JP2837241B2 - Backlight control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a backlight control device for a device having a display device with a backlight, such as a word processor or a personal computer.

(Prior Art) Liquid crystal display devices (hereinafter, referred to as "LCD") are widely used as display devices for portable word processors, personal computers and the like. Devices having such an LCD are provided with another light source such as a backlight and a sidelight in order to improve the visibility of the LCD. In this specification, other light sources such as a backlight and a sidelight for a display device are collectively referred to as “backlight”. As a backlight, a thin film
EL elements, cold cathode tubes and the like are used.

On the other hand, portable devices of this type use AC adapters
It can be driven by any one of a plurality of power supplies such as a power supply, a dry cell, and a rechargeable battery (such as NiCd). FIG. 2 shows a circuit of a backlight control device in such an apparatus.

The device shown in FIG. 2 is an AC adapter 1a, a dry cell 1b, or
It is driven by the NiCd battery pack 1c. One of the drive power supplies 1a to 1c connected to the terminal unit 2 is connected to an inverter circuit 4 via a switching transistor circuit (hereinafter abbreviated as "SWTR circuit") 3. Inverter circuit 4
Is supplied to a cold-cathode tube 5 used as a backlight, and the light emission of the cold-cathode tube 5 is controlled by controlling the output of the inverter circuit 4. The output of the SWTR circuit 3 is also input to the stabilizer 9. Stabilization circuit 9
Is for controlling on / off of the output voltage of the SWTR circuit 3. The output of the stabilizing circuit 9 is provided to the control circuit 10. The output of the control circuit 10 is given to the SWTR circuit 3,
The output of the SWTR circuit 3 is turned on when the output of the control circuit 10 is on, and the output of the SWTR circuit 3 is turned on when the output of the control circuit 10 is off.
The output of the TR circuit 3 is set to be low. In other words, the duty ratio of the output of the SWTR circuit 3 is controlled by the output of the control circuit 10. This prevents a change in the input voltage of the inverter circuit 4 due to a change in the type of the employed power supply. That is, when the output voltage is high (about 13 V) and the AC adapter 1a is connected, SWT
Since the output voltage of the R circuit 3 increases, the duty ratio is reduced as shown in FIG.
7.2V) SWTR when NiCd battery pack 1c is connected
Since the output voltage of the circuit 3 decreases, the duty ratio is increased as shown in FIG.

(Problems to be Solved by the Invention) As described above, in the conventional backlight control device, the SWTR
The output voltage of the circuit 3 is monitored, and the output of the SWTR circuit 3, that is, the duty ratio of the input of the inverter circuit 4 is changed according to the fluctuation. Therefore, the stabilizing circuit 9 and the control circuit 10
Must be provided. Therefore, there are problems that the number of parts of the backlight control device increases, the cost increases, and the size increases.

SUMMARY OF THE INVENTION An object of the present invention is a backlight control device useful in a device driven by a plurality of types of power supplies, which requires a small number of parts, is low in cost, and has no increase in size. It is to provide a control device.

(Means for Solving the Problems) A backlight control device of the present invention is a backlight control device for a device that can be driven by a plurality of types of power supplies and includes a display device having a backlight. Power supply type detecting means for detecting which of the plurality of types of power supplies is being driven, and a detection result of the power supply type detecting means, and when the device is driven by a power supply having a low voltage supply level, Control means for increasing the supply voltage to the backlight while controlling the supply voltage to the backlight low when the device is driven by a power supply having a high voltage supply level. Objective is achieved.

(Operation) The brightness of the backlight varies depending on the level of the voltage supplied thereto. That is, when the device is driven by a power supply having a low voltage supply level, the luminance is low because the supply voltage (applied voltage) to the backlight is low.
On the other hand, when the device is driven by a power supply having a high voltage supply level, the supply voltage to the backlight is also high.
Its brightness increases.

Here, in the present invention, the supply voltage to the backlight is increased when the device is driven by a power supply having a low voltage supply level, while the backlight is provided when the device is driven by a power supply having a high voltage supply level. Supply voltage is controlled to be low.

Therefore, according to the present invention, the brightness of the backlight can be controlled to a constant level even when the type of power supply is different.

Further, in the present invention, as described above, even if the type of power supply is different, the brightness of the backlight can be controlled at a constant level, so that the drive voltage in the preceding stage of the inverter circuit conventionally performed is It is not necessary to constantly monitor the value. Therefore, since such a circuit is not required,
The number of parts can be reduced.

(Examples) The present invention will be described below with reference to examples.

