JP4557834B2 - Cold cathode discharge tube drive circuit - Google Patents

Description

  The present invention relates to a driving circuit for a fluorescent lamp used for a backlight of a liquid crystal display device.

  Conventionally, cold cathode discharge tubes have been widely used as backlights for office automation equipment and liquid crystal televisions. The cold cathode discharge tube has a pair of rod-shaped main electrodes, one end of which is opposed to the inside of the cylindrical glass bulb, and the other end is exposed to the outside. Both ends are sealed.

  Here, since the impure gas etc. remains inside the cold cathode discharge tube, the discharge path between the electrodes is blocked by this impure gas and cannot go straight, and as a result, the discharge density locally changes. As a result, a phenomenon (snaking phenomenon) that causes a bright and dark pattern in the cold cathode discharge tube may occur. In particular, if the voltage or current supplied to the cold cathode discharge tube fluctuates greatly, this affects the discharge intensity between the electrodes, so that there is a high possibility that a snake phenomenon will occur. In addition, even when the temperature of the cold cathode discharge tube fluctuates greatly, it affects the degree of generation of impure gas (the degree to which impure gas molecules cooled and adsorbed on the surface of the lamp tube jump out), resulting in the occurrence of a snake phenomenon. The possibility increases.

  When such a snake phenomenon occurs, unevenness of light and flicker occur on the screen of the image display device in which the cold cathode discharge tube is used as a backlight, and the display quality deteriorates.

As a conventional technique for avoiding such a problem, for example, in Patent Document 1, when the occurrence of a snakeing phenomenon in a cold cathode discharge tube (fluorescent lamp) is detected, the adsorption of impure gas is sufficiently performed and the snakeing phenomenon disappears. Until now, a technique for eliminating the snakeing phenomenon by repeatedly turning on and off the cold cathode discharge tube is disclosed.
3-125331

  However, according to the prior art according to Patent Document 1, the cold cathode discharge tube is repeatedly turned on and off during the period from the occurrence of the snakeing phenomenon to the extinction thereof. For this reason, when the snake phenomenon frequently occurs, the light emitting performance of the cold cathode discharge tube may be deteriorated as a result of repeated lighting and extinction.

  Under such circumstances, in order to maintain the light emission performance of the cold cathode discharge tube, it is important to prevent the occurrence of the snake phenomenon in advance. Therefore, an object of the present invention is to provide a cold cathode discharge tube driving device capable of preventing the occurrence of a snakeing phenomenon in the cold cathode discharge tube as much as possible.

  In order to solve the above problems, a cold cathode discharge tube driving device according to the present invention comprises a cold cathode discharge comprising an inverter circuit that converts a DC voltage into an AC voltage having a value corresponding to an input signal and supplies the AC voltage to the cold cathode discharge tube. A controller for controlling a voltage supplied to the cold cathode discharge tube by adjusting the input signal and a value of a voltage supplied to the cold cathode discharge tube; Detecting means for detecting any one of a value of a supplied current; a temperature of the cold cathode discharge tube; and whether the detected value deviates from a preset allowable range. If it is determined that there is a deviation, the control is performed so that the detected value falls within the allowable range (first configuration).

  As described above, fluctuations in the voltage supplied to the cold cathode discharge tube, fluctuations in the current supplied to the cold cathode discharge tube, and fluctuations in the temperature of the cold cathode discharge tube are significant inducing factors of the snake phenomenon. Since the current supplied to the cold cathode discharge tube and the temperature of the cold cathode discharge tube are both closely related to the voltage supplied to the cold cathode discharge tube, the input signal is controlled (to the cold cathode discharge tube). These can be adjusted by controlling the supply voltage).

  Therefore, according to the present configuration, an allowable range of fluctuation that does not induce a snake phenomenon is generated with respect to any one of the voltage supplied to the cold cathode discharge tube, the current supplied to the cold cathode discharge tube, and the temperature of the cold cathode discharge tube. By setting in advance, control is performed so that the detected value falls within the permissible range. As a result, it is possible to prevent these from fluctuating in advance, and to prevent the snakeing phenomenon occurring in the cold cathode discharge tube as much as possible.

