JP2005251580A - Discharge tube lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge tube lighting device which complies with UL standards even in large current drive or multi-light drive. <P>SOLUTION: An output current of a transformer TR is detected by a current detection circuit 16, and the result is compared with a current reference value Iref by a current comparator 24. An output voltage of the transformer TR is detected by a voltage detecting circuit 18, and the result is compared with a voltage reference value Vref by a voltage comparator 26. Then, the logical product of the comparison result of the current comparator 24 and the comparison result of the voltage comparator 26 is calculated by an AND-operator 22, and the result is outputted to a controlling circuit 12. The controlling circuit 12 suspends lighting control of discharge tubes 14-1 to 14-20, when an H level signal is outputted from both the current comparator 24 and the voltage comparator 26. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a discharge tube lighting device, and particularly to a discharge tube lighting device having a current limiting function.

  In a discharge tube lighting device that lights a discharge tube when a high voltage is generated, an overcurrent protection function is provided in order to eliminate an overcurrent state caused by a short circuit of the discharge tube or other abnormality. As this overcurrent protection function, generally known is a function that detects the value of a current flowing through a high-voltage line and stops the lighting operation when the detection result exceeds a predetermined reference value.

  The reference value for overcurrent protection is set to be equal to or higher than the rated current of the discharge tube. For example, if the alternating current flowing per discharge tube is 5 mA, the peak value is about 7 mA, which is twice the root, so the reference value for overcurrent protection is set to about 10 mA.

  On the other hand, in the UL standard, the maximum current value of the high voltage line is defined for the purpose of preventing electric shock. For example, in the current limiting test clause of UL1950, when a 2 kΩ resistor equivalent to a human body is added between the high voltage line and GND, the current value flowing through the 2 kΩ resistor should be a maximum peak value of 70 mA or less. Is stipulated.

  Therefore, when determining the reference value for overcurrent protection, it is necessary to satisfy the condition that the peak value is 70 mA or less when 2 kΩ is added, which is a UL standard value. Here, when only a few discharge tubes with a rated current of 5 mA are driven as in the above-described example, there is no problem because the reference value of the overcurrent can be set smaller than the UL standard of 70 mA, but the rated current is 70 mA or more. When using 20 discharge tubes of 5 mA rated, for example, when driving 20 discharge tubes with a rated current of 5 mA, it is necessary to drive with a current of 70 mA or more. The lamp could not be controlled.

Here, the following documents are known regarding overcurrent detection or protection.
JP 11-26177 A Japanese Patent Laid-Open No. 2002-110388 In Japanese Patent Laid-Open No. 4-141988, as described in FIG. 1 and FIG. 3 of the same document, two voltage reference values are set in order to distinguish an end-of-life state (Emiless state) from an abnormal state. A method for providing overvoltage protection by utilizing the fact that the voltage behavior changes depending on the state of the discharge tube is provided.

  However, even if two reference values are provided, it is necessary to protect at 70 mA, which is the UL standard value, and this method cannot cope with a configuration of driving at 70 mA or more.

  In Patent Document 2, as described in paragraph 0021 and FIG. 6 of the same document, in multi-lamp control for driving a plurality of discharge tubes, the tube current of each discharge tube is detected by logical sum, and either discharge is performed. A configuration is disclosed in which the drive is stopped when there is an abnormality in the pipe.

  However, in this method, since the tube current of each discharge tube is detected by a logical sum, it cannot be evaluated by the total current of each discharge tube, and a case where a current of 70 mA or more flows when the number of discharge tubes increases is assumed. The

  In Patent Document 3, both the voltage value supplied to the discharge tube and the tube current flowing through the discharge tube are detected (see FIGS. 4 and 7 of the same document), and the V-I and characteristics of the discharge tube are taken into consideration. (See FIG. 1 of the same document), and a technique for improving overshoot and undershoot (see FIG. 2 of the same document) is disclosed.

  However, this method is difficult to apply to the method of setting the overcurrent reference value when 2 kΩ is added because the behavior of voltage and current is controlled to conform to a predetermined profile (see the lower right column on P6).

  Therefore, the present invention provides a discharge tube lighting device that can comply with the UL standard even when driven by a large current or driven by multiple lamps.

