KR100799404B1 - Cold cathode tube lighting device, tube current detecting circuit used in cold cathode tube lighting device, and tube current controlling method - Google Patents

Abstract

assignment

Provided is a cold cathode tube lighting device which obtains stable luminance when driving from input terminals on both sides of a plurality of cold cathode tubes.

Resolution

The currents flowing through the coils 39b and 40b in the coils 39 and 40 on both sides of the cold cathode tubes 41 and 42 are detected by the voltage detectors 43 and 44, and are added by the adder 47 at the same angle. The driving currents e1 and e2 are obtained so that the tube current value α flowing through the cold cathode tube 42 is obtained based on the addition value of the value, and the tube current value α is set to a predetermined value by the DUTY control unit 32. The duty of is set, and the luminance of the cold cathode tubes 41, 42 is constant.

Cold cathode tube lighting device, tube current detection circuit

Description

COLD CATHODE TUBE LIGHTING DEVICE, TUBE CURRENT DETECTING CIRCUIT USED IN COLD CATHODE TUBE LIGHTING DEVICE, AND TUBE CURRENT CONTROLLING METHOD}

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing an electrical configuration of a main part of a cold cathode tube lighting device which is a first embodiment of the present invention.

FIG. 2 is a diagram showing the transformer drive circuits 33 and 34, the transformers 35 and 36, the resonant capacitors 37 and 38, and the cold cathode tubes 41 and 42 in FIG.

3 is a time chart illustrating the operation of FIG. 2;

Fig. 4 is a block diagram showing an electrical configuration of main parts of a cold cathode tube lighting device which is a second embodiment of the present invention.

Fig. 5 is a block diagram showing an electrical configuration of main parts of a cold cathode tube lighting device which is a third embodiment of the present invention.

Fig. 6 is a block diagram showing an electrical configuration of main parts of a cold cathode tube lighting device which is a fourth embodiment of the present invention.

Fig. 7 is a block diagram showing an electrical configuration of main parts of a cold cathode tube lighting device which is a fifth embodiment of the present invention.

Fig. 8 is a block diagram showing the electrical configuration of main parts of a cold cathode tube lighting device which is a sixth embodiment of the present invention.

FIG. 9 is a diagram illustrating a connection state of coils when three cold cathode tubes are used. FIG.

FIG. 10 is a diagram illustrating a connection state of coils when four cold cathode tubes are used. FIG.

11 is a diagram illustrating a modification of the transformer.

12 is a block diagram showing an electrical configuration of a drive device for a piezoelectric transformer described in Patent Document 1. FIG.

<Description of the code>

31, 31A: Oscillator (part of inverter)

32: DUTY control unit (part of the tube current control means)

33, 34: transformer driving circuit (part of the inverter)

35, 36, 100: transformer (part of inverter)

37, 38, 39, 40: resonant capacitor (part of inverter)

39, 40, 39A, 40A, 92, 93, 95, 96: coil (ballast element)

39c, 40c: coil for pressure reduction

41, 42, 91, 94: cold cathode tube

43, 44, 43A, 44A: voltage detector (part of tube current control means)

45, 46, 45A, 46A: divider (part of tube current control means)

47, 47A: Adder (part of tube current control means)

48: delay circuit (part of the tube current control means)

49: voltage controlled oscillator (part of inverter)

50: frequency detector (part of the tube current control means)

51 multiplier (part of the tube current control means)

61: integrator (part of tube current control means)

62: oscillator (part of inverter)

63: comparator (part of the tube current control means)

64 switch (part of tube current control means)

65: power supply (part of the inverter)

66: resonant capacitor (part of the inverter)

67 resonant circuit (part of the inverter)

71: backlight temperature detector (part of the temperature detection means)

72: voltage converter (part of the temperature detection means)

81, 82, 83, 84: voltage detector (part of voltage monitoring means)

85: OR circuit (part of voltage monitoring means)

Field of technology

The present invention relates to a cold cathode tube lighting device, a tube current detection circuit used for the cold cathode tube lighting device, and a tube current control method. In particular, the present invention relates to an input terminal on both sides of a plurality of cold cathode tubes used for a backlight of a liquid crystal display device. The present invention relates to a cold cathode tube lighting apparatus suitable for use in the case of driving in a furnace, a tube current detection circuit used in the cold cathode tube lighting apparatus, and a tube current control method.

Conventional technology

Background Art In recent years, liquid crystal displays have been used not only as monitors for personal computers but also as various types of displays such as liquid crystal televisions, and in particular, liquid crystal panels have been enlarged in size. For this reason, the backlight used for a liquid crystal display device also becomes large, and the cold cathode tube used for a backlight also becomes long. When the cold cathode tube is turned on, in a short cold cathode tube, one input terminal is placed at the low pressure side, and a driving pulse is input from the input terminal on the other high pressure side, but when the long cold cathode tube or the cold cathode tube is small in diameter, Since the impedance of the cathode tube becomes high, when the driving pulse is input from the input terminal (high pressure side) of one side of the same cold cathode tube and driven, the vicinity of the input terminal on the high voltage side is bright, and the vicinity of the input terminal on the low pressure side is dark, resulting in a luminance gradient. do. For this reason, the inclination of the luminance is prevented by the two-side high-pressure driving method in which the driving pulses are applied from the input terminals on both sides of the cold cathode tube in reverse phase with each other to light. In addition, in order to improve the efficiency of the backlight, both sides of the high-pressure driving method may be used even when the shape of the cold cathode tube is small, for example, in the case of the "U" type or the "c" type, and the diameter of the cold cathode tube is small. have. In addition, there is a method of lighting a plurality of cold cathode tubes with one inverter. In this method also, when the cold cathode tubes are long, luminance inclination occurs in the cold cathode tubes unless high pressure is input from input terminals on both sides of the cold cathode tubes.

The luminance of the cold cathode tube is determined by the tube current flowing through the cold cathode tube, and in the one-side high pressure driving method in which a drive pulse is applied to an input terminal on one side of the cold cathode tube, the current is configured by resistance or the like on the low pressure side where the drive pulse is not applied. Although a circuit is provided and control to keep the brightness of the cold cathode tube constant based on the detected current value, in both high-pressure driving methods, the driving pulses applied to both input terminals of the cold cathode tube are high voltage, and current such as resistance. Since the detection circuit cannot be inserted, it is difficult to detect the tube current of the same cold cathode tube.

Conventionally, as this kind of technique, there exist some which were described in the following documents, for example.

