JP2002110388A - Lighting device of discharge tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lighting device for discharge tube that can stop lighting action of plural discharge lamps when any one of the plural discharge lamps has a failure in the structure wherein the lighting control of plural discharge lamps is made in batch by one lighting circuit. SOLUTION: In the discharge lamp abnormality detecting circuit 51, a voltage (detected voltage) which is the tube current flowing in cold-cathode tubes 7, 8 converted into a direct current voltage is divided in voltage and received by a base of NPN bipolar transistors 28, 29. The transistors 28, 29 are set so that, when the cold-cathode tubes 7, 8 are lighted normally, the transistors work 'on' action and the collector potential becomes 0 V and, when there happens and abnormality, the transistors work deg.ff' action and the collector potential becomes a power source voltage Vcc. Further, NPN bipolar transistors 30, 31 that receive the collector potentials of the transistors 28, 29 into the bases are provided, and when there happens an abnormality in the cold-cathode tube 7 or 8, the collector potential of the transistor 30 or 31 is made 0 V.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge tube lighting device, and more particularly to a protection circuit therefor.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram showing a conventional discharge tube lighting device disclosed in Japanese Patent Application Laid-Open No. 8-335497. As shown in the figure, by applying a DC voltage that causes a predetermined potential difference between the DC voltage input terminal 1 and the GND input terminal 2, the voltage between the high voltage output terminal 3, the tube current output terminal 4 and the high voltage output terminal 5, the tube This is a device for lighting the cold cathode tubes 7 and 8 connected to the current output terminal 6, respectively.

The lighting circuit block 9 includes a P-channel FET
101, flywheel diode 102, choke coil 103, capacitor 104, transformer 105, resonance capacitor 106, N-channel FET 107, and N
A channel FET 108 is provided.

The P-channel FET 101 has one electrode connected to the DC voltage input terminal 1, the other electrode connected to one end of the choke coil 103, and a gate receiving a control signal S10 from the control IC 10. The other end of the choke coil 103 is connected to the center (center tap) of the primary winding (primary side) of the transformer 105.

The flywheel diode 102 has an anode connected to the GND input terminal 2, a cathode connected to the other electrode of the P-channel FET 101, and a capacitor 10.
4 is inserted between the other end of the choke coil 103 and the GND input terminal 2.

The resonance capacitor 106 includes a transformer 105
The one electrode of the N-channel FET 107 is connected to one end of the primary winding of the transformer 105, and the other electrode is connected to the GND input terminal 2. One electrode of the N-channel FET 108 is the transformer 1
05 is connected to the other end of the primary winding, and the other electrode is connected to the GND input terminal 2.

A ballast capacitor 11 outside the lighting circuit block 9 is inserted between one end of the secondary winding (secondary side) of the transformer 105 and the high voltage output terminal 3, and a ballast capacitor 12 is connected to the secondary of the transformer 105. The cold cathode tube 7 is inserted between one end of the winding and the high voltage output terminal 5, the cold cathode tube 7 is inserted between the high voltage output terminal 3 and the tube current output terminal 4, and the cold cathode tube 8 is connected to the high voltage output terminal 5 and the tube current It is inserted between the output terminals 6.

The tube current detecting resistors 13 and 14 are inserted between the other end of the secondary winding of the transformer 105 and the tube current output terminals 4 and 6, respectively, and the anodes of the rectifier diodes 15 and 16 are connected to the transformer 105. The other ends of the secondary windings are commonly connected, and the cathodes are connected to the tube current output terminals 4 and 6, respectively. The other end of the secondary winding of the transformer 105 is connected to the GND input terminal 2.

The anodes of the rectifier diodes 17 and 18 are connected to the tube current output terminals 4 and 6, respectively, and the cathodes are connected to the node N10.

The control IC 10 has a 0V detection circuit (ZVD) 1
09, a flip-flop circuit 110, an arithmetic circuit 111,
Resistor 112, capacitor 113, zener diode 1
14, an arithmetic circuit 115 and a reference waveform generating circuit 116.