  The cold cathode discharge tube driving device of the present invention is a cold cathode discharge tube driving device including an inverter circuit that converts a DC voltage into an AC voltage having a value corresponding to an input signal and supplies the AC voltage to the cold cathode discharge tube. The control means comprises a control means for controlling the voltage supplied to the cold cathode discharge tube by adjusting the input signal, and a detection means for detecting the temperature of the inverter circuit. It is determined whether or not the set allowable range is deviated. If deviated, the control is performed so that the detected value falls within the allowable range (second configuration).

  The change in the temperature of the inverter circuit is considered to be caused by the change in the heat generation state due to the Joule heat generated in the circuit. Therefore, when the temperature of the inverter circuit is fluctuating, the voltage value inside the circuit fluctuates, and as a result, the voltage supplied to the cold cathode discharge tube is also fluctuating. Therefore, according to this configuration, by setting in advance a permissible range of fluctuation that does not induce the snakeing phenomenon with respect to the temperature of the inverter circuit, control is performed so that the detected value falls within the permissible range. As a result, it is possible to prevent the voltage supplied to the cold cathode discharge tube from fluctuating greatly, and to prevent the snake phenomenon that occurs in the cold cathode discharge tube as much as possible.

  Further, in the first or second configuration, the detection process by the detection unit and the control process by the control unit may be continuously executed during the driving of the cold cathode discharge tube (third configuration). Good.

  Variations in the supply voltage or the like to the cold cathode discharge tube may occur at times other than when the cold cathode discharge tube starts to be driven, for example, due to an external variation factor or a change in load (lamp) with time. Therefore, in this configuration, the detection process and the control process are continuously executed while the cold cathode discharge tube is being driven, so that it is possible to cope with such fluctuations.

  The cold cathode discharge tube driving apparatus according to any one of the first to third configurations, wherein the input signal is a pulse wave, and the inverter circuit is turned on-duty when a pulse of the input signal arrives. The control means increases the pulse width and / or increases the pulse frequency when the voltage is to be increased, and reduces the pulse width and / or the pulse frequency when the voltage is to be decreased. A configuration (fourth configuration) may be employed in which the input signal is controlled so as to reduce the pulse frequency.

  According to this configuration, the voltage value supplied to the cold cathode discharge tube can be controlled easily and accurately, so that the voltage control according to any one of the first to fourth configurations can be easily realized. It becomes possible.

  Further, in a liquid crystal display device using a cold cathode discharge tube as a backlight, if the liquid crystal display device having the cold cathode discharge tube driving device according to any one of the first to fourth configurations is used, the snake in the backlight is used. Occurrence of the phenomenon can be prevented as much as possible, and deterioration of display quality due to light unevenness and flicker on the display screen can be suppressed as much as possible.

  As described above, in the cold cathode discharge tube driving circuit according to the present invention, the voltage supplied to the cold cathode discharge tube, the current supplied to the cold cathode discharge tube, the temperature of the cold cathode discharge tube, or the inverter By setting a permissible range of fluctuation that does not induce a snakeing phenomenon for any of the circuit temperatures, control is performed so that the detected value falls within the permissible range. As a result, it is possible to prevent these from fluctuating in advance, and to prevent the snakeing phenomenon occurring in the cold cathode discharge tube as much as possible.

[Example 1]
The configuration of the fluorescent lamp driving apparatus according to the first embodiment of the present invention will be described with reference to the configuration diagram of FIG. This embodiment includes a control unit 1, an inverter circuit 2, a fluorescent lamp 3, a voltage detection unit 4, and the like.

  The control unit 1 sends an input signal to the inverter circuit 2 and controls the AC voltage output from the inverter circuit 2. The control is performed so that the voltage value output to the fluorescent lamp 3 does not exceed or falls below a predetermined allowable range based on the detection value of the voltage detector 4. This will be discussed again.