  In order to achieve the above object, the first means of the present invention includes a discharge tube connected to a high voltage line, a lighting control unit that controls lighting of the discharge tube, and an amount of current flowing through the high voltage line within a reference value. In a discharge tube lighting device including a current limiting circuit for limiting, the reference value of the current limiting circuit is switched according to a state of a load connected to the high voltage line.

  Here, one or a plurality of discharge tubes may be connected to the high-voltage line. When one discharge tube is controlled by a single lamp, use a discharge tube whose rated current exceeds the UL standard value when 2 kΩ is added. In addition, when a plurality of discharge tubes are controlled in multiple lamps, a multiple lamp configuration in which the total current of each discharge tube exceeds the standard value when UL 2 kΩ is added is possible.

  The current limiting circuit detects a current flowing through the high voltage line, performs overcurrent protection at a predetermined reference value, and when a load connected to the high voltage line, for example, a load equivalent to 2 kΩ is connected, Switch the reference value for overcurrent protection to a reference value different from the normal value.

  Considering a more specific example, when driving 20 discharge tubes rated at 5 mA, assuming a total current of peak value 7 mA × 20 lines = 140 mA, the peak value is a normal overcurrent reference value. When 150 mA is set and 2 kΩ is added, the reference value of the overcurrent is switched to the peak value of 70 mA, which is the UL standard value.

  As will be described later, it is desirable to detect the load state connected to the high-voltage line based on a change in the voltage applied to the high-voltage line. You may use it combining suitably, such as these combinations.

  The high-voltage power supplied to the high-voltage line is preferably generated using a well-known inverter circuit including a transformer. Especially when a large-sized liquid crystal backlight inverter is configured, the discharge tube lighting device is reduced in size and cost. In order to achieve this, it is desirable to have a multiple lamp control configuration in which a plurality of discharge tubes are connected in parallel to one transformer.

  The second means of the present invention includes: a discharge tube connected to the high voltage line; a lighting control unit that controls lighting of the discharge tube; and a current limiting circuit that limits a current amount flowing through the high voltage line to a reference value. In the discharge tube lighting device provided, the operating state of the current limiting circuit is controlled in accordance with a state of a load connected to the high voltage line.

  Here, the mode for controlling the operating state of the current limiting circuit includes a mode for changing the reference value of the current limiting circuit as described above and a mode for temporarily stopping the function of the current limiting circuit. For example, the function of the current limiting circuit is stopped in normal times, and the current limiting circuit is made to function when a load equivalent to 2 kΩ is connected, or the first current limiting circuit that functions in normal time and equivalent to 2 kΩ It is possible to apply a configuration in which a second current limiting circuit that functions when a load is connected is provided, and the first and second current limiting circuits are switched according to the state of the load.

  The third means of the present invention comprises: a discharge tube connected to the high voltage line; a lighting control unit that controls lighting of the discharge tube; and a current limiting circuit that limits a current amount flowing through the high voltage line to a reference value. The discharge tube lighting device includes a voltage detection unit that detects a voltage value applied to the high-voltage line, and a current detection unit that detects an amount of current flowing through the high-voltage line, and the current-limiting circuit includes: The reference value is determined using the detected voltage value and current amount.

  Since the behavior of the voltage and current appearing in the high-voltage line varies depending on the state of the load, it is possible to determine whether or not a resistance equivalent to 2 kΩ has been added by detecting these values and observing the behavior. It is effective to determine the reference value of the current limiting circuit using the voltage value and current amount of the line.

  According to a fourth aspect of the present invention, there is provided a discharge tube connected to the high voltage line, a lighting control unit that controls the lighting of the discharge tube, and a current limiting circuit that limits an amount of current flowing through the high voltage line within a reference value. The discharge tube lighting device includes a voltage detection unit that detects a voltage value applied to the high-voltage line, and a current detection unit that detects an amount of current flowing through the high-voltage line, and the current-limiting circuit includes: The operation of the lighting control unit is stopped based on the detected voltage value and current amount.

  Since it can be determined whether or not a resistance equivalent to 2 kΩ has been added based on the behavior of voltage and current appearing in the high voltage line, if a resistance equivalent to 2 kΩ is added, it is assumed that the human body has touched the high voltage line. Stop power supply to the line.