As shown in FIG. 12, the piezoelectric transformer driving device described in Patent Document 1 includes a power source 11, a driving circuit 12, a variable oscillation circuit 13, an oscillation control circuit 14, and a piezoelectric element. The transformer 15, the voltage detection circuit 16, the current detection circuit 17, the phase difference detection circuit 18, and the effective current detection circuit 19 are comprised. In addition, a cold cathode tube 20 is connected between the piezoelectric transformer 15 and the current detection circuit 17. In the vicinity of the cold cathode tube 20, an earthed reflecting plate 21 is provided, and a floating capacitor Cx is formed between the cold cathode tube 20 and the reflecting plate 21. In this piezoelectric transformer driving device, the tube current (output current of the piezoelectric transformer 15) of the cold cathode tube 20 is detected by the current detection circuit 17, and the phase difference between the output current and the voltage of the piezoelectric transformer 15 is increased. It is detected by the phase difference detection circuit 18. Based on this phase difference, the oscillation control circuit 14 changes so that the active current which flows into the cold cathode tube 20 is detected by the active current detection circuit 19, and the active current becomes equal to a predetermined set value. The piezoelectric transformer 15 is drive-controlled through the oscillation circuit 13 and the drive circuit 12.

In the multi-lighting discharge tube inverter circuit described in Patent Literature 2, drive pulses are applied from a single inverter to a plurality of discharge tubes (cold cathode tubes) through a branch transformer, and each cold cathode tube is turned on. The split transformer has an inductance that exceeds the negative resistance characteristics of the cold cathode tube. By adjusting the inductance, the tube current flowing through each cold cathode tube becomes uniform.

In the cold cathode tube dimmer of patent document 3, the drive pulse from the high voltage side of an inverter is applied to the input terminal of the one side (high voltage side) of several cold cathode tubes through a ballast capacitor.

On the low voltage side of the inverter, a current detection circuit composed of a resistor is provided, the duty of the driving pulse is controlled on the basis of the detected current value, and control is performed to keep the luminance of the cold cathode tube constant.

The type of inverter described in Patent Document 4 includes an inverter transformer in which a primary coil is a push-pull configuration, two switching elements for on / off control of both ends of the same primary winding, and a clock of two phases opposite to each other in the two switching elements. A clock signal generation circuit for supplying a signal is provided. For this reason, the oscillation frequency can be set freely without being bound to the resonance frequency of the inverter transformer.

In the discharge lamp lighting apparatus described in Patent Document 5, in a video apparatus using a cold cathode tube as a light source, a drive pulse from the high voltage side of the inverter is applied to an input terminal on one side (high pressure side) of one cold cathode tube. On the low voltage side of the inverter, a current detecting circuit composed of a resistor is provided, and based on the detected current value, control of the tube current of the cold cathode tube is performed by pulse width modulation (PWM), and the resolution of the PWM is applied to the bit reduction circuit. Is enlarged by.

In the cold cathode tube lighting device described in Patent Literature 6, a plurality of cold cathode tubes are uniformly and stably lit by a common low power supply with a plurality of ballasts connected to at least one of the plurality of cold cathode tubes. .

In the lamp driving apparatus described in Patent Document 7, a temperature sensor is provided in the vicinity of the external electrode of the lamp, and the state of the lamp is monitored. Thus, when the temperature of the lamp falls within the critical temperature range, the tube current decreases, and when the temperature exceeds the threshold temperature range, the power supply to the lamp is turned off.

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-017090 (Summary, FIG. 1)

Patent Document 2: Japanese Patent Application Laid-Open No. 2004-335443 (Summary, FIG. 1)

Patent Document 3: Japanese Patent Application No. 3096242 (Summary, FIG. 1)

Patent Document 4: Japanese Patent Application Laid-Open No. 2001-052891 (Summary, FIG. 1)

Patent Document 5: Japanese Patent Application Laid-Open No. 2004-235123 (Summary, FIG. 1)

Patent Document 6: Japanese Patent Application Laid-Open No. 2005-063941 (Summary, FIG. 1)

Patent Document 7: Japanese Patent Application Laid-Open No. 2005-063970 (Summary, FIG. 3)

However, the above conventional technology has the following problems.

That is, in the drive device of the piezoelectric transformer described in Patent Document 1, since the output voltage of the piezoelectric transformer 15 is high, it is necessary to make the component to which this output voltage is applied as a high breakdown voltage component, and the cost becomes high. have. In addition, since the tube current is detected on one side of the cold cathode tube 20, there is a problem that the copper tube current cannot be accurately detected depending on the deviation of the terminals of the piezoelectric transformer 15 and the cold cathode tube 20.

In addition, in the inverter circuit for discharge tubes described in Patent Literature 2, the tube current flowing through each cold cathode tube becomes uniform, but since the value of the tube current cannot be changed, the control to keep the luminance of the same cold cathode tube constant is not performed. Do not. The cold cathode tube dimming device described in Patent Literature 3 is one in which each cold cathode tube is driven by a single-side high pressure driving method. The type-driven inverter described in Patent Document 4 independently dimmes a plurality of cold cathode tubes, and therefore, the present invention is different from the present invention.

The discharge lamp lighting apparatus described in Patent Literature 5 is one in which a cold cathode tube is driven by a one-side high-pressure driving method. The cold cathode tube lighting device described in Patent Literature 6 is driven by a plurality of cold cathode tubes by a single-side high-pressure driving method, and therefore, the present invention is different from the present invention in terms of the cold cathode tube lighting device. The lamp driving apparatus described in Patent Document 7 detects the temperature of a lamp by a temperature sensor and controls the power supply to the lamp, and therefore, the present invention and the construction are different.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and in the case where a plurality of cold cathode tubes are driven at high pressure by both inverters, a cold cathode tube lighting device in which the luminance does not change by constant tube current flowing through these cold cathode tubes, the cold An object of the present invention is to provide a tube current detection circuit and a tube current control method for use in a cathode tube lighting device.

In order to solve the said subject, the invention of Claim 1 uses the drive pulse output from an inverter to the input terminal of each side of a some cold cathode tube through each ballast element for equalizing the tube current of each said cold cathode tube. A cold cathode tube lighting device for lighting by applying the phase out of phase to each other, the tube current control means for detecting the tube current flowing through each cold cathode tube based on each current flowing through each ballast element, and controlling the tube current to a predetermined value It is characterized by being provided.

The invention according to claim 2 relates to the cold cathode tube lighting device according to claim 1, wherein the inverter comprises first and second target inverters, and the tube current control means includes the plurality of cold Detects each current flowing through the ballast elements on each side of the cathode tube, obtains the tube current based on the addition value of the respective currents, and applies the respective drive pulses to the respective inverters such that the tube current is the predetermined value. It is characterized by the structure which sets a duty.

The invention according to claim 3 relates to the cold cathode tube lighting apparatus according to claim 1, wherein each inverter comprises first and second target inverters, and the tube current control means includes a plurality of Detecting each current flowing in the ballast elements on each side of the cold cathode tube, obtaining the tube current based on the addition value of the respective currents, and driving the respective drive pulses for the respective inverters such that the tube current is the predetermined value. It is characterized in that it is configured to set the frequency of.

The invention according to claim 4 relates to the cold cathode tube lighting device according to claim 1, wherein each inverter comprises first and second self-contained inverters, and the tube current control means includes a plurality of Detecting each current flowing through the ballast elements on each side of the cold cathode tube, obtaining the tube current based on the addition value of the respective currents, and driving the respective drive pulses to the self-supporting inverter such that the tube current is the predetermined value. It is characterized in that it is configured to control the time width for outputting the.

