JPH11354285A - Cold cathode tube lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a cold cathode tube from being put in a lighting impossible state by operating a protective function of an inverter by a dark effect of the cold cathode tube. SOLUTION: An inverter circuit 21 contains an inverter main circuit 31 for generating voltage required to light a cold cathode tube 26 and a protective circuit 32. When the cold cathode tube 26 delays in lighting by a dark effect, the protective circuit 32 cuts off input of a power source by judging it as an opening state. A cutoff of the power source is detected by an electric current detecting amplifier 29 as a change in end-to-end voltage of an electric current detecting resistance 24. A microcomputer 30 repeatedly controls stopping and a restart of operation of the inverter circuit 21 through an FET 28 to continue operation of the inverter circuit 21 as it is when a lighting current corresponding to lighting of the cold cathode tube 26 is detected in a range of a repetitive condition decided in response to the dark effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-cathode tube lighting device for lighting a cold-cathode tube used for a backlight or the like of a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, liquid crystal display devices for displaying images have been widely used in personal computers, word processors, portable information terminal devices and the like. Among the liquid crystal display devices, a transmission type liquid crystal display device is provided with a backlight in order to brighten a display screen and make images easy to see. Generally, a cold cathode tube is often used as a backlight.

FIG. 7 shows an example of Japanese Patent Application Laid-Open No. 5-34318.
7 shows a power supply circuit of the cold cathode tube disclosed in FIG. The inverter circuit 1 generates a high voltage. The power supply voltage is supplied between the power supply terminal 2 and the ground terminal 3. The value of the current supplied from the power supply is detected by the comparator 4.
The inverter circuit 1 boosts the voltage supplied to the power supply terminal 5 with an internal high-frequency transformer and supplies the boosted voltage to the cold cathode tube 6. The open circuit voltage of the inverter circuit 1 is about 1500 V, which is higher than the lighting start voltage of the cold cathode tubes 6. Cold cathode tube 6
During lighting, a voltage of about 500 V to 800 V is required, and is generated from the inverter circuit 1. The inverter circuit 1 is also provided with a ground terminal 7. A voltage dividing resistor 8 is inserted between the power supply terminal 5 and the ground terminal 7 of the inverter circuit 1, and a freewheel diode 9 is also inserted. In the diode 9, the cathode electrode side is connected to the power supply terminal 5 side and the anode electrode side is connected to the ground terminal 7 side, respectively, so that the directions are opposite in a normal state.

[0006] Between the power supply terminal 2 and the power supply terminal 5 of the inverter circuit 1, an emitter-collector connection of a PNP transistor 10 is connected for switching control. The base of the transistor 10 is connected to a DC-DC converter circuit 11 formed as an IC. The voltage between the power supply terminal 5 and the ground terminal 7 of the inverter circuit 1 that is divided by the voltage dividing resistor 8 is also input to the DC-DC converter circuit 11. The DC-DC converter circuit 11 also has a function of outputting a reference voltage. This reference voltage is divided by a voltage dividing resistor 12 and becomes a reference voltage of the comparator 4. The output of the comparator 4 is input to the control circuit 13. A current detection resistor 14 is inserted between the ground terminal 7 of the inverter circuit 1 and the entire ground terminal 3. Comparator 4
Converts the voltage generated across the current detection resistor 4 into a voltage dividing resistor 1
2. When an overcurrent is detected by comparing with a reference voltage based on the control circuit 2, a signal is supplied from the control circuit 13 to the DC-DC converter circuit 11, the transistor 10 is turned off, and the inverter circuit 1 is turned off.
Stop supplying power to the

Another prior art related to a cold cathode tube lighting device is disclosed in Japanese Patent Application Laid-Open No. Hei 9-129382. In this prior art, a protection circuit is provided inside a portion corresponding to the inverter circuit 1 in FIG. 7 to protect against an overcurrent and an open state and to cope with the dark effect of the cold cathode fluorescent lamp. For this reason, the current on the secondary side of the transformer that generates a high voltage and the current flowing through the cold-cathode tube are both detected, and an overcurrent and an open state are detected while comparing with each other while distinguishing from the dark effect. I have.

The phenomenon of the dark effect of the cold cathode tube occurs when the cold cathode tube is left in a dark place. When this phenomenon occurs, lighting of the cold-cathode tube is delayed by several seconds to several tens of seconds.
When the dark effect occurs, it is difficult to distinguish the open state from the open state, and it is easy to determine that the state is the open state and stop the power supply.

[0007]

SUMMARY OF THE INVENTION FIG.
In the configuration like the prior art of No. 343187, it is possible to prevent the overcurrent, but it is not possible to appropriately cope with the occurrence of the dark effect of the cold-cathode tube 6. When the power supply current does not flow through the inverter circuit 1 due to the dark effect, the comparator 4 provides the control circuit 13 with an output corresponding to the open state. If the control circuit 13 has a protection function corresponding to the opening, the DC-DC converter circuit 11 operates to stop the operation of the inverter circuit 1, and the supply of the high voltage to the cold cathode tubes 6 is stopped. Will not be done.

When the control circuit 13 does not have the protection function corresponding to the open state, the supply of the power supply voltage to the inverter circuit 1 continues. In the open state,
Approximately 150 corresponding to the lighting start voltage
If a high voltage of about 0 V is generated and continues to be generated for a long time, a discharge may occur in a wiring or a terminal. Further, in the configuration of FIG. 7, about 10 parts are required, and the number of parts increases.

Also, as in the prior art of Japanese Patent Application Laid-Open No. Hei 9-129382, a method of detecting an abnormality in a secondary circuit of a transformer used inside an inverter also requires a current flowing through the secondary side of the transformer and a cold cathode fluorescent lamp. When the difference from the current flowing through is small, the determination becomes very difficult. Publication No. 002
The fourth paragraph states that the dark effect is similar to the case where the discharge tube is not connected. From this description, it is presumed that when the discharge tube is connected and is in the open state due to the failure of the discharge tube, it is more difficult to distinguish from the dark effect. Further, it does not clearly describe how to deal with the case where the lighting delay is detected due to the dark effect.

An object of the present invention is to provide a cold-cathode tube lighting device having a protection function of preventing a lighting failure due to a dark effect.

[0011]

According to the present invention, there is provided an inverter circuit having a protection function for generating a voltage necessary for lighting a cold cathode tube and cutting off a power supply input when a load is open.
A switching circuit for controlling ON / OFF of the inverter circuit, a current detection circuit for detecting a current supplied to the inverter circuit, and when the power is turned on, the switching circuit is controlled to start the operation of the inverter circuit. When the lighting current in a predetermined range corresponding to the lighting of the cold-cathode tube is detected, the operation of the inverter circuit is continued, and when the power input cutoff based on the protection function of the inverter circuit is detected by the current detection circuit, the inverter circuit is activated. The operation of the circuit is repeatedly stopped and restarted, and if the lighting current is detected within a range of repetition conditions set in advance corresponding to the dark effect of the cold cathode fluorescent lamp, the operation of the inverter circuit is continued. A control circuit for controlling a switching circuit so as to stop operation if a lighting current is not detected. A tube lighting instrumentation.

According to the present invention, the inverter circuit has a protection function of cutting off the power supply input when the load is in an open state, and generates a voltage necessary for lighting the cold-cathode tube. The switching circuit controls ON / OFF of the inverter circuit.
The current detection circuit detects a current supplied to the inverter circuit. The control circuit controls the switching circuit when the power is turned on to start the operation of the inverter circuit, and when the current detection circuit detects a lighting current in a predetermined range corresponding to the lighting of the cold-cathode tube, the inverter circuit The operation of is continued. When the power supply interruption based on the protection function of the inverter circuit is detected by the current detection circuit, the control circuit repeatedly stops and restarts the operation of the inverter circuit, and is preset in accordance with the dark effect of the cold-cathode tube. If the lighting current is detected within the range of the repetition condition, the operation of the inverter circuit is continued. If the lighting current is not detected within the range corresponding to the dark effect, the control circuit controls the switching circuit so as to stop the operation of the inverter circuit. This can provide appropriate protection against the open state of the inverter circuit.