  The voltage detection unit 4 detects the voltage value output to the fluorescent lamp 3 and transmits the value to the control unit 1. Specifically, as shown in FIG. 1, the divided voltage of the output voltage is obtained using a dividing capacitor or the like provided in the front stage of the fluorescent lamp 3. This partial pressure is transmitted as detection information to the voltage detection terminal (V-SENCE) of the control unit 1 via a resistor.

  The inverter circuit 2 converts the continuously supplied DC voltage into an AC voltage having a value corresponding to the input signal input from the control unit 1. The DC voltage is obtained, for example, by rectifying and smoothing a commercial AC power supply. The inverter circuit 2 may be of any type as long as it can output a voltage having a value corresponding to the input signal. In this embodiment, as an example, a push-pull inverter circuit widely used in a fluorescent lamp driving device or the like is employed. Hereinafter, the push-pull inverter circuit will be briefly described.

  The circuit configuration includes a pulse input transistor 51, starting resistors 52a and 52b, push-pull operation transistors 53a and 53b, a resonance capacitor 54, a transformer 55, a choke coil 56, and the like, as shown in FIG. Are connected to each other.

  When no input signal (pulse signal) is input to the base of the transistor 51, the transistors 53a and 53b do not operate, so that no potential difference occurs at the out terminal. However, when an input signal is input to the base of the transistor 51, the transistors 53a and 53b are also in an operating state.

  First, the lower transistor of the threshold voltages of the transistors 53a and 53b is turned on. For example, if the threshold voltage of the transistor 53a is smaller, the transistor 53a is turned on, and a current flows through the collector of the transistor 53a. The change in the collector current is transmitted to the secondary winding through the transformer 55, and the base potential of the transistor 53a connected to the tertiary winding is increased and the base potential of the transistor 53b is decreased. Induces a voltage in the winding.

  Next, as the collector current of the transistor 53a increases, the emitter current of the transistor 53a also increases and the base-emitter voltage also increases. Since the emitters of the transistors 53a and 53b are commonly grounded, the transistor 53b is turned on when the base-emitter voltage reaches the threshold voltage of the transistor 53b.

  As a result, current flows through the collector of the transistor 53b, and the current of the primary winding of the transformer 55 is obtained by subtracting the collector current of the transistor 53b from the collector current of the transistor 53a. This current change becomes a current flowing through the transformer 55 to the secondary winding side, and the base potential of the transistor 53a connected to the tertiary winding is decreased, and the base winding of the transistor 53b is increased. Induces a voltage at

  As a result, the transistor 53a is turned off, the transistor 53b is turned on, and the collector current of the transistor 53a cannot flow between the collector and the emitter of the transistor 53a, so that the capacitor 54 is charged.

  Thereafter, a steady state is reached, and a current oscillating at the resonance frequency of the resonance circuit flows in the primary winding of the transformer 55 by the resonance circuit composed of the capacitor 54 and the primary winding of the transformer 55. As described above, the above-described push-pull operation is performed only during the period in which the transistor 51 is turned on by the input signal from the control means. As a result, an alternating voltage having a value corresponding to the input signal can be output.

  Next, the operation of the fluorescent lamp driving device according to the present embodiment will be described with reference to FIG. The control unit 1 outputs an input signal (pulse signal) to the signal input terminal of the inverter circuit 2 in response to a drive start instruction from the user. Thereby, the inverter circuit 2 converts the supplied DC voltage into an AC voltage having a value corresponding to the input signal, and supplies the AC voltage to the fluorescent lamp 3 (step S1). At the start of driving, the input signal has a pulse waveform set in advance so that the fluorescent lamp 3 can be driven properly. However, as will be described later, when the pulse waveform of the input signal is adjusted, the adjusted pulse waveform is obtained.

  While the fluorescent lamp 3 is being driven in this way, the control unit 1 continuously detects the voltage value output to the fluorescent lamp 3 through the voltage detection unit 4 (step S2). Then, the control unit 1 determines whether the detected value is within a predetermined allowable range. This allowable range is set in advance as a range in which the occurrence of the snakeing phenomenon in the fluorescent lamp 3 can be suppressed.

