JPH05165424A - Inverter for lcd back light - Google Patents

Abstract

PURPOSE:To stabilize the input voltage of an inverter and to perform power saving in a system by a device in which an LCD with back light is used as a display device, and which drives the system with a battery. CONSTITUTION:This inverter is equipped with a switching circuit 17 which switches the input voltage of the inverter being the power source of a back light arbitrarily based on whether it is stabilized by a DC/DC converter or a battery voltage is inputted directly, a mode control circuit 11 for performing the switching control of the switching circuit 17 and a compulsory switching circuit 12. Also, a CFL current monitoring circuit 6 is provided so as to eliminate the luminance difference of the back light between each mode when the input voltage of the inverter is automatically switched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a power saving LCD (Liquid).
The present invention relates to a CFL inverter in a backlight system of d Crystal Display), and more particularly to an inverter capable of arbitrarily switching a direct input of a power source and a converter input.

[0002]

2. Description of the Related Art Conventionally, control methods for turning on and off a CFL tube backlight behind a liquid crystal display (LCD) have been proposed. That is, if the character processing remains unused for a period of time while the power is on, the life of the backlight is shortened. Therefore, it is necessary to turn off the backlight in the unused state. For example, when the next key input is detected, the backlight is turned on, and when the predetermined time is over, the backlight is turned off (see Japanese Patent Application Laid-Open No. 1-121914). It is determined whether the battery is used or not and the battery is used. The battery life is extended by turning off the backlight while it is in use (see Japanese Patent Laid-Open No. 2-81089), and the method is used to turn off the backlight when the timer times out to save unnecessary power consumption. (See Kaihei 2-100447), detecting the external light intensity and eliminating the power consumption of the CFL backlight system when the external light is strong.
A method of extending the FL life (see Japanese Patent Laid-Open No. 3-38616), or when the display door is opened, the ambient illuminance is above or below a certain illuminance, so that the backlight is not illuminated or lit ( JP-A-2-170126)) and the like.

[0003]

Conventionally, as the circuit system of the LCD backlight inverter, a voltage dimming system,
There are a chopping method and a current feedback method. this house,
In the voltage dimming method and the current feedback method, input voltage is DC / D
Since the light is stabilized by the C converter and input to the inverter, the backlight is turned on stably, but when the battery is driven, the loss increases by that amount because it passes through the DC / DC converter. Then, the efficiency decreases. As a result, the battery operating time of the system is shortened. On the other hand, a chopping method of directly converting DC power of different voltage by intermittently connecting DC power is often used. However, when a method of controlling chopping by a CFL tube current of a backlight is used, an additional circuit can be provided. Since the loss increases with the increase, the efficiency also decreases. Further, in the chopping method, since the DC / DC converter does not stabilize, the loss is small. However, since the input voltage of the inverter is simply chopped and dimmed by the chopper at a certain cycle, when the battery is driven, for example, when a unit with a large current consumption such as a flexibility disk drive is driven, the battery voltage Drops occur. When the battery voltage changes due to the voltage drop, the brightness of the backlight also changes, so the lighting quality of the chopping method was not very good. Further, when the CFL is lit, considering the low temperature lighting when the volatility volume is minimum, the starting voltage is large as shown in FIG. 6, so the output voltage of the inverter becomes considerably high when the volume is maximum, Inver
Efficiency is reduced. Further, as described in the above-mentioned conventional publication, if there is no key input for a certain period of time, there is a method for reducing power consumption by turning off the backlight, but the period actually used by the user Among them, there is no power saving effect.

A first object of the present invention is to solve these conventional problems and to reduce the power consumption of the system in the case of stabilizing the input voltage of the inverter in an apparatus for driving the system with a battery. It is an object to provide an inverter for an LCD backlight that can be used. A second object of the present invention is to provide an LCD backlight inverter capable of preventing deterioration of display quality due to fluctuation of battery voltage when a system is driven by a battery and saving power. To do. A third object of the present invention is an apparatus for driving a system with a battery, which is a user of using the system.
It is an object of the present invention to provide an inverter for an LCD backlight in which the circuit system of the inverter can be arbitrarily selected depending on the purpose of the inverter or the operator. A fourth object of the present invention is an LCD capable of satisfying the conditions of minimum volatility volume, low temperature, and lighting of a backlight without reducing efficiency, in order to save power in the system. It is to provide an inverter for a backlight. A fifth object of the present invention is to automatically switch a plurality of modes without changing the volatility of the backlight due to the difference in the input voltage of the inverter in each mode. It is to provide an LCD backlight inverter that can be switched over. A sixth object of the present invention is to provide an LCD backlight inverter which can inform the user or the operator of the remaining battery capacity of the system without newly providing a remaining capacity detection circuit. Especially. A seventh object of the present invention is to realize an inverter for an LCD backlight which can be realized so that the mounting space and the cost are not doubled when the inverter of two circuit systems is used in the system. To provide. An eighth object of the present invention is, when the system is driven by an AC adapter, an LCD capable of automatically switching to a circuit passing through a DC / DC converter and canceling a power saving mode. It is to provide an inverter for a backlight.

[0005]

In order to achieve each of the above objects, an LCD backlight inverter of the present invention comprises:
(B) In an LCD backlight inverter which is built in a system having a display device and is driven by a battery, the direct input voltage of the battery or the DC / DC converter is used as the input voltage of the backlight inverter. A switching circuit for switching to one of the input voltage via
The present invention is characterized by comprising a mode control circuit for switching and controlling the switching circuit by inputting a mode signal from the system, and a forced switching circuit for switching and controlling the switching circuit by inputting a power-on signal from the system. is there.
The (b) switching circuit is switched by a voltage drop detection circuit that monitors the power supply line of the battery while being driven by the direct input voltage of the battery and outputs a switching signal when a voltage drop of a predetermined time length is detected, Another feature is that the direct input voltage is automatically switched to the input voltage via the DC / DC converter. In addition, (c) the switching circuit is a mode that automatically switches to the input voltage via the DC / DC converter while being driven by the direct input voltage of the battery, and is also fixed at the direct input voltage of the battery. Another feature is that the mode and the fixed mode driven by the input voltage via the DC / DC converter can be manually switched. Also, the (c) switching circuit is
Only when the backlight is started, the input voltage via the DC / DC converter is switched by the switching signal from the forced switching circuit, and the CFL tube current is fed back to the CFL current monitoring circuit, and the CFL current monitoring circuit turns on the CFL. Is notified, DC / D by the forced switching circuit
Another feature is that the input voltage via the C converter is released. In addition, (c) the switching circuit, when switching from the mode of the direct input voltage of the battery to the mode of the input voltage via the DC / DC converter, displays the information of the volatility volume (remaining battery capacity). C to shut off and monitor the CFL tube current
Another feature is that by controlling the output so that the current value monitored by the FL current monitoring circuit will not occur, the difference in the volatility of the backlight between both modes will not occur. Further, (d) the switching circuit operates in the mode of the direct input voltage of the battery to the mode of the input voltage via the DC / DC converter.
When you manually switch to the flash mode, the backlight volatility and the volatility volume position after switching will allow you to know the remaining capacity of the battery. It is also characterized by displaying the corresponding battery remaining capacity scale. Further, (e) the inverter having two circuit systems of the direct input voltage of the battery and the input voltage via the DC / DC converter is also characterized in that one transformer is commonly used. Furthermore, (f) In addition to the configuration in which the system is driven by the input voltage of the battery, AC
With the configuration that drives the system with an adapter,
An AC adapter detection circuit for detecting the input of the AC adapter is provided, and when the AC adapter detection circuit detects the input by the AC adapter, the switching circuit is automatically switched to the input voltage via the DC / DC converter. There is also a feature.

