JP2018190489A - Led illumination unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED illumination unit in which a circuit according to a power supply is not increased in size even if the LED illumination unit is mounted to a liquid display device displaying an image by a field sequential color system.SOLUTION: In an LED illumination unit 10, an LED drive current 13a obtained by rectifying a commercial AC power supply 10a directly flows into LED arrays 141, 142, 143 emitting light in red, green and blue, respectively. The LED arrays 141, 142, 143 are switched in accordance with a full-wave rectified voltage V11a obtained by rectifying the commercial AC power supply 10a. More specifically, the LED illumination unit 10 eliminates the need for capacitors and coils that force an increase in size thereof when smoothing and voltage conversion are performed.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an LED illumination device suitable for a liquid crystal display device employing a field sequential color system.

  In the field sequential color method, one screen is divided into a red screen, a green screen, and a blue screen, and then the red screen, the green screen, and the blue screen are displayed in succession to reconstruct the one screen described above. As a liquid crystal display device adopting a field sequential color system, for example, Patent Document 1 discloses a TFT active matrix liquid crystal panel (hereinafter referred to as “liquid crystal panel”) employing bend light distribution liquid crystal, and red and green from the back of the liquid crystal panel. In addition, a liquid crystal display including a surface light source that sequentially emits three colors of blue light is shown. This liquid crystal display emits red light when a red screen is drawn on the liquid crystal panel, then emits green light when a green screen is drawn, and emits blue light when a blue screen is drawn. Further, if these processes are repeated at a high speed for a plurality of screens, a color moving image can be displayed.

  Recently, LED lighting devices that obtain red, green, and blue three-color light from LEDs have become widespread. This LED lighting device normally supplies power to the LED by a power source provided with a switching regulator. The above-described surface light source can be easily replaced with this LED illumination device.

Japanese Patent Laid-Open No. 11-14988 (FIG. 1)

  Since the power supply for illumination handles relatively large power, the above-described switching regulator requires a coil having a large allowable current and a capacitor having a large capacity. That is, in a liquid crystal display device that includes a liquid crystal panel and displays an image by a field sequential method, the conventional LED lighting device has a problem that a circuit related to a power source for illumination is enlarged.

  Accordingly, the present invention has been made in view of the above problems, and provides an LED lighting device in which a circuit relating to a power source for lighting does not increase in size even when attached to a liquid crystal display device that displays an image by a field sequential color method. The purpose is to do.

  In order to solve the above-described problems, an LED lighting device according to the present invention includes a rectifier circuit for full-wave rectification of a commercial AC power supply, and first, second, and third LEDs that are connected to the rectifier circuit and emit light in red, green, and blue. Depending on the voltage output from the rectifier circuit, the first, second and third constant current circuits and the first, second and third switches connected in series to the first, second and third LED strings, respectively. Controller for controlling the first, second, and third switches, and the first, second, and third LED arrays emit light in one cycle of the voltage waveform output from the rectifier circuit, respectively. Second and third periods are provided, and the first, second, and third periods do not overlap each other.

In the LED lighting device of the present invention, the current obtained by rectifying the commercial AC power supply is directly red,
It flows into the LED row that emits green and blue light. In addition, the LED strings that emit light are switched according to the value of the voltage obtained by rectifying the commercial AC power supply. For this reason, smoothing and voltage conversion are not performed after the commercial AC power supply is rectified. In other words, capacitors and coils that have to be increased in size when smoothing or voltage conversion is required are not required. As a result, even if the LED illumination device of the present invention is attached to a liquid crystal display device that displays an image by a field sequential color system, the circuit related to the power supply for illumination does not increase in size.

It is a block diagram of the liquid crystal projector incorporating the LED lighting apparatus shown as embodiment of this invention. It is a circuit diagram of the LED lighting apparatus shown in FIG. It is operation | movement explanatory drawing of the LED lighting apparatus shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. In addition, the same block, member, and control signal are attached | subjected the same number between drawings, and description is not repeated. The invention specific matters shown in the scope of claims are described in ().

  FIG. 1 is a block diagram of a liquid crystal projector 20 including an LED illumination device 10 shown as an embodiment of the present invention. In addition to the LED lighting device 10, the liquid crystal projector 20 includes a liquid crystal panel 21, a projection lens 22, and a liquid crystal panel drive circuit 23.