The invention according to claim 5 relates to the cold cathode tube lighting device according to claim 1, 2, 3, or 4, wherein each ballast element is each composed of a coil, and First and second pressure reducing coils are provided which are inductively coupled to each of the coils provided at input terminals on both sides of one cold cathode tube of the plurality of cold cathode tubes to generate a voltage lower than the voltage at both ends of the respective coils. The tube current control means is configured to detect a current flowing in each of the coils based on a voltage generated in each of the reducing coils.

The invention according to claim 6 relates to the cold cathode tube lighting device according to claim 1, wherein a temperature detecting means for detecting the temperature of each cold cathode tube is provided, and the tube current control means is provided to each ballast element. The tube current flowing through each said cold cathode tube is detected based on each current flowing and the temperature of the said cold cathode tube detected by the said temperature detection means, and it is characterized by the structure which controls the said tube current to a predetermined value.

The invention according to claim 7 and 8 relates to the cold cathode tube lighting device according to claim 1 or 6, wherein the voltage of each driving pulse applied to each input terminal of each cold cathode tube is detected. And voltage monitoring means for stopping the operation of the respective inverters when an abnormality occurs in the voltage of at least one driving pulse.

According to the invention of claim 9, the respective driving pulses output from the inverter are applied to the input terminals on both sides of the plurality of cold cathode tubes in reverse phase with each other through respective ballast elements for equalizing the tube current of the cold cathode tubes. It relates to the tube current detection circuit which is used for the cold cathode tube lighting device which turns on, and detects the tube current which flows through each said cold cathode tube based on each electric current which flows in each said ballast element, Each coil which comprises each said ballast element, Consists of first and second pressure reducing coils which are inductively coupled to each of the coils provided at input terminals on both sides of one of the plurality of cold cathode tubes to generate a voltage lower than the voltage at both ends of the respective coils. It is characterized by that.

The invention according to claim 10 relates to a tube current control method, and each ballast element for equalizing the tube current of each cold cathode tube to each drive pulse output from an inverter at an input terminal of each side of the plurality of cold cathode tubes. It is used in a cold cathode tube lighting device which is applied to the reverse phase to each other through the phase, and detects the tube current flowing through each cold cathode tube based on each current flowing through each ballast element, and controls the tube current to a predetermined value. Doing.

In addition, it is preferable that each device means comprises a semiconductor integrated circuit having a single chip configuration.

According to the configuration of the present invention, the tube current control means detects the tube current flowing through each cold cathode tube based on the current flowing through each ballast element, and the tube current is controlled to a predetermined value, so that the luminance of each cold cathode tube is controlled. I can make it constant.

In addition, the tube current control means detects each current flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtains the tube current based on the addition value of the same current, and makes the tube current be a predetermined value. Since the duty of each driving pulse is set with respect to, the luminance of each cold cathode tube can be made constant.

In addition, the tube current control means detects each current flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtains the tube current based on the addition value of the same current, and makes the tube current be a predetermined value. Since the frequency of each drive pulse is set with respect to, the luminance of each cold cathode tube can be made constant.

In addition, the tube current control means detects each current flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtains the tube current based on the addition value of the respective currents, and the self-powered inverter so that the tube current becomes a predetermined value. Since the time width for outputting the respective driving pulses is controlled with respect to, the luminance of each cold cathode tube can be made constant. In addition, since the current which flows into each coil as a ballast element is detected by the tube current control means based on the voltage which generate | occur | produces in each pressure reduction coil, the said tube current control means can be comprised using the component of a low voltage specification. In addition, since the tube current control means detects the tube current flowing through each cold cathode tube based on the temperature of the cold cathode tube detected by each current flowing through each ballast element and the temperature detecting means, and the tube current is controlled to a predetermined value. It is possible to make the luminance of each cold cathode tube constant.

In addition, the voltage monitoring means detects the voltage of each drive pulse applied to each input terminal of each cold cathode tube and stops the operation of each inverter when an abnormality occurs in the voltage of at least one drive pulse. While the luminance of the cathode tube can be made constant, an accident due to excessive voltage of the driving pulse can be prevented.

The duty of the drive pulse so that each current flowing through the coils as ballast elements on both sides of the plurality of cold cathode tubes is detected, and the tube current value flowing through the cold cathode tube is determined based on the addition value of the respective currents, and the tube current value becomes a predetermined value. Another embodiment provides a cold cathode tube lighting device in which a frequency is set and the luminance of the same cold cathode tube is constant.

Example 1

1 is a block diagram showing an electrical configuration of main parts of a cold cathode tube lighting device which is a first embodiment of the present invention.

As shown in the drawing, the cold cathode tube lighting apparatus of this example includes an oscillator 31, a DUTY control unit 32, transformer drive circuits 33 and 34, transformers 35 and 36, With resonant capacitors 37 and 38, coils 39 and 40, cold cathode tubes 41 and 42, voltage detectors 43 and 44, dividers 45 and 46 and adder 47. Consists of. The oscillator 31 generates an output signal p such as a square wave or a triangular wave of a predetermined frequency, and its oscillation frequency includes the inductance of the secondary sides 35b and 36b of the transformers 35 and 36 and the resonance capacitor 37. And 38, it is fixedly set near the resonance frequency of the resonance circuit. The DUTY control part 32 inputs the output signal p of the oscillator 31, and controls by the duty corresponding to the tube current value (alpha) from the adder 47, and outputs the high frequency pulses pa and pb.

The transformer driving circuits 33 and 34 are constituted by, for example, a buffer by a MOSFET, and are based on the high frequency pulses pa and pb from the DUTY control unit 32, and the primary side 35a of the transformers 35 and 36. , High frequency pulses pc and pd at a level corresponding to 36a) are output. The transformers 35 and 36 input the high frequency pulses pc and pd from the transformer driving circuits 33 and 34 to the primary sides 35a and 36a, and reverse each other from the high voltage side of the secondary sides 35b and 36b. The driving pulses e1 and e2 are output in phase. The voltage of these drive pulses e1 and e2 is set to a value sufficient to light up the cold cathode tubes 41 and 42. The resonant capacitors 37 and 38 constitute resonant circuits in combination with inductances of the secondary sides 35b and 36b of the transformers 35 and 36, respectively. By these transformer drive circuits 33 and 34, the transformers 35 and 36, and the resonance capacitors 37 and 38, two type inverters are comprised.