The 0 V detection circuit 109 is connected to the center of the primary winding of the transformer 105 and outputs a detection result to the flip-flop circuit 110. Flip-flop circuit 11
“0” indicates that one of the output Q and the inverted output bar Q is “H” and the other is “L” based on the detection result of the 0 V detection circuit 109.
The N-channel FET 107 and the N-channel FET 108 are turned on alternately by alternately switching the operation of

The arithmetic circuit 111 has a negative input connected to the node N10 via a resistor 112, a positive input connected to the cathode of a Zener diode 114, and a capacitor 113 inserted between the output and the negative input.

A resistor 112 is connected to the negative input of the reference waveform generating circuit 1.
A reference waveform such as a triangular wave having a certain period is received from one end of the circuit 16, the output of the arithmetic circuit 111 is received at a positive input, and the output is applied to the gate of the P-channel FET 101 of the lighting circuit block 9. Further, the cathode of the Zener diode 114 and the other end of the reference waveform generating circuit 116 are grounded.

In such a configuration, the input terminal 1 and G
A DC voltage applied so that a predetermined potential difference is set between the ND input terminals 2 is a DC voltage used in a circuit by a step-down DC / DC converter including a P-channel FET 101, a flywheel diode 102, and a choke coil 103. The value is converted to a value, and at the same time, the energy (current) supplied to the center of the primary winding of the transformer 105 is controlled.

In this state, the N-channel FETs 107 and 1 are controlled by the flip-flop circuit 110 of the control IC 10.
When one of 08 is turned on and the other is turned off, oscillation is started by the inductance of the primary winding of the transformer 105 and the resonance capacitor 106, and the voltage waveform across the capacitor 104 becomes a sine wave.

The flip-flop circuit 11 of the control IC 10
The 0 switches the output Q and the inverted output bar Q between "H" and "L" based on the detection result of the 0V detection circuit 109, thereby switching the N-channel FETs 107 and 108 alternately to maintain oscillation.

When the primary winding of the transformer 105 oscillates, an alternating voltage is generated in the secondary winding to a level at which the cold-cathode tube can be discharged according to the turns ratio of the transformer winding.
Ballast capacitors 11 and 12 for stably discharging the cold cathode tubes 7 and 8 are provided at one end (on the high voltage output terminals 3 and 5 side) of the cold cathode tubes 7 and 8 and are generated in the secondary winding of the transformer. The cold cathode tubes 7 and 8 are turned on by the high AC voltage.

When the cold-cathode tubes 7 and 8 are turned on, an AC voltage proportional to the tube current is generated at both ends of the tube current detecting resistors 13 and 14, and rectifying diodes 15 connected to the respective tube current detecting resistors. , 16 convert only the positive side from the 0V potential to a half-wave rectified waveform.

The half-wave rectified waveform voltages generated by the rectifier diodes 15 and 16 are compared by the rectifier diodes 17 and 18 connected by OR, and only the higher voltage is input to the control IC 10 via the node N10. You. This waveform is converted into a DC voltage level by an arithmetic circuit 111 inside the control IC 10, and is subjected to a comparison arithmetic processing with respect to a reference waveform by an arithmetic circuit 115.
P-channel FE is applied to the gate of T101.
The operation ratio of T101 is controlled.

As described above, the conventional discharge tube lighting device shown in FIG. 7 controls the lighting of two discharge tubes (cold cathode tubes 7, 8) by a set of lighting circuits (lighting circuit blocks 9, 10). Can only be done by

[0021]

In the conventional discharge tube lighting device, the tube current is detected and rectified from the cold cathode tubes 7 and 8 connected in parallel between both ends of the secondary winding of the transformer 105 as described above. The configuration is a logical sum connection using the diodes 17 and 18.

Therefore, the cold cathode tubes 7, 8 connected in parallel
Of the cold cathode tube, short circuit between the ballast capacitor output side and the ground, etc. A voltage is generated in N10.
As a result, the influence of the cold cathode tube in which the failure occurred
Since it does not appear as 0, there is a problem that the lighting circuit block 9 continues to operate under the control of the control IC 10 and short-circuit causes electrical stress on components on the primary winding side of the transformer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a configuration in which lighting control of a plurality of discharge tubes is collectively performed by one lighting circuit. An object of the present invention is to provide a discharge tube lighting device capable of stopping the lighting operation of a plurality of discharge tubes when it occurs.