  The LED lighting device 10 includes a rectifier circuit 11, a controller 12, an LED drive circuit 13, and an RGB light source 14. The rectifier circuit 11 receives the commercial AC power supply 10a and outputs a rectified voltage (full-wave rectified voltage V11a, see FIG. 3A) and current (LED drive current 13a) (power line 11a). The power line 11 a is connected to the controller 12 and the RGB light source 14. The controller 12 generates control signals 12a and 12b based on the voltage value of the power line 11a, and outputs the control signal 12a to the LED drive circuit 13 and the control signal 12b to the liquid crystal panel drive circuit 23. The LED drive circuit 13 causes the RGB light source 14 to emit light based on the control signal 12a. At this time, the LED drive current 13 a returns from the RGB light source 14 to the rectifier circuit 11 via the LED drive circuit 13. The liquid crystal panel drive circuit 23 supplies a drive control signal and a power source 23 a to the liquid crystal panel 21.

  The light output from the RGB light source 14 becomes parallel light by the parabolic mirror 15 and enters the liquid crystal panel 21. A screen displayed on the liquid crystal panel 21 by this light is projected onto a screen (not shown) via the projection lens 22. In response to the control signal 12b, the liquid crystal panel drive circuit 23 causes the liquid crystal panel 21 to display a red screen, a green screen, and a blue screen in synchronization with the timing at which the RGB light source emits red light, green light, and blue light.

  FIG. 2 is a circuit diagram of the LED lighting device 10 shown in FIG. The LED lighting device 10 includes a rectifier circuit 11, an LED array 141 (first LED array) that emits red light, an LED array 142 (second LED array) that emits green light, and an LED array 143 (third LED array) that emits blue light. , Constant current circuits 131, 132, 133 (first, second and third constant current circuits), FETs 134, 135, 136 (first, second and third switches) operating as switches, and a controller 12. ing.

The rectifier circuit 11 includes four diodes 111, 112, 113, and 114. The diodes 111 to 114 constitute a diode bridge. The input terminals 101 and 102 of the rectifier circuit 11 are connected to the commercial AC power supply 10a. The rectifier circuit 11 includes a terminal from which a current is output and a terminal from which the current returns. In FIG. 2, the terminal from which the current is output is the power line 11a,
The terminal to which the current returns is set to the ground level. A voltage waveform at a terminal from which a current is output as viewed from the ground level is a full-wave rectified waveform (full-wave rectified voltage V11a, see FIG. 3A).

  In the LED row 141 that emits red light, a plurality of LEDs 141a that emit red light are connected in series. Similarly, in the LED rows 142 and 143 that emit green and blue light, a plurality of LEDs 142a and 143a that emit green and blue light are connected in series. The anode terminals of the LED strings 141 to 143 are connected to a terminal (power line 11a) from which the current of the rectifier circuit 11 is output.

  The constant current circuits 131, 132, 133 include pull-up resistors 131a, 132a, 133a, FETs 131b, 132b, 133b, bipolar transistors 131c, 132c, 133c, and current detection resistors 131d, 132d, 133d. The current input terminals of the constant current circuits 131, 132, 133 are connected to the cathode terminals of the LED rows 141, 142, 143. The current output terminals of the constant current circuits 131, 132, 133 are connected to the drains of the FETs 134, 135, 136. The main current path of the constant current circuits 131, 132, 133 is a series circuit including FETs 131b, 132b, 133b and current detection resistors 131d, 132d, 133d. The constant current circuits 131, 132, 133 operate at a constant current so as to maintain the voltage across the current detection resistors 131d, 132d, 133d at 0.6V.

  The sources of the FETs 134, 135, and 136 are connected to the ground. That is, the LED drive current 13a (LED drive currents I131a, I132a, I133a, see FIG. 3B) output from the FETs 134, 135, and 136 returns to the rectifier circuit 11. Control signals 121a, 122a, and 123a are input from the controller 12 to the gates of the FETs 134, 135, and 136 (indicated by the control signal 12a in FIG. 1). The controller 12 measures the voltage value of the full-wave rectified voltage V11a (see FIG. 3A), and generates control signals 121a, 122a, and 123a based on the measured result. In parallel with this, the controller 12 creates a control signal 12b and outputs it to the liquid crystal panel drive circuit 23 (see FIG. 1).

  The constant current circuits 131, 132, 133 and the FETs 134, 135, 136 constitute the LED drive circuit 13 shown in FIG. The LED rows 141, 142, and 143 serve as light sources that emit red, green, and blue light of the RGB light source 14 shown in FIG.