The coils 39 and 40 are composed of coils 39a and 39b and coils 40a and 40b, respectively, and are connected to input terminals (electrodes) on both sides of the cold cathode tubes 41 and 42, respectively. It is a ballast element for equalizing the tube current of 42). Here, in the case where a driving pulse is applied to a plurality of cold cathode tubes from one transformer (inverter), a ballast element by a coil or a capacitor is not inserted between each of the cold cathode tubes between the output side of the transformer and the same cold cathode tube. Due to the negative resistance characteristic, only one particular cold cathode tube lights up. For this reason, it is necessary to connect a ballast element for each cold cathode tube. The voltage detectors 43 and 44 detect voltages va and vb at both ends of the coils 39b and 40b to generate voltage detection signals vc and vd. The dividers 45 and 46 drive the voltage detection signals vc and vd from the voltage detectors 43 and 44 to the impedances 2πfL, L; inductance f of the coils 39b and 40b which are set in advance. The current values ia and ib of the coils 39b and 40b are generated by dividing by the values of the pulse voltages e1 and e2. The adder 47 adds the current value ia and the current value ib to generate the tube current value α of the cold cathode tube 42. The DUTY control unit 32 controls the duty so that the tube current value α from the adder 47 becomes a predetermined value with respect to the output signal p from the oscillator 31 so as to have a predetermined value. Outputs The voltage detectors 43 and 44, the dividers 45 and 46, the adder 47, and the DUTY controller 32 constitute tube current control means, and these are constituted as integrated chips of one chip.

FIG. 2 is a diagram showing the transformer drive circuits 33 and 34, the transformers 35 and 36, the resonant capacitors 37 and 38, and the cold cathode tubes 41 and 42 in FIG.

As shown in FIG. 2, the trans drive circuit 33 includes a p-channel MOSFET (hereinafter referred to as "pMOS") 33a and an n-channel MOSFET (hereinafter referred to as "nMOS") 33b. Has The pMOS 33a is controlled on / off by the pch (channel) pulse 1 of the high frequency pulse pa output from the DUTY control unit 32, and the nMOS 33b is nch of the same high frequency pulse pa. On / off control is performed by the pulse 1. The transformer driving circuit 34 has a pMOS 34a and an nMOS 34b. The pMOS 34a is controlled on / off by the pch pulse 2 of the high frequency pulse pb output from the DUTY control unit 32, and the nMOS 34b is the nch pulse 2 of the same high frequency pulse pb. On / off control.

3 is a time chart illustrating the operation of FIG. 2.

With reference to this figure, the process content of the tube current control method used for the cold cathode tube lighting device of this example is demonstrated.

In this cold cathode tube lighting device, drive pulses e1 and e2 are applied to the input terminals on both sides of cold cathode tubes 41 and 42 in reverse phase with each other via coils 39 and 40, and the coils 39 and 40 are applied. The tube current flowing through the cold cathode tube 42 is detected on the basis of the currents flowing through the coils 39b and 40b in Fig. 2), and the duty of the driving pulses e1 and e2 is controlled so that the tube current becomes a predetermined value.

In other words, an output signal p of a predetermined frequency is generated from the oscillator 31 and input to the DUTY control unit 32. The high frequency pulses pa and pb controlled by the duty corresponding to the tube current value α are output from the DUTY control unit 32. The high frequency pulses pc and pd are output from the transformer drive circuits 33 and 34 based on the high frequency pulses pa and pb. The high frequency pulses pc and pd are input to the primary sides 35a and 36a of the transformers 35 and 36, and the drive pulses e1 and e2 in phases out of each other are output from the high voltage side of the secondary sides 35b and 36b. do. The drive pulses e1 and e2 are applied to the cold cathode tubes 41 and 42 via the coils 39 and 40, and the cold cathode tubes 41 and 42 light up.

The voltage detectors 43 and 44 detect the voltages va and vb at both ends of the coils 39b and 40b in the coils 39 and 40 to generate the voltage detection signals vc and vd. The voltage detection signals vc and vd are divided by the dividers 45 and 46 to the values of the impedances 2πfL of the coils 39b and 40b, and the current values ia and ib of the coils 39b and 40b. Is generated. The current value ia and the current value ib are added by the adder 47 to generate a tube current value α of the cold cathode tube 42. The duty is controlled by the DUTY control unit 32 so that the tube current value α becomes a predetermined value with respect to the output signal p from the oscillator 31.

That is, as shown in FIG. 3A by the DUTY control unit 32, the pulse width a of the pch pulses 1 and 2 and the pulse width b of the nch pulses 1 and 2 are: By changing at the same rate, the on-times of the pMOS 33a, 34a and the nMOS 33b, 34b are equalized, and the same on-time is controlled in response to the tube current value? Output from the adder 47, The tube current of the cold cathode tubes 41 and 42 becomes a predetermined value. For example, when the tube current is increased, as shown in FIG. 3 (b), the on time is increased, and when the tube current is reduced, as shown in FIG. 3 (c), the on time is shortened. By this control, the tube current of the cold cathode tubes 41 and 42 becomes a predetermined value, and the luminance of the cold cathode tubes 41 and 42 is kept constant.

As described above, in this first embodiment, each current flowing through the coils 39b and 40b in the coils 39 and 40 on both sides of the cold cathode tubes 41 and 42 is detected, and the added value of the same currents is obtained. Based on this, the tube current value α flowing through the cold cathode tube 42 is obtained, and the duty of the driving pulses e1 and e2 is set so that the tube current value α becomes a predetermined value. The luminance of 42 becomes constant.

Example 2

Fig. 4 is a block diagram showing the electrical configuration of the main part of the cold cathode tube lighting device which is the second embodiment of the present invention. The elements common to those in Fig. 1 showing the first embodiment are denoted by the same reference numerals. have.

In the cold cathode tube lighting apparatus of this example, as shown in FIG. 4, the oscillator 31 and the DUTY control unit 32 in FIG. 1 are deleted, and the delay circuit 48, the voltage controlled oscillator 49, and the frequency detector ( 50) and a multiplier 51 is provided. In addition, instead of the dividers 45 and 46 in FIG. 1, the dividers 45A and 46A which have another function are provided. The delay circuit 48 outputs the tube current value α output from the adder 47 until the current starts to stably flow in the cold cathode tubes 41 and 42, for example, when the cold cathode tube lighting device is powered on. After the current starts to stably flow through the cold cathode tubes 41 and 42, the tube current value α is sent to the voltage controlled oscillator 49 as the tube current value αb.

The voltage controlled oscillator 49 sets the oscillation frequency so that the tube current value? B sent from the delay circuit 48 becomes a predetermined value and outputs high frequency pulses pe and pf. The frequency detector 50 detects the frequencies of the high frequency pulses pe and pf and generates a frequency detection signal ve. The multiplier 51 multiplies the frequency detection signal ve with the inductance L of the coils 39b and 40b to obtain an impedance (2πfL, L; inductance, f; driving pulse voltages e1 and e2) corresponding to one coil. Frequency), and an impedance value v is generated. The dividers 45A and 46A divide the voltage detection signals vc and vd from the voltage detectors 43 and 44 by the impedance value v to determine the current values ia and ib of the coils 39b and 40b. Create In addition, the transformer driving circuits 33 and 34 have a level corresponding to the primary sides 35a and 36a of the transformers 35 and 36 based on the high frequency pulses pe and pf from the voltage controlled oscillator 49. The high frequency pulses pc and pd are output. The other thing is the same structure as FIG. Tube voltage control by the voltage detectors 43 and 44, the dividers 45A and 46A, the adder 47, the delay circuit 48, the voltage controlled oscillator 49, the frequency detector 50, and the multiplier 51. Means are configured, and they are configured as an integrated circuit of one chip.