  According to a fifth aspect of the present invention, there is provided a discharge tube connected to the high voltage line, a lighting control unit that controls the lighting of the discharge tube, and a current limiting circuit that limits an amount of current flowing through the high voltage line within a reference value. The discharge tube lighting device includes a voltage detection unit that detects a voltage value applied to the high-voltage line, and a current detection unit that detects an amount of current flowing through the high-voltage line, and the current-limiting circuit includes: A voltage comparator that compares a detected voltage value with a voltage reference value; a current comparator that compares the detected current amount with a current reference value; and an output of the voltage comparator and an output of the current comparator. And an AND operation unit for obtaining a logical product.

  The voltage reference value and the current reference value distinguish the difference in voltage and current behavior appearing in the high voltage line, that is, the difference between the behavior when a resistance equivalent to 2 kΩ is added and the behavior when no resistance is added. The voltage comparator and the current comparator function as a threshold value, and the voltage comparator and the current comparator compare the threshold value with the voltage value and current amount of the high voltage line, respectively, and whether or not 2 kΩ is added by taking the logical product of these comparison results. Is judged.

  Further, the output of the voltage comparator transitions from a first level to a second level when the detected voltage value reaches the voltage reference value, and the output of the current comparator is detected. It is desirable to transition from the second level to the first level when the amount of current reaches the current reference value. With this configuration, a resistance equivalent to 2 kΩ is added without operating normally. A current limiting circuit that operates sometimes can be constructed.

  According to a sixth aspect of the present invention, there is provided a discharge tube connected to the high voltage line, a lighting control unit that controls the lighting of the discharge tube, and a current limiting circuit that limits a current amount flowing through the high voltage line to a reference value. The discharge tube lighting device includes a voltage detection unit that detects a voltage value applied to the high-voltage line, and a current detection unit that detects an amount of current flowing through the high-voltage line, and the current-limiting circuit includes: A voltage comparator that compares the detected voltage value with a voltage reference value, a current comparator that compares the detected current amount with a current reference value, and is disposed between the voltage comparator and the current comparator. The voltage comparator and the current comparator are cascade-connected via the gate circuit.

  Even with such a configuration, the same protective operation as that of the fifth means described above can be performed.

  As described above, according to the present invention, it is possible to provide a discharge tube lighting device that can comply with the UL standard even when driven by a large current or driven by multiple lamps.

  Hereinafter, a discharge tube lighting device according to the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments described below, and can be modified as appropriate.

  FIG. 1 is a circuit block diagram showing the configuration of the discharge tube lighting device according to the first embodiment of the present invention. The discharge tube lighting device shown in the figure exemplifies a full bridge type inverter unit for lighting a plurality of discharge tubes, and a multiple lamp control in which a control circuit and a transformer are provided for each of the plurality of discharge tubes. It has a configuration.

  As shown in the figure, a DC power source 10 is connected to a full bridge circuit composed of switching elements SW1 to SW4, and a transformer TR is connected to a subsequent stage of the full bridge circuit via a capacitor C. An inverter circuit that outputs high-voltage power from the secondary side is configured. The subsequent stage from the secondary side of the transformer TR is a high-pressure line. Note that the configuration and operation example of the inverter circuit are also described in the above-described Patent Documents 1 to 3, and thus the description thereof is omitted in this embodiment.

  In the subsequent stage of the inverter circuit, 20 discharge tubes 14-1 to 14-20 are connected in parallel to the high voltage line, and the amount of current flowing through the high voltage line is between the secondary winding of the transformer TR and GND. And a voltage detection circuit 18 for detecting a voltage value applied to the high voltage line.

  Between the discharge tubes 14-1 to 14-20 and GND, a tube current detection circuit 20 for detecting the total current amount of each discharge tube is arranged, and the detection result of the tube current detection circuit 20 is output to the control circuit 20. The The control circuit 20 controls the switching elements SW1 to SW4 based on the output of the tube current detection circuit 20, and performs constant current feedback control for keeping the current flowing through the discharge tubes 14-1 to 14-20 constant.