[0006]

In the present invention, the chopping system, that is, the system in which the battery is directly used as the input voltage and the voltage dimming or current feedback system in which the input voltage is supplied via the DC / DC converter are automatically and arbitrarily selected. To be able to switch to. Therefore, a switching circuit for selectively switching between the chopper circuit connection and the DC / DC converter circuit connection, a mode control circuit for switching control of the switching circuit by inputting a mode signal from the system, and a system control circuit By inputting the power-on signal, the switching circuit is controlled only when the backlight is started, and the forced switching circuit for switching to the mode via the DC / DC converter and the DC / DC by detecting the voltage drop. A voltage drop detection circuit for switching to the input voltage mode via the converter and a CFL current monitoring circuit for feeding back and monitoring the CFL tube current are provided. This allows the Inver
It is possible to reduce the loss until input to the inverter, improve the efficiency of the inverter, and extend the battery-operated operation time of the system.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of an LCD backlight inverter showing an embodiment of the present invention. In FIG. 1, 1 is an LCD, 2 is a backlight CFL tube, and 3
Is an inverter circuit, 4 is a filter, 5 is an oscillation circuit, 6 is a CFL current monitoring circuit, 7 is an AC adapter detection circuit, 8 is a DC / DC converter, 9 is a chopper, and 10 is a volatility volume ( Battery remaining capacity scale), 11 is a mode control circuit, 1
2 is a forced switching circuit, 13 is an OR circuit, 14 is an AC adapter, 15 is a battery, and 16 voltage drop detection circuit. The output from the AC adapter 14 or the battery 15 is input to the DC / DC converter 8 or the chopper circuit 9 by being switched by the switching circuit 17 through the OR circuit 13. These converters 8
Alternatively, the chopper circuit 9 outputs a pulse waveform having a certain period. In the case of the DC / DC converter 8, the position of the volatility volume 10 and the CFL current monitoring circuit 6
The output pulse width is modulated by the information of. In the case of the chopper circuit 9, the output pulse is chopped and output at a constant cycle (several KHz) depending on the position of the volatility volume 10. Then, according to the output waveform of the converter 8 or the chopper circuit 9, the oscillation circuit 5 causes the inverter circuit 3 to operate.
Is oscillated and boosted by the inverter circuit 3, and DC / AC
Convert. That is, A output from the inverter circuit 3
The CFL 2 is turned on by the C waveform and is used as the light source of the backlight of the LCD 1.

FIG. 2 is a block diagram of the battery voltage drop detection circuit in FIG. 1, and FIG. 3 is an operation time chart of the battery voltage drop detection circuit in FIG. Next, the mode switching of FIG. 1 will be described. Now, the mode 1 is a fixed mode via the DC / DC converter 8.
The mode 2 is a fixed mode via the chopper circuit 9, and the mode 3 is an automatic switching mode via the DC / DC converter 8 and the chopper circuit 9. First, when switching between mode 1 and mode 2, if the user selects a mode, the mode signal of the selected mode is input from the system to the mode control circuit 11. .. Mode control circuit 11
Controls the switching circuit 17 by the control signal, supplies the battery output voltage to the circuit corresponding to the selected mode, and drives it. Next, at the time of automatic switching of the mode 3, the battery voltage drop detection circuit 16 constantly monitors the power supply line of the battery 15 and generates a switching signal when a voltage drop of a specified level occurs for a specified time. , DC / DC by controlling the switching circuit 17
The power supply is switched to the converter 8 side or the chopper 9 side. As shown in FIG. 2, the battery voltage drop detection circuit 16 inputs the voltage line of the battery to a differentiating circuit composed of C, R, and a differential amplifier 21, detects the change in the battery voltage by the output of the differentiating circuit, The comparator 1 of the differential amplifier 22 outputs a drop start pulse, and the comparator 2 of the differential amplifier 23 outputs a drop end pulse. The outputs of these comparators 1 and 2 are input to the set terminal and reset terminal of the flip-flop (1) 24.