In the tube current control method used for the cold cathode tube lighting device, drive pulses e1 and e2 are applied to the input terminals on both sides of the cold cathode tubes 41 and 42 in reverse phase with each other via the coils 39 and 40, The tube current flowing through the cold cathode tube 42 is detected based on the currents flowing through the coils 39b and 40b in the coils 39 and 40, and the frequencies of the drive pulses e1 and e2 are increased so that the tube current becomes a predetermined value. Controlled.

That is, the voltage controlled oscillator 49 oscillates at a predetermined frequency immediately after the power is turned on, and the high frequency pulses pe and pf are sent to the transformer driving circuits 33 and 34. In the transformer drive circuits 33 and 34, the high frequency pulses pc and pd are output based on the high frequency pulses pe and pf. The transformers 35 and 36 are driven corresponding to the frequencies of the high frequency pulses pc and pd. In addition, the frequencies of the high frequency pulses pe and pf are detected by the frequency detector 50, and the frequency detection signal ve is output to the multiplier 51. In the multiplier 51, the frequency detection signal ve and the inductance L of the coils 39b and 40b are multiplied to calculate an impedance (2? FL) corresponding to one coil, and an impedance value v is generated.

The voltage detection signals vc and vd from the voltage detectors 43 and 44 are divided by the impedance values v in the dividers 45A and 46A to generate current values ia and ib of the coils 39b and 40b. do. The current value ia and the current value ib are added by the adder 47, and the tube current value α of the cold cathode tube 42 is generated. The tube current value α is sent to the voltage controlled oscillator 49 as the tube current value αb via the delay circuit 48 after the current starts to flow stably in the cold cathode tubes 41 and 42. In the voltage controlled oscillator 49, the oscillation frequency is set so that the tube current value? B becomes a predetermined value, and high frequency pulses pe and pf are output. By repeating this operation, the luminance of the cold cathode tubes 41 and 42 becomes constant.

Example 3

Fig. 5 is a block diagram showing the electrical configuration of the main part of the cold cathode tube lighting apparatus which is the third embodiment of the present invention, and the elements common to those in Fig. 1 showing the first embodiment are denoted by the same reference numerals. have.

In the cold cathode tube lighting apparatus of this example, as shown in FIG. 5, the coils 39A and 40A and the voltage detector having different configurations are replaced with the coils 39 and 40 and the voltage detectors 43 and 44 in FIG. 1. 43A and 44A are provided. In the coils 39A and 40A, the pressure reducing coils which are inductively coupled to the coils 39b and 40b respectively to generate voltages vf and vg lower than the voltages va and vb at both ends of the coils 39b and 40b ( 39c, 40c) are provided. In this case, the decompression coils 39c and 40c share the core with the coils 39b and 40b. These coils 39A and 40A constitute a tube current detection circuit. The voltage detectors 43A and 44A detect voltages vf and vg at both ends of the pressure reducing coils 39c and 40c to generate voltage detection signals vc and vd. The other thing is the same structure as FIG. In the voltage detectors 43A and 44A, the dividers 45 and 46, the adder 47, and the DUTY controller 32, tube current control means is configured, and these are configured as an integrated chip of one chip.

In the tube current control method used for this cold cathode tube lighting device, the voltages vf and vg lower than the voltages va and vb of both ends of the coils 39b and 40b are generated by the pressure reducing coils 39c and 40c. . For this reason, in addition to the advantages of the first embodiment, the voltage detectors 43A and 44A can be configured by components having a low voltage specification.

Example 4

Fig. 6 is a block diagram showing the electrical configuration of main parts of the cold cathode tube lighting device which is the fourth embodiment of the present invention.

In the cold cathode tube lighting apparatus of this example, as illustrated in FIG. 6, the oscillator 31, the DUTY control unit 32, the transformer driving circuits 33 and 34, and the resonance capacitors 37 and 38 in FIG. 1 are deleted. , An integrator 61, an oscillator 62, a comparator 63, a switch 64, a power supply 65, and a resonant capacitor 66. The resonant capacitor 66 constitutes the resonant circuit 67 by a combination with the inductances of the primary sides 35a and 36a of the transformers 35 and 36. These resonance capacitors 66 and the transformers 35 and 36 form a self-contained inverter. This self-converted inverter is operated by the resonant circuit 67 when the power supply voltage vh of the power supply 65 is applied to the primary sides 35a and 36a of the transformers 35 and 36 via the switch 64. Start the rash.

The integrator 61 detects the effective value of the current flowing in the cold cathode tube 42 at a predetermined unit time by integrating the tube current value α from the adder 47, and the current detection signal (voltage value) αc. ) The oscillator 62 oscillates at a frequency that is sufficiently slower than the resonance circuit 67 and does not cause neck sensation, and a reference voltage corresponding to the same frequency by an F / V (frequency / voltage) converter (not shown) is shown. pg). The comparator 63 compares the current detection signal αc with the reference voltage pg, and controls the switch 64 on / off so that the current flowing in the cold cathode tube 42 at a predetermined unit time becomes a predetermined value. Send a signal sc. The switch 64, based on the on / off control signal sc, uses the power supply voltage vh of the power supply 65 as the power supply voltages vj and vk, and the primary sides 35a and 36a of the transformers 35 and 36. ) Is intermittently applied. The tube current control means comprises the voltage detectors 43 and 44, the dividers 45 and 46, the adder 47, the integrator 61, the oscillator 62, the comparator 63 and the switch 64 in FIG. In addition, these are configured as an integrated circuit of one chip.

In the tube current control method used for the cold cathode tube lighting device, drive pulses e1 and e2 are applied to the input terminals on both sides of the cold cathode tubes 41 and 42 in reverse phase with each other via the coils 39 and 40, The tube current flowing through the cold cathode tube 42 is detected based on each current flowing through the coils 39b and 40b in the coils 39 and 40, and the driving pulse e1 is applied to the self-supporting inverter so that the tube current becomes a predetermined value. , e2) output time width is controlled.

That is, by integrating the tube current value α from the adder 47 by the integrator 61, the effective value of the current flowing through the cold cathode tube 42 at a predetermined unit time is detected, and the current from the dynamic integrator 61 is detected. The detection signal αc is output. The current detection signal αc and the reference voltage pg from the oscillator 62 are compared in the comparator 63, and the on / off control signal sc is output to the switch 64. Based on the on / off control signal sc, the power supply voltage vh of the power supply 65 passes through the switch 64 as the power supply voltages vj and vk as the primary sides 35a, It is intermittently applied to 36a), and the cold cathode tubes 41 and 42 are driven by PWM (Pulse Width Modulation) so that the tube current value (alpha) becomes a predetermined value. As a result, the current flowing through the cold cathode tubes 41 and 42 at a predetermined time becomes constant, and the luminance of the cold cathode tubes 41 and 42 becomes constant.

Example 5

Fig. 7 is a block diagram showing the electrical configuration of main parts of a cold cathode tube lighting device which is a fifth embodiment of the present invention.