  The control circuit 20 further captures the detection result of the current detection circuit 16 and compares it with a predetermined reference value. When the detection result exceeds the reference value, the control circuit 20 performs overcurrent protection, and the voltage detection circuit 18 The detection result is taken in and compared with a predetermined reference value. When the detection result exceeds the reference value, overvoltage protection is performed.

  The control circuit 20 uses the current comparator 24, the voltage comparator 26, and the AND calculator 22 in addition to the overcurrent protection and overvoltage protection described above, and the limit when a resistance equivalent to 2 kΩ is added to the high voltage line. Execute the flow operation.

  FIG. 2 is a characteristic diagram showing the behavior of the voltage and current appearing in the high-voltage line when starting up. The upper graph in the figure shows the behavior of the output voltage Vout of the transformer, and the lower graph in the figure shows the behavior of the output current Iout of the transformer. Note that the voltage value and current value shown in FIG.

  As these graphs show, the voltage and current appearing in the high voltage line behave differently depending on the load state, that is, when 2 kΩ is added (dotted line) and when it is not added (solid line). For example, the voltage at the time of 25 μs after activation is about 400 V when there is no 2 kΩ, and is about 100 V when there is 2 kΩ. Similarly, the current at the time of 25 μs after startup is about 25 mA when there is no 2 kΩ, and is about 50 mA when there is 2 kΩ.

  This difference in voltage and current behavior is considered to be based on the difference between the load characteristic of the discharge tube and the load characteristic of the fixed resistance. That is, in a discharge tube such as a cold-cathode tube, the transformer output voltage gradually rises based on the soft start function of the inverter, but if the voltage required for lighting does not reach, Only a small amount of current flows to the stray capacitance generated between them.

  Although the discharge voltage of the discharge tube varies depending on the type of the discharge tube, it is generally proportional to the length of the discharge tube, and a voltage of 1000 V or more can be found in a large liquid crystal such as a liquid crystal TV. Thus, the current flowing through the discharge tube behaves differently before and after the lighting voltage is reached, and in the case of no 2 kΩ, as shown in FIG. 2, it gradually starts to flow out from around 1000 V and exceeds 1500 V. It will behave as if it flows greatly from around.

  On the other hand, when a fixed resistance of 2 kΩ is added, since this 2 kΩ resistance becomes more dominant than the impedance of the discharge tube, the current increases as the voltage increases according to Ohm's law. At this time, since the effective power on the load side is larger when there is a 2 kΩ resistor, the voltage rise characteristic tends to be delayed compared to when there is no 2 kΩ.

  As described above, since there is a difference in the behavior of voltage and current depending on the presence or absence of 2 kΩ, in this embodiment, the reference value for overcurrent protection is set using this difference.

  FIG. 3 is a conceptual diagram showing a setting concept of the voltage reference value Vref and the current reference value Iref. This figure shows the setting concept of the voltage reference value Vref and the current reference value Iref on the graph of FIG. 2 by a one-dot chain line, and the protection reference at the time of startup can be obtained by the method shown in FIG. it can. Hereinafter, a method for obtaining the protection standard at the start-up will be described with reference to FIG.

  First, assuming a case where a predetermined margin is taken from the UL standard value of 70 mA and protection is performed at 50 mA, it is necessary to stop the lighting control when the current exceeds 50 mA, so the current reference value Iref is set to 50 mA.

  Next, the 50 mA arrival time with 2 kΩ is obtained using the current characteristic diagram on the lower side of FIG. In the example shown in this figure, about 25 μsec is the 50 mA arrival time. Subsequently, using the 50 mA arrival time as a guide, the voltage reference value Vref is obtained using the voltage characteristic diagram on the upper side of FIG. The voltage reference value Vref is set to a reference value that can distinguish between a voltage characteristic with 2 kΩ and a voltage characteristic without 2 kΩ at a 50 mA arrival time with 2 kΩ.

  Without 2 kΩ, the voltage rises faster than when 2 kΩ is present, so it is necessary to provide a configuration without 2 kΩ protection until the 50 mA arrival time with 2 kΩ. Assuming the realization of this configuration, the upper limit of the voltage reference value Vref is 400 V at which the voltage without 2 kΩ rises in the 50 mA arrival time with 2 kΩ.

  On the other hand, when 2 kΩ is present, considering that protection must be applied at 50 mA, the lower limit of the voltage reference value Vref is 100 V at which the voltage with 2 kΩ rises when the current with 2 kΩ reaches 50 mA. Therefore, in the example shown in FIG. 3, the voltage reference value Vref may be set between 100V and 400V.

  If the soft start is extremely small, there is a possibility that the peak will rise to 1100 V at a stroke. Therefore, it is desirable to set the upper limit of the voltage reference value Vref to 1100 V. Similarly, when the soft start time is very long, it is desirable to set the lower limit of the voltage reference value Vref to 0V. As described above, the value of the voltage reference value Vref may be set as appropriate in accordance with the soft start condition, but is usually set between 10V and 1000V.

  Hereinafter, the current limiting circuit unit in FIG. 1 will be described using an example in which the voltage reference value Vref is set to 300 V and the current reference value Iref is set to 50 mA.

  The current limiting circuit unit in FIG. 1 compares the detection result of the current detection circuit 16 with the current reference value Iref and outputs a pulse signal, the detection result of the voltage detection circuit 18 and the voltage reference value Vref. And a voltage comparator 26 that outputs a pulse signal and an AND calculator 22 that obtains a logical product of the pulse signals of the current comparator 24 and the voltage comparator 26.

  Here, the output of the current detection circuit 16 is connected to the non-inverting terminal of the current comparator 24, and the reference voltage corresponding to the current reference value Iref is connected to the inverting terminal of the current comparator 24. Similarly, the output of the voltage detection circuit 18 is connected to the inverting terminal of the voltage comparator 26, and the reference voltage corresponding to the voltage reference value Vref is connected to the non-inverting terminal of the voltage comparator 26.

  Since the control circuit 12 stops the discharge tube lighting control when the AND calculator 22 outputs the H level, the overcurrent protection is provided when both the current comparator 24 and the voltage comparator 26 output the H level. Will be activated.

  FIG. 4 is an operation explanatory diagram showing a current limiting operation when 2 kΩ is not added. As shown in the figure, when there is no 2 kΩ, when the output voltage of the transformer reaches 300 V, the output b of the voltage comparator 26 changes from H level to L level, and the output current of the transformer reaches 50 mA. At this point, the output a of the current comparator 24 changes from the L level to the H level. As a result, since there is no period in which both comparators are at the H level, the output c of the AND operation unit 22 is maintained at the L level, and the lighting control is continued without being protected even if it exceeds 50 mA.

  FIG. 5 is an operation explanatory diagram showing a current limiting operation when 2 kΩ is added. As shown in the figure, when 2 kΩ is added, the output a of the current comparator 24 transitions from the L level to the H level when the output current of the transformer reaches 50 mA. At this time, since the output b of the voltage comparator 26 starts from the H level, the output c of the AND computing unit 22 transitions from the L level to the H level at the moment when the output current of the transformer reaches 50 mA.

  At the moment when the output c of the AND operator 22 becomes H level, the lighting control is stopped, and both the output a of the current comparator 24 and the output b of the voltage comparator 26 change from H level to L level. At this time, the lighting control stop state is maintained by the latch function provided in the control circuit 12.

  FIG. 6 is a circuit block diagram showing a configuration of a discharge tube lighting device according to the second embodiment of the present invention. In this embodiment, a configuration example of the current detection circuit 16 and the voltage detection circuit 18 is specifically shown, and a thyristor 30 is provided at the output of the AND calculator 22. Other configurations are the same as those of the first embodiment described above.

  As shown in the figure, the current detection circuit 16 according to the present embodiment is configured by a diode and a resistor, and the output of the diode is connected to the current comparator 24. Similarly, the voltage detection circuit 18 includes a diode and two capacitors, and the output of the diode is connected to the voltage comparator 26.

  As shown in the figure, the thyristor 30 includes a diode, a resistor, and a capacitor, and is connected between the terminal T1 and the AND calculator 22. The ON / OFF signal of the control circuit 12 is input from the outside to the terminal T1, and when the H level signal is input to the terminal T1, the control circuit 12 becomes active and the lighting control of the discharge tube is started. .