[0024]

Means for Solving the Problems Claim 1 according to the present invention.
The discharge tube lighting device according to the aspect of the invention includes a plurality of discharge tubes, a lighting circuit unit configured to perform a lighting operation of lighting the plurality of discharge tubes collectively using a transformer, and a plurality of tubes flowing through each of the plurality of discharge tubes. A discharge tube lighting protection unit that determines whether each of the plurality of discharge tubes is normal or abnormal based on the current, and forcibly stops the lighting operation by the lighting circuit unit when any of the plurality of discharge tubes is detected as abnormal; It has.

According to a second aspect of the present invention, in the discharge tube lighting device according to the first aspect, the discharge tube lighting protection unit converts the plurality of tube currents into a plurality of detection voltages. Means for determining whether each of the plurality of discharge tubes is normal or abnormal based on the plurality of detected voltages, and outputting a discharge tube abnormality detection signal indicating an abnormal state when any of the plurality of discharge tubes is detected as abnormal. A discharge tube abnormality detection unit, and a lighting circuit control unit that receives the discharge tube abnormality detection signal and forcibly stops the lighting operation by the lighting circuit unit when the discharge tube abnormality detection signal indicates an abnormal state. Including.

According to a third aspect of the present invention, in the discharge tube lighting device according to the second aspect, the lighting circuit control unit receives the plurality of detected voltages as a feedback voltage, and performs the lighting based on the feedback voltage. The discharge tube abnormality detection unit has a function of controlling the operation content of the lighting operation by a circuit unit, and when the discharge tube abnormality detection unit detects any abnormality of the plurality of discharge tubes, sets the feedback voltage to a level that indicates an abnormal state, The discharge tube abnormality detection signal includes the feedback voltage.

According to a fourth aspect of the present invention, there is provided the discharge tube lighting device according to the second or third aspect, wherein the discharge tube abnormality detecting section has a switching element, and any one of the plurality of discharge tubes. When the abnormality is detected, the switching element is turned on to set the abnormality detection signal to a predetermined level indicating the abnormal state.

The invention according to claim 5 is the discharge tube lighting device according to claim 4, wherein the switching element includes a thyristor.

According to a sixth aspect of the present invention, in the discharge tube lighting device according to the second aspect, the lighting circuit section performs the lighting operation under the control of the lighting circuit control section, and controls the lighting circuit control. When released from the control of the unit, the execution of the lighting operation is stopped, and the lighting circuit control unit stops its operation when the abnormality detection signal indicates an abnormal state.

[0030]

<First Embodiment> FIG. 1 is a circuit diagram showing a configuration of a discharge tube lighting device according to a first embodiment of the present invention. The lighting circuit block 42 is a P-channel FET
101, flywheel diode 102, choke coil 103, transformer 105, resonance capacitor 10
6, resistors 117 and 118, and NPN bipolar transistors 119 and 120.

The P-channel FET 101 is of an enhancement type. One electrode of the P-channel FET 101 is connected to the DC voltage input terminal 1, the other electrode is connected to one end of the choke coil 103, and the control signal S43 from the chopper output of the control IC 43 is connected to the gate electrode. Receive. The other end of choke coil 103 is connected to the center of the primary winding of transformer 105.

The flywheel diode 102 has an anode connected to the GND input terminal 2 and a cathode connected to the other electrode of the P-channel FET 101. The primary winding of the transformer 105 is connected to the first region 71, which is
The second region 72 is smaller than the region 71. The black circles provided on the primary winding and the secondary winding of the transformer 105 in FIG. 1 indicate the start of winding of the winding, and determine the direction of the magnetic field generated by the coil (winding).