In the cold cathode tube lighting apparatus of this example, as shown in FIG. 7, an adder 47A having another function is provided in place of the adder 47 in FIG. 1, and the backlight temperature detector 71 and the voltage converting unit are provided. 72 is provided. The backlight temperature detector 71 detects the tube wall temperature t of the cold cathode tube 42. The voltage converter 72 converts the tube wall temperature t of the cold cathode tube 42 detected by the backlight temperature detector 71 into a voltage value u. The adder 47A adds the voltage value u, the current value ia from the divider 45, and the current value ib from the divider 46 and outputs a voltage α. The other thing is the same structure as FIG. In addition, the tube current control means is composed of the voltage detectors 43 and 44, the dividers 45 and 46, the adder 47A, the duty controller 32, the backlight temperature detector 71 and the voltage converter 72. Moreover, these are comprised as an integrated circuit of 1 chip.

As a tube current control method used for this cold cathode tube lighting device, each current flowing through the coils 39b and 40b in the coils 39 and 40 and the temperature of the cold cathode tube 42 detected by the backlight temperature detector 71 are used. Thus, the tube current flowing through the cold cathode tube is detected, and the duty of the driving pulses e1 and e2 is controlled so that the tube current becomes a predetermined value. That is, the tube wall temperature t of the cold cathode tube 42 is detected by the backlight temperature detector 71. The tube wall temperature t is converted into the voltage value u by the voltage converter 72. The voltage value u, the current value ia from the divider 45 and the current value ib from the divider 46 are added in the adder 47A to output the voltage α. Thereafter, the same processing as in the first embodiment is performed. Thereby, the change of the current which flows through the cold cathode tubes 41 and 42, and the change of the brightness | luminance of the copper cold cathode tubes 41 and 42 by temperature change are suppressed, and the brightness of the said cold cathode tubes 41 and 42 becomes constant.

Example 6

Fig. 8 is a block diagram showing the electrical configuration of main parts of a cold cathode tube lighting device which is a sixth embodiment of the present invention.

In the cold cathode tube lighting apparatus of this example, as shown in FIG. 8, instead of the oscillator 31 in FIG. 1, an oscillator 31A having another function is provided, and the voltage detectors 81, 82, 83, 84) and an OR circuit 85 are provided. The voltage detector 81 is configured by, for example, a comparison circuit, and compares the voltage v1 of the connection point between the coil 39a and the cold cathode tube 41 with a predetermined reference voltage, and the same voltage v1 is determined. When larger than the same reference voltage, the abnormal voltage detection signal m1 is generated. The voltage detector 82 compares the voltage v2 at the connection point between the coil 39b and the cold cathode tube 42 with a predetermined reference voltage, and detects an abnormal voltage when the voltage v2 is greater than the same reference voltage. Generate signal m2. The voltage detector 83 compares the voltage v3 at the connection point between the coil 40a and the cold cathode tube 41 with a predetermined reference voltage, and detects an abnormal voltage when the voltage v3 is greater than the same reference voltage. Generate signal m3. The voltage detector 84 compares the voltage v4 at the connection point between the coil 40b and the cold cathode tube 42 with a predetermined reference voltage, and detects an abnormal voltage when the voltage v4 is greater than the same reference voltage. Generate signal m4.

The OR circuit 85 generates the abnormality detection signal m5 when at least one of the abnormality voltage detection signals m1, m2, m3, and m4 is generated. The oscillator 31A stops operating when the abnormality detection signal m5 is generated in the OR circuit 85. Voltage monitoring means is constituted by the voltage detectors 81, 82, 83, 84 and the OR circuit 85. In addition, the voltage detectors 43 and 44, the dividers 45 and 46, the adder 47, the duty controller 32, the voltage detectors 81, 82, 83, 84, and the OR circuit 85 are formed of one chip. It is configured as an integrated circuit.

In the tube current control method used for this cold cathode tube lighting device, the voltage of the driving pulses e1 and e2 applied to the input terminals of the cold cathode tubes 41 and 42 is detected by the voltage monitoring means. When an abnormality occurs in the voltage of at least one driving pulse, such as when the voltage of the driving pulses e1 and e2 becomes excessive due to a poor connection of the cathode tubes 41 and 42, the operation of the oscillator 31A is stopped. The operation of each inverter is stopped. That is, when an abnormality is detected in at least one of the voltages v1, v2, v3, and v4 by the voltage detectors 81, 82, 83, and 84, the abnormal voltage detection signals m1, m2, m3, and m4 are detected. The corresponding detection signal is generated, and the abnormality detection signal m5 is generated from the OR circuit 85. Then, the operation of the oscillator 31A is stopped. Thereby, while the brightness | luminance of the cold cathode tubes 41 and 42 is kept constant, the accident by the voltage of the drive pulses e1 and e2 becoming excessive is prevented.

As mentioned above, although the Example of this invention was described in detail by drawing, a specific structure is not limited to the said Example, Even if there exists a design change etc. of the range which does not deviate from the summary of this invention, it is contained in this invention.

For example, in each said embodiment, although the example which illuminates the two cold cathode tubes 41 and 42 by the cold cathode tube lighting apparatus was shown, even when many more cold cathode tubes are lit, it respond | corresponds to the number of cold cathode tubes. By setting it as a structure, the action and effect similar to each said Example can be acquired. For example, as shown in Fig. 9, when the three cold cathode tubes 41, 42 and 91 are turned on, the coils 92 and 93 are added to detect the voltages va and vb. By performing the same control as in the example, almost the same action and effect can be obtained. As shown in Fig. 10, when the four cold cathode tubes 41, 42, 91 and 94 are turned on, coils 95 and 96 are added to detect the voltages vc and vd. By performing the same control as in the example, almost the same action and effect can be obtained.

In each of the above embodiments, the transformers 35 and 36 have primary sides 35a and 36a and secondary sides 35b and 36b, respectively, but as shown in FIG. It is good also as a structure which made the vehicle side 100a common, and provided the secondary side 100b, 100c inductively coupling with the primary side 100a. When this transformer 100 is used, the resonant capacitor 37 and the coil 39 are connected to the secondary side 100b, and the resonant capacitor 38 and the coil 40 are connected to the secondary side 100c. . In addition, a transformer driving circuit is connected to the primary side 100a. In this case, since only one transformer driving circuit is required, the number of components can be reduced as compared with the two transformer driving circuits 33 and 34 used in the above embodiments.

Instead of the coils 39 and 40 and the voltage detectors 43 and 44 in FIG. 4 showing the second embodiment, the coils 39A and 40A and the voltage detector in FIG. 5 showing the third embodiment. You may make it the structure which provided 43A, 44A. Similarly, instead of the coils 39 and 40 and the voltage detectors 43 and 44 in FIG. 6 showing the fourth embodiment, the coils 39A and 40A and the voltage detectors 43A and 44A in FIG. 5 are provided. It is good also as a structure. In addition to the adder 47 shown in Figs. 4, 5 or 6, the adder 47A shown in Fig. 7 showing the fifth embodiment, the backlight temperature detector 71 and the voltage converter 72 are provided. It is good also as a structure.

Instead of the oscillator 31 shown in FIGS. 1, 5, or 7, the oscillator 31A, the voltage detectors 81, 82, 83, 84, and the OR circuit of FIG. 8 showing the sixth embodiment are shown. 85) may be provided. In this case, the voltage detectors 81, 82, 83, 84, and the OR circuit 85, the voltage detectors 43, 44, the dividers 45, 46, the adder 47, and the DUTY controller 32 in FIG. 1. ) May be configured as an integrated circuit of one chip. Further, the voltage detectors 81, 82, 83, 84, the OR circuit 85, the voltage detectors 43A, 44A, the dividers 45, 46, the adder 47, and the DUTY controller 32 in FIG. Or an integrated circuit of one chip. The voltage detectors 81, 82, 83, 84, the OR circuit 85, the voltage detectors 43, 44, dividers 45, 46, the adder 47A, the DUTY controller 32, The backlight temperature detector 71 and the voltage converter 72 may be configured as a single chip integrated circuit.

In addition, the voltage detectors 81, 82, 83, 84 and the OR circuit 85 are provided in the cold cathode tube lighting device shown in FIG. 4, and the voltage controlled oscillator 49 in FIG. The operation may be stopped by the abnormality detection signal m5 from. In this case, the voltage detectors 81, 82, 83, 84, the OR circuit 85, the voltage detectors 43, 44, dividers 45A, 46A, the adder 47, and the delay circuit 48 in FIG. The voltage controlled oscillator 49, the frequency detector 50, and the multiplier 51 may be configured as an integrated chip of one chip. In addition, the voltage detectors 81, 82, 83, 84 and the OR circuit 85 are provided in the cold cathode tube lighting device shown in FIG. 6, and the oscillator 62 in FIG. The operation may be stopped by the abnormality detection signal m5. In this case, the voltage detectors 81, 82, 83, 84, the OR circuit 85, the voltage detectors 43, 44, dividers 45, 46, the adder 47, the integrator 61, The oscillator 62, the comparator 63, and the switch 64 may be configured as an integrated circuit of one chip.

In each of the above embodiments, a coil is used as the ballast element. However, except in the third embodiment, even when a capacitor is used, the same effects and effects as in the above embodiments can be obtained. In this case, however, more expensive driving pulses e1 and e2 are required.

INDUSTRIAL APPLICABILITY The present invention can be applied to an overall cold cathode tube lighting apparatus driven by an inverter with respect to input terminals on both sides of a plurality of cold cathode tubes used for a backlight of a liquid crystal display device.

According to the configuration of the present invention, the tube current control means detects the tube current flowing through each cold cathode tube based on the current flowing through each ballast element, and the tube current is controlled to a predetermined value, so that the luminance of each cold cathode tube is controlled. I can make it constant.

Further, the tube current control means detects each current flowing through the ballast elements on each side of the plurality of cold cathode tubes, obtains the tube current based on the addition value of the respective currents, and sets the tube current to a predetermined value. Since the duty of each drive pulse is set for the inverter, the luminance of each cold cathode tube can be made constant.

In addition, the tube current control means detects each current flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtains the tube current based on the addition value of the same current, and makes the tube current be a predetermined value. Since the frequency of each drive pulse is set with respect to, the luminance of each cold cathode tube can be made constant.

In addition, the tube current control means detects each current flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtains the tube current based on the addition value of the respective currents, and the self-powered inverter so that the tube current becomes a predetermined value. Since the time width for outputting the respective driving pulses is controlled with respect to, the luminance of each cold cathode tube can be made constant. In addition, since the current which flows into each coil as a ballast element is detected by the tube current control means based on the voltage which generate | occur | produces in each pressure reduction coil, the said tube current control means can be comprised using the component of a low voltage specification. In addition, since the tube current control means detects the tube current flowing through each cold cathode tube based on the temperature of the cold cathode tube detected by each current flowing through each ballast element and the temperature detecting means, and the tube current is controlled to a predetermined value. It is possible to make the luminance of each cold cathode tube constant.

In addition, the voltage monitoring means detects the voltage of each drive pulse applied to each input terminal of each cold cathode tube and stops the operation of each inverter when an abnormality occurs in the voltage of at least one drive pulse. While the luminance of the cathode tube can be made constant, an accident due to excessive voltage of the driving pulse can be prevented.

Claims (31)

