JP4858993B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention includes a positive phase transformer and a negative phase transformer that step up high frequency voltages generated by a drive circuit in mutually opposite phases, and each high voltage side of each secondary winding of the positive phase transformer and the negative phase transformer. The present invention relates to a discharge lamp lighting device that connects and discharges a discharge lamp between terminals, detects a current flowing through the discharge lamp, and controls a current flowing through the discharge lamp by a drive circuit based on the detected current.

The discharge lamp includes a cold cathode tube and a hot cathode tube, and in particular, the cold cathode tube has recently been adopted as a backlight of a liquid crystal display device, and various usage methods have been put into practical use depending on the size. .
FIG. 16 is a block diagram showing a configuration example of a separately excited cold cathode tube lighting device which is an example of a conventional discharge lamp lighting device. In the following description, a separately excited secondary resonance type inverter is exemplified, but a self-excited type inverter may be used.
In this cold-cathode tube lighting device, a drive control circuit 10 including an inverter generates a high-frequency voltage of about 30 to 80 kHz, and a positive-phase high-voltage transformer (positive-phase transformer) TX3 and a negative-phase high-voltage transformer (reverse-phase transformer). TX4 boosts the high-frequency voltage generated by the drive control circuit 10 in mutually opposite phases.

The low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3 is grounded through the resistor R65, and the low voltage side terminal of the secondary winding of the negative phase high voltage transformer TX4 is grounded. Capacitors C2 and C3 are connected in parallel to the next winding.
The cold cathode tube 1 is connected to the high-voltage side terminals of the secondary windings of the transformers TX3 and TX4, and the high-frequency voltage boosted by the transformers TX3 and TX4 is applied in the opposite phase to light up.

  The rectifier circuit 31 rectifies the voltage across the resistor R65 (the low-voltage side terminal voltage of the secondary winding of the positive-phase high-voltage transformer TX3), detects it as a current value flowing through the cold cathode tube 1, and drives and controls the current value. The circuit 10 is fed back. The drive control circuit 10 performs feedback control based on the given current value so that the current passed through the cold cathode tube 1 becomes a predetermined value.

FIG. 17 is a circuit diagram showing an equivalent circuit in which the cold cathode tube 1 of the cold cathode tube lighting device shown in FIG. 16 is exemplified by a resistor and a capacitor (capacitor). However, here, the cold-cathode tube 1 is a U-shaped tube frequently used in a liquid crystal display device, and the rectifier circuit 31 is omitted from the block diagram described above.
The positive-phase high-voltage transformer TX3 and the negative-phase high-voltage transformer TX4 boost the high-frequency power source from the drive control circuit 10 in opposite phases, and the tube current is supplied from the secondary winding of the positive-phase high-voltage transformer TX3 to resistors R1 to R14. Through the secondary winding of the negative-phase high-voltage transformer TX4 and flows to the ground side, and returns to the transformer TX3 through the resistor R65. Capacitors C10, C11, C12,... C22 schematically show stray capacitances between the cold cathode fluorescent lamp 1 and its supporting structure (not shown), and have resistances R1-R2, R2-R3, R3-R4,... R13-R14 are connected between the connection nodes and the ground terminal.

In this state, the output voltages of the positive-phase high-voltage transformer TX3 and the negative-phase high-voltage transformer TX4 are equal, and the currents flowing through the capacitors C2 and C3 are also equal. Further, each step-down portion of the resistors R1 to R7 corresponding to the resistance of one straight pipe portion constituting the U-shaped tube is equal to each step-down portion of the resistors R14 to R8 corresponding to the resistance of the other straight pipe portion. Therefore, the current flowing in the capacitors C10 to C15 corresponding to the stray capacitance of one straight tube portion is equal to the current flowing in the capacitors C22 to C17 corresponding to the stray capacitance of the other straight tube portion.
Therefore, the currents flowing through all the resistors and capacitors connected to the positive phase high voltage transformer TX3, the currents flowing through all the resistors and capacitors connected to the negative phase high voltage transformer TX4, and the current flowing through the resistor R65 are all in an equilibrium state.

FIG. 18 is a waveform diagram showing a waveform of a current flowing through the resistor R65 in the equivalent circuit of FIG. 17. A solid line A is a current waveform in the above-described equilibrium state, and a one-dot chain line B is a capacitor intentionally. It is a current waveform that flows through the resistor R65 when the equilibrium state is broken assuming that C22, C21, and C20 (part of the stray capacitance) do not exist.
Thus, it can be seen that the current flowing through the resistor R65 is affected by the stray capacitance due to the change when a part of the stray capacitance does not exist. Therefore, when the conventional circuit shown in FIG. 16 is affected by the stray capacitance, the current flowing through the resistor R65 for detecting the tube current fluctuates. Stable feedback control cannot be performed.

In Patent Document 1, both electrodes of a cold-cathode tube are connected to one terminal of each secondary winding of the first oscillation transformer and the second oscillation transformer, and the opposite phases of the electrodes are connected to one terminal of each secondary winding. A cold-cathode tube lighting device is disclosed in which an oscillation voltage is applied and the other terminal of the secondary winding of the second oscillation transformer is grounded via a tube current detection resistor. In this case, the tube current is measured from the ground side of the secondary winding of the second oscillation transformer.
In Patent Document 2, the output of a piezoelectric transformer is connected to both end electrodes of a cold cathode discharge lamp, a current transformer is provided on the line between the piezoelectric transformer and the cold cathode discharge lamp, and the tube current is detected. Discloses a piezoelectric transformer drive circuit that is input to a differential amplifier at the input end of the tube current detection processing unit. In this case, the tube current is measured under the high voltage of the piezoelectric transformer.

  In Patent Document 3, two transformers are connected between a drive unit and two lamps so as to correspond to two lamps, and a drive signal from the drive unit is supplied to the lamp through the transformer. A backlight driving device for a liquid crystal display device in which the secondary sides of the transformers are connected to each other is disclosed. The two lamps are connected in series through resistors, and the tube currents of the two lamps are detected and feedback controlled by the voltage obtained by rectifying the voltage across the resistors. In this case, the tube current is measured on the high voltage side of the secondary winding of the transformer.

  In Patent Document 4, a 1-input 2-output-type piezoelectric transformer that outputs AC voltages of opposite phases from two output electrodes and two cold cathode tubes connected in series between the two output electrodes are inserted. A cold-cathode tube lighting drive device including a current detection element and a differential amplifier to which a voltage across the current detection element is input is disclosed. Based on the output of the differential amplifier, the drive frequency of the piezoelectric transformer is controlled so that the current flowing through the cold cathode tube is constant. In this case, the tube current is measured under the high voltage of the piezoelectric transformer.

  In Patent Document 5, the tube current of a discharge lamp driven in reverse phase is applied to both ends of each resistor connected between each low voltage side terminal and ground terminal of each secondary winding of the positive phase high voltage transformer and the negative phase high voltage transformer. A discharge lamp driving device that detects a higher one of the voltages and performs feedback control using a digital filter so as to obtain a current value corresponding to the target brightness of the discharge lamp, and lights the discharge lamp by burst dimming is disclosed. . In this case, the tube current is measured from the ground side of each secondary winding of the positive-phase high-voltage transformer and the negative-phase high-voltage transformer.

In Patent Document 6, each ballast element for boosting a drive pulse output from an inverter by a positive-phase high-voltage transformer and a negative-phase high-voltage transformer and equalizing the tube current of each cold-cathode tube of each secondary winding is disclosed. A cold-cathode tube lighting device is disclosed in which light is applied to the input terminals on both sides of a plurality of cold-cathode tubes in opposite phases to each other to light them. The detected currents flowing through the ballast elements are added, a tube current is obtained based on the added value, and the duty of the inverter drive pulse is set so that the tube current becomes constant. In this case, the tube current is measured on the high voltage side of each secondary winding of the positive phase high voltage transformer and the negative phase high voltage transformer.
Japanese Utility Model Publication No. 06-19299 JP 2003-249393 A JP 2004-54294 A JP 2004-241266 A JP 2006-294328 A JP 2007-59155 A

  In cold-cathode tube lighting devices that perform reverse phase lighting, as a method of detecting the tube current, a method of measuring from the high voltage side or the ground side of the secondary winding of the high voltage transformer is considered. 6 is measured from the high-voltage side of the secondary winding, and those described in Patent Documents 1 and 5 are measured from the ground side of the secondary winding. In order to measure from the high voltage side of the secondary winding, it is necessary to pass through an insulation transformer, which increases the cost of parts. Even if it can be detected, the effect of stray capacitance between the cold cathode tube and its supporting structure cannot be eliminated, and the tube current cannot be accurately detected, so the tube current is controlled to be constant by feedback. There is a problem that you can not.

  In Patent Documents 2 and 4, a piezoelectric transformer is used and no winding as in the present invention is used, but the tube current is measured under the high voltage of the piezoelectric transformer, It is impractical because it requires pressure resistance and leakage current countermeasures, and there is no means for separating currents due to stray capacitance components, so the correct tube current cannot be measured. Further, as described above (FIG. 16), even if the current detection resistor R65 is provided on the ground side of the secondary winding of the high voltage transformer, the influence of the stray capacitance between the cold cathode tube and the supporting structure can be eliminated. Absent.

  In addition, in the tube current measurement of a U-shaped cold cathode tube frequently used in liquid crystal display devices, there is no method other than measuring the secondary current of the transformer, and the currently measured tube current measurement value is There is a problem that it is not accurate because it is affected by the stray capacitance between the cold cathode tube and the support structure, and the tube current cannot be controlled constant by feedback. This problem also applies to the tube current measurement of a straight tube type cold cathode tube. Moreover, also in what was disclosed by the said patent documents 1-6, the influence of the stray capacitance between a cold cathode tube and a support structure is not excluded, or is not considered at all.

The present invention has been made in view of the above-described circumstances. In the first and second inventions, the discharge current that is hardly affected by the stray capacitance between the discharge lamp and its supporting structure and can accurately detect the tube current. An object is to provide an electric lighting device.
It is an object of the third and fourth inventions to provide a discharge lamp lighting device that includes a plurality of discharge lamps, is less susceptible to stray capacitance between the discharge lamp and its supporting structure, and can accurately detect tube current. .

A discharge lamp lighting device according to a first aspect of the present invention is configured such that a driving circuit that generates an AC voltage for driving and a low-voltage side terminal of a secondary winding are connected to a ground potential side, respectively, and an AC voltage generated by the driving circuit is generated. and a positive-phase transformers and reversed-phase transformer for boosting the opposite phase, by connecting the discharge lamp between the high-voltage side terminal of the positive-phase transformer and the negative-phase transformer for each secondary winding is lit, detects a current flowing through the discharge lamp, based on the detected current, the discharge lamp lighting device is arranged to control the current the driving circuit is flowing through said discharge lamp constant,
A first resistor and a second resistor which each one terminal in each low-voltage side terminal of the positive-phase transformer and the negative-phase transformer secondary winding is connected, one terminal of which is connected to the ground potential side and a third resistor, and a differential amplifier, the first resistor, the respective other terminal of the second resistor and the third resistor is connected, between said first resistor and said second respective one terminal of the resistor Is provided to the differential amplifier,
The third resistor and the differential amplifier cancel the current caused by the stray capacitance generated between the discharge lamp and the ground so that only the current flowing through the discharge lamp is detected. .

In this discharge lamp lighting device, a positive-phase transformer and a negative-phase transformer, each of which has a low-voltage side terminal of the secondary winding connected to the ground potential side, boosts the AC voltage generated by the drive circuit in opposite phases to each other. . A discharge lamp is connected between each high-voltage side terminal of each secondary winding of the normal phase transformer and the reverse phase transformer to light it, the current flowing through the discharge lamp is detected, and the drive circuit is released based on the detected current. The current flowing through the lamp is controlled to be constant.
Each terminal of the first resistor and the second resistor is connected to each of the low voltage side terminals of the secondary windings of the positive phase transformer and the negative phase transformer, and one terminal of the third resistor is connected to the ground potential side. Has been. The other terminals of the first resistor, the second resistor, and the third resistor are connected, and the voltage between the one terminal of the first resistor and the second resistor is applied to the differential amplifier.
Then, the third resistor and the differential amplifier cancel out the current caused by the stray capacitance generated between the discharge lamp and the ground, and only the current flowing through the discharge lamp is detected.

  A discharge lamp lighting device according to a second aspect of the present invention is configured such that a driving circuit that generates a driving AC voltage and a low-voltage side terminal of a secondary winding are connected to a ground potential side, respectively, and an AC voltage generated by the driving circuit is generated. A positive-phase transformer and a negative-phase transformer that step up in opposite phases with each other, and connect a discharge lamp between each high-voltage side terminal of each secondary winding of the positive-phase transformer and the negative-phase transformer to light it. In the discharge lamp lighting device configured to detect the current flowing through the discharge lamp and to control the current flowing through the discharge lamp to be constant based on the detected current, the positive phase transformer and the reverse A primary winding connected between the low-voltage side terminals of each secondary winding of the phase transformer, the middle point being connected to the ground potential side, and the secondary winding having one terminal connected to the ground potential side And the discharge lamp based on the current flowing in the secondary winding of the transformer. Characterized in that is arranged to detect the current.

In this discharge lamp lighting device, a positive-phase transformer and a negative-phase transformer, each of which has a low-voltage side terminal of the secondary winding connected to the ground potential side, boosts the AC voltage generated by the drive circuit in opposite phases to each other. . A discharge lamp is connected between each high-voltage side terminal of each secondary winding of the normal phase transformer and the reverse phase transformer to light it, the current flowing through the discharge lamp is detected, and the drive circuit is released based on the detected current. The current flowing through the lamp is controlled to be constant.
The primary winding of the transformer is connected between the low-voltage side terminals of the secondary windings of the positive phase transformer and the negative phase transformer. The midpoint of the primary winding of the transformer is connected to the ground potential side, and one terminal of the secondary winding is connected to the ground potential side. Based on the current flowing through the secondary winding of the transformer, the current flowing through the discharge lamp is detected.

  According to a third aspect of the present invention, there is provided a discharge lamp lighting device in which one or a plurality of drive circuits for generating a driving AC voltage and a low-voltage side terminal of a secondary winding are connected to the ground potential side, respectively, A positive-phase transformer and a negative-phase transformer for each of the plurality of discharge lamps for boosting the alternating voltage in mutually opposite phases, and each high-voltage side terminal of each secondary winding of the positive-phase transformer and the negative-phase transformer A discharge lamp configured to connect and discharge the discharge lamp in between, detect a current flowing through the discharge lamp, and control the current flowing through the discharge lamp at a constant level based on the detected current In the lighting device, a first resistor and a second resistor connected in series between the low-voltage side terminals of the secondary winding of the positive phase transformer of one discharge lamp and the reverse phase transformer of another discharge lamp, A connection node between the first resistor and the second resistor and a third resistor connected between the ground potential sides; A differential amplifier that is provided for each of the plurality of discharge lamps and that is supplied with a voltage across one of the series circuit of the first resistor and the second resistor is provided, and the current of the discharge lamp is detected based on the output of the differential amplifier Further, it is configured to be provided to the one or a plurality of drive circuits.

In this discharge lamp lighting device, one or a plurality of drive circuits generate a driving AC voltage, and the positive phase transformer and the reverse phase transformer for each of the plurality of discharge lamps have a low voltage side terminal of the secondary winding. Each of them is connected to the ground potential side, and boosts the AC voltage generated by the drive circuit in mutually opposite phases. A discharge lamp is connected between each high-voltage side terminal of each secondary winding of the normal phase transformer and the reverse phase transformer to light it, the current flowing through the discharge lamp is detected, and the drive circuit is released based on the detected current. The current flowing through the lamp is controlled to be constant.
A first resistor and a second resistor are connected in series between the low-voltage side terminals of the secondary winding of the positive phase transformer of one discharge lamp and the negative phase transformer of the other discharge lamp, and the third resistor is the first resistor The first and second resistors are connected between the connection node and the ground potential side. The differential amplifier is given a voltage across either one of the series circuit of the first resistor and the second resistor, detects the current of the discharge lamp based on the output of the differential amplifier, and supplies it to one or a plurality of drive circuits.

  According to a fourth aspect of the present invention, there is provided a discharge lamp lighting device in which one or a plurality of driving circuits for generating a driving AC voltage and a low-voltage side terminal of a secondary winding are connected to a ground potential side, and the driving circuit generates the driving voltage. A positive-phase transformer and a negative-phase transformer for each of the plurality of discharge lamps for boosting the alternating voltage in mutually opposite phases, and each high-voltage side terminal of each secondary winding of the positive-phase transformer and the negative-phase transformer A discharge lamp configured to connect and discharge the discharge lamp in between, detect a current flowing through the discharge lamp, and control the current flowing through the discharge lamp at a constant level based on the detected current In the lighting device, both terminals are connected between the low-voltage side terminals of the secondary windings of the positive phase transformer of one discharge lamp and the reverse phase transformer of the other discharge lamp in an arbitrary pair of the discharge lamps. A primary winding whose middle point is connected to the ground potential side and one terminal of the ground winding A transformer having a secondary winding connected to the side of the discharge lamp, and one of the low-voltage side terminals of the secondary winding of the reverse-phase transformer of one of the discharge lamps in the other one or more pairs of the discharge lamp. A first resistor having a terminal connected thereto, a second resistor having one terminal connected to the low voltage side terminal of the secondary winding of the positive phase transformer of the other discharge lamp, and one terminal being connected to the ground potential side. A third resistor connected to the other terminal of the first resistor, the second resistor, and the third resistor, and a current flowing through the discharge lamp based on a current flowing through the secondary winding of the transformer. Is detected and applied to the one or a plurality of driving circuits.

  In this discharge lamp lighting device, one or a plurality of drive circuits generate a driving AC voltage, and the positive phase transformer and the reverse phase transformer for each of the plurality of discharge lamps have a low voltage side terminal of the secondary winding. Each of them is connected to the ground potential side, and boosts the AC voltage generated by the drive circuit in mutually opposite phases. A discharge lamp is connected between each high-voltage side terminal of each secondary winding of the normal phase transformer and the reverse phase transformer to light it, the current flowing through the discharge lamp is detected, and the drive circuit is released based on the detected current. The current flowing through the lamp is controlled to be constant.

The primary winding of the transformer is connected between the low-voltage side terminals of the secondary windings of the positive phase transformer of one discharge lamp and the negative phase transformer of the other discharge lamp in any pair of discharge lamps. Are connected, the middle point thereof is connected to the ground potential side, and one terminal of the secondary winding is connected to the ground potential side.
In the other one or more pairs of discharge lamps, one terminal of the first resistor is connected to the low voltage side terminal of the secondary winding of the reverse phase transformer of one discharge lamp, and the positive phase of the other discharge lamp One terminal of the second resistor is connected to the low-voltage side terminal of the secondary winding of the transformer, and one terminal of the third resistor is connected to the ground potential side, and the first resistor, the second resistor, and the third resistor Each other terminal is connected. Based on the current flowing through the secondary winding of the transformer, the current flowing through the discharge lamp is detected and applied to one or more drive circuits.

  According to the discharge lamp lighting device according to the first and second inventions, the influence of the stray capacitance component on the current flowing through the current detection circuit can be reduced. Therefore, it is possible to realize a discharge lamp lighting device that can detect the tube current accurately. Further, since the tube current can be controlled to be constant by feedback, luminance unevenness hardly occurs in the liquid crystal display device when used for a backlight.

  According to the discharge lamp lighting device according to the third and fourth inventions, since the influence of the stray capacitance component on the current flowing through the current detection circuit can be reduced, the discharge lamp includes a plurality of discharge lamps, and the support structure thereof. It is possible to realize a discharge lamp lighting device that is less susceptible to stray capacitance between objects and can accurately detect tube current. Further, since the tube current can be controlled to be constant by feedback, luminance unevenness hardly occurs in the liquid crystal display device when used for a backlight.

Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof.
(Background of the invention)
14 is replaced with the resistor R65 connected to the secondary winding of the positive phase high voltage transformer TX3 of the cold cathode tube lighting device shown in FIG. 17 and the grounding of the secondary winding of the negative phase high voltage transformer TX4, It is a circuit diagram which shows the equivalent circuit which connected the primary winding of transformer TX1 between each low voltage | pressure side terminal of the secondary winding of positive phase high voltage transformer TX3, and the secondary winding of reverse phase high voltage transformer TX4.

  FIG. 15 is a waveform diagram showing a waveform of a current flowing through the resistor R19 connected to both ends of the secondary winding of the transformer TX1 in FIG. 14, and a solid line A represents a case of an equilibrium state where the stray capacitance is stable. A one-dot chain line B is a current waveform that flows in the resistor R19 when the equilibrium state is broken assuming that the capacitors C22, C21, and C20 (part of the stray capacitance) do not exist intentionally. There is almost no difference between the two, and it can be seen that the current flowing through the resistor R19 is hardly affected by the stray capacitance.

That is, assuming that the capacitors C22, C21, and C20 (part of the stray capacitance) do not exist, the unbalanced current when the balanced state is lost is the balanced state between the capacitors C2 and C3 and the capacitors (floating capacitances) C10 to C22. It can be seen that this is caused by the potential difference between the potential determined by the above and the ground potential of the positive-phase high-voltage transformer TX3 and the negative-phase high-voltage transformer TX4.
Further, when configured as shown in FIG. 14, the tube current of the cold cathode tube (U-shaped tube) 1 is transferred from the secondary winding of the positive phase high voltage transformer TX3 to the secondary winding of the transformer TX4 through the resistors R1 to R14. A flowing loop is formed, and the relationship with the ground potential is small. However, as a practical matter, floating the primary side of the transformer TX1 from the ground potential is unacceptable for safety reasons, so the following configuration is adopted.

(Embodiment 1)
FIG. 1 is a circuit diagram showing a main configuration of a cold cathode tube lighting device which is Embodiment 1 of a discharge lamp lighting device according to the present invention.
In this cold-cathode tube lighting device, a drive control circuit (drive circuit) 10 including an inverter generates a high-frequency voltage of about 30 k to 80 kHz and performs feedback control so that the tube current flowing through the cold-cathode tube 1 becomes a predetermined value. . The high-frequency voltage generated by the drive control circuit 10 is applied to the positive-phase high-voltage transformer (normal-phase transformer) TX3 and the negative-phase high-voltage transformer (negative-phase transformer) TX4. The positive-phase high-voltage transformer TX3 and the negative-phase high-voltage transformer TX4 boost the given high-frequency voltages in mutually opposite phases.

One terminals of a resistor R56 and a resistor R57 are connected to the low-voltage side terminals of the secondary windings of the positive-phase high-voltage transformer TX3 and the negative-phase high-voltage transformer TX4, respectively. One terminal of the resistor R58 is grounded, and the other terminals of the resistors R56, R57, and R58 are commonly connected. The other terminal of the capacitor C2, whose one terminal is grounded, is connected to the high voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3. The other terminal of the capacitor C3 with one terminal grounded is connected to the high voltage side terminal of the secondary winding of the negative phase high voltage transformer TX4.
The cold cathode tube 1 is connected between the high-voltage side terminals of the secondary windings of the positive-phase high-voltage transformer TX3 and the reverse-phase high-voltage transformer TX4. Here, the cold cathode tube 1 is a U-shaped tube frequently used in a liquid crystal display device.

  Both ends of the resistors R56 and R57 are given to both input terminals of the differential amplifier 20, and the differential amplifier 20 outputs a voltage corresponding to the given both-ends voltage and gives it to the rectifier circuit 30. The rectifier circuit 30 rectifies the applied voltage, detects it as a current value flowing through the cold cathode tube 1, and feeds back the current value to the drive control circuit 10. The drive control circuit 10 performs feedback control based on the given current value so that the current passed through the cold cathode tube 1 becomes a predetermined value.

  In the differential amplifier 20, one terminal potential of the resistor 56 is given to the base of the NPN transistor Q9 through the capacitor C72. One terminal potential of the resistor 57 is given to the base of the NPN transistor Q10 through the capacitor C73. The collector of the transistor Q9 is connected to the power supply V6 through the resistor R72, and the emitter is connected to the positive terminal of the constant current source I1 whose negative terminal is grounded through the resistor R74. The collector of the transistor Q10 is connected to the power source V6 through the resistor R73, and the emitter is connected to the positive terminal of the constant current source I1 through the resistor R75.

One terminal of a resistor R78 is connected to the base of the transistor Q9, and the other terminal of the resistor R78 is divided by resistors R76 and R77 connected between the power supply V6 and the ground terminal. One terminal of a resistor R79 is connected to the base of the transistor Q10, and the other terminal of the resistor R79 is divided by resistors R76 and R77 connected between the power supply V6 and the ground terminal.
The collector of the transistor Q9 is grounded through a capacitor C71 and a resistor R70, and a diode D2 whose anode is grounded is connected in parallel to the resistor R70.

  The collector of the transistor Q10 is grounded through a capacitor C70 and a resistor R71, and a diode D1 whose anode is grounded is connected in parallel to the resistor R71. The anode of the diode D3 is connected to the cathode of the diode D1, the anode of the diode D4 is connected to the cathode of the diode D2, and the cathodes of the diodes D3 and D4 are connected in common. As a result, the rectifier circuit 30 performs full-wave rectification on the output of the differential amplifier 20 and feeds back the tube current to the drive control circuit 10.

  FIG. 2 is a circuit diagram showing the cold-cathode tube lighting device of FIG. 1. In FIG. 2, the cold-cathode tube (U-shaped tube) 1 is displayed as an equivalent circuit by resistors R1 to R14 and capacitors (capacitors) C10 to C22. 2 is a block diagram showing the rectifier circuit 30 in blocks. The equivalent circuit of the cold cathode tube 1 is the same as the equivalent circuit of the cold cathode tube 1 shown in FIGS.

  In the cold cathode tube lighting device having such a configuration, the tube current is supplied to the high voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3, the high voltage side terminal of the secondary winding of the cold cathode tube 1 and the negative phase high voltage transformer TX4. The low-voltage side terminal, resistors R57 and R56, and the low-voltage side terminal of the secondary winding of the positive phase high-voltage transformer TX3 flow. When the voltage across the resistors R56 and R57 is taken out by the differential amplifier 20, the current flowing between the stray capacitance and the ground terminal is canceled by the resistor R58 by the operation of the differential amplifier 20, which will be described later. Only the tube current returning from TX3 to transformer TX4 can be taken.