The resonance capacitor 106 includes a transformer 105
Is inserted between one end and the other end of the first region 71 of the primary winding. NPN bipolar transistor 119 and NPN
The bipolar transistors 120 have their emitters connected in common. The emitter of the NPN bipolar transistor 119 is connected to the GND input terminal 2, the collector is connected to the other end of the first region 71 of the primary winding of the transformer 105, and the base is connected via the resistor 118 to the choke coil 103.
Is connected to the other end. NPN bipolar transistor 1
The emitter 20 is connected to the GND input terminal 2, the collector is connected to one end of the first region 71 of the primary winding of the transformer 105, and the base is connected to the other end of the choke coil 103 via the resistor 117.

A resistor 117 is interposed between the other end of the choke coil 103 and one end of the second region 72 of the primary winding of the transformer 105. A resistor 118 is connected between the other end of the choke coil 103 and the primary winding of the transformer 105. And the other end of the second region 72.

The ballast capacitor 11 outside the lighting circuit block 42 is inserted between one end of the secondary winding of the transformer 105 and the high-voltage output terminal 3, and
Is inserted between one end of the secondary winding of the transformer 105 and the high voltage output terminal 5, the cold cathode tube 7 is inserted between the high voltage output terminal 3 and the tube current output terminal 4, and the cold cathode tube 8 is It is inserted between the output terminal 5 and the tube current output terminal 6. The other end of the secondary winding of the transformer 105 is grounded. The tube current output terminals 4 and 6 are grounded via rectifying capacitors 19 and 20.

The tube current detecting resistors 13 and 14 are interposed between the other end of the secondary winding of the transformer 105 and the tube current output terminals 4 and 6, respectively. The other ends of the secondary windings are commonly connected, and the cathodes are connected to the tube current output terminals 4 and 6, respectively.

The anodes of the rectifier diodes 17 and 18 are connected to the tube current output terminals 4 and 6, respectively, and the cathodes are commonly connected to the node N10. The node N10 is connected to the discharge tube abnormality detection circuit 51 via the resistor 47, and is grounded via the rectifying capacitor 21.

The discharge tube abnormality detecting circuit 51 includes resistors 22 to 2
7. NPN bipolar transistors 28-31. The resistors 22 and 23 are connected in series between the tube current output terminal 6 and the ground, and the resistors 24 and 25 are connected in series between the tube current output terminal 4 and the ground.

The NPN bipolar transistor 28 has a collector connected to the power supply voltage Vcc via the resistor 27, an emitter grounded, and a base connected to the node N between the resistors 24 and 25.
Connected to 1. The NPN bipolar transistor 29 has a collector connected to the power supply voltage Vcc via the resistor 26,
The emitter is grounded, and the base is connected to node N2 between resistors 22 and 23.

The collector of NPN bipolar transistor 30 is connected to node N 3, which is the other end of resistor 47, the emitter is grounded, and the base is connected to the collector of NPN bipolar transistor 28. The collector of NPN bipolar transistor 31 is connected to node N3, the emitter is grounded, and the base is connected to the collector of NPN bipolar transistor 29.

The feedback (F / B) input of the control IC 43, which is the main part of the discharge tube lighting circuit control block 35, is connected to the node N3 of the discharge tube abnormality detection circuit 51 via the resistor 32.
, And grounded via a resistor 33, and a dimming input receives a dimming signal SD for changing luminance through an input terminal. The control IC 43 is electrically connected to a driving power supply 48 and a ground level.

FIG. 2 is a circuit diagram showing the internal configuration of the control IC 43. As shown in the figure, the arithmetic circuit 61 amplifies the potential difference between the signals obtained from the feedback input (positive input) and the dimming input (negative input), and outputs an amplified signal S61 to the comparator 62 and the arithmetic circuit 65.

The comparator 62 compares the amplified signal S61 from the arithmetic circuit 61 with a reference voltage VR (about half of the power supply voltage inside the control IC 43) and outputs the amplified signal S61.
The comparison result S62 based on the comparison result between
Is output, and when the cycle exceeds an arbitrarily set cycle as the latch data of the latch circuit 63, the data is latched. That is,
The comparison result S62 becomes “H” when S61> VR, and S
It becomes "L" when 61 <VR. Further, the latch circuit 6
Reference numeral 3 outputs an inverted output signal S63 obtained by inverting the comparison result S62.