The driving pulses output from the inverters are applied to the input terminals on both sides of the plurality of cold cathode tubes by applying them in reverse phase to each other through the respective ballast elements for equalizing the tube currents of the cold cathode tubes, respectively, and flowing through the respective ballast elements. In the cold cathode tube lighting device provided with the tube current control means which detects the tube current which flows through each said cold cathode tube based on an electric current, and controls the said tube current to a predetermined value, The inverter is composed of the first and second type inverters, The tube current control means, Detecting respective currents flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtaining the tube currents based on the added values of the respective currents, and for the respective inverters such that the tube currents are the predetermined values. A cold cathode tube lighting device, characterized in that it is configured to set the duty of each driving pulse. The method of claim 1, Each ballast element is composed of a coil, First and second pressure reducing coils are provided which are inductively coupled to each of the coils provided at input terminals on both sides of one of the plurality of cold cathode tubes to generate a voltage lower than the voltage at both ends of the respective coils. Also, The tube current control means, A cold cathode tube lighting device, characterized in that it is configured to detect a current flowing in each of the coils based on a voltage generated in each of the reducing coils. The method of claim 1, Temperature detection means for detecting the temperature of each said cold cathode tube is provided, The tube current control means, The tube current flowing through each said cold cathode tube is detected based on each electric current which flows into each said ballast element, and the temperature of the said cold cathode tube detected by the said temperature detection means, The said tube current is controlled to a predetermined value, It is characterized by the above-mentioned. Cold cathode tube lighting device. The method of claim 1, Voltage monitoring means for detecting a voltage of each driving pulse applied to each input terminal of each cold cathode tube and stopping the operation of each inverter when an abnormality occurs in the voltage of at least one driving pulse; Cold cathode tube lighting device. The method of claim 3, wherein Voltage monitoring means for detecting a voltage of each driving pulse applied to each input terminal of each cold cathode tube and stopping the operation of each inverter when an abnormality occurs in the voltage of at least one driving pulse; Cold cathode tube lighting device. The method of claim 1, And said tube current control means comprises an integrated circuit of a one-chip configuration. The method of claim 3, wherein And said temperature detecting means and said tube current control means are integrated circuits integrated in one chip. The method of claim 4, wherein And the tube current control means and the voltage monitoring means are integrated circuits integrated in one chip. The method of claim 5, And said temperature detecting means, said tube current controlling means and said voltage monitoring means are integrated circuits integrated in one chip. The driving pulses output from the inverters are applied to the input terminals on both sides of the plurality of cold cathode tubes by applying them in reverse phase to each other through the respective ballast elements for equalizing the tube currents of the cold cathode tubes, respectively, and flowing through the respective ballast elements. In the cold cathode tube lighting device provided with the tube current control means which detects the tube current which flows through each said cold cathode tube based on an electric current, and controls the said tube current to a predetermined value, Each said inverter is comprised with the 1st and 2nd type inverter, The tube current control means, Detecting respective currents flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtaining the tube currents based on the added values of the respective currents, and for the respective inverters such that the tube currents are the predetermined values. A cold cathode tube lighting device, characterized in that it is configured to set the frequency of each drive pulse. The method of claim 10, Each ballast element is composed of a coil, First and second pressure reducing coils are provided which are inductively coupled to each of the coils provided at input terminals on both sides of one of the plurality of cold cathode tubes to generate a voltage lower than the voltage at both ends of the respective coils. Also, The tube current control means, A cold cathode tube lighting device, characterized in that it is configured to detect a current flowing in each of the coils based on a voltage generated in each of the reducing coils. The method of claim 10, Temperature detection means for detecting the temperature of each said cold cathode tube is provided, The tube current control means, The tube current flowing through each said cold cathode tube is detected based on each electric current which flows into each said ballast element, and the temperature of the said cold cathode tube detected by the said temperature detection means, The said tube current is controlled to a predetermined value, It is characterized by the above-mentioned. Cold cathode tube lighting device. The method of claim 10, Voltage monitoring means for detecting a voltage of each driving pulse applied to each input terminal of each cold cathode tube and stopping the operation of each inverter when an abnormality occurs in the voltage of at least one driving pulse; Cold cathode tube lighting device. The method of claim 12, Voltage monitoring means for detecting a voltage of each driving pulse applied to each input terminal of each cold cathode tube and stopping the operation of each inverter when an abnormality occurs in the voltage of at least one driving pulse; Cold cathode tube lighting device. The method of claim 10, And said tube current control means comprises an integrated circuit of a one-chip configuration. The method of claim 12, And said temperature detecting means and said tube current control means are integrated circuits integrated in one chip. The method of claim 13, And the tube current control means and the voltage monitoring means are integrated circuits integrated in one chip. The method of claim 14, And said temperature detecting means, said tube current controlling means and said voltage monitoring means are integrated circuits integrated in one chip. The driving pulses output from the inverters are applied to the input terminals on both sides of the plurality of cold cathode tubes by applying them in reverse phase to each other through the respective ballast elements for equalizing the tube currents of the cold cathode tubes, respectively, and flowing through the respective ballast elements. In the cold cathode tube lighting device provided with the tube current control means which detects the tube current which flows through each said cold cathode tube based on an electric current, and controls the said tube current to a predetermined value, Each said inverter is comprised by the 1st and 2nd self-supporting inverter, Moreover, The tube current control means, Detecting respective currents flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtaining the tube currents based on the sum of the respective currents, and for the self-supporting inverters so that the tube currents are the predetermined values. A cold cathode tube lighting device, characterized in that it is configured to control a time width for outputting each driving pulse. The method of claim 19, Each ballast element is composed of a coil, First and second pressure reducing coils are provided which are inductively coupled to each of the coils provided at input terminals on both sides of one of the plurality of cold cathode tubes to generate a voltage lower than the voltage at both ends of the respective coils. Also, The tube current control means, A cold cathode tube lighting device, characterized in that it is configured to detect a current flowing in each of the coils based on a voltage generated in each of the reducing coils. The method of claim 19, Temperature detection means for detecting the temperature of each said cold cathode tube is provided, The tube current control means, The tube current flowing through each said cold cathode tube is detected based on each electric current which flows into each said ballast element, and the temperature of the said cold cathode tube detected by the said temperature detection means, The said tube current is controlled to a predetermined value, It is characterized by the above-mentioned. Cold cathode tube lighting device. The method of claim 19, Voltage monitoring means for detecting a voltage of each driving pulse applied to each input terminal of each cold cathode tube and stopping the operation of each inverter when an abnormality occurs in the voltage of at least one driving pulse; Cold cathode tube lighting device. The method of claim 21, Voltage monitoring means for detecting a voltage of each driving pulse applied to each input terminal of each cold cathode tube and stopping the operation of each inverter when an abnormality occurs in the voltage of at least one driving pulse; Cold cathode tube lighting device. The method of claim 19, And said tube current control means comprises an integrated circuit of a one-chip configuration. The method of claim 21, And said temperature detecting means and said tube current control means are integrated circuits integrated in one chip. The method of claim 22, And the tube current control means and the voltage monitoring means are integrated circuits integrated in one chip. The method of claim 23, wherein And said temperature detecting means, said tube current controlling means and said voltage monitoring means are integrated circuits integrated in one chip. It is used in the cold cathode tube lighting apparatus which applies each driving pulse output from an inverter to the input terminal of each side of a plurality of cold cathode tubes, and applies them in antiphase with each other through each ballast element for equalizing the tube current of each said cold cathode tube. In the tube current detection circuit for detecting the tube current flowing in each of the cold cathode tube on the basis of each current flowing through each ballast element, Each coil constituting each ballast element, Consists of first and second pressure reducing coils which are inductively coupled to each of the coils provided at input terminals on both sides of one of the plurality of cold cathode tubes to generate a voltage lower than the voltage at both ends of the respective coils. A tube current detection circuit, characterized in that. The driving pulses output from the inverter are applied to the input terminals on both sides of the plurality of cold cathode tubes, respectively, in an antiphase to each other through each ballast element for equalizing the tube current of the cold cathode tubes, and the inverter is turned on. And a cold cathode tube lighting device constituted by a second type inverter, detecting tube current flowing through each cold cathode tube based on each current flowing through each ballast element, and controlling the tube current to a predetermined value. In the method, Detecting respective currents flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtaining the tube currents based on the added values of the respective currents, and for the respective inverters such that the tube currents are the predetermined values. A tube current control method characterized by setting the duty of each drive pulse. The driving pulses output from the inverter are applied to the input terminals on both sides of the plurality of cold cathode tubes, respectively, in an antiphase to each other through each ballast element for equalizing the tube current of the cold cathode tubes, and the inverter is turned on. And a cold cathode tube lighting device constituted by a second type inverter, detecting tube current flowing through each cold cathode tube based on each current flowing through each ballast element, and controlling the tube current to a predetermined value. In the method, Detecting respective currents flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtaining the tube currents based on the added values of the respective currents, and for the respective inverters such that the tube currents are the predetermined values. A tube current control method, characterized in that it is configured to set the frequency of each drive pulse. The driving pulses output from the inverter are applied to the input terminals on both sides of the plurality of cold cathode tubes, respectively, in an antiphase to each other through each ballast element for equalizing the tube current of the cold cathode tubes, and the inverter is turned on. And a cold cathode tube lighting device constituted by a second type inverter, detecting tube current flowing through each cold cathode tube based on each current flowing through each ballast element, and controlling the tube current to a predetermined value. In the method, Detecting respective currents flowing through the ballast elements on both sides of the plurality of cold cathode tubes, obtaining the tube currents based on the sum of the respective currents, and for the self-supporting inverters so that the tube currents are the predetermined values. A tube current control method characterized in that it is configured to control the time width for outputting each driving pulse.

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