3 and 4 are waveform diagrams showing the operation of the differential amplifier 20 shown in FIGS.
When the cold-cathode tube lighting device of FIGS. 1 and 2 is in an equilibrium state in which the stray capacitance of the cold-cathode tube 1 is stable, as shown in FIG. 3C, the base voltages of the transistors Q9 and Q10 are Amplitude is equal in antiphase. Therefore, since the emitter currents of the transistors Q9 and Q10 have the opposite phases and the same amplitude, no voltage fluctuation occurs in the constant current source I1 as shown in FIG. Therefore, the input to the transistors Q9 and Q10 is only the voltage to each base without adding the voltage fluctuation of the constant current source I1, and the difference is amplified. For example, the voltage across the resistor R70 is shown in FIG. As shown in a).

  When the cold-cathode tube lighting device of FIGS. 1 and 2 is in an unbalanced state (for example, when the capacitors C22, C21, and C20 (part of the stray capacitance) of FIG. 2 are not present), FIG. As shown in FIG. 4, the base voltages of the transistors Q9 and Q10 are different from each other, and as shown in FIG. 4B, the difference appears as a voltage fluctuation of the constant current source I1. Since the true input to the transistor Q9 is a voltage difference between the voltage to the base (broken line in FIG. 4C) and the voltage of the constant current source I1 (FIG. 4B), the amplitude is reduced accordingly. On the other hand, the true input to the transistor Q10 is a voltage difference between the voltage to the base (solid line in FIG. 4 (c)) and the voltage of the constant current source I1 (FIG. 4 (b)), but in opposite phases. Therefore, the amplitude becomes large.

Therefore, the true input difference to the transistors Q9 and Q10 eliminates the common component. As a result, as shown in FIG. 4A, the voltage across the resistor R70 is obtained when the cold-cathode tube lighting device is in an equilibrium state. When this occurs (when capacitors C22, C21, and C20 are present), the voltage is equal to the voltage across resistor R70 (FIG. 3A). Here, the common component is a fluctuation component of a voltage generated when the current flowing between the stray capacitance and the ground terminal varies due to the variation of the stray capacitance, and the current flowing between the resistor R58 and the ground terminal varies. is there.
Thus, since the current due to the fluctuation of the stray capacitance is removed as a common component of the two inputs of the differential amplifier 20, it does not affect the voltage across the resistor R70. Is the same.

  5 is a waveform diagram showing a waveform of the voltage across the resistor R71 serving as a load of the differential amplifier 20 shown in FIG. 1. A solid line A is a current waveform in an equilibrium state, and a one-dot chain line B is This is a current waveform when the equilibrium state is broken assuming that the capacitors C22, C21, and C20 (part of the stray capacitance) in FIG. It is the same as the waveform diagram of FIG. 15 described above, and it can be seen that the tube current of the cold cathode tube 1 flowing through the resistors R56 and R57 is hardly affected by the stray capacitance.

(Embodiment 2)
FIG. 6 is a block diagram showing a main configuration of a cold cathode tube lighting device which is Embodiment 2 of the discharge lamp lighting device according to the present invention.
This cold cathode tube lighting device is provided with a differential transformer TX2 instead of the resistors R56, R57, R58, the differential amplifier 20 and the like of the cold cathode tube lighting device shown in FIG.

Instead of the resistors R56 and R57, the primary winding of the differential transformer TX2 is connected between the low-voltage side terminals of the secondary winding of the positive-phase high-voltage transformer TX3 and the secondary winding of the negative-phase high-voltage transformer TX4. The midpoint of the primary winding is grounded.
One terminal of the secondary winding of the differential transformer TX2 is grounded, and the other terminal of the secondary winding is connected to the rectifier circuit 31. A resistor R19 is connected in parallel to the secondary winding of the differential transformer TX2, and the voltage generated in the secondary winding is rectified by the rectifier circuit 31 and applied to the drive control circuit 10. Other configurations are the same as those of the cold-cathode tube lighting device (FIG. 1) described in the first embodiment, and thus description thereof is omitted.

  FIG. 7 is an equivalent circuit diagram showing an equivalent circuit of the cold cathode tube (U-shaped tube) 1 with resistors R1 to R14 and capacitors (capacitors) C10 to C22 in the block diagram showing the cold cathode tube lighting device of FIG. FIG. 15 is a circuit diagram showing a case where a differential transformer TX2 is connected instead of the transformer TX1 shown in FIG. The equivalent circuit of the cold cathode tube 1 is the same as the equivalent circuit of the U-shaped tube 1 shown in FIGS.

  In the cold-cathode tube lighting device having such a configuration, the current flows from the high-voltage side terminal of the secondary winding of the positive-phase high-voltage transformer TX3 → the cold-cathode tube 1 → the high-voltage side terminal of the secondary winding of the reverse-phase high-voltage transformer TX4 → A loop is formed in which the low voltage side terminal → the primary winding of the differential transformer TX2 → the low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3. At this time, the current flowing between the stray capacitance and the ground terminal cancels out due to the current flowing between the midpoint of the primary winding of the differential transformer TX2 and the secondary winding and the ground terminal, so that the positive-phase high-voltage transformer TX3 Can be taken from the secondary winding of the differential transformer TX2 only in relation to the current returning from the reverse phase high voltage transformer TX4.

  In the transformer TX1 shown in FIG. 14, the primary side is floated from the ground potential. However, in the differential transformer TX2 in FIG. 7, there is no safety problem because the midpoint of the primary winding is grounded. Further, the waveform of the current flowing through the resistor R19 is the same as the waveform diagram shown in FIG. 15 and is not easily affected by the stray capacitance, so that the tube current of the cold cathode tube 1 can be accurately detected.

(Embodiment 3)
FIG. 8 is a block diagram showing a main configuration of a cold cathode tube lighting device which is Embodiment 3 of the discharge lamp lighting device according to the present invention.
The cold-cathode tube lighting device includes cold-cathode tubes (U-shaped tubes) 1, 2, 3, and the positive-phase high-voltage transformer TX 3 and the reverse-phase high-voltage transformer TX 4 of the cold-cathode tube 1 are mutually connected from the drive control circuit 10. A high-frequency voltage with an opposite phase is given. The positive-phase high-voltage transformer TX5 and the negative-phase high-voltage transformer TX6 of the cold-cathode tube 2 are given high-frequency voltages of opposite phases from the drive control circuit 11, and the positive-phase high-voltage transformer TX7 and the negative-phase high-voltage transformer TX8 of the cold-cathode tube 3 are The drive control circuit 12 applies high-frequency voltages having opposite phases to each other.

The cold cathode tube 1 is connected between the high-voltage side terminals of the secondary windings of the positive-phase high-voltage transformer TX3 and the negative-phase high-voltage transformer TX4. One terminal of the resistor R56 is connected to the low-voltage side terminal of the negative-phase high-voltage transformer TX4, and the other terminal is connected to one terminal of the resistor R57. The other terminal of the resistor R57 is connected to the low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX5. The connection point between the resistors R56 and R57 is grounded through the resistor R58.
The other terminal of the capacitor C2, whose one terminal is grounded, is connected to the high voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3. The other terminal of the capacitor C3 with one terminal grounded is connected to the high voltage side terminal of the secondary winding of the negative phase high voltage transformer TX4.

The cold cathode tube 2 is connected between the high-voltage side terminals of the secondary windings of the positive-phase high-voltage transformer TX5 and the negative-phase high-voltage transformer TX6. One terminal of the resistor R59 is connected to the low voltage side terminal of the negative phase high voltage transformer TX6, and the other terminal is connected to one terminal of the resistor R60. The other terminal of the resistor R60 is connected to the low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX7. The connection point of the resistors R59 and R60 is grounded through the resistor R61.
The other terminal of the capacitor C4 whose one terminal is grounded is connected to the high voltage side terminal of the secondary winding of the positive phase high voltage transformer TX5. The other terminal of the capacitor C5 whose one terminal is grounded is connected to the high-voltage side terminal of the secondary winding of the negative-phase high-voltage transformer TX6.

  The cold cathode tube 3 is connected between the high-voltage side terminals of the secondary windings of the positive-phase high-voltage transformer TX7 and the negative-phase high-voltage transformer TX8. One terminal of the resistor R62 is connected to the low voltage side terminal of the negative phase high voltage transformer TX8, and the other terminal is connected to one terminal of the resistor R63. The other terminal of the resistor R63 is connected to the low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3. The connection point between the resistors R62 and R63 is grounded through the resistor R64.

The other terminal of the capacitor C6 whose one terminal is grounded is connected to the high voltage side terminal of the secondary winding of the positive phase high voltage transformer TX7. The other terminal of the capacitor C7 whose one terminal is grounded is connected to the high voltage side terminal of the secondary winding of the negative phase high voltage transformer TX8.
Both input terminals of the differential amplifier 20 are given voltages across the connected resistors R56 and R57, and the output of the differential amplifier 20 is given to the rectifier circuit 30. The output rectified by the rectifier circuit 30 is given to each drive control circuit 10, 11, 12.

  With the above-described configuration, in this cold cathode tube lighting device, the cold cathode tube 1 is lit by the voltage boosted by the positive phase high voltage transformer TX3 and the negative phase high voltage transformer TX4 in opposite phases. The cold-cathode tube 2 is lit by a voltage boosted in the opposite phase by the positive-phase high-voltage transformer TX5 and the negative-phase high-voltage transformer TX6. The cold-cathode tube 3 is lit by a voltage boosted in the opposite phase by the positive-phase high-voltage transformer TX7 and the negative-phase high-voltage transformer TX8.

  The differential amplifier 20 amplifies the voltage across the resistors R56 and R57 and supplies the amplified voltage to the rectifier circuit 30. The rectifier circuit 30 rectifies the applied voltage and supplies it to the drive control circuits 10, 11, 12 as a detected value of the tube current of the cold cathode tube 1. Each drive control circuit 10, 11, 12 performs feedback control of the output high-frequency voltage so that the tube current of the cold cathode tube 1 becomes a predetermined value based on the given detection value.

  In this cold-cathode tube lighting device, the current flows from the positive-phase high-voltage transformer TX3 → the cold-cathode tube 1 → the negative-phase high-voltage transformer TX4 → the resistors R56, R57 → the positive-phase high-voltage transformer TX5 → the cold-cathode tube 2 → the negative-phase high-voltage transformer TX6 → A loop is formed in which the resistors R59, R60 → positive phase high voltage transformer TX7 → cold cathode tube 3 → reverse phase high voltage transformer TX8 → resistors R62, R63 → positive phase high voltage transformer TX3.

  Therefore, by detecting the voltage across the resistors R56 and R57 with the differential amplifier 20 and detecting the tube current of the cold cathode tube 1, it is possible to detect the tube currents of the other cold cathode tubes 2 and 3 that are equal thereto. it can. Therefore, by supplying the detected tube current value to the respective drive control circuits 10, 11, 12 of the cold cathode tubes 1, 2, 3, each tube current of the cold cathode tubes 1, 2, 3 is set to a predetermined value. Can be feedback controlled. Note that the same can be achieved if the differential amplifier 20 detects the voltage across the resistors R59 and R60 or the resistors R62 and R63 instead of the resistors R56 and R57.

FIG. 9 is an equivalent circuit diagram in which the cold cathode tubes (U-tubes) 1, 2, and 3 are represented by equivalent circuits in terms of resistance and capacitance in the block diagram showing the cold cathode tube lighting device of FIG. The rectifier circuit 30 is not shown.
Here, the cold cathode tube 1 has resistors R1 to R14 and capacitors (capacitors) C10 to C22, the cold cathode tube 2 has resistors R21 to R34 and capacitors (capacitors) C30 to C42, and the cold cathode tube 3 has resistors R41 to R54. In addition, equivalent circuits are indicated by capacitances (capacitors) C50 to C62.
The capacities (capacitors) C10 to C22 of the cold cathode tubes 1, the capacities (capacitors) C30 to C42 of the cold cathode tubes 2, and the capacities (capacitors) C50 to C62 of the cold cathode tubes 3 are the cold cathode tubes 1, 2, 3 schematically shows the stray capacitance between 3 and its supporting structure (not shown).

In the cold cathode tube 1, the tube current is supplied from the high voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3 through the resistors R1 to R14 to the high voltage side terminal and the low voltage side terminal of the secondary winding of the negative phase high voltage transformer TX4. And flows to the low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX5 of the cold cathode tube 2 through the resistors R56 and R57.
In the cold cathode tube 2, the tube current is supplied from the high-voltage side terminal of the secondary winding of the positive-phase high-voltage transformer TX5 through the resistors R21 to R34 to the high-voltage side terminal and the low-voltage side terminal of the secondary winding of the negative-phase high-voltage transformer TX6. And flows to the low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX7 of the cold cathode tube 3 through the resistors R59 and R60.

In the cold cathode tube 3, the tube current is supplied from the high-voltage side terminal of the secondary winding of the positive-phase high-voltage transformer TX7 through the resistors R41 to R54 to the high-voltage side terminal and the low-voltage side terminal of the secondary winding of the negative-phase high-voltage transformer TX8. And flows to the low voltage side terminal of the secondary winding of the positive phase high voltage transformer TX3 of the cold cathode tube 1 and flows from the high voltage side terminal to the cold cathode tube 1 through the resistors R62 and R63.
Thus, a loop of tube current flowing through the cold cathode tubes 1, 2, 3 is formed. At this time, in the cold cathode tubes 1, 2 and 3, the current flowing between the stray capacitance and the ground terminal is canceled by the current flowing between the resistors R58, R61 and R64 and the ground terminal, and the tube current is converted into the differential amplifier 20. Therefore, the stray capacitance hardly affects the tube current.