Further, according to the present invention, there is provided an inverter circuit for generating a voltage required for lighting a cold cathode tube,
A switching circuit for N / OFF control, a current detection circuit for detecting a current supplied to the inverter circuit, and a control circuit for controlling the switching circuit to start operation of the inverter circuit when power is turned on. When a current equal to or higher than a predetermined reference is detected, the operation of the inverter circuit is stopped, and a lighting current in a predetermined range corresponding to the lighting of the cold-cathode tube is detected by the current detection circuit. When the lighting current is not detected by the current detection circuit, the operation of the inverter circuit is repeatedly stopped and restarted, and is preset in accordance with the dark effect of the cold cathode fluorescent lamp. If the lighting current is detected within the range of the repetition condition, the operation of the inverter circuit is continued, and the lighting current is not detected. A cold cathode tube lighting device which comprises a control circuit for controlling the switching circuit to stop the operation if Re.

According to the present invention, the inverter circuit generates a voltage necessary for lighting the cold cathode tube. The switching circuit controls ON / OFF of the inverter circuit. The current detection circuit detects a current supplied to the inverter circuit.
When the power supply is turned on, the control circuit controls the switching circuit to start the operation of the inverter circuit. When the current detection circuit detects a lighting current in a predetermined range corresponding to lighting of the cold-cathode tube, the inverter circuit The operation of is continued. When the current detection circuit detects a current that is equal to or higher than a predetermined reference value that is regarded as an overcurrent in the inverter circuit, the operation of the inverter circuit is stopped,
Protect from overcurrent. When the current detection circuit detects a lighting current in a predetermined range corresponding to the lighting of the cold-cathode tube, the operation of the inverter circuit is continued. When the lighting current is not detected by the current detection circuit,
The operation of the inverter circuit is repeatedly stopped and restarted, and if the lighting current is detected within a range of the repetition conditions set in advance corresponding to the dark effect of the cold cathode fluorescent lamp, the operation of the inverter circuit is continued and the lighting current is continued. If is not detected, control is performed to stop the operation. Thus, the overcurrent protection function and the control for the dark effect can be realized together, and the number of components can be reduced.

Further, the present invention provides an inverter circuit which generates a voltage necessary for lighting a cold cathode tube and has a function of protecting a load from being opened and an overcurrent;
/ OFF control switching circuit, a protection detection circuit for detecting the operation state of the protection function of the inverter circuit, and when the power is turned on, the switching circuit is controlled to start the operation of the inverter circuit. When it is detected that the protection function is not operating, the operation of the inverter circuit is continued. When the protection detection circuit detects that the protection function of the inverter circuit is operating, the operation of the inverter circuit is stopped. When the lighting current is detected within the range of the repetition condition set in advance corresponding to the dark effect of the cold cathode fluorescent lamp, the operation of the inverter circuit is continued, and the lighting current is detected. And a control circuit for controlling the switching circuit so as to stop the operation if not provided.

According to the present invention, the inverter circuit generates a voltage necessary for lighting the cold-cathode tube, and has a function of opening a load and protecting against overcurrent. The switching circuit controls ON / OFF of the inverter circuit. The protection detection circuit detects an operation state of a protection function of the inverter circuit. When the power is turned on, the control circuit controls the switching circuit to start the operation of the inverter circuit. When the protection detection circuit detects that the protection function of the inverter circuit does not operate, the control circuit continues the operation of the inverter circuit. . When the protection function does not operate, the cold-cathode tube lights up and the lighting state continues. When the protection detection circuit detects that the protection function of the inverter circuit is operating, the control circuit repeatedly stops and restarts the operation of the inverter circuit, and sets in advance according to the dark effect of the cold cathode fluorescent lamp. If the operation of the protection function is not detected within the range of the repeated condition, the lighting of the cold cathode tube delayed by the dark effect is started and the lighting state can be continued. Even when the operation of the inverter circuit is repeatedly stopped and restarted, when the protection function is operating, the operation of the inverter circuit is stopped, so that protection against failure can be provided.

In the present invention, the inverter circuit can be turned on / off by an external input, and the switching circuit has a switching element for turning on / off the external input of the inverter circuit. It is characterized by.

According to the present invention, the switching element of the switching circuit controls the external input of the inverter circuit to perform ON / OFF control of the operation. Thus, a switching element having a small current capacity can be used.

According to the present invention, the control circuit includes a microcomputer which performs control according to a preset program.

According to the present invention, since the control circuit includes the microcomputer which performs control according to a preset program, it is easy to determine whether or not the lighting of the cold-cathode tube is delayed based on the dark effect. be able to.

[0021]

FIG. 1 shows a schematic electrical configuration of a cold-cathode tube lighting device 20 according to a first embodiment of the present invention. A power supply voltage supplied between the power supply terminal 22 and the ground terminal 23 is applied to the inverter circuit 21.
The power supply voltage Vin applied to the power supply terminal 22 is supplied to the power supply terminal 25 of the inverter circuit 21 via the current detection resistor 24.
Given to. The inverter circuit 21 generates a lighting start voltage of about 1500 V necessary for lighting the cold cathode tube 26 and a high voltage of about 800 to 500 V required during lighting.
The ground terminal 27 of the inverter circuit 21 is connected to the ground terminal 23 of the cold cathode tube lighting device 20 as a whole.

The ON / OFF operation of the inverter circuit 21 can be controlled by an external input via a field effect transistor (hereinafter abbreviated as "FET") 28 as a switching element. The voltage generated across the current detection resistor 24 is detected by a current detection amplifier 29, and a current detection output is input to a microcomputer (hereinafter abbreviated as “microcomputer”) 30. Microcomputer 3 as control circuit
0 operates as a one-chip microcontroller in which a preset control program is stored.
ON / O of the operation of the inverter circuit 21 by driving the
The FF is controlled. The current detection amplifier 29 is formed by a comparator.

In the inverter circuit 21, a cold cathode tube 26 is provided.
And a protection circuit 32 that protects the inverter main circuit 31. The protection circuit 32 performs protection corresponding to at least the open state of the load of the inverter circuit 21,
The operation of the inverter main circuit 31 for detecting the open state is stopped. The protection circuit 32 may have a protection function against an overcurrent of the load of the inverter circuit 21. The protection circuit 32 can be configured similarly to the above-described prior art. Further, instead of the FET 28, another switching element can be used.

FIG. 2 shows a control procedure when the power of the microcomputer 30 of FIG. 1 is turned on. In step a1, the power is turned on, and in step a2, the FET 28 is turned on to start the operation of the inverter circuit 21. In step a3,
It is determined whether or not the current detection amplifier 29 detects that a voltage corresponding to a current set in advance corresponding to the lighting of the cold cathode tube 26 is generated at both ends of the current detection resistor 24. When the current corresponding to lighting is not detected, it is determined in step a4 whether the current value is small and corresponds to the open state. If it is determined that it corresponds to the open state, it is determined in step a5 whether the condition is within a range of a predetermined repetition condition corresponding to the dark effect. If it is determined that it is within the range, the FE is determined in step a6.
The inverter circuit 21 is temporarily turned off via T28, and the process returns to step a2 to turn the inverter circuit 21 on within a predetermined range.

The repetition condition of step a5 is set based on the number of times the inverter circuit 21 is ON and the total time in consideration of the fact that the dark effect appears as a delay of the lighting start of several seconds to several tens of seconds. . If the open state continues even if the condition is not satisfied, it is determined in step a7 that the failure is open. If it is determined in step a4 that it is not in the open state, it is determined in step a8 that the failure is in another mode such as an overcurrent. Step a3
Then, when a current corresponding to the lighting of the cold-cathode tube is detected, the ON state of the inverter circuit 21 is continued as it is,
At step a9, the control procedure ends.

FIG. 3 shows a schematic electrical configuration of a cold-cathode tube lighting device 40 as a second embodiment of the present invention. In the present embodiment, portions corresponding to the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. The inverter circuit 41 of the present embodiment includes only the inverter main circuit 51 and does not particularly have a protection circuit. The microcomputer 50, which is the control circuit of the present embodiment, also determines whether the current value detected by the current detection resistor 24 is an overcurrent. Therefore, an operational amplifier is used as the current detection amplifier 49, and an analog / digital (A / D) conversion circuit is built in the microcomputer 50. In the present embodiment, the number of parts used can be reduced.

