gradation period.SOLUTION: A light-emitting element driving circuit 10 makes a plurality of light-emitting elements 110 emit light according to a luminance setting value a corresponding to each of a plurality of light-emitting elements 110. The light-emitting element driving circuit 10 includes an automatic graduation-luminance-setting circuit 40 that gradually changes and outputs a luminance value between an initial luminance value 0 and a final luminance value a×b corresponding to the luminance setting value a and controls variation of the luminance value per unit time so that the gradual change in the luminance value is finished in a predetermined gradation period T, and a PWM circuit 30 outputting a luminance signal for making the light-emitting elements 110 emit light at a luminance corresponding to the luminance value.

Description

  The present invention relates to a light emitting element driving circuit, and more particularly to a light emitting element driving circuit that drives a light emitting element with a luminance corresponding to a luminance setting value.

  In recent years, lighting control of a light emitting element is sometimes performed by PWM control, and the duty of PWM control is appropriately changed in order to adjust the luminance of the light emitting element. When so-called gradation lighting is performed in which the luminance of the light emitting element is gradually changed, the duty of PWM control is changed little by little by a serial setting signal from the CPU.

  As a technique related to the present invention, for example, in Patent Document 1, as a light emitting element driving circuit, illuminance information from an illuminance sensor is acquired, brightness is determined, the determination result is output, and brightness change information is also provided. The brightness determination unit to be output, the brightness setting based on the brightness determination result of the brightness determination unit, the brightness setting information that outputs the brightness setting information and the brightness change information, and the brightness setting unit And a light emitting element driving unit that drives the light emitting element with a current having a current value corresponding to the luminance setting information. The light emitting element driving circuit further detects a terminal voltage of one terminal of the light emitting element and compares it with a predetermined voltage, and detects at least one of brightness change information or brightness change information. Based on the output of the comparison unit, a boost determination unit that determines whether or not to boost the terminal voltage of the other side terminal of the light emitting element, and when the boost determination unit determines to boost, the other side terminal of the light emitting element A boosting circuit unit that boosts the terminal voltage and does not boost the terminal voltage of the other terminal of the light emitting element when it is determined by the boosting determination unit that boosting is not performed.

JP 2010-67749 A

  By using a counter, a luminance value is gradually changed by a certain amount between an initial luminance value and an end luminance value corresponding to a predetermined luminance setting value, and a PWM luminance signal output based on the luminance value is used. The gradation lighting can be realized by causing the light emitting element to emit light. However, when the brightness setting value is different, the gradation lighting period is also different according to the brightness setting value. In this case, for example, when setting a different luminance setting value for a red light-emitting element that displays red, a green light-emitting element that displays green, and a blue light-emitting element that displays blue and performing gradation lighting. Since the gradation lighting periods are different, when the above three light emitting elements are viewed, there is a possibility that the lighting may be somewhat uncomfortable. Therefore, it is desirable to gradually change the luminance value in a predetermined gradation period regardless of the luminance setting value.

  An object of the present invention is to provide a light emitting element driving circuit capable of gradually changing a luminance value in a predetermined gradation period.

  A light emitting element driving circuit according to the present invention is a light emitting element driving circuit for causing a plurality of light emitting elements to emit light according to a luminance setting value for each of the plurality of light emitting elements, and corresponds to an initial luminance value and a luminance setting value. The luminance value is output by changing gradually from the luminance value, and the amount of change in the luminance value per unit time is adjusted so that the gradual change of the luminance value is completed in a predetermined gradation period. A luminance value output circuit and a luminance signal generation circuit that outputs a luminance signal for causing the light emitting element to emit light with luminance corresponding to the luminance value are provided.

  According to the light emitting element driving circuit having the above configuration, the amount of change in the luminance value per unit time can be adjusted so that the gradual change in the luminance value is completed in a predetermined gradation period. Accordingly, for example, when a different luminance setting value is set for each of a red light emitting element that displays red, a green light emitting element that displays green, and a blue light emitting element that displays blue, gradation lighting is performed. The gradation period can be aligned.