In the above-described configuration, even when the voltages of the drive control circuits 10, 11, and 12 are different, a tube current loop is formed. Therefore, variations in tube current are averaged, and the cold cathode tubes 1, 2, and 3 are Tube currents are equal.
With the above-described configuration, even when a plurality of cold cathode tubes (U-shaped tubes) are used, the number of tube current detection circuits may be one, so that component costs can be reduced.
In the above-described configuration, the configuration drive control circuits 10, 11, and 12 are used. However, the single-phase high-voltage transformers TX3, TX5, and TX7 and the negative-phase high-voltage transformers TX4 and TX6 can be substituted by one drive control circuit. , TX8 may be connected in parallel.

Moreover, not only the U-shaped tube but also, for example, even when using two straight tubes on each of the upper and lower edges of the liquid crystal panel unit, the upper and lower four straight tubes can be looped by connecting them in series. The current of each straight pipe becomes equal. Further, as in the case of the U-shaped tube, the influence on the tube current due to the stray capacitance can be reduced.
For example, when a cold-cathode tube lighting device including two drive control circuits 10, 11 of the three drive control circuits 10, 11, 12 shown in FIG. 8 is configured, as shown in FIG. For the upper edge of the straight tube type cold cathode tubes 1-1 and 1-2, between the high-voltage side terminals of the secondary winding of the positive phase high-voltage transformer TX3 and the secondary winding of the negative-phase high-voltage transformer TX4 Connect in series. Further, for the lower edge of the liquid crystal panel unit 35, a straight tube type cold cathode tube 2- is provided between the high voltage side terminals of the secondary winding of the positive phase high voltage transformer TX5 and the secondary winding of the negative phase high voltage transformer TX6. 1 and 2-2 are connected in series.

By connecting in this way, in this cold-cathode tube lighting device, the current flows from the positive-phase high-voltage transformer TX3 → cold-cathode tube 1-1 → cold-cathode tube 1-2 → reverse-phase high-voltage transformer TX4 → resistors R56 and R57 → A loop is formed in which the positive-phase high-voltage transformer TX5 → the cold cathode tube 2-1 → the cold-cathode tube 2-2 → the reverse-phase high-voltage transformer TX6 → the resistors R62 and R63 → the positive-phase high-voltage transformer TX3.
Therefore, the cold-cathode tubes 1-1, 1-2, 2-1 and 2 are detected by detecting the voltage across the resistors R56 and R57 or the resistors R62 and R63 with the differential amplifier 20 and detecting the current flowing through the loop. -2 tube current can be detected. Further, by providing the detected tube current values to the drive control circuits 10 and 11, feedback control is performed so that the tube currents of the cold cathode tubes 1-1, 1-2, 2-1, and 2-2 become predetermined values. can do.

  When a cold-cathode tube lighting device having two drive control circuits 10 and 11 is also configured, a straight-tube cold-cathode tube 1-1 is used for the upper edge of the liquid crystal panel unit 35 as shown in FIG. , 1-2 are provided for the lower edge of the liquid crystal panel unit 35 as straight-type cold cathode tubes 2-1, 2-2. In this arrangement, the cold cathode tubes 1-1 and 2-2 are connected in series between the high-voltage side terminals of the secondary winding of the positive-phase high-voltage transformer TX3 and the secondary winding of the negative-phase high-voltage transformer TX4, and the positive-phase Cold cathode tubes 1-2 and 2-1 are connected in series between the high-voltage side terminals of the secondary winding of the high-voltage transformer TX5 and the secondary winding of the reverse-phase high-voltage transformer TX6.

By connecting in this way, in this cold cathode tube lighting device, the current flows from the positive phase high voltage transformer TX3 → the cold cathode tube 1-1 → the cold cathode tube 2-2 → the negative phase high voltage transformer TX4 → resistors R56, R57 → A loop is formed in which the positive-phase high-voltage transformer TX5 → the cold cathode tube 1-2 → the cold-cathode tube 2-1 → the reverse-phase high-voltage transformer TX6 → the resistors R62 and R63 → the positive-phase high-voltage transformer TX3.
Therefore, the cold-cathode tubes 1-1, 1-2, 2-1 and 2 are detected by detecting the voltage across the resistors R56 and R57 or the resistors R62 and R63 with the differential amplifier 20 and detecting the current flowing through the loop. -2 tube current can be detected. Further, by providing the detected tube current values to the drive control circuits 10 and 11, feedback control is performed so that the tube currents of the cold cathode tubes 1-1, 1-2, 2-1, and 2-2 become predetermined values. can do.

  When a cold-cathode tube lighting device comprising two drive control circuits 10 and 11 is also configured, a straight-tube cold-cathode tube 1-1 is used for the upper edge of the liquid crystal panel unit 35 as shown in FIG. , 1-2 are provided for the lower edge of the liquid crystal panel unit 35 as straight-type cold cathode tubes 2-1, 2-2. In this arrangement, the cold cathode tubes 1-1 and 2-2 are connected in series between the high-voltage side terminals of the secondary winding of the positive-phase high-voltage transformer TX3 and the secondary winding of the negative-phase high-voltage transformer TX4, and the positive-phase Cold cathode tubes 2-1 and 1-2 are connected in series between the high-voltage side terminals of the secondary winding of the high-voltage transformer TX5 and the secondary winding of the reverse-phase high-voltage transformer TX6.

By connecting in this way, in this cold cathode tube lighting device, the current flows from the positive phase high voltage transformer TX3 → the cold cathode tube 1-1 → the cold cathode tube 2-2 → the negative phase high voltage transformer TX4 → resistors R56, R57 → A loop is formed in which the positive-phase high-voltage transformer TX5 → the cold-cathode tube 2-1 → the cold-cathode tube 1-2 → the reverse-phase high-voltage transformer TX6 → the resistors R62 and R63 → the positive-phase high-voltage transformer TX3.
Therefore, the cold-cathode tubes 1-1, 1-2, 2-1 and 2 are detected by detecting the voltage across the resistors R56 and R57 or the resistors R62 and R63 with the differential amplifier 20 and detecting the current flowing through the loop. -2 tube current can be detected. Further, by providing the detected tube current values to the drive control circuits 10 and 11, feedback control is performed so that the tube currents of the cold cathode tubes 1-1, 1-2, 2-1, and 2-2 become predetermined values. can do.