FIG. 4 shows a control procedure of the microcomputer 50 of FIG. When the power is turned on in step b1, step b
2 so that the inverter circuit 41 is turned on by the FET.
28 is controlled. In step b3, it is determined whether or not a voltage corresponding to the overcurrent is generated at both ends of the current detection resistor 24 based on the output of the current detection amplifier 49. If an overcurrent is detected, it is determined that a failure has occurred in step b4, and the inverter circuit 21 is turned off to end the operation. If no overcurrent is detected in step b3,
In step b5, it is determined whether or not a current corresponding to cold-cathode tube lighting has been detected. If it is not detected, it is determined in step b6 whether or not it is in the open state. When it is determined to be in the open state, in step b7,
It is determined whether the condition is within the range of the repetition condition. If it is within the range of the repetition condition, the inverter circuit 41 is turned off at step b8, and the process returns to step b2 to control the inverter circuit 41 on. Step b7
If it is determined that the open state continues even after the end of the range of the repetition condition, it is determined in step b9 that the failure is in the original open state, and the inverter circuit 41 is turned off to control the entire control procedure. To end. If it is determined in step b6 that the circuit is not in the open state, it is determined in step b10 that another failure such as an overcurrent has occurred, and the inverter circuit 4
1 is turned off, and the control procedure is ended as a whole. If a current corresponding to cold-cathode tube lighting is detected in step b5, the control procedure is terminated as it is in step b11, and lighting of the cold-cathode tube 26 is continued.

FIG. 5 shows a schematic electrical configuration of a cold-cathode tube lighting device 60 according to a third embodiment of the present invention. In the present embodiment, the operation of the protection function of the inverter circuit 61 is detected, and the microcomputer 70 as the control circuit performs control to avoid the dark effect. The inverter circuit 61 includes an inverter main circuit 71, a protection circuit 72, and a latch circuit 73 for storing the operation state of the protection circuit 72. The microcomputer 70 detects the output of the latch circuit 73 and detects the protection operation by the protection circuit 72. The protection circuit 72
Can be configured in the same manner as in the prior art described above.

FIG. 6 shows a control procedure of the microcomputer 70 of FIG. When the power is turned on in step c1, step c2
To control the FET 28 to the ON state, and the inverter circuit 6
1 is started. In step c3, the operation of the protection circuit 72 in the inverter circuit 61 is confirmed by detecting the output of the latch circuit 73. If it is determined that the protection operation is being performed, the process proceeds to step c4, and it is determined whether the protection operation is within a predetermined repetition condition. If it is determined that the current value falls within the range of the repetition condition, the process proceeds to step c5, in which the FET 28 is turned off and the inverter circuit 6
1 is temporarily stopped. Next, returning to step c2,
Hereinafter, the stop and restart of the operation of the inverter circuit 61 are repeated. If it is determined in step c4 that the number of repetitions is out of the preset repetition condition range, it is determined in step c6 that a failure has occurred, and the operation of the inverter circuit 61 is stopped. If it is determined in step c3 that the protection operation has not been performed, the operation of the inverter circuit 61 is continued as it is in step c7. This is because it can be determined that an appropriate lighting current is flowing through the cold-cathode tube 26 when the protection operation does not occur.

[0030]

As described above, according to the present invention, it is possible to prevent the protection function of the inverter from operating due to the dark effect, thereby preventing the cold-cathode tube from becoming unlit and appropriately protecting the load of the inverter circuit. Can also be done.

According to the present invention, it is possible to prevent a state in which the cold-cathode tube cannot be turned on due to a dark effect under the control of the control circuit, and to effectively protect against overcurrent.
The number of parts can be reduced.

Further, according to the present invention, the operation state of the protection function provided in the inverter circuit can be detected to prevent the cold cathode fluorescent lamp from being turned off due to the dark effect.

Further, according to the present invention, the ON / OFF control of the inverter circuit can be performed with a small-capacity switching element.

Further, according to the present invention, the inoperative state of the cold cathode tube due to the dark effect can be easily avoided by the program operation of the microcomputer.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic electrical configuration of a cold-cathode tube lighting device 20 as a first embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of a microcomputer 30 of FIG.

FIG. 3 is a block diagram showing a schematic electrical configuration of a cold-cathode tube lighting device 40 as a second embodiment of the present invention.

4 is a flowchart showing a control procedure of a microcomputer 50 in FIG.

FIG. 5 is a block diagram showing a schematic electrical configuration of a cold-cathode tube lighting device 60 as a third embodiment of the present invention.

6 is a flowchart showing a control procedure of the microcomputer 70 in FIG.

FIG. 7 is a block diagram showing a schematic electrical configuration of a conventional cold cathode tube lighting device.

[Explanation of symbols]

 20, 40, 60 Cold cathode tube lighting device 21, 41, 61 Inverter circuit 24 Current detection resistor 26 Cold cathode tube 28 FET 29, 49 Current detection amplifier 30, 50, 70 Microcomputer 31, 51, 71 Inverter main circuit 32, 72 Protection circuit 73 Latch circuit

Claims (5)

[Claims] Generating a voltage required for lighting a cold cathode tube;
An inverter circuit having a protection function of cutting off a power supply input when the load is in an open state; a switching circuit for controlling ON / OFF of the inverter circuit; a current detection circuit for detecting a current supplied to the inverter circuit; Control the switching circuit to start the operation of the inverter circuit, and when the current detection circuit detects a lighting current in a predetermined range corresponding to the lighting of the cold-cathode tube, the operation of the inverter circuit is continued to detect the current. When the circuit detects a power input cutoff based on the protection function of the inverter circuit, the operation of the inverter circuit is repeatedly stopped and restarted within a range of a predetermined repetition condition corresponding to the dark effect of the cold-cathode tube. If the lighting current is detected, the operation of the inverter circuit is continued, and if the lighting current is not detected, the operation of the inverter circuit is continued. Cold-cathode tube lighting device, wherein a and a control circuit for controlling the switching circuit to stop. 2. An inverter circuit for generating a voltage required to turn on a cold cathode tube, a switching circuit for controlling ON / OFF of the inverter circuit, a current detection circuit for detecting a current supplied to the inverter circuit, Controls the switching circuit to start the operation of the inverter circuit at the time of power-on, and stops the operation of the inverter circuit when the current detection circuit detects a current equal to or higher than a predetermined reference value that considers that an overcurrent has occurred in the inverter circuit. When the current detection circuit detects a lighting current in a predetermined range corresponding to the lighting of the cold-cathode tube, the operation of the inverter circuit is continued. When the lighting current is not detected by the current detection circuit, the operation of the inverter circuit is stopped. The operation is repeatedly stopped and restarted, and a repetition condition set in advance corresponding to the dark effect of the cold cathode fluorescent lamp is set. And a control circuit that controls the switching circuit so that the operation of the inverter circuit is continued if the lighting current is detected, and the operation is stopped if the lighting current is not detected. Cold cathode tube lighting device. Generating a voltage required for lighting the cold-cathode tube;
An inverter circuit having a protection function against load opening and overcurrent; a switching circuit for controlling ON / OFF of the inverter circuit; a protection detection circuit for detecting an operation state of the protection function of the inverter circuit; The switching circuit is controlled to start the operation of the inverter circuit. When the protection detection circuit detects that the protection function of the inverter circuit is not operating, the operation of the inverter circuit is continued. When it is detected that the protection function of the circuit is operating, the stop and restart of the operation of the inverter circuit are repeated, and within a range of a repetition condition set in advance corresponding to the dark effect of the cold cathode fluorescent lamp, If the lighting current is detected, the operation of the inverter circuit is continued, and if the lighting current is not detected, the operation is stopped. Cold-cathode tube lighting device which comprises a control circuit for controlling the switching circuit so. 4. The inverter circuit is capable of ON / OFF control of operation by an external input, and the switching circuit has a switching element for controlling ON / OFF of an external input of the inverter circuit. The cold-cathode tube lighting device according to claim 1. 5. The cold-cathode tube lighting device according to claim 1, wherein the control circuit includes a microcomputer that performs control according to a preset program.