When the inverted output signal S63 is "L" (the comparison result S62 is "H"), the arithmetic circuit 65 outputs the amplified signal S
61 and a reference waveform obtained from the reference waveform generating circuit 66 to output a control signal S43, and output an inverted output signal S63.
Is "H" (the comparison result S62 is "L"), a control signal S43 at a level for turning off the P-channel FET 101 is output. Although not shown in FIG. 2, the arithmetic circuit 61, the comparator 62, the latch circuit 63, and the arithmetic circuit 65 are electrically connected to the driving power supply 48 and the ground level, respectively.

That is, the control IC 43 outputs the amplified signal S6
When 1 is equal to or higher than the reference voltage VR, the control signal S, which is a chopper output, is obtained based on a comparison result between the dimming signal SD received at the dimming input and the voltage Va received at the feedback input.
43 is the P-channel FET 101 of the lighting circuit block 42
When the amplified signal S61 is equal to or lower than the reference voltage VR, a control signal S43 having a level for forcibly turning off the P-channel FET 101 is output.

When the voltage Va serving as the feedback input of the control IC 43 is at the GND level, the potential difference between the dimming signal SD of about 0.5 to 1.25 V and the feedback input occurs at a negative level. The amplified signal S61 always has a negative level and becomes equal to or lower than the reference voltage VR, the comparison result S62 becomes "L", the inverted output signal S63 becomes "H", and the arithmetic circuit 65 outputs a P-channel FET.
A control signal S43 at a level for forcibly turning off the signal 101 is output.

On the other hand, in a normal state, the voltage Va as the feedback input is designed to always exceed the dimming signal SD in the cycle in which the latch circuit 63 latches the comparison result S62. Is generated at a positive level, the amplification factor of the arithmetic circuit 61 is set to a predetermined value or more, so that the amplified signal S6
1 always exceeds the reference voltage VR. Therefore, the control signal S43 based on the comparison result between the dimming signal SD and the voltage Va is applied to the gate of the P-channel FET 101 of the lighting circuit block 42 by the arithmetic circuit 65.

The lighting circuit block 42 uses a so-called push-pull type voltage resonance type circuit which is different from the conventional lighting circuit block 9. Transistors 119 and 120
In addition, both ends of the second region 72 of the primary winding are connected to the bases of NPN bipolar transistors 119 and 120 in consideration of the phase as shown in FIG. By constructing the feedback, the NPN bipolar transistor 119 for oscillation can be used.
And 120 are alternately turned on / off, oscillation is started by the inductance of the primary winding of the transformer 105 and the resonance capacitor 106, and the voltage waveform across the resonance capacitor 106 is sinusoidal.

When the primary winding of the transformer 105 oscillates, an AC voltage is generated in the secondary winding to a level at which the cold-cathode tube can be discharged according to the turns ratio of the transformer winding.
Ballast capacitors 11 and 12 for stably discharging the cold cathode tubes 7 and 8 are provided at one end (on the high voltage output terminals 3 and 5 side) of the cold cathode tubes 7 and 8 and are generated in the secondary winding of the transformer. The cold cathode tubes 7 and 8 are turned on by the high AC voltage.
Thus, the lighting circuit block 42 performs the lighting operation of the cold cathode tubes 7 and 8.

The secondary winding of the transformer 105 has ballast capacitors 11 and 12, cold cathode tubes 7 and 8, tube current detecting resistors 13 and 14, and rectifier diodes 15, 16, 17 and 18.
Are connected in the same manner as in the conventional configuration shown in FIG. 7, and the currents flowing through the cold-cathode tubes 7, 8 are converted into voltages by the tube current detecting resistors 13, 14, and this voltage is converted into a rectifying capacitor 1.
According to 9 and 20, it is converted into a DC voltage waveform. Rectifier diodes 17, 1 that are OR-connected voltages converted to DC voltage
8, the one with the larger voltage is the node N10 and the resistor 47
The voltage Va is applied as a voltage Va to the feedback input of the control IC 43 via the resistor 32, and the control IC 43 controls the switching operation of the FET 101 by using the voltage Va to control the operation content of the lighting operation of the lighting circuit block 42.

