JP2010153151A - Led planar lighting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce noise resulting from lighting driving, in an LED planar lighting system having a large number of two-dimensionally disposed LEDs. <P>SOLUTION: The two-dimensionally disposed LEDs are divided into a region A and a region B to lightingly drive the LEDs for each region by PWM drive signals having different patterns. The LEDs in the region A are lightingly driven by the PWM drive signal (b) in which the position of a rising edge is fixed and a pulse width wa is controlled, and the LEDs in the region B are lightingly driven by the PWM drive signal (c) in which the position of a falling edge is fixed and a pulse width wb is controlled. Thereby, since timing for ON action or OFF action of transistors in a driving circuit shifts, switching noise disperses, and the peak of a noise level falls. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an LED planar illumination device in which a large number of LEDs (light emitting diodes) are two-dimensionally arranged, and in particular, illuminates a flat object substantially uniformly and applies the transmitted light and reflected light to the object. The present invention relates to an LED planar illumination device suitable for use in inspecting an object.

  In order to inspect defects such as a large liquid crystal panel on a production line, an inspection apparatus as disclosed in Patent Document 1, for example, is used. This inspection apparatus includes an inspection backlight device (inspection) including linear light sources such as a plurality of cold-cathode tubes arranged in parallel and an optical sheet for converting light emitted from the linear light sources into a planar shape. Lighting device).

  In recent years, even such illumination devices for inspection are required to have even more illuminance uniformity, longer life, and lower power consumption. On the other hand, the performance improvement of LEDs, in particular, the increase in brightness has been greatly progressed recently, and high-brightness LEDs have come to be used as illumination light sources. In such a flow, LEDs have come to be used also in the above-described inspection illumination device.

  In the case of configuring the planar illumination device as described above, it is conceivable to adjust the luminance by arranging a large number of high-brightness LEDs two-dimensionally and driving each LED by PWM (pulse width modulation). However, as the number of LEDs is increased in order to increase the size of the light source unit, switching noise in a circuit that generates a PWM drive signal increases, and adverse effects on external devices due to unnecessary radiation become a problem. In particular, in the case of an inspection lighting device, if the noise described above causes a malfunction of an imaging device or an image processing circuit for photographing an object, an appropriate inspection cannot be performed, and a defective product is overlooked or a normal product is mistaken. There is a risk of causing serious problems such as judgment.

JP 2007-25132 A

  The present invention has been made in view of the above problems, and has as its main purpose to reduce noise in an LED planar illumination device using a large number of LEDs.

The present invention made to solve the above problems includes a planar light source unit in which a plurality of LEDs are two-dimensionally arranged, an LED driving unit that drives the plurality of LEDs by PWM (pulse width modulation), In the LED planar illumination device comprising:
The LED drive unit generates at least two different patterns of PWM drive signals having different rising edge positions and falling edge positions, and for each LED included in each of the regions divided into a plurality in the light source unit, It is characterized in that lighting driving is performed by the PWM drive signals of different patterns.

  In the LED planar illumination device according to the present invention, the LED driving unit drives the LED to light by a plurality of different patterns of PWM drive signals, thereby supplying a driving current to the LEDs included in the light source unit (that is, a lighting period). Can be dispersed in time. As a result, switching noise generated in accordance with the on / off operation of circuit elements such as transistors included in the LED driving unit is dispersed, and the peak value of the noise level is reduced.

  In addition, since the supply period of the drive current to the LEDs is dispersed, the operating rate of the power supply that supplies the current is also averaged to some extent. As a result, the ripple current is reduced, so that the stress on the circuit elements constituting the power source is reduced, failure is less likely to occur, and reliability is improved.

  As a preferable aspect of the LED planar illumination device according to the present invention, N (N is 2 or more) different patterns have a pulse width when the duty ratio of each PWM drive signal is less than (100 / N)%. A pattern that does not overlap is good.

  Specifically, for example, the PWM drive signal includes first and second PWM drive signals having different patterns, and the rising edge position of the first PWM drive signal and the falling edge position of the second PWM drive signal are And the falling edge position of the first PWM drive signal changes according to the pulse width, and the rising edge position of the second PWM drive signal changes according to the pulse width.