(Embodiment 4)
FIG. 13: is a block diagram which shows the principal part structure of the cold cathode tube lighting device which is Embodiment 4 of the discharge lamp lighting device which concerns on this invention.
This cold-cathode tube lighting device replaces the resistors R56, R57, R58, differential amplifier 20, rectifier circuit 30 and the like of the cold-cathode tube lighting device shown in FIG. The primary winding of the differential transformer TX2 is connected between the low-voltage side terminals of the secondary winding of the phase high-voltage transformer TX5, and one terminal of the secondary winding is grounded. The midpoint of the primary winding of the differential transformer TX2 is grounded. The other terminal of the secondary winding of the differential transformer TX2 is connected to the rectifier circuit 31, and the voltage generated in the secondary winding is rectified and supplied to the drive control circuits 10, 11, and 12. Other configurations are the same as those of the cold-cathode tube lighting device (FIG. 8) described in the third embodiment, and thus description thereof is omitted.

  With this configuration, in this cold-cathode tube lighting device, the current flows from the positive-phase high-voltage transformer TX3 → the cold-cathode tube 1 → the negative-phase high-voltage transformer TX4 → the primary winding of the differential transformer TX2 → the positive-phase high-voltage transformer TX5 → A cold current tube 2 → reverse phase high voltage transformer TX6 → resistances R59, R60 → positive phase high voltage transformer TX7 → cold cathode tube 3 → reverse phase high voltage transformer TX8 → resistances R62, R63 → positive phase high voltage transformer TX3 is formed. . At this time, in the cold cathode tubes 1, 2 and 3, the current flowing between the stray capacitance and the ground terminal is generated between the midpoint of the primary winding of the differential transformer TX2, the secondary winding, the resistors R61 and R64 and the ground terminal. Since it was canceled by the current flowing between them, the stray capacitance hardly affects the tube current.

Therefore, by detecting the voltage generated in the secondary winding of the differential transformer TX2 and detecting the tube current of any one of the cold cathode tubes 1, 2, 3, another cold cathode tube 1, 2 equal to that is detected. , 3 tube currents can be detected. Therefore, by supplying the detected tube current value to the respective drive control circuits 10, 11, 12 of the cold cathode tubes 1, 2, 3, each tube current of the cold cathode tubes 1, 2, 3 is set to a predetermined value. Can be feedback controlled.
In the above-described configuration, the configuration drive control circuits 10, 11, and 12 are used. However, the single-phase high-voltage transformers TX3, TX5, and TX7 and the negative-phase high-voltage transformers TX4 and TX6 can be substituted by one drive control circuit. , TX8 may be connected in parallel.

It is a circuit diagram which shows the principal part structure of the cold cathode tube lighting device which is Embodiment 1 of the discharge lamp lighting device which concerns on this invention. In the circuit diagram showing the cold cathode tube lighting device of FIG. 1, it is a block diagram in which the cold cathode tube is represented by an equivalent circuit with a resistor and a capacitor (capacitor). It is a wave form diagram which shows operation | movement of the differential amplifier shown to FIG. It is a wave form diagram which shows operation | movement of the differential amplifier shown to FIG. It is a wave form diagram which shows the waveform of the both-ends voltage of resistance R71 used as the load of the differential amplifier shown in FIG. It is a block diagram which shows the principal part structure of the cold cathode tube lighting device which is Embodiment 2 of the discharge lamp lighting device which concerns on this invention. FIG. 7 is a circuit diagram showing an equivalent circuit of a cold cathode tube with a resistor and a capacitor (capacitor) in the block diagram showing the cold cathode tube lighting device of FIG. 6. It is a block diagram which shows the principal part structure of the cold cathode tube lighting device which is Embodiment 3 of the discharge lamp lighting device which concerns on this invention. FIG. 9 is a circuit diagram showing an equivalent circuit of a cold cathode tube by resistance and capacitance in the block diagram showing the cold cathode tube lighting device of FIG. 8. It is a block diagram which shows the example of a connection in the case of lighting a some straight tube | pipe type cold cathode tube in the discharge lamp lighting device which concerns on this invention. It is a block diagram which shows the example of a connection in the case of lighting a some straight tube | pipe type cold cathode tube in the discharge lamp lighting device which concerns on this invention. It is a block diagram which shows the example of a connection in the case of lighting a some straight tube | pipe type cold cathode tube in the discharge lamp lighting device which concerns on this invention. It is a block diagram which shows the principal part structure of the cold cathode tube lighting device which is Embodiment 4 of the discharge lamp lighting device which concerns on this invention. FIG. 18 is a circuit diagram in which the primary winding of the transformer is connected between the low-voltage side terminals of the secondary winding of the positive-phase high-voltage transformer and the secondary winding of the negative-phase high-voltage transformer shown in FIG. 17. It is a wave form diagram which shows the waveform of the electric current which flows into the resistance connected to the both ends of the secondary winding of the transformer shown in FIG. It is a block diagram which shows the structural example of the separately excited cold cathode tube lighting device which is an example of the conventional discharge lamp lighting device. It is a circuit diagram which shows the equivalent circuit which illustrated the cold cathode tube of the cold cathode tube lighting device shown in FIG. 16 by resistance and a capacity | capacitance (capacitor). It is a wave form diagram which shows the waveform of the electric current which flows into resistance R65 in the equivalent circuit of FIG.

Explanation of symbols

1, 2, 3 Cold cathode tube (U-shaped tube, discharge lamp)
1-1, 1-2, 2-1, 2-2 Cold cathode tube (straight tube, discharge lamp)
10, 11, 12 Drive control circuit (drive circuit)
20 Differential amplifier 30, 31 Rectifier circuit 35 Liquid crystal panel unit R19, R56 to R64 Resistor TX2 Differential transformer (transformer)
TX3, TX5, TX7 Positive phase high voltage transformer (positive phase transformer)
TX4, TX6, TX8 Reverse phase high voltage transformer (Reverse phase transformer)

Claims (1)

A drive circuit that generates an AC voltage for driving, a low-voltage side terminal of the secondary winding connected to the ground potential side, and a positive-phase transformer that boosts the AC voltage generated by the drive circuit in opposite phases to each other; and a reverse-phase transformer, the positive-phase transformer and is turned to connect the discharge lamp between the high-voltage side terminal of the secondary winding of the reverse-phase transformer, detecting a current flowing through the discharge lamp and, based on the detected current, the discharge lamp lighting device is arranged to control the current the driving circuit is flowing through said discharge lamp constant,
A first resistor and a second resistor which each one terminal in each low-voltage side terminal of the positive-phase transformer and the negative-phase transformer secondary winding is connected, one terminal of which is connected to the ground potential side and a third resistor, and a differential amplifier, the first resistor, the respective other terminal of the second resistor and the third resistor is connected, between said first resistor and said second respective one terminal of the resistor Is provided to the differential amplifier,
The third resistor and the differential amplifier cancel the current caused by the stray capacitance generated between the discharge lamp and the ground so that only the current flowing through the discharge lamp is detected. Discharge lamp lighting device.

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