In parallel with the above-described operation, the discharge tube abnormality detection operation by the discharge tube abnormality detection circuit 51 is performed as follows. The discharge tube abnormality detection circuit 51 converts voltages (detection voltages) obtained by converting the tube currents flowing through the cold cathode tubes 7 and 8 into DC voltages by the tube current detecting resistors 13 and 14 and the rectifying capacitors 19 and 20, respectively. Received via output terminals 4 and 6. Then, the discharge tube abnormality detection circuit 51
Voltages V1 and V2 obtained from nodes N1 and N2 by voltage division by resistance division by resistors 4, 25 and resistors 22, 23 are applied to the bases of NPN bipolar transistors 28 and 29, respectively.

If the voltages V1 and V2 are set to 0.6 V or more when the cold cathode tubes 7, 8 are normally lit, the cold cathode tubes 7, 8 are normally lit. , NP
The N bipolar transistors 28 and 29 are turned on, and the collector potentials of the transistors 28 and 29 become 0 V (GND level). On the other hand, if the CCFLs 7 and 8 are abnormal due to some trouble, the NPN bipolar transistor 2
8 and 29 are turned off, and the collector potentials of the transistors 28 and 29 become the power supply voltage Vcc. That is, by turning on / off the NPN bipolar transistors 28 and 29,
It is possible to determine whether the cold cathode tubes 7 and 8 are normal or abnormal.

Therefore, when both the cold cathode tubes 7 and 8 are normally lit, the NPN bipolar transistor 30
And 31 are both turned off. If at least one of the cold cathode tubes 7 and 8 is abnormal, the NPN bipolar transistor 3 is turned off.
At least one of 0 and 31 is turned on.

The control IC 43 includes a discharge tube abnormality detection circuit 51
In the normal state where no abnormality is detected, the control signal S43 is output based on the comparison result between the voltage Va and the dimming signal SD, and the lighting circuit block 42 performs feedback control of the lighting operation. That is, the voltage Va functions as a feedback voltage for controlling the lighting operation of the lighting circuit block 42.

Here, consider a case where an abnormality occurs in which the tube current does not flow only through the cold cathode tube 7. In this case, the tube current flowing through the normally-lit cold-cathode tube 8 is converted into a voltage by the tube current detection resistor 14, the rectifier diode 16, and the rectifier capacitor 20.

However, since no tube current flows through the cold cathode fluorescent lamp 7, no voltage is applied to the base of the NPN bipolar transistor 28, the transistor 28 is turned off, and the power supply voltage Vcc is generated at the collector of the transistor 28. As a result, the power supply voltage Vcc generated at the collector of the NPN bipolar transistor 28 is applied to the base of the NPN bipolar transistor 30, the transistor 30 is turned on, and the voltage Va input to the feedback input of the control IC 43 is applied via the node N3. Forced to GND level.

Here, the control IC 43 compares the dimming signal SD with the voltage Va in a normal state to calculate the P-channel FE.
T101 is controlled. When the input voltage Va becomes the GND level, the amplified signal S61 is controlled as described above.
Becomes lower than the reference voltage VR (recognition at the time of abnormality).
C43 outputs a control signal S43 at a level for forcibly turning off the P-channel FET 101, and the lighting circuit block 4
2 to stop the lighting operation. That is, the voltage Va functions as an abnormality detection signal, and the GND level becomes a signal level indicating an abnormal state.

Therefore, since the P-channel FET 101 is forcibly turned off, no current is supplied to the push-pull type voltage resonance type circuit, and the push-pull type voltage resonance type circuit stops oscillation. That is, since the lighting operation is stopped, the cold cathode tubes 7 and 8 are turned off.

In the conventional configuration shown in FIG.
In this configuration, rectifier diodes for detecting tube currents from two cold-cathode tubes connected in parallel to the secondary winding No. 5 are OR-connected.

For this reason, one of the cold-cathode tubes connected in parallