JP2011070957A - Lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting device capable of performing smooth dimming control at the time of dimming control with PWM. <P>SOLUTION: The lighting device has a light source section 14 having LEDs, a drive circuit 32 for lighting up an LED circuit in response to inputting of a PWM signal, and a PWM control circuit 33 for outputting the PWM signal corresponding to a degree of dimming of an input dimming signal and changing a level of frequency by following to the level of the degree of dimming to the drive circuit 32. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an illumination device using an LED as a light source.

  This type of lighting device is particularly used for lighting for production, etc., and PWM (pulse width modulation) is used to perform dimming control without changing the color temperature characteristics (see Patent Document 1). .

  The dimming control by PWM is control of the lighting time and extinguishing time of the LED. Therefore, when the illumination target is imaged by the television camera, flicker called flicker due to the PWM frequency occurs in the captured image. In order to suppress this flicker, a sufficiently high frequency is adopted as the PWM frequency that is an integer multiple of the frequency of the vertical synchronization signal of the image captured by the camera (see Patent Document 2).

JP 2006-40872 A JP 2006-79990 A

  However, when the PWM frequency is increased as described above, the time width of one cycle is narrowed, so that dimming control by PWM with a large number of gradations becomes difficult. When the number of gradations is small, the luminance change due to the light control becomes stepwise light control that can be recognized by human eyes, and smooth light control is difficult. This phenomenon is particularly noticeable in a low gradation state with low luminance.

  The present invention has been made as a solution to the problems in the lighting device as described above, and an object thereof is to provide a lighting device capable of performing smooth dimming control by PWM.

  A lighting device according to the present invention includes: a light source unit including an LED; and a PWM signal that corresponds to the dimming degree of the input dimming signal and changes the frequency level according to the dimming level to the drive circuit. And a drive circuit for lighting the LED in response to the input of the PWM signal.

  In the above, the light source unit may be separate from or integrated with other configurations. The frequency used on the low dimming side is 500 Hz to 1 Kz, and the frequency used on the high dimming side is about 5 Kz.

  In the illumination device according to the present invention, the PWM control circuit changes the level of the frequency in the PWM signal stepwise or continuously.

  According to the present invention, the PWM signal in which the frequency level is changed by following the dimming level is output to the drive circuit. Therefore, when the dimming level is low, the frequency of the PWM signal is low, so that one period of time is required. Becomes longer, the number of gradations can be increased, the on-duty ratio is gradually changed, dimming control is performed, and the luminance can be changed smoothly. On the other hand, when the dimming degree is high, the frequency of the PWM signal is increased, so that one cycle time is shortened and the number of gradations cannot be increased, but the on-duty ratio of the PWM signal cannot be changed greatly. Therefore, the luminance changes smoothly despite the small number of gradations.

  According to the present invention, since the level of the frequency in the PWM signal is changed stepwise or continuously, an appropriate on-duty ratio can be realized in a low dimming region and a high dimming region, and smooth dimming is achieved. Control can be performed.

The block diagram of the illuminating device which concerns on embodiment of this invention. The front view of the light source part in the illuminating device which concerns on embodiment of this invention. The circuit diagram in the illuminating device which concerns on embodiment of this invention. The table | surface which shows the content of the memory table used for the light control by the illuminating device which concerns on embodiment of this invention. The graph which shows the relationship between the light control degree used as suitable light control, and brightness. The graph which shows an example of the PWM signal waveform corresponding to the predetermined light control degree in the light control by the illuminating device which concerns on embodiment of this invention.

  Embodiments of a lighting device according to the present invention will be described below with reference to the accompanying drawings. In each figure, the same components are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 shows a configuration diagram of a spotlight 11 that is an illumination apparatus according to an embodiment. The spotlight 11 includes a light source unit 12 and a projection unit 13. Light is emitted from the light source unit 12. This light is projected by the projection unit 13 onto the illumination target.

  The projection unit 13 includes projection lenses 21a and 21b that collect light and project it to the outside, and adjustment handles 22a and 22b that adjust the projection distribution. The light emitted from the light source unit 12 is projected onto the illumination target by the projection unit 13.

  The light source unit 12 includes a light source unit 14 that is a planar light source, and heat generated by the light source unit 14 is radiated by a radiator 15. The light source unit 12 includes a power supply unit 16 that supplies lighting power to the light source unit 14, a control unit 17 that controls lighting of the light source unit 14, an operation unit 18 that performs a lighting operation of the light source unit 14, a cylindrical optical path 19, a cutter A unit 20 and the like are provided. The cylindrical optical path 19 guides the light from the light source unit 14 to the projection unit 13, and the cutter unit 20 controls the shape of the light emitted from the cylindrical optical path 19.

  As shown in FIG. 2, the light source unit 14 has a configuration in which a plurality of chip-like LEDs 26 are mounted on a flat printed board 25. The light source unit 14 uses an LED 26 that emits white light. In addition, you may use LED26 which radiate | emits red, green, and blue light for complementary colors.

    In the light source unit 14, a plurality of LEDs 26 are connected in series and are grouped into a plurality of LED circuits 27 arranged in a rectangular shape. By combining a plurality of these LED circuits 27, the light emission area is configured to approximate the virtual circle 28.

  In the embodiment shown in FIG. 2, an example in which ten LED circuits 27a to 27j are grouped is shown. Each LED circuit 27a-27j has power supply terminals 29a-29j individually, and lighting power is supplied from the power supply unit 16 to the power supply terminals 29a-29j by lighting control of the control unit 17, and each LED circuit 27a. The LEDs 26 of ~ 27j are lit.