In embodiment which concerns on this invention, it is a figure which shows the connection relation of a light emitting element drive circuit, CPU, and a light emitting element. FIG. 5 is a diagram showing each element of a PWM circuit and an automatic gradation PWM circuit in the embodiment according to the present invention. FIG. 6 is a diagram illustrating a state in which a count value b and a count value c are compared in a comparison circuit and a comparison result is output in the embodiment according to the invention. In embodiment which concerns on this invention, it is a figure which shows the change of the output of a multiplication circuit in the case of carrying out gradation lighting of a red light emitting element, a green light emitting element, and a blue light emitting element. FIG. 5 is a diagram showing each element of a PWM circuit and an automatic gradation PWM circuit in the embodiment according to the present invention.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. In the following description, the oscillator and the frequency dividing circuit are described as components of the light emitting element driving circuit, but the oscillator and the frequency dividing circuit may be external components of the light emitting element driving circuit.

  Also, in the following, in all the drawings, the same symbols are attached to the same elements, and the duplicate description is omitted. In the description in the text, the symbols described before are used as necessary.

  FIG. 1 is a diagram illustrating a connection relationship among the light emitting element driving circuit 10, the CPU 100, and the light emitting element 110. The light emitting element driving circuit 10 includes a serial I / F circuit 20, an oscillator 22, a frequency dividing circuit 24, a PWM circuit 30, an automatic gradation luminance setting circuit 40, and a driver circuit 50. The light emitting element driving circuit 10 has a function of causing the light emitting element 110 to emit light based on a luminance setting value transmitted from the CPU 100.

  The light emitting element 110 is a circuit element that emits light when a voltage is applied in the forward direction to the anode terminal (anode) with respect to the cathode terminal (cathode). The light emitting element 110 may be a red light emitting element that displays red, a green light emitting element that displays green, or a blue light emitting element that displays blue.

  The CPU 100 generates a luminance setting value, a gradient setting value, and an ON / OFF setting value for the automatic gradation luminance setting circuit 40 based on an external setting or the like, converts these values into a serial signal, and converts the serial I to serial I value. / F circuit 20 has a function to transmit. Here, the luminance setting value is a setting value corresponding to the luminance of the light emitting element 110. The tilt setting value is a setting value for selecting the magnitude of the clock frequency input to the automatic gradation UP / DOWN counter 404. Further, the ON / OFF set value is a value corresponding to either ON or OFF. When the ON / OFF set value is ON, the automatic gradation UP / DOWN counter 404 is used as an up counter in order to perform a fade-in process in which the luminance of the light emitting element 110 gradually changes from a small value to a large value. It is a setting to be used. When the ON / OFF set value is OFF, the automatic gradation UP / DOWN counter 404 is used as a down counter in order to perform a fade-out process in which the luminance of the light emitting element 110 gradually changes from a large value to a small value. This is the setting.

  The serial I / F circuit 20 receives the serial signal from the CPU 100, cuts out the luminance setting value, the inclination setting value, and the ON / OFF setting value from the serial signal, and uses these setting values as the automatic gradation luminance setting circuit 40. It is an interface circuit which has a function to transmit to.

  The oscillator 22 is an oscillation circuit that generates and outputs a pulse signal (clock) having a predetermined clock frequency f. The clock generated by the oscillator 22 is input to the PWM circuit 30 and the frequency dividing circuit 24.

  The frequency dividing circuit 24 divides the clock of the clock frequency f input from the oscillator 22 by a frequency dividing ratio such as frequency division by 2, 3, frequency division, or frequency division, and the divided clocks are used for automatic gradation. This is a circuit for inputting to the luminance setting circuit 40.

  FIG. 2 is a diagram showing each element of the PWM circuit 30 and the automatic gradation luminance setting circuit 40. The automatic gradation luminance setting circuit 40 includes a clock frequency selection circuit 402, an automatic gradation UP / DOWN counter 404, and a multiplication circuit 406. The luminance setting circuit for automatic gradation 40 outputs the luminance value by gradually changing the luminance value between 0 which is the initial luminance value and a × m which is the final luminance value corresponding to the luminance setting value a. Functions as a luminance value output circuit that adjusts the amount of change in luminance value per unit time so that the gradual change is completed in a predetermined gradation period T (see FIG. 4).

  The clock frequency selection circuit 402 selects a clock frequency corresponding to the slope setting value from among the clocks input from the frequency dividing circuit 24, and supplies the clock having the selected clock frequency to the automatic gradation UP / DOWN counter 404. Has a function to input.

