JPH09120051A - Light control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce radio disturbance simply and effectively without impairing the light control function by shifting somewhat fundamental frequency itself of PWM and positively changing its high frequency. SOLUTION: A PWM controller is provided with a function to monitor a receiving frequency in a broadcasting radio receiver 7 and shift a fundamental frequency of the PWM wave according to the received frequency. Concretely, a monitor 6a monitors the received frequency from channel selection information in a control unit 7a of the broadcasting radio receiver 7. And, by adopting the monitored and received frequency as a keyword and referring to a table 6b, it is checked whether or not the higher harmonics of the PWM wave are adjacent to the received frequency. Further, a frequency shifter 6c controls the fundamental frequency according to the information on this table 6b. The high frequency is kept away from the received frequency by shifting somewhat the fundamental frequencies of the PWM signal according to the monitored and received frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dimming control device suitable for dimming and driving a light emitter for a backlight of a liquid crystal display device.

[0002]

2. Description of the Related Art Recently, liquid crystal displays as monitors for various OA equipments, portable televisions, and car navigation devices have been remarkably spread. In particular, a transmissive type that controls the amount of light transmitted from the rear surface to perform display has become widespread with the recent trend of color display.

By the way, a liquid crystal display incorporated in a car navigation system has a built-in dimming control device which adjusts the amount of backlight exclusively according to the brightness of the surroundings.
FIG. 3 shows an example of a typical dimming control device, where 1 is a liquid crystal display driven by the LCD driver 2 and 3
Is a light emitter for the backlight. The drive source of the light emitter 3 is constructed as a DC-AC converter 4 which is switching-driven by a semiconductor (transistor). Then, the PWM controller 6 generates a modulation wave having a pulse width corresponding to the output of the optical sensor 5 that detects the brightness (outside light) around the light emitter 3, and the switching signal of the converter 4 is generated by this modulation wave. The light emission amount of the light emitter 3 is adjusted by performing intermittent control.

For example, the converter is turned on by changing the pulse width of a PWM wave having a fundamental frequency of 500 Hz in accordance with external light.
The ratio is controlled, and the light emission amount of the light emitter 3 is digitally and stably controlled according to the duty.

[0005]

In the dimming control device described above, dimming can be performed simply and accurately, but the converter 4 that operates by receiving the signal modulated by the PWM wave is 100 kHz. Since the light emitting device 3 is driven to be lit at the above frequency and at a voltage of about 1 kV, it is easy to give a reception failure to a radio receiver or the like arranged in the vicinity thereof. P
The WM wave is generated in consideration of the flicker in the light emitter 3, for example, a signal having a fundamental frequency of 500 Hz in 256 (= 2 to the 8th power) steps. In this case, 500 × 256 = 128 as shown in FIG. Harmonics which are integral multiples of kHz are generated by the converter 4, and these harmonics interfere with the radio receiver 7.

Especially for AM radio broadcasting in Japan, 1026, 1152, 1278, 1404, 1530
Many places use the broadcast frequency of kHz. On the other hand, the 8 to 12 times higher harmonic component is 1
024,1152,1280,1408,1536kHz
And is close to the above-mentioned broadcast frequency. Therefore,
For a receiver with a frequency selectivity of only a few kHz at most,
The above harmonics are harmful interfering waves.

By the way, even a television receiver has a high video frequency of several hundreds of MHz, but it is also an AM wave, and is therefore easily affected by reception interference. The present invention has been made in consideration of such circumstances, and an object thereof is to simply and effectively provide a backlight without giving a large reception obstacle to a receiver such as a radio or a television arranged in proximity. An object of the present invention is to provide a dimming control device capable of adjusting the amount.

[0008]

According to the present invention, a PWM signal having a pulse width corresponding to the illuminance around the display (brightness of external light) is generated, and the PWM signal is used for backlighting the display. The dimming control device for automatically adjusting the brightness of the light-emitting device by controlling the conduction period of the AC-DC converter driving the light-emitting device, and particularly the reception frequency of the receiver arranged near the display device. By monitoring and slightly shifting the fundamental frequency of the PWM signal according to the monitored reception frequency, avoiding harmonics thereof far from the reception frequency,
The feature is that the reception failure is reduced.

[0009]

Function: The reception frequency is monitored, and the reception frequency is PW.
When it is close to the harmonic of the M wave, if the fundamental frequency itself of the PWM wave is slightly shifted, the frequency of the harmonic is also shifted accordingly. As a result, the harmonics of the PWM wave can be moved outside the reception frequency selection width in the receiver, and the reception trouble can be reduced.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A dimming control device according to an embodiment of the present invention will be described below with reference to FIGS. FIG.
The same parts as those of the conventional device shown in FIG.