  As a result, when it is determined that the detected value is below the lower limit value of the allowable range (Y in step S3), the control unit 1 pulses the input signal so as to increase the value of the voltage output to the fluorescent lamp 3. Is adjusted (step S5). Conversely, if it is determined that the detected value exceeds the upper limit value of the allowable range (Y in step S4), the control unit 1 pulses the input signal so as to decrease the value of the voltage output to the fluorescent lamp 3. Is adjusted (step S6).

  In adjusting the pulse of the input signal, when the value of the voltage output to the fluorescent lamp 3 is increased, the inverter circuit is increased by increasing the pulse width and / or increasing the pulse frequency as shown in FIG. 2 is increased, and the output voltage to the fluorescent lamp 3 is substantially increased. Conversely, when the value of the voltage output to the fluorescent lamp 3 is reduced, the on-duty of the inverter circuit 2 is reduced by reducing the pulse width and / or decreasing the pulse frequency, and the output to the fluorescent lamp 3 is reduced. Let the voltage be reduced substantially. Thus, by adjusting the pulse width or frequency of the input signal, the voltage value supplied to the cold cathode discharge tube can be controlled easily and accurately.

  As a result, even if the voltage value output to the fluorescent lamp 3 deviates from the allowable range for some reason, the voltage value is corrected and can be prevented from fluctuating greatly. Therefore, the occurrence of the snakeing phenomenon can be suppressed as much as possible.

[Example 2]
Next, FIG. 5 shows the configuration of the fluorescent lamp driving device according to the second embodiment. The present embodiment includes a control unit 11, an inverter circuit unit 12, a fluorescent lamp 13, a current detection unit 14, and the like.

  The control unit 11 sends an input signal to the inverter circuit 12 to control the AC voltage output from the inverter circuit 12. The control is performed so that the current value output to the fluorescent lamp 13 does not exceed or falls below a predetermined allowable range based on the detection value of the current detection unit 14.

  The current detection unit 14 detects a current value output to the fluorescent lamp 13 and transmits the value to the control unit. Specifically, as shown in FIG. 5, a voltage corresponding to the magnitude of the current is obtained using a resistor provided in series with the fluorescent lamp 13. This voltage is transmitted as detection information to the current detection terminal (I-SENCE). The configuration of the inverter circuit 12 is the same as that of the first embodiment.

  The operation of the fluorescent lamp driving apparatus according to the present embodiment will be described with reference to FIG. The process for supplying voltage to the fluorescent lamp 13 (step S1) is the same as in the first embodiment. However, in step S2 of the first embodiment, the control unit 1 detects the voltage value output to the fluorescent lamp 3, whereas the control unit 11 in the present embodiment is output to the fluorescent lamp 13 through the current detection unit 14. The detected current is continuously detected (step S2).

  If the detected current value is below the lower limit value of the allowable range (Y in step S3), the control unit 11 adjusts the pulse of the input signal so as to increase the current value output to the fluorescent lamp 13. (Step S5). Conversely, if the detected value exceeds the upper limit of the allowable range (Y in step S4), the pulse of the input signal is adjusted so as to decrease the current value output to the fluorescent lamp 13 (step S6). This allowable range is set in advance as a range in which the occurrence of the snakeing phenomenon in the fluorescent lamp 13 can be suppressed.

  If the load is normal, the input signal should be adjusted to increase the supply voltage to increase the current value and decrease the supply voltage to decrease the current value. However, if the voltage-current characteristics of the fluorescent lamp are negative (the current in the tube decreases as the supply voltage increases), the supply voltage is increased to decrease the current value, and the supply voltage is decreased to increase the current value. Adjust the input signal as follows. Further, the adjustment of the pulse is performed by changing the width and frequency of the pulse as in the case of the first embodiment.

  As a result, even if the current value output to the fluorescent lamp 13 begins to deviate from the allowable range for some reason, the current value is corrected each time, and it is possible to prevent a large fluctuation from occurring. Therefore, the occurrence of the snakeing phenomenon can be suppressed as much as possible.