  The automatic gradation UP / DOWN counter 404 is a counter that counts up or down at the clock frequency of the clock input from the clock frequency selection circuit 402. The automatic gradation UP / DOWN counter 404 functions as an UP counter that counts up from 0 to m when the ON / OFF set value transmitted from the serial I / F circuit 20 is ON. When the ON / OFF set value is OFF, it functions as a DOWN counter that counts down from m to 0.

  The multiplication circuit 406 multiplies the brightness setting value a (0 ≦ a ≦ n) from the serial I / F circuit 20 and the count value b (0 ≦ b ≦ m) from the automatic gradation UP / DOWN counter 404 (a ≦ a ≦ n). Xb), and a function of outputting the calculation result to the comparison circuit 304 as a luminance value.

  The PWM circuit 30 includes a PWM creation counter 302 and a comparison circuit 304. Further, the PWM circuit 30 functions as a luminance signal generation circuit that outputs a PWM luminance signal for causing the light emitting element 110 to emit light with luminance corresponding to the luminance value (a × b) output from the multiplication circuit 406.

  The PWM creation counter 302 is an N-ary counter that counts up from 0 to N at the clock frequency of the clock input from the oscillator 22. The count value c of the PWM creation counter 302 is output to the comparison circuit 304.

  The comparison circuit 304 compares the count value c from the PWM creation counter 302 with the luminance value (a × b) from the multiplication circuit 406, and when the count value c is larger than the luminance value (a × b). , Low, and when the count value c is smaller than the luminance value (a × b), it has a function of outputting High.

  FIG. 3 is a diagram illustrating a state in which the comparison circuit 304 compares the luminance value (a × b) with the count value c and outputs the comparison result as a PWM luminance signal. The upper diagram of FIG. 3 is a diagram illustrating the output of the comparison circuit 304 when the PWM creation counter 302 is counting up, and the PWM luminance signal that is the output of the comparison circuit 304 gradually increases in the High period. Widening fade-in processing is done. The lower diagram of FIG. 3 is a diagram illustrating the output of the comparison circuit 304 when the PWM creation counter 302 is counting down, and the PWM luminance signal that is the output of the comparison circuit 304 is a fade-out process in which the High period is gradually narrowed. Has been made.

  The driver circuit 50 is a current source for causing a current to flow in the forward direction of the light emitting element 110 (direction from the anode terminal to the cathode terminal). Specifically, the driver circuit 50 is turned on during the High period of the PWM luminance signal that is the output signal of the comparison circuit 304. At this time, a current flows through the light emitting element 110, and the PWM luminance signal that is the output signal of the comparison circuit 304 It is turned off during the Low period, and at this time, no current flows through the light emitting element 110.

  Next, the operation of the light emitting element driving circuit 10 having the above configuration will be described with reference to FIG. In order to explain the operation of the light emitting element driving circuit 10 in an easy-to-understand manner, it is assumed that the three light emitting elements 110 are emitting light by the light emitting element driving circuit 10. The three light emitting elements 110 include a red light emitting element 110a that displays red, a green light emitting element 110b that displays green, and a blue light emitting element 110c that displays blue. FIG. 4 shows the output of the multiplication circuit 406 when the red light emitting element 110a (FIG. 4A), the green light emitting element 110b (FIG. 4B), and the blue light emitting element 110c (FIG. 4C) are lit in gradation. It is a figure which shows the mode of a change of the luminance value (axb) which is.

With the setting from the outside, the CPU 100 generates a luminance setting value a ₁ for the red light emitting element 110a, generates a luminance setting value a ₂ for the green light emitting element 110b, and generates a luminance setting value a ₃ for the blue light emitting element. . The relationship between the magnitudes of the brightness setting values a ₁ , a ₂ , and a ₃ is a ₁ <a ₂ <a ₃ , respectively.