Assuming that a battery voltage drop occurs as shown in FIG. 3A, the differentiating circuit shown in FIG.
A pulse output as shown in (b) is supplied, the output of the comparator 1 indicates the drop start position as shown in FIG. 3 (c), and the output of the comparator 2 as shown in FIG. 3 (d). The drop end positions are shown respectively. Each comparator 1,
The output of 2 gives the output waveform shown in FIG. 3E by controlling the setting and resetting of the flip-flop 1. Next, when the clock signal shown in FIG. 2 is input in the cycle of FIG. 3 (f), the flip-flop 2 is latched by the rising of this clock, as shown in FIG. As shown in (j), the flip-flops 3 and 4 are latched by the rise of the clock obtained by inverting this clock. The output of the flip-flop 2 is further latched by the flip-flop 3, and the output of the flip-flop 3 and the output of the flip-flop 4 are ANDed to obtain a mode switching signal (see FIG. 3 (k)). At this time, a short drop such as the second drop shown in FIG. 3A, that is, an instantaneous drop that does not affect the inverter output is absorbed here. Therefore, when a drop having a length of a predetermined time or more, such as the first drop in FIG. 3A, occurs,
A mode switching signal will be output. In this way, when a drop occurs for a predetermined time or longer in the mode via the chopper circuit, the mode 3 can automatically switch to the circuit via the DC / DV converter.

FIG. 4 is a diagram showing the conditions for calculating the battery drive operating time, and FIG. 5 is a diagram showing an example of the battery drive operating time. Here, the time (T1) from the start of the drop to the start of the switching and the battery drive operation time of the modes 1, 2, 3 will be examined. The time T1 from the start of the drop to the start of the switching is set to match the response time from the battery voltage fluctuation to the inverter output fluctuation.
Further, the cycle of the clock signal shown in FIGS. 2 and 3 (f) is a threshold value of time that does not affect the output of the inverter. In other words, by making the time that does not affect the inverter output and the clock cycle substantially coincide with each other, it is possible to avoid switching for drops that do not require switching. Further, the reference voltage of the comparator is set so that the detected drop level is output at a threshold value that does not affect the inverter output. As a result, as in the case described above, it is possible to avoid switching for drops that do not require switching. FIG. 4 shows the calculation conditions of the battery drive operation time. In this example, the battery has a capacity of 1700 mAH × 6, and the current consumption of the system other than the backlight is 1200 mA.
(7.2V), the current consumption of the backlight unit in mode 1 is 300mA (7.2V), the current consumption of the backlight unit in mode 2 is 200mA (7.2V), Do 3
At that time, the current consumption of the backlight unit is 220 mA (7.2
V). Now, assuming that the switching via the DC / DC converter is 20% of the entire system usage time, 200 (mA) x (80/100) + 300 (mA) x (20/100) = 220 (mA)・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (1) In the above mode 1, the input of the inverter is DC.
A fixed mode via a DC / DC converter, a mode 2 is a fixed mode in which the input of the inverter does not pass through the DC / DC converter, and a mode 3 is an input of the inverter. Is a mode for automatically switching to a DC / DC converter.
In addition, the current consumption of the system in mode 1 is 1200 + 300 = 1500 (mA) .... (2) The current consumption of the system in mode 2 is , 1200 + 200 = 1400 (mA) ... (3) The current consumption of the system in mode 3 is 1200 + 220 = 1420 (mA) .... (4) Further, as is apparent from FIG. 4, the operating time through mode 1, that is, the original DC / DC converter is 1.13.
(H), the operating time through mode 1, that is, via the chopper can be extended to 1.21 (H), and the operating time in mode 3, that is, when automatically switchable is 1.
It becomes 19 (H). FIG. 5 is a characteristic diagram in which current consumption is plotted on the horizontal axis and operating time is plotted on the vertical axis. In Mode 1, the operating time is short and the current consumption is high, but in Mode 3 and Mode 3. -With Do 2, the operating time can be lengthened and at the same time
The current consumption can also be reduced (1 in mode 1
700mA-1500mA, Mode 2 1400m
1420 mA in mode A and mode 3).

Next, the operation at the time of starting the backlight will be described. FIG. 6 is a characteristic diagram showing changes in the CFL starting voltage depending on the ambient temperature. At the time of starting the backlight, a higher voltage than that at the time of lighting is required, and the starting voltage thereof also changes depending on the ambient temperature, as shown in FIG. That is, -10
1 for the starting voltage at 40 ° C and the starting voltage at 40 ° C
There is a difference between 400V and 650V. The operating temperature guarantee range of the system is usually guaranteed in a fairly wide range of 0 ° C. to 40 ° C., but the applied voltage greatly differs between 0 ° C. and 40 ° C. By the way, when the chopping is controlled by the CFL tube current, the number of additional circuits is increased, so that the loss is increased and the efficiency is lowered. Therefore, the chopping circuit 9 of the present invention uses the CFL in order to emphasize efficiency.
Not monitoring tube current. As a result, if starting is possible when the volatility volume is minimum, the starting voltage becomes extremely high when the volatility volume is maximum, and the circuit design is inefficient under normal lighting conditions. Therefore, in the present invention, the circuit is automatically switched to the circuit via the DC / DC converter for monitoring the CFL tube current only at the time of starting. That is, by inputting a power-on signal (LCD lighting signal) from the system to the forced switching circuit 12, the circuit 12 is activated and the CFL tube current monitoring circuit 6 is operated. That is, the CFL tube current is voltage-converted by the resistance and fed back to the CFL current monitoring circuit 6. Further, the compulsory switching circuit 12 notifies the switching circuit 17 of the CFL lighting, thereby forcibly canceling the circuit via the DC / DC converter and switching to the circuit via the chopper. In this way, at the time of start-up, the power-on signal from the system is input to the compulsory switching wholesale circuit 12 and converted into a signal for switching to the circuit via the DC / DC converter, thereby switching the switching signal to the switching circuit 17. Is output.

FIG. 7 is a diagram showing an example of how the CFL current changes with the battery voltage and the remaining battery charge. next,
When a battery voltage drop occurs in mode 3,
The operation of the volatility control when automatically switching to the circuit via the DC / DC converter will be described. In FIG. 7, the horizontal axis represents the battery voltage, and the vertical axis represents the remaining battery charge and CFL.
Chopping dimming method and DC / D when tube current is taken
The characteristic diagram of the C converter system is shown. As shown in FIG. 7, depending on the battery voltage at that time, the tube current (volatility) is different even at the same volatility position (remaining battery capacity) as when the DC / DC converter is used. . Therefore, in the present invention, when switching to the DC / DC converter, flicker on the screen due to the difference in volatility is prevented by flowing the same tube current regardless of the volatility volume position. Now, the position of the volatility volume during operation of the chopping circuit is the position of A in FIG. 7, that is, the volatility volume.
It is assumed that the position is moved by a from the position of MAX. The tube current at that time is 5 mArms. The CFL current monitoring circuit 6 shown in FIG. 1 monitors this current value (effective value) via the filter 4. DC / DC converter
When the battery 8 is switched to the DC / DC converter via the battery voltage drop, the CFL current monitoring circuit 6
The output is controlled so that the current value monitored by is the same as the current value monitored by.
At that time, the information of the volatility volume is the switching circuit 1
Blocked by 7. Therefore, as shown in FIG. 7, originally, at the time of switching to the DC / DC converter,
The current value of 5.8 mArms, which is the current value at the position moved by a from the volatility volume MAX position via the converter, should flow, but the monitoring current value becomes 5 mArms by cutting the volatility volume information. Thus, the change in volatility at the time of switching does not occur. At this time, the volatility volume does not function, but since it is only when the battery voltage drops, it can sufficiently cope with it. DC / DC
The distinction between mode 1 and mode 3 via the converter is that the mode control circuit 11 inputs the mode signal from the system to the switching circuit 17
Switch control.

