JPH02147015A - Liquid crystal display device for cooker - Google Patents

Abstract

PURPOSE:To hold the luminance of a light emitting element, which illuminates a liquid crystal display element, fixed by executing pulse drive for tuning on a light emitting element group and providing a light emitting element control means to variably control a duty cycle in correspondence to the fluctuation of a power source voltage to be supplied. CONSTITUTION:When a display program to be displayed to an LCD19 is executed and both bidirectional thyrister driving circuits 31 and 32 are turned off, for the liquid crystal display device of a cooker, an LED turning-on time is defined as 5ms and the luminance of LEDs 11-18 is lowered in the half of a period. Then, the illumination of the LED19 is prevented from being too much bright. When a turning-on signal is outputted, the LED turning-on time is set to 10ms and the LED is turned on during the whole period. Then, the illumination of the LED19 is prevented from being too much dark. When the turning signal is outputted to only one of the circuits 31 and 32, the LED turning-on time is set to 7ms and the pulse drive of the LEDs 11-18 is executed by the set duty cycle. Afterwards, display is outputted to the LED19. Accordingly, the luminance of the light emitting element group is held fixed regardless of the fluctuation of the power source voltage.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a liquid crystal display device for a cooking appliance.

2. Description of the Related Art Conventional liquid crystal display devices for cooking appliances use reflective liquid crystal display elements that do not emit light, and therefore various lighting devices are used on the back side of the liquid crystal display elements.

An example of a liquid crystal display device for a cooking appliance having this type of lighting device will be explained based on the configuration diagram of FIG. 5.

In FIG. 5, 1 is a light emitting board, and this light emitting board 1
The device is constructed by mounting a plurality of chip-type light emitting elements (LEDs) IA on a substrate, and connecting the chip-type LEDIAs with patterns and bonding wires. Further, above the light emitting substrate 1, a diffusion plate 2 for diffusing light from the light emitting substrate 1 is provided, and a reflective liquid crystal display element 3 is further provided on the diffusion plate 2, and furthermore, this light emitting substrate 1 is installed on a printed circuit board 4 on which electronic components are mounted.

With this configuration, the liquid crystal display element 3 receives light from the chip-type LEDIA mounted on the light emitting substrate 1 from the back side via the diffuser plate 2, so that the display contents of the liquid crystal display element 3 can be confirmed even in a dark place. Can be done.

Problems to be Solved by the Invention However, in the conventional configuration described above, the power supplied to the light emitting element IA for illuminating the liquid crystal display element 3 is usually not kept at a constant voltage because the light emitting element IA has a large extinction current. Furthermore, since the capacity of the power transformer is set to the minimum necessary capacity to reduce costs, the output voltage of the power transformer fluctuates depending on the presence or absence of other loads. Therefore, the power supply voltage supplied to the light-emitting element IA fluctuates, and the brightness of the light-emitting element IA frequently changes depending on the operating state of the cooking appliance, resulting in problems such as being extremely difficult to see.

The present invention is intended to solve such problems, and aims to provide a liquid crystal display device for a cooking appliance in which the brightness of a light emitting element illuminating the liquid crystal display element is constant.

Means for Solving the Problems To solve the above problems, a liquid crystal display device for a cooker according to the present invention includes a transmissive liquid crystal display element, a light emitting element group for illuminating the liquid crystal display element from the back side, and the light emitting element group. The light emitting element control means controls the lighting of the light emitting element by pulse driving and variably controls the duty cycle according to fluctuations in the power supply voltage supplied to the light emitting element group.

Effect With the above configuration, when the power supply voltage supplied to the light emitting element group is at the center of voltage fluctuation, the duty cycle of the light emitting element drive pulse is set to a predetermined value by the light emitting element control means, and the duty cycle of the light emitting element driving pulse is set to a predetermined value immediately after the power is turned on. When the power supply voltage supplied to light-load special light emitting elements in standby mode etc. increases, the duty
By reducing the cycle, the brightness of the light emitting elements is lowered to prevent the illumination of the liquid crystal display element from getting too bright.On the other hand, when the load is heavy and the power supply voltage supplied to the light emitting elements is low, the duty cycle is increased. to increase the brightness of the light emitting element group,
The illumination of the liquid crystal display element is prevented from becoming dark, and the illuminance of the liquid crystal display element is maintained constant.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

FIG. 1 is a configuration diagram of a liquid crystal display device showing one embodiment of the present invention. In FIG. 1, 10 is a printed circuit board,
Diode type light emitting elements (LEDs) 11 to 18 are arranged on the surface of this printed circuit board 10. 19 is a transmissive liquid crystal display element (LCD); 20 is a light diffusion plate disposed between the LEDs 11 to 18 and the liquid crystal display element 19;
These liquid crystal display element 19 and light diffusing plate 20 are attached to a frame portion 21 that holds and blocks light.

FIG. 2 shows a circuit diagram of the same liquid crystal display device. In FIG. 2, 22 is a microcomputer which is a light emitting element control means, and the microcomputer 22 outputs the pulse width (LED ON) of the pulse shown in FIG. time)T
2 to control the brightness of the LEDs 11 to 18.