[Example 3]
Next, the configuration of Example 3 is shown in FIG. The present embodiment includes a control unit 21, an inverter circuit 22, a fluorescent lamp 23, a temperature detection unit 24, and the like.

  The control unit 21 sends an input signal to the inverter circuit 22 and controls the AC voltage output from the inverter circuit 22. The control is performed based on the detection value of the temperature detector 24 so that the temperature of the fluorescent lamp does not exceed or falls below a predetermined allowable range.

  The temperature detection unit 24 detects the temperature of the fluorescent lamp 23 and transmits the information to the control unit 21. Specifically, a temperature sensor (a device that converts temperature into voltage) is provided in the vicinity of the fluorescent lamp 23 to obtain a voltage according to the temperature state. And this voltage is transmitted to the temperature detection terminal (T-SENCE) of the control part 21 as detection information. The configuration of the inverter circuit 22 is the same as that of the first embodiment.

  The operation of the fluorescent lamp driving apparatus according to the present embodiment will be described with reference to FIG. Also in the case of the present embodiment, the process of supplying power to the fluorescent lamp 23 (step S1) is the same as in the case of the first embodiment. However, in step S <b> 2 of the first embodiment, the control unit 1 detects the voltage value output to the fluorescent lamp 3, whereas the control unit 21 of the present embodiment passes the temperature detection unit 24 through the temperature near the fluorescent lamp 23. Is detected (step S2).

  If the detected temperature is below the lower limit of the allowable range (Y in step S3), the control unit 21 increases the current value output to the fluorescent lamp 23 in order to increase the heat generation inside the fluorescent lamp 23. Thus, the pulse of the input signal is adjusted (step S5). On the other hand, if the detected value exceeds the upper limit of the allowable range (Y in step S4), the input signal is used so as to reduce the current value output to the fluorescent lamp 23 in order to reduce the heat generation inside the fluorescent lamp 23. Adjust the pulse. This allowable range is set in advance as a range in which the occurrence of the snakeing phenomenon in the fluorescent lamp 3 can be suppressed.

  If the load is normal, the input signal should be adjusted to increase the supply voltage to increase the current value and decrease the supply voltage to decrease the current value. However, if the voltage-current characteristics of the fluorescent lamp are negative (the current in the tube decreases as the supply voltage increases), the supply voltage is increased to decrease the current value, and the supply voltage is decreased to increase the current value. Adjust the input signal as follows. Further, the adjustment of the pulse is performed by changing the width and frequency of the pulse as in the case of the first embodiment.

  As a result, even if the temperature of the fluorescent lamp 23 begins to deviate from the allowable range for some reason, the temperature is corrected and can be prevented from fluctuating greatly. Therefore, the occurrence of the snakeing phenomenon can be suppressed as much as possible.

  Moreover, the temperature sensor mentioned above is good also as providing in the vicinity of the inverter circuit 22 and detecting the temperature state of an inverter circuit. The change in the temperature of the inverter circuit 22 is considered to be caused by the change in the heat generation state due to the Joule heat generated in the circuit. Therefore, when the temperature of the inverter circuit 22 exceeds the upper limit value of the allowable range, the voltage in the circuit is excessive, and as a result, the voltage supplied to the fluorescent lamp 23 is considered excessive. Adjust the input signal to reduce the supply voltage. Conversely, when the value is below the lower limit, the input signal is adjusted so as to increase the supply voltage.

  Further, the detection process and the control process in the first to third embodiments described above are continuously executed while the fluorescent lamp is being driven. Here, “continuous” means not only at the start of driving of the fluorescent lamp but also during driving, for example, it is repeated at a frequency of once per second. Thus, for example, it is possible to cope with fluctuations in the supply voltage and the like that occur not only at the start of driving of the cold cathode discharge tube due to, for example, external fluctuation factors or load (lamp) changes over time.