  Each of the LED circuits 27a to 27j is formed by arranging a plurality of LEDs 26 in a rectangular shape, but is classified into three types in which the plurality of LEDs 26 are arranged in a rectangular shape having a different size. Each of the three types of LED circuits 27a to 27j has the same rectangular short side length. Seven LEDs 26 are connected in series in the short side direction, and the series-connected circuits are connected in parallel in units of groups. ing. The LED circuits 27c and 27h at the center of the light source unit 14 are the longest group having the longest long rectangular side, and the LED circuits 27a, 27e, 27f, and 27j at the both ends have long rectangular sides. The LED groups 27b, 27d, 27g, and 27i in the middle part between the shortest group and the shortest group are the shortest group that is the shortest group.

  As shown in FIG. 3, the control unit 17 includes a plurality of drive circuits 32 that drive the LEDs 26 for each LED circuit 27 according to the input of the PWM signal, and a PWM control circuit 33. The PWM control circuit 33 outputs a PWM signal to the drive circuit 32 in accordance with the supplied dimming signal.

  Each drive circuit 32 has a switching element such as an FET, the switching element is turned on / off in response to the input of the PWM signal, and the current flows from the LED 26 of each LED circuit 27 with a constant current from the power supply unit 16. To control the lighting time of the LED 26.

  The PWM control circuit 33 generates a PWM signal according to the dimming degree (dimming level) 0 to 100% of the dimming signal, and outputs the PWM signal to the drive circuit 32 in a lighting cycle of a predetermined lighting frequency for lighting the LED 26. Output. For example, a 256-level dimming signal is input to the PWM control circuit 33, and the PWM control circuit 33 converts it into a large number of gradations such as 1024 gradations or 2048 gradations and outputs a PWM signal.

  The PWM control circuit 32 outputs a PWM signal corresponding to the dimming level of the applied dimming signal, changes the level of the frequency in the PWM signal by following the dimming level, and outputs the PWM signal to the drive circuit.

  It is assumed that the dimming signal is sent as a DMX signal from a dimming table (not shown) or the like. The DMX signal is a digital signal used in a production field or the like standardized by the American Theater Technology Association (USITT), and indicates the DMX 512 used as a standard of a dimming signal for dimming control. The DMX 512 is a signal having a structure in which 512 channels each composed of 8 bits, each sandwiched between a start code and a stop bit, are multiplexed into one frame. A dimming signal of 256 gradations (8 bits) for performing dimming control to the optical device. The start of one frame is detected by detecting a break (BREAK) and a start code. The channel corresponding to the PWM control circuit 33 as a dimmer provided in the spotlight 11 is detected by counting how many channels sandwiched between the start code and the stop bit have arrived from the start of the frame. To do.

  The PWM control circuit 32 includes, for example, a memory table that stores the frequency of the DMX signal in association with the frequency of the PWM signal. Further, the PWM control circuit 32 includes a memory table for obtaining the gradation degree of the PWM signal from the dimming degree of the DMX signal. This memory table can be divided into 4 (generally n) stages and assigned frequencies as shown in FIG. 4A, for example. Further, as shown in FIG. 4B, a memory table in which continuous allocation is performed so that one frequency is allocated to one gradation of the PWM signal can be employed.

  When the change in the gradation corresponding to the brightness (luminance) of the light source with respect to the dimming degree of the DMX signal changes along the exponential curve shown in FIG. I feel that

  That is, when the change in the dimming level on the horizontal axis is constant (equal intervals), as apparent from FIG. In the region, the change in brightness with respect to the change in one gradation is large. For this reason, the number of gradations (the number of time divisions that can be changed per 100% of the very high level) increases in the low dimming region, and the number of gradations decreases in the high luminance region.

  Based on the contents of the memory table shown in FIG. 4 (a), the PWM output when the LED current has gradations corresponding to 0%, 25%, 50%, 75%, and 100%, respectively. The waveform of the signal is shown in FIG. As apparent from FIG. 6, the frequency level of the PWM signal is changed in accordance with the level of gradation (LED current).

  Referring to FIG. 6, in the low dimming region, since the frequency of the PWM signal used is low, the time width of one cycle is long, and the on-duty ratio of the PWM signal is finely changed by increasing the number of gradations. It is understood that is possible. On the other hand, in the high light intensity region, since the frequency of the PWM signal used is high, the time width of one cycle is short, and it is difficult to increase the number of gradations. The ratio is not changed finely.

  As described above, the PWM control circuit 32 outputs the PWM signal by controlling the on-duty ratio and the frequency of the PWM signal, so that the brightness (luminance) change of the light source changes along the curve shown in FIG. As a result, people feel that the brightness changes smoothly. Further, since the frequency of the PWM signal is increased in the high light intensity region, it is possible to suppress flicker in the camera image.

DESCRIPTION OF SYMBOLS 11 Spotlight 12 Light source unit 13 Projection unit 14 Light source part 32 Drive circuit 33 PWM control circuit

Claims (2)

A light source unit comprising an LED;
A PWM control circuit for outputting to the drive circuit a PWM signal corresponding to the dimming degree of the input dimming signal and changing the frequency level by following the dimming level;
And a drive circuit that turns on the LED in response to the input of the PWM signal. The lighting device according to claim 1, wherein the PWM control circuit changes the level of the frequency in the PWM signal stepwise or continuously.

Images