One embodiment of the present invention is shown in FIG. This embodiment is similar to the conventional example shown in FIG.
1b, or provided in a device driven by the NiCd battery pack 1c. One of the drive power sources 1a to 1c is connected to the terminal unit 2. The terminal unit 2 includes a terminal 2a for the AC adapter 1a and a terminal 2b for the dry battery 1b or the NiCd battery pack 1c.
And Since the dry battery 1b or the NiCd battery pack 1c is used by being arranged in a battery housing (not shown) of the device, the terminal 2b is arranged in the battery housing.

A first voltage detection circuit 6 is connected to the terminal unit 2.
The first voltage detection circuit 6 outputs a high signal when the voltage appearing at the terminal unit 2 is equal to or higher than a predetermined value (for example, 12 V).
Therefore, when the AC adapter 1a having an output voltage of 13 V is connected to the terminal unit 2, the first detection circuit 6 outputs a high signal. When a dry battery (1.5 V × 6 batteries) 1 b having an output voltage of 9 V or a NiCd battery pack 1 c having an output voltage of 7.2 V is connected to the terminal section 2, the detection circuit 6 outputs a low signal.

Further, in this embodiment, a NICd battery detection terminal 2c is provided in addition to the normal terminal 2b provided in the battery storage unit. The NiCd battery pack 1c used is provided with an auxiliary terminal 11 in addition to the output terminal. NICd battery detection terminal
The second voltage detection circuit 7 is connected to 2c. The second voltage detection circuit 7 outputs a high signal when a voltage is applied to the detection terminal 2c. Therefore, when the NiCd battery pack 1c is inserted into the battery housing, the terminal 2c and the auxiliary terminal 11
And the second voltage detection circuit 7 outputs a high signal.

The terminal 2 is connected to the SWTR circuit 3, and the output of the SWTR circuit 3 is input to the inverter circuit 4 as in the conventional example. The output of the inverter circuit 4 is supplied to a cold-cathode tube 5 used as a backlight, and the emission of the EL element 5 is controlled by controlling the output of the inverter circuit 4.

Outputs of the first and second voltage detection circuits 6 and 7 are provided to a CPU 8 via an interface (not shown). CPU8
Supplies one of three types of control signals having different duty ratios to the SWTR circuit 3 according to the output states of the first and second voltage detection circuits 6 and 7. That is, when the output of the first voltage detection circuit 6 is high (when driven by the AC adapter 1a), the control signal (a) having the duty ratio of 25% (first
) Is given to the SWTR circuit 3. When the outputs of both the first and second voltage detection circuits 6 and 7 are low (when driven by the dry battery 1b), the control signal (b) having a duty ratio of 50% is given to the SWTR circuit 3. When the output of the second voltage detection circuit 7 is high (when driven by the NiCd battery pack 1c), a control signal (c) having a duty ratio of 65% is given to the SWTR circuit 3.

As described above, since the SWTR circuit 3 is driven by any of the control signals (a) to (c) given according to the type of the driving power source, the brightness of the cold cathode tubes 5 is determined by the type of the driving power source 1a to 1c. It is controlled accordingly. Therefore, even if the type of the driving power source changes and the driving voltage changes, the brightness of the cold cathode tube 5 is kept constant.

The terminal 2c may not be provided in the battery storage unit, and a contact that opens and closes in accordance with the projection of the protrusion may be provided. In this case, a recess is provided in a portion corresponding to the protrusion of the NiCd battery pack 2c, and when the NiCd battery pack 2c is inserted into the battery storage portion, the protrusion protrudes to close the contact. The second voltage detection circuit 7 is unnecessary.

(Effect of the Invention) According to the present invention, when the device is driven by a power supply having a low voltage supply level, the supply voltage to the backlight is increased, while when the device is driven by a power supply having a high voltage supply level, The supply voltage to the backlight is controlled to be low.

Therefore, according to the present invention, it is possible to achieve an effect that the brightness of the backlight can be controlled to a constant level even when the type of power supply is different.

Further, according to the present invention, as described above, even if the type of power supply is different, the brightness of the backlight can be controlled to a constant level, so that the driving performed in the previous stage of the inverter circuit conventionally performed is performed. Since it is not necessary to constantly monitor the voltage value, such a circuit is not required. As a result, it is possible to achieve an effect that the number of parts can be reduced, the cost can be reduced, and the system can be reduced in size.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional circuit, and FIG. 3 is a waveform diagram showing a control signal input to a switching transistor circuit. 2 ... terminal section, 3 ... switching transistor circuit, 5 ...
Cold cathode tube.

Claims (1)

(57) [Claims] A display device having a backlight;
A backlight control device for a device that can be driven by a plurality of types of power supplies, comprising: a power type detection unit configured to detect which of the plurality of types of power sources the device is driven; Upon receiving the detection result, the supply voltage to the backlight is increased when the device is driven by a power supply having a low voltage supply level, and is increased when the device is driven by a power supply having a high voltage supply level. A backlight control device comprising: a control unit configured to control a supply voltage to the backlight to be low.