Here, the multiplication circuit 406 uses the brightness setting value a (0 ≦ a ≦ n) from the serial I / F circuit 20 and the count value b (0 ≦ b ≦ m) from the automatic gradation UP / DOWN counter 404. Multiplication is performed and the result is output to the comparison circuit 304 as a luminance value (a × b). Therefore, for example, when the automatic gradation UP / DOWN counter 404 functions as an UP counter, the increments per unit time when the luminance setting values a ₁ , a ₂ , and a ₃ are set are respectively a ₁ × b (FIG. 4 (a)), a ₂ × b (FIG. 4 (b)), a ₃ × b (FIG. 4 (c)), and a value that changes with the increase amount is output from the comparison circuit 304. The In other words, even if the luminance setting values are different among the red light emitting element 110a, the green light emitting element 110b, and the blue light emitting element 110c, the fade-in end period in which the luminance value changes is the same, in other words, the gradation period is Be the same. As a result, even when different luminance setting values are set for the red light emitting element 110a, the green light emitting element 110b, and the blue light emitting element 110c, gradation lighting can be performed with no sense of incongruity. In the above description, the automatic gradation UP / DOWN counter 404 functions as an UP counter (counting up) and fade-in processing is performed. However, the automatic gradation UP / DOWN counter 404 uses the DOWN counter ( Even when the fade-out process is performed after counting down, the gradation period T is the same regardless of the luminance setting value.

  FIG. 5 is a diagram showing a light emitting element driving circuit 11 which is a modification of the light emitting element driving circuit 10. The difference between the light-emitting element drive circuit 11 and the light-emitting element drive circuit 10 is that a division circuit 407 is provided instead of the multiplication circuit 406. Therefore, the difference will be mainly described.

  The division circuit 407 divides the count value b (0 ≦ b ≦ m) from the automatic gradation UP / DOWN counter 404 by the luminance setting value a (0 ≦ a ≦ n) from the serial I / F circuit 20 (b ÷ a) and a function of outputting to the comparison circuit 304.

According to the configuration of the light emitting element driving circuit 11 having the above configuration, when the automatic gradation UP / DOWN counter 404 functions as an UP counter, the unit when the luminance set values a ₁ , a ₂ , and a ₃ are set. The increments per time are b ÷ a ₁ , b ÷ a ₂ , and b ÷ a ₃ , and values that change with the increments are output from the comparison circuit 304. That is, even if the luminance setting values are different among the red light emitting element 110a, the green light emitting element 110b, and the blue light emitting element 110c, the fade-in end period in which the luminance value changes is the same, in other words, the gradation period T Are the same. As a result, even when different luminance setting values are set for the red light emitting element 110a, the green light emitting element 110b, and the blue light emitting element 110c, gradation lighting can be performed with no sense of incongruity.

  10, 11 Light emitting element drive circuit, 20 serial I / F circuit, 22 oscillator, 24 frequency divider circuit, 30 PWM circuit, 40 automatic gradation brightness setting circuit, 50 driver circuit, 110 light emitting element, 110a red light emitting element, 110b green Light emitting element, 110c Blue light emitting element, 302 PWM creation counter, 304 comparison circuit, 402 clock frequency selection circuit, 404 automatic gradation UP / DOWN counter, 406 multiplication circuit, 407 division circuit.

Claims (3)

A light emitting element driving circuit for causing the plurality of light emitting elements to emit light according to a luminance setting value for each of the plurality of light emitting elements;
The luminance value is gradually changed between the initial luminance value and the final luminance value corresponding to the luminance setting value and outputted, and the gradual change of the luminance value is completed in a predetermined gradation period. A luminance value output circuit for adjusting the amount of change in the luminance value per unit time;
A luminance signal generation circuit that outputs a luminance signal for causing the light emitting element to emit light at a luminance corresponding to the luminance value;
A light-emitting element driving circuit comprising: In the light emitting element drive circuit according to claim 1,
The luminance value output circuit includes:
In the gradation period, a count circuit that counts up from a predetermined initial count value to a predetermined end count value, or counts down from the end count value to the initial count value;
A multiplication circuit that multiplies the output value of the count circuit and the brightness setting value and outputs the result as the brightness value;
A light emitting element driving circuit comprising: In the light emitting element drive circuit according to claim 1,
The luminance value output circuit includes:
In the gradation period, a count circuit that counts up from a predetermined initial count value to a predetermined end count value, or counts down from the end count value to the initial count value;
A division circuit for dividing the output value of the count circuit by the luminance setting value and outputting the luminance value;
A light emitting element driving circuit comprising:

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