  Each of the fluorescent lamp driving devices according to the first to third embodiments both determines whether the detected value deviates from the upper limit of the allowable value and determines whether the detected value deviates from the lower limit of the allowable value. In practice, only one of them may be determined.

  In addition, in a liquid crystal display device using a fluorescent lamp as a backlight, if each of the fluorescent lamp driving devices from the first embodiment to the third embodiment is provided, the occurrence of a snakeing phenomenon in the backlight is prevented as much as possible. Therefore, it is possible to suppress deterioration of display quality due to light unevenness and flicker on the display screen as much as possible.

  In addition to the above embodiment, the configuration of the present invention can be variously modified without departing from the gist of the invention. In the above description, the fluorescent lamp is exemplified as the cold cathode discharge tube, but other types of cold cathode discharge tubes may be used.

It is a block diagram of the fluorescent lamp drive device of Example 1. It is a block diagram of the inverter circuit used in each Example. 3 is a flowchart of processing in the fluorescent lamp driving device according to the first embodiment. It is explanatory drawing which concerns on control of an input signal. It is a block diagram of the fluorescent lamp drive device of Example 2. It is a flowchart of the process in the fluorescent lamp drive device of Example 2. It is a block diagram of the fluorescent lamp drive device of Example 3. 12 is a flowchart of processing in the fluorescent lamp driving device according to the third embodiment.

Explanation of symbols

1, 11, 21 Control unit (control means)
2, 12, 22 Inverter circuit 3, 13, 23 Fluorescent lamp (cold cathode discharge tube)
4 Voltage Detection Circuit 14 Current Detection Circuit 24 Temperature Detection Circuit 51 Pulse Input Transistors 52a and 52b Start-up Resistors 53a and 53b Push-Pull Operation Transistors 54 Resonance Capacitors 55 Transformers 56 Choke Coils

Claims (5)

In a cold cathode discharge tube driving device comprising an inverter circuit for converting a direct current voltage into an alternating voltage having a value corresponding to an input signal and supplying the alternating voltage to the cold cathode discharge tube,
Control means for controlling a voltage supplied to the cold cathode discharge tube by adjusting the input signal; a value of a voltage supplied to the cold cathode discharge tube; a value of a current supplied to the cold cathode discharge tube Detecting means for detecting any one of the temperature of the cold cathode discharge tube;
The control means includes
It is determined whether or not the detected value deviates from a preset allowable range, and if it deviates, the control is performed so that the detected value falls within the allowable range ,
The allowable range is
A driving device for a cold cathode discharge tube, which is set in advance as a range in which the occurrence of a snakeing phenomenon in the cold cathode discharge tube can be suppressed . In a cold cathode discharge tube driving device comprising an inverter circuit for converting a direct current voltage into an alternating voltage having a value corresponding to an input signal and supplying the alternating voltage to the cold cathode discharge tube,
A control means for controlling the voltage supplied to the cold cathode discharge tube by adjusting the input signal, and a detection means for detecting the temperature of the inverter circuit;
The control means includes
It is determined whether or not the detected value deviates from a preset allowable range, and if it deviates, the control is performed so that the detected value falls within the allowable range ,
The allowable range is
A driving device for a cold cathode discharge tube, which is set in advance as a range in which the occurrence of a snakeing phenomenon in the cold cathode discharge tube can be suppressed .   3. The cold cathode discharge tube according to claim 1, wherein the detection process by the detection unit and the control process by the control unit are continuously performed while the cold cathode discharge tube is being driven. Drive device. The cold cathode discharge tube driving device according to any one of claims 1 to 3, wherein the input signal is a pulse wave, and the inverter circuit becomes on-duty when a pulse of the input signal arrives. There,
The control means increases the pulse width and / or increases the pulse frequency when the voltage is to be increased, and decreases the pulse width and / or reduces the pulse frequency when the voltage is to be decreased. A cold-cathode discharge tube driving device characterized in that it is reduced.   5. A liquid crystal display device using a cold cathode discharge tube as a backlight, comprising the cold cathode discharge tube driving device according to any one of claims 1 to 4.

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