This device is characterized by the PWM controller 6, which has a function of monitoring the reception frequency in the radio receiver 7 and shifting the fundamental frequency of the PWM wave according to the reception frequency. That is the point. Specifically, the monitor 6a monitors the reception frequency from the channel selection information in the control unit 7a of the radio receiver 7. Then, the table 6b is drawn by using the monitored reception frequency as a keyword, and the PW
Check whether the harmonic of the M wave is close to the reception frequency.

In this table 6b, for example, the relationship between the harmonics and the frequency of the radio broadcast channel when the fundamental frequency of PWM is 500 Hz is registered in advance, and the shift of the fundamental frequency corresponds to the reception frequency. Information is required when it is needed. Frequency shifter 6c
Is the pulse width modulator 6 according to the information in this table 6b.
The fundamental frequency is shift-controlled with respect to d.

In the case where the PWM controller 6 is integrally configured with one control unit 7a of the radio receiver 7 by one microprocessor, the PWM controller 6 is determined from the reception channel information set for the radio receiver 7. The reception frequency may be directly obtained and the shift control of the fundamental frequency of the PWM wave may be performed by software processing.

In the apparatus thus constructed, for example, when it is judged that the radio receiver 7 is receiving the broadcast wave of 1152 kHz, the fundamental frequency is set to 500.
In the case of PWM wave with Hz, 9 times higher harmonic is 11
Since the frequency is 52 kHz, the fundamental frequency is shifted within a range that does not affect the flicker prevention of the light emitter 3. Specifically, the fundamental frequency is shifted by 2% to 490 Hz. Then, as shown in FIG. 2, the 9 times higher harmonic becomes 1129 Hz, and the 10 times higher harmonic becomes 1254 Hz, which is far from the above reception frequency, and even if the range of frequency selectivity of the radio receiver 7 is several kHz. , Out of the reception band.

As a result, the operation of the converter 4 for adjusting the backlight light amount of the display device 3 in accordance with the external light amount, that is, P
The influence of the WM wave on the broadcast reception by the radio receiver 7 is greatly reduced. Moreover, even if the basic frequency of the PWM wave is shifted in this way, the basic function of the PWM controller 6 is not impaired, so that the dimming function thereof can be sufficiently exerted.

Although the fundamental frequency of the PWM wave is reduced in the above-mentioned embodiment, it is also possible to perform shift control so that the fundamental frequency may be increased to the contrary. In addition to the radio receiver 7, it is also possible to monitor the video frequency from the reception channel of the television receiver and shift-control the fundamental frequency of the PWM wave to reduce the image reception failure. Further, it is of course possible not only to positively monitor the reception frequency from the PWM controller 6 side but also to configure the system so that the receiver side gives the reception information to the PWM controller 6. Other,
The present invention can be implemented with various modifications without departing from the scope of the invention.

[0017]

As described above, according to the present invention, the operation of the converter (the higher harmonics of PWM) for dimming the backlight emitter of the display is broadcast by the receiver arranged in the vicinity thereof. PW when close to the receiving frequency
Since the fundamental frequency of M is slightly shifted to positively change the frequency of its harmonics, it is possible to easily and effectively reduce reception interference without impairing the dimming function.
Its practical advantages are enormous.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a dimming control device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the operation of the embodiment apparatus.

FIG. 3 is a schematic configuration diagram of a conventional apparatus.

FIG. 4 is a diagram showing a relationship between a harmonic of a PWM wave and a radio broadcasting frequency.

[Explanation of symbols]

 1 Liquid crystal display 2 LCD driver 3 Light emitter 4 DC-AC converter 5 Optical sensor 6 PWM controller 6a Monitor 6b Table 6c Frequency shifter 6d Pulse width modulator 7 Radio receiver 7a Control part

Claims (2)

[Claims] 1. A pulse width P according to the illuminance around the display.
A dimming control device for automatically adjusting the brightness of the light emitting device by generating a WM signal and controlling the conduction period of an AC-DC converter that drives a light emitting device for a backlight with respect to the display device by the PWM signal. And a means for monitoring a reception frequency of a receiver arranged in the vicinity of the display, and a means for shifting a fundamental frequency of the PWM signal according to the monitored reception frequency. Light control device. 2. A means for shifting the fundamental frequency of a PWM signal is such that when one of the harmonics of the PWM signal is close to the reception frequency, the fundamental of the PWM signal is such that the harmonic deviates from the fundamental frequency. The dimming control device according to claim 1, wherein the frequency is changed.