FIG. 8 is a diagram showing an example of the remaining battery charge display, and FIG. 9 is an external view of the inverter board. In the display of the battery remaining capacity, as shown in FIG. 7, the relationship between the change in the battery voltage and the volatility (tube current) is checked in advance, and DC /
Check the width of change in the tube current and the width of movement of the volatilization volume when passing through the DC converter. Next, the remaining battery capacity (voltage) corresponding to the movement width is displayed next to the volume. As an example of the display, as shown in FIG. 8, on the display of BRIGHTNESS BATT on the side of the screen, MA
With a scale of X and MIN, 100% to 0% between them
Divide into sections and slide with a scale 82 to read the coincident points. To check the remaining capacity, first manually D
By switching to the C / DC converter and adjusting the volatility volume until the volatility difference disappears by repeating the switching many times so that the brightness is the same as the volatility when driving the chopping circuit. .. At this time, the automatic volatility adjustment is disabled. Next, confirm the adjusted volume position on the remaining capacity scale displayed horizontally. Further, normally, when two inverter circuits of different systems are used, two transformers are also required. However, in the present invention, two transformers are not driven at the same time, so one transformer is commonly used. .. The inverter board has an appearance as shown in FIG. 9, and is equipped with an input connector 91, a contrast volume 92, a transformer 93, a volatility volume 94, and an output connector 95. In FIG. 1, when the input is set to AC100V, it is driven by the AC adapter, so there is no need to save power. Therefore, when the AC adapter detection circuit 7 monitors the input voltage and detects that the input is via the AC adapter 14, the switching circuit 17 is switched to the DC / DC converter fixed. Further, when the AC adapter 14 is removed, only the input from the battery 15 is required.
The mode control circuit 11 immediately receives the mode signal from the system.
And the switching signal is output from the mode control circuit 11 to the switching circuit 17 to switch to the designated mode.

[0014]

As described above, according to the present invention,
(A) Normally, the input voltage of the inverter is DC / DC
Since it is input to the inverter through the chopper circuit without passing through the converter, there is little loss until the input to the inverter. As a result, the efficiency of the inverter is increased, and the battery-operated operation time of the system can be extended. (B) When the backlight is lit by the chopping dimming method, a voltage drop often occurs when a unit with a large current consumption such as a floppy disk drive is driven, but a battery voltage drop occurs. Automatically, the input voltage of the inverter is DC / D
Since the output can be switched to the C converter output, the display quality can be maintained. Also, (c) manually,
Since the chopping dimming method and the method via the DC / DC converter can be automatically selected and switched, the chopping method is used when the battery operation time of the system is important, and the DC is used when the display quality is important. It is possible to select a system via the / DC converter. (D) When the backlight is turned on, the input voltage to the inverter can be automatically switched to the circuit for feeding back the CFL tube current via the DC / DC converter. It is possible to satisfy the conditions of minimum lighting and low temperature lighting without deteriorating the efficiency of the chopping circuit. Further, when the input voltage of the (e) inverter is automatically switched, the DC / DC converter is fed back so that the difference in the volatility of the backlight does not occur between the modes. When switching to a DC converter, it can be lit with the same tube current (volatility) as when chopping.
The user can switch smoothly without being aware of the switch. (F) When manually switching in a mode not passing through the DC / DC converter, depending on the volatility of the backlight and the position of the volatility volume after switching, the user or the operator. Since it is possible to know the remaining capacity of the battery, it is not necessary to newly provide a remaining capacity detection circuit, which is effective in terms of mounting space and cost. (G) Although it is an inverter for mounting a converter having two circuit systems, the same transformer can be shared, which is effective in terms of mounting space and cost. Furthermore, (h) AC
When driven by an adapter, it can be automatically switched to the DC / DC converter, so that it is not necessary to manually switch the mode, and labor can be saved.

[0015]

[Brief description of drawings]

FIG. 1 is a block diagram of an LCD backlight inverter showing an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a battery voltage drop detection circuit in FIG.

FIG. 3 is an operation time chart of the battery voltage drop detection circuit in FIG.

FIG. 4 is a diagram showing a battery drive operating time calculation condition of the present invention.