  According to this configuration, the supply period of the drive current to the LEDs can be appropriately distributed, which is advantageous for noise reduction and averaging of the power supply operation rate. In addition, since the second PWM drive signal falls when the first PWM drive signal rises, there is an effect of reducing noise associated with on / off operations of circuit elements such as transistors for generating the PWM drive signal. I can expect.

  In addition, although the said some area | region in a light source part can be set suitably, it is good to make it become a different area | region for every line of LED, for example.

  According to the LED planar illumination device according to the present invention, the noise level associated with the operation is lowered, so that it is possible to prevent adverse effects on external devices due to unnecessary radiation. As a result, when the planar illumination device is incorporated into an inspection device, it is possible to prevent malfunction of the circuit of the inspection device body and perform a good inspection. In addition, according to the LED planar illumination device according to the present invention, since stress on the circuit elements constituting the power source is reduced, failure is unlikely to occur, and reliability can be improved by extending the life.

  An embodiment of an LED planar illumination device according to the present invention will be described with reference to the drawings. FIG. 4 is a schematic view of an inspection apparatus which is one usage pattern of the LED planar illumination device of this embodiment.

  In FIG. 4, the planar illumination device of this embodiment has a planar light source unit 1 in which a number of LEDs are arranged in a plane (FIG. 4 is a side view thereof) and LEDs that drive and drive each LED. And the lighting device 2. In the planar light source unit 1, the light energy per unit time is substantially constant, and the luminance of the planar irradiation surface (upper surface in FIG. 4) is substantially uniform. An inspection object 3 such as a liquid crystal panel is disposed between the planar light source unit 1 and the imaging device 4. The imaging device 4 images the inspection object 3 illuminated from the back side by the planar light source unit 1, and the image processing device 5 processes the captured image to identify the presence or absence of minute defects in the inspection object 3. .

  FIG. 3 is a plan view of the planar light source unit 1. The same type of high-intensity white LEDs 11 are arranged in a grid pattern on one substrate 12, and the planar light source unit 1 is configured by arranging 20 substrates 12 in a plane. In this example, different areas A and B are set for each line of the LED 11, and the LEDs 11 included in the area A and the LEDs 11 included in the area B are driven to be lit by PWM drive signals having different patterns. It is like that.

  FIG. 1 is a schematic configuration diagram of the LED lighting device 2 in the LED planar lighting device of this embodiment, and FIG. 2 is a time chart for explaining the operation of the LED lighting device 2.

  The LED lighting device 2 has a PWM drive unit 21 whose function is achieved by a microcomputer including a CPU, a ROM, a RAM, and the like, and a drive that supplies a drive current to the LED 11 in accordance with a drive signal supplied from the PWM drive unit 21. Circuits 26A and 26B. The PWM drive unit 21 outputs PWM drive signals having different patterns, the drive circuit 26A supplies drive current to the LEDs 11 included in the region A described above, and the drive circuit 26B applies to the LEDs 11 included in the region B described above. Supply drive current. The PWM drive unit 21 includes a reference pulse generation unit 22, a drive pulse A generation unit 23, a drive pulse B generation unit 24, and a pulse width control unit 25 as functional blocks achieved by a microcomputer.

The operation of the LED lighting device 2 will be described with reference to FIG.
The reference pulse generation unit 22 includes a 1 / n frequency division counter that counts a reference clock having a predetermined frequency generated by, for example, a crystal oscillator. The output value of this counter is incremented sequentially from 0 to n as shown in FIG. 2A, and reset to 0 when n is reached. Therefore, the output of the reference pulse generator 22 is a triangular wave pulse signal as shown in FIG. The cycle of this triangular wave pulse signal can be set to 80 [kHz], for example.

  The triangular wave pulse signal is input to the drive pulse A generator 23 and the drive pulse B generator 24. The drive pulse A generation unit 23 generates, as the first PWM drive signal, a rectangular wave pulse signal that rises when the triangular wave pulse signal has a counter value = 0 and falls when the counter value reaches p (p ≦ n) (FIG. 2). (See (b)). On the other hand, the drive pulse B generation unit 24 converts the square wave pulse signal that rises when the counter value of the triangular wave pulse signal reaches q (= n−p) and falls when the counter value becomes 0 to the second PWM drive signal. (See FIG. 2C). That is, the rising edge of the first PWM drive signal is coincident with the falling edge of the second PWM drive signal.