  The operation of the LED lighting device 10 shown in FIG. 2 will be described with reference to FIG. In the description of FIG. 3, reference is made to FIGS. 3A and 3B are diagrams for explaining the operation of the LED lighting device 10, wherein FIG. 3A is a waveform diagram of the full-wave rectified voltage V11a, FIG. 3B is a waveform diagram of the LED drive current 13a flowing out from the RGB light source, and FIGS. ), (E) are waveform diagrams of the control signals 121a, 122a, 123a, and (f) is an enlarged view of a part of (d) and (e). The vertical axis of (a) is the voltage V, the vertical axis of (b) is the current I, the horizontal axis of (a) to (e) is the time t, and the reference point and interval between (a) and (e). Is common.

  In FIG. 3, (a) shows two cycles of the full-wave rectified waveform as the voltage of the power line 11a (full-wave rectified voltage V11a). The full-wave rectified voltage V11a is a sine wave (positive part) having a period of 10 ms and a peak of 144 V. The control signal 121a shown in (c) rises at 1.25 ms and falls at 3.75 ms (first period). Similarly, the control signal 122a shown in (d) rises at 3.75 ms and falls at 6.25 ms (second period). Similarly, the control signal 123a shown in (e) rises at 6.25 ms and falls at 8.75 ms (third period). That is, the width of the period during which the control signals 121a, 122a, 123a are at the high level (first, second, and third periods) is 2.5 ms.

  As shown in FIG. 3B, in the first period, when the control signal 121a becomes high level, the FET 134 is turned on, and the LED drive current I131a determined by the constant current circuit 131 flows to the LED array 141. Similarly, when the control signal 122a becomes high level in the second period, the FET 135 is turned on, and the LED drive current I132a determined by the constant current circuit 132 flows to the LED string 142. In the third period, when the control signal 123 a becomes high level, the FET 136 is turned on, and the LED drive current I 133 a determined by the constant current circuit 133 flows to the LED array 143.

  The current value in FIG. 3B is an example determined under the following conditions. Here, the brightness of the LED array 141 is n (stage) × I 131a (A), and the brightness of the LED array 142 is m (stage) × I 132a (A). n and m are the number of serial stages of the LEDs 141a and 141b in the LED rows 141 and 142, respectively. The LED 141a and the LED 142a are a combination of a blue LED die and a phosphor, and each forward drop voltage Vf is 3V. As shown in (a), since the full-wave rectified voltage V11a at 1.25 ms is 55 V, n is 18 (55 (V) ÷ 3 (V)). Similarly, since the full-wave rectified voltage V11a at 3.75 ms is 133 V, m is 44. When the luminance of the LED row 141 and the luminance of the LED row 142 are made equal, I131a (A)> I132a as shown in (b). In FIG. 5B, the values of I131a and I133a are made equal.

  In the above cases, the difference in phosphor efficiency is ignored. Further, the LED 141a, the LED 142a, and the LED 143a may be LEDs including dies that emit light in red, green, and blue, respectively. In this case, each LED 141a, LED 142a, LED 143a has a different forward drop voltage Vf. That is, according to the conditions of the forward drop voltage Vf and at which timing the first to third periods are set, V11a (V)> Vf ( V) × k (stage), so that the number of series stages k of the LED strings 141, 142, and 143 is determined. At this time, the LED rows 141, 142, and 143 may be series-parallel circuits in which the number of series stages of the LEDs 141a, 142a, and 143a is k. Further, the values of the LED drive currents I131a, I132a, and I133a are adjusted by the current limiting resistors 131d, 132d, and 133d.

  As shown in FIG. 3F, it is preferable to shift the falling timing of the control signal 122a and the rising timing of the control signal 123a (the relationship between the control signal 121a and the control signal 122a is the same). That is, the RGB light source 14 is turned off during this shifted period. In this shifted period, the liquid crystal panel 21 is rewritten from the green screen to the blue screen to stabilize the display screen. Thereafter, the RGB light source 14 emits blue light, so that the image projected on the screen is not disturbed and the image quality is improved.

  As described above, when a red screen is displayed on the liquid crystal panel 21, the liquid crystal projector 20 projects the red screen by irradiating the liquid crystal panel 21 with red light from the LED illumination device 10. Similarly, when the green and blue screens are displayed on the liquid crystal panel 21, the liquid crystal projector 20 projects the green and blue screens by irradiating the liquid crystal panel 21 with green and blue light from the LED illumination device 10. At this time, in the LED lighting device 10, the LED drive current 13 a obtained by rectifying the commercial AC power supply 10 a flows directly into the LED rows 141, 142, and 143 that emit light in red, green, and blue, and the commercial AC power supply 10 a The emission color switches according to the voltage value of. That is, the LED drive current 13a is distributed to the LED drive currents I131a, I132a, and I133a for the first, second, and third periods. For this reason, smoothing and voltage conversion are not performed after the commercial AC power supply 10a is rectified. In other words, capacitors and coils that have to be increased in size when smoothing or voltage conversion is required are not required. As a result, even if the LED illumination device 10 is attached to the liquid crystal projector 20 (liquid crystal display device) that projects and displays an image by the field sequential color system, the circuit related to the illumination power source does not increase in size.

  In the LED lighting device 10, the first period for emitting red light is 1.25 to 3.75 ms, the second period for emitting green light is 3.75 to 6.25 ms, blue with respect to the zero cross point of the full-wave rectified voltage V11a. The third period for light emission was 6.25 to 8.75 ms. However, in the LED lighting device of the present invention, the light emission period of each color is not limited to this. For example, for the LED lighting device 10, the third period for emitting blue light is 1.25 to 2.50 ms and 7.50 to 8.75 ms, and the first period for emitting red light is 2.50 to 3.75 ms and 6.25. The second period of green light emission may be set to 3.75 to 6.25 ms. At this time, since the number of series stages of the LED array 141 can be set to 34 (the full-wave rectified voltage V11a at 2.50 ms is 102 V and the forward drop voltage of the LED 141 a is 3 V), power loss in the constant current circuit 131 is reduced. The luminous efficiency can be improved.

  The LED lighting device 10 is based on the premise that the voltage (effective value) of the commercial AC power supply 10a is stable. However, the effective value of the commercial AC power supply 10a may fluctuate. At this time, if the first to third periods are set based on the instantaneous voltage (full-wave rectified voltage V11a) of the commercial AC power supply 10a, the widths of the first to third periods also change in conjunction with fluctuations in the effective value. End up. Therefore, it is preferable to measure the effective value (or peak voltage) and adjust the voltage that determines the first to third periods. For example, the reference voltage of the comparator built in the controller 12 may be finely adjusted in accordance with the effective value fluctuation of the commercial AC power supply 10a. Since the controller 12 is usually an IC, there is no size problem and various well-known functions can be incorporated. Furthermore, the controller 12 and the liquid crystal panel drive circuit 23 may be integrated. To set the first to third periods, a timer based on the zero cross point of the full-wave rectified voltage V11a may be used. In addition, it is necessary to set the number of series stages so that a current can flow through the LED strings 141 to 143 even when the effective value of the commercial AC power supply 10a decreases.

10 ... LED lighting device,
10a ... Commercial AC power supply,
11 ... rectifier circuit,
11a ... power line,
12 ... Controller,
12a, 12b, 121a, 122a, 123a ... control signals,
13 ... LED drive circuit,
13a, I131a, I132a, I133a ... LED drive current,
14 ... RGB light source,
15 ... Parabolic mirror,
20 ... LCD projector,
21 ... Liquid crystal panel,
22 ... projection lens,
23 ... Liquid crystal panel drive circuit,
23a: Control signal and power supply for driving the liquid crystal panel,
101, 102 ... input terminals,
111-114 ... a diode,
131-133 ... constant current circuit (first, second, third constant current circuit),
131a, 132a, 133a ... pull-up resistors,
131b, 132b, 133b ... FET,
131c, 132c, 133c ... bipolar transistors,
131d, 132d, 133d, current detection resistors,
134 to 136... FET (first, second, and third switches),
141-143 ... LED rows (first, second, third LED rows),
141a ... Red light emitting LED,
141b ... Green light-emitting LED,
141c ... Blue light emitting LED,
V11a: full-wave rectified voltage.

Claims (1)

A rectifier circuit for full-wave rectification of a commercial AC power supply;
A first, second and third LED array connected to the rectifier circuit and emitting red, green and blue light;
First, second, and third constant current circuits and first, second, and third switches connected in series to the first, second, and third LED strings, respectively;
A controller for controlling the first, second and third switches according to a voltage output from the rectifier circuit;
In one cycle of the voltage waveform output from the rectifier circuit, first, second, and third periods in which the first, second, and third LED arrays emit light are provided,
The LED lighting device, wherein the first, second, and third periods do not overlap each other.