FIG. 5 is a diagram showing an example of a battery drive operation time of the present invention.

FIG. 6 is a characteristic diagram showing a change in CFL starting voltage according to ambient temperature.

FIG. 7 is a diagram showing an example of correspondence between changes in CFL current and remaining battery capacity depending on battery voltage.

FIG. 8 is an external view showing a battery remaining capacity display example of the present invention.

FIG. 9 is an external view of the inverter board of the present invention.

[Explanation of symbols]

 1 LCD 2 CFL 3 Inverter Circuit 4 Filter 5 Oscillation Circuit 6 CFL Current Monitoring Circuit 7 AC Adapter Detection Circuit 8 DC / DC Converter 9 Chopper Circuit 10 Volatility Volume (Battery Remaining Capacity Scale) 11 Mode Control circuit 12 Forced switching circuit 13 OR circuit 14 AC adapter 15 Battery 16 Voltage drop detection circuit 17 Switching circuit

Claims (8)

[Claims] 1. A built-in system having a display device,
In an LCD backlight inverter driven by a battery, the input voltage of the backlight inverter is switched to either a direct input voltage of the battery or an input voltage via a DC / DC converter. A circuit and a mode control circuit for controlling the switching circuit by inputting a mode signal from the system,
An inverter for LCD backlight, comprising: a forced switching circuit for controlling switching of the switching circuit by inputting a power-on signal from the system. 2. The LCD backlight inverter according to claim 1, wherein the switching circuit monitors a power supply line of the battery during driving with a direct input voltage of the battery to detect a voltage drop of a predetermined time length. It is switched by a voltage drop detection circuit that outputs a switching signal when detected, and is automatically switched from the direct input voltage to an input voltage via a DC / DC converter.
Inverter for CD backlight. 3. The inverter for LCD backlight according to claim 1, wherein the switching circuit automatically drives DC / DC while being driven by a direct input voltage of a battery.
In addition to the mode to switch to the input voltage via the converter,
A fixed mode driven by the direct input voltage of the battery,
An inverter for LCD backlight, characterized in that it can be manually switched to a fixed mode driven by an input voltage via the DC / DC converter. 4. The inverter for LCD backlight according to claim 1, 2 or 3, wherein the switching circuit is via a DC / DC converter by a switching signal from the forced switching circuit only when the backlight is started. Input voltage of the CFL and the CFL tube current is fed back to the CFL current monitoring circuit.
An inverter for LCD backlight, which releases the input voltage via the DC / DC converter by the forced switching circuit when the FL lighting is notified. 5. The inverter for LCD backlight according to any one of claims 1 to 4, wherein the switching circuit includes a DC / DC switch from a direct input voltage mode of the battery.
When switching to the mode of the input voltage via the DC converter, the current value monitored by the CFL current monitoring circuit that shuts off the information of the volatility volume (battery remaining capacity) and monitors the CFL tube current. By controlling the output so that the backlight volatility does not differ between both modes, the LCD backlight inver is characterized.
Ta. 6. The inverter for LCD backlight according to any one of claims 1 to 5, wherein the switching circuit changes the DC / DC from the direct input voltage mode of the battery.
When manually switching to the mode of the input voltage via the DC converter, it is possible to know the remaining capacity of the battery by the volatility of the backlight and the position of the volatility volume after switching. An LCD backlight inverter, which is characterized by displaying a battery remaining capacity scale corresponding to the scale next to the volatility volume scale. 7. The LCD backlight inverter according to claim 1, wherein there are two circuit methods, a direct input voltage of the battery and an input voltage via the DC / DC converter. An inverter having an LCD backlight inverter using one transformer in common. 8. The inverter for LCD backlight according to claim 1, wherein the system is driven by an input voltage of the battery, and the system is driven by an AC adapter. And an AC adapter detection circuit for detecting the input of the AC adapter, and when the AC adapter detection circuit detects the input by the AC adapter, the switching circuit is automatically switched to a DC / DC converter. Inverter for LCD backlight, which is characterized by input voltage via.