  The pulse width control unit 25 instructs the drive pulse A generation unit 23 on the p value and instructs the drive pulse B generation unit 24 on the q value according to the light amount setting value specified from the outside. When increasing the amount of light, the p value is increased while the q value is decreased. As a result, the pulse width wa of the first PWM drive signal generated by the drive pulse A generator 23 and the pulse width wb (= wa) of the second PWM drive signal generated by the drive pulse B generator 24. Spreads. Since the first PWM drive signal has a fixed rising edge position and the second PWM drive signal has a fixed falling edge position, when the duty ratio of both PWM drive signals is less than 50%, the pulse width wa and wb do not overlap.

  That is, when the duty ratio of both PWM drive signals is less than 50%, the LEDs 11 included in the region A and the LEDs 11 included in the region B are alternately lit. Since one cycle of the PWM lighting drive is sufficiently shorter than the one-frame imaging cycle by the imaging device 4, all the LEDs have the same luminance as when the LEDs are driven to light by the same PWM driving signal having the pulse width wa.

  The drive circuits 26A and 26B include transistors and the like that are turned on / off by a PWM drive signal, and switching noise is generated during the on / off operation. In the LED planar illumination device of this embodiment, the rising edge position and the falling edge position are different between the PWM drive signal supplied to the drive circuit 26A and the PWM drive signal supplied to the drive circuit 26B. And the transistor included in the drive circuit 26B are not simultaneously turned off → on or turned on → off, and their timings are shifted in time. Therefore, switching noise is temporally dispersed, and the peak value of the noise level is lowered.

  When the duty ratio of both PWM drive signals is less than 50%, the transistors included in the drive circuit 26A and the transistors included in the drive circuit 26B are not turned on at the same time. Therefore, the operation rate of the power supply that supplies the drive current is averaged, and the ripple current of the power supply current is reduced. This reduces stress on the circuit elements of the power supply.

  It should be noted that the above embodiment is merely an example of the present invention, and it is obvious that modifications, corrections, and additions as appropriate within the scope of the present invention are included in the claims of the present application.

  For example, in the above embodiment, all the LEDs are divided into two areas A and B, but they may be lit and driven by three or more different PWM drive signals. Further, the method for generating the PWM drive signal is not limited to that described above.

The schematic block diagram of the lighting drive device in the LED planar illumination device by one Example of this invention. The time chart of operation | movement description of the lighting drive device of FIG. The top view of the planar light source part in the LED planar illuminating device of a present Example. Schematic of the inspection apparatus which is one usage pattern of the LED planar illumination apparatus of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Planar light source part 11 ... LED
DESCRIPTION OF SYMBOLS 12 ... Board | substrate 2 ... LED lighting device 21 ... PWM drive part 22 ... Reference pulse production | generation part 23 ... Drive pulse A production | generation part 24 ... Drive pulse B production | generation part 25 ... Pulse width control part 26A, 26B ... Drive circuit 3 ... Test object 4 ... Imaging device 5 ... Image processing device

Claims (3)

In an LED planar illumination device comprising: a planar light source unit in which a plurality of LEDs are arranged two-dimensionally; and an LED driving unit that drives the plurality of LEDs by PWM (pulse width modulation).
The LED drive unit generates at least two different patterns of PWM drive signals having different rising edge positions and falling edge positions, and for each LED included in each of the regions divided into a plurality in the light source unit, An LED planar illumination device that is lit and driven by the PWM drive signals having different patterns. The LED planar illumination device according to claim 1,
The N (N is 2 or more) types of different patterns are patterns in which the pulse widths do not overlap when the duty ratio of each PWM drive signal is less than (100 / N)%. . The LED planar illumination device according to claim 2,
The PWM drive signal includes first and second PWM drive signals having different patterns, and the rising edge position of the first PWM drive signal coincides with the falling edge position of the second PWM drive signal. The LED planar illumination device is characterized in that the falling edge position of the PWM drive signal changes according to the pulse width, and the rising edge position changes according to the pulse width of the second PWM drive signal.

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