24 is an AC power supply, and the heater 2 is connected to this AC power supply 24.
Bidirectional thyristor 27 that controls energization of 5 and heater 25
A series circuit consisting of a heater 26 and a bidirectional thyristor 28 for controlling energization of the heater 26 are connected in parallel. 29 consists of a transformer whose primary side is connected to the AC power supply 24, a diode bridge connected to the secondary side of this transformer, and a smoothing electrolytic capacitor, and supplies power to LEDs 11 to 18. The power supply circuit 30 is a stabilized power supply circuit that is composed of a Zener, a resistor, and a transistor, and supplies power to the microcomputer 22. Further, 31.32 is a drive circuit for the bidirectional thyristor 27.28, which is composed of a photothyristor, a transistor, and a resistor, and can drive the bidirectional thyristor 27.28 independently by a control signal from the microcomputer 22. . The power supply for these bidirectional thyristor drive circuits 31 and 32 is an unregulated power supply circuit 29.
It is supplied by more.

The display operation by the microcomputer 22 in the liquid crystal display device of the cooker configured as described above will be explained based on the flowchart of FIG. 4.

First, when a display program to be displayed on the LCD 19 is executed, in step 101, the bidirectional thyristor drive circuit 3
1.32 is off, and if both are off, the process proceeds to step 102, where the power load on the unregulated power supply 29 is light and the voltage is high, and the L E D connected to the same power supply In order to prevent the brightness of 11 to 18 from increasing, the LED on time shown in FIG. 3 is set to 20. Binding, period T1 104. Divide in half and L E D 11-18
If the on signal is output to any of the bidirectional thyristor drive circuits 31 and 32 in step 101, the process proceeds to step 103; It is determined whether ON signals are being output to both the thyristor drive circuits 31 and 32, and if both are outputting ON signals, the process proceeds to step 104, and due to the influence of the voltage drop of the unregulated power supply 29, the LEDs 11 to 32 In order to prevent the brightness of 18 from decreasing, the LED on time time tone 201. is set to ON for all cycles to prevent the illumination of the LCD 19 from becoming dark. Also, if both of them do not output an ON signal in step 103, that is, one of the bidirectional thyristor drive circuits 31, 3
If the ON signal is output only to 2, step 105
Since the voltage of the unregulated power supply 29 is the center of voltage fluctuation, set the LED on time to the sound 2□.Next, in steps 102, 104, and
When the D on time time tone 2 is set, the process proceeds to step 106, where LEDs 11 to 18 are pulse-driven at the set duty cycle and turned on.Next, in step 107, the LEDs 11 to 18 are displayed on the LCD 19. Outputs and exits.

In addition, in this embodiment, in order to change the brightness of LBD11 to LBD18, the duty cycle is adjusted by the period T.
1 is constant and the LED on time is changed to 2 sounds, but L
It goes without saying that the ED on time may be set to 2 constant times and adjusted by changing the period T1.

In this way, the lighting of the LEDs 11 to 18 is driven by pulses, and by providing the microcomputer 22 that variably controls the duty cycle of this pulse, a photothyristor etc. for driving the bidirectional thyristors 27 and 28 can be used. L E due to on/off operation of large loads
Even if the voltage of the unregulated power supply circuit 29, which is the power source for D11 to D18, fluctuates, the duty cycle of the driving pulses for LEDs11 to 18 is adjusted to compensate for the fluctuation.
There is no change in the brightness of D11-18, and L CD 19
The brightness of the illumination is always constant, making it possible to make the LCD 19 very easy to see.

Effects of the Invention As described above, according to the present invention, by variably controlling the duty cycle of the pulse for lighting the light emitting element group according to the fluctuation of the power supply voltage supplied to the light emitting element group by the light emitting element control means, The brightness of the light emitting element group can be kept constant regardless of fluctuations in the power supply voltage, and therefore,
The illuminance of the liquid crystal display element illuminated from the back side by the light emitting element group can be kept constant, and the liquid crystal display element can be made very easy to see.

[Brief explanation of the drawing]

Fig. 1 is an exploded perspective view of a liquid crystal display device of a cooking device showing an embodiment of the present invention, Fig. 2 is a circuit diagram of the liquid crystal display device of the cooking device, and Fig. 3 is a diagram of the liquid crystal display device of the cooking device. A waveform diagram of the pulses output by the microcomputer to drive the LED drive device, Fig. 4 is a flowchart showing the display operation of the liquid crystal display device of the cooking device, and Fig. 5 is an exploded view of the liquid crystal display device of the conventional cooking device. FIG. DESCRIPTION OF SYMBOLS 11-18... Light emitting element (LED), 19... Liquid crystal display element (LCD), 22... Microcomputer (light emitting element control means), 23... LED drive device, 2
9...Unregulated power supply circuit. Agent Yoshihiro Morimoto is shown//-/β- from 'M! ) (LEp) Genryufuli”Kl (LCD) Figure 5

Claims (1)

[Claims] 1. A transmissive liquid crystal display element, a light emitting element group that illuminates the liquid crystal display element from the back side, lighting of the light emitting element group is driven by a pulse, and the duty cycle of this pulse is determined by the power supply supplied to the light emitting element group. A liquid crystal display device for a cooker, comprising a light emitting element control means that performs variable control according to voltage fluctuations.