  In the present embodiment, when the AND calculator 22 outputs H level, the thyristor 30 shifts the signal input from the terminal T1 to the control circuit 12 to L level, and as a result, lighting control stops.

  FIG. 7 is a circuit block diagram showing a configuration of a discharge tube lighting device according to the third embodiment of the present invention. The present embodiment is an example in which a current limiting circuit is configured using two comparators and one transistor, and other configurations are the same as those of the second embodiment described above.

  The current limiting circuit according to the present embodiment includes a current comparator 24, a voltage comparator 26, a transistor Tr, and a resistor R1, and performs an operation equivalent to that of the current limiting circuit of the second embodiment described above. . Here, the output of the current detection circuit 16 is connected to the non-inverting terminal of the current comparator 24 via the resistor R1, and the collector terminal of the transistor is connected.

  On the other hand, the output of the voltage detection circuit 18 is connected to the non-inverting terminal of the voltage comparator 26, and a reference voltage corresponding to the voltage reference value Vref is connected to the inverting terminal side. In this example, since the current comparator 24 is enabled when the output of the voltage comparator 26 becomes L level, the current limiting circuit of this embodiment is the same as that of the first and second embodiments described above. The same operation as that of the embodiment is performed.

  In other words, the current limiting circuit is configured by cascade connection of the current comparator 24 and the voltage comparator 26, and the transistor Tr functions as the gate circuit of the cascade connection. As a result, similarly to the AND calculator 22 described above, the lighting control is stopped when both the current comparator 24 and the voltage comparator 26 become H level. Therefore, the same operation can be performed even if the output of the current comparator 24 is connected to the voltage comparator 26 via the transistor Tr and the output of the voltage comparator 26 is connected to the thyristor 30.

  FIG. 8 is a circuit block diagram showing a configuration of a discharge tube lighting device according to the fourth embodiment of the present invention. In the present embodiment, an application example to a differential inverter that performs lighting control by applying voltages of different polarities to both ends of a discharge tube is shown. Other configurations are the same as those of the third embodiment described above.

  In the present embodiment, a differential voltage is generated by the transformer TR1 and the transformer TR2, and different polarity voltages are applied to both ends of the discharge tubes 14-1 to 14-20. The tube current detection circuit 20 includes two resistors and a diode, and is connected to the secondary winding of the transformer TR2.

  Here, the current detection mechanism will be described. In the present embodiment, the current detection circuit 16 detects the output current of the transformer TR1, and outputs the result to the non-inverting terminal of the current comparator 24 via the resistor R1. Similarly, the tube current detection circuit 20 detects the output current of the transformer TR2, and outputs the result to the non-inverting terminal of the current comparator 24-2 via the resistor R2. The tube current feedback signal is output from the secondary winding of the transformer TR2 to the control circuit 12 via a diode.

  On the other hand, the voltage detection mechanism will be described. In this embodiment, the voltage detection circuit 18 detects the output voltage of the transformer TR1 and outputs the result to the non-inverting terminal of the voltage comparator 26. Similarly, the voltage detection circuit 18-2 detects the output voltage of the transformer TR2, and outputs the result to the non-inverting terminal of the voltage comparator 26-2. The feedback signal of the load voltage is generated as a logical sum of the outputs of the voltage detection circuit 18 and the voltage detection circuit 18-2, and is output to the control circuit 12.

  In the present embodiment, a first current limiting circuit constituted by a current comparator 24, a transistor Tr1, and a voltage comparator 26, a current comparator 24-2, a transistor Tr2, and a voltage comparator 26-2. And a first current limiting circuit connected to the thyristor 30 via diodes D1 and D2, respectively. With such a configuration, when an H level signal is output from either the first current limiting circuit or the second current limiting circuit, lighting control of the discharge tube is stopped.

  In each of the above-described embodiments, as shown in FIG. 2, the current reference value Iref and the voltage reference value Vref are set based on the voltage and current characteristics at the time of startup. It can also be applied to protection. When applied in a steady state, the voltage drop characteristic when 2 kΩ is added and the voltage drop characteristic when 2 kΩ is not added are measured, and the current reference is performed in the same procedure as described with reference to FIG. The value Iref and the voltage reference value Vref may be determined.

  For example, in a configuration in which the total current of each discharge tube flows 150 mA, if 2 kΩ is added, a voltage of 2 kΩ × 150 mA = 300 V is generated. Therefore, if the lower limit of the voltage reference value Vref is set to 300 V, Can be detected. In the above-described example, since the setting range of the voltage reference value Vref at the time of startup is 100 V to 400 V, it is desirable to set the voltage reference value Vref within a range of 300 V to 400 V in consideration of protection after startup.

  According to the present invention, large current driving or multiple lamp driving compliant with the UL standard is possible, and therefore, application to a large-sized liquid crystal backlight inverter requiring miniaturization is expected.

It is a circuit block diagram which shows the structure of the discharge tube lighting device which concerns on the 1st Embodiment of this invention. It is a characteristic view which shows the behavior at the time of starting of the voltage and current which appear in a high voltage line. It is a conceptual diagram which shows the setting concept of the voltage reference value Vref and the electric current reference value Iref. It is operation | movement explanatory drawing which shows the current-limiting operation | movement when 2k (ohm) is not added. It is operation | movement explanatory drawing which shows the current limiting operation | movement when 2 kohm is added. It is a circuit block diagram which shows the structure of the discharge tube lighting device which concerns on the 2nd Embodiment of this invention. It is a circuit block diagram which shows the structure of the discharge tube lighting device which concerns on the 3rd Embodiment of this invention. It is a circuit block diagram which shows the structure of the discharge tube lighting device which concerns on the 4th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... DC power supply, 12 ... Control circuit, 14 ... Discharge tube, 16 ... Current detection circuit, 18 ... Voltage detection circuit, 20 ... Tube current detection circuit, 22 ... AND computing unit, 24 ... Current comparator, 26 ... Voltage comparison 30, Thyristor

Claims (6)

In a discharge tube lighting device comprising: a discharge tube connected to a high-voltage line; a lighting control unit that controls lighting of the discharge tube; and a current-limiting circuit that limits a current amount flowing through the high-voltage line to a reference value;
A discharge tube lighting device, wherein the reference value of the current limiting circuit is switched according to a state of a load connected to the high voltage line. In a discharge tube lighting device comprising: a discharge tube connected to a high-voltage line; a lighting control unit that controls lighting of the discharge tube; and a current-limiting circuit that limits a current amount flowing through the high-voltage line to a reference value;
The discharge tube lighting device characterized by controlling an operating state of the current limiting circuit according to a state of a load connected to the high voltage line. In a discharge tube lighting device comprising: a discharge tube connected to a high-voltage line; a lighting control unit that controls lighting of the discharge tube; and a current-limiting circuit that limits a current amount flowing through the high-voltage line to a reference value;
A voltage detection unit for detecting a voltage value applied to the high-voltage line;
A current detector for detecting the amount of current flowing through the high-voltage line;
The discharge current lighting device, wherein the current limiting circuit determines the reference value using the detected voltage value and current amount. In a discharge tube lighting device comprising: a discharge tube connected to a high-voltage line; a lighting control unit that controls lighting of the discharge tube; and a current-limiting circuit that limits a current amount flowing through the high-voltage line to a reference value;
A voltage detection unit for detecting a voltage value applied to the high-voltage line;
A current detector for detecting the amount of current flowing through the high-voltage line;
The current limiting circuit stops the operation of the lighting control unit based on the detected voltage value and current amount. In a discharge tube lighting device comprising: a discharge tube connected to a high-voltage line; a lighting control unit that controls lighting of the discharge tube; and a current-limiting circuit that limits a current amount flowing through the high-voltage line to a reference value;
A voltage detection unit for detecting a voltage value applied to the high-voltage line;
A current detector for detecting the amount of current flowing through the high-voltage line;
The current limiting circuit is
A voltage comparator for comparing the detected voltage value with a voltage reference value;
A current comparator for comparing the detected amount of current with a current reference value;
An AND operation unit for obtaining a logical product of the output of the voltage comparison unit and the output of the current comparison unit. The output of the voltage comparator transitions from a first level to a second level when the detected voltage value reaches the voltage reference value;
6. The discharge tube lighting device according to claim 5, wherein the output of the current comparator transitions from a second level to a first level when the detected current amount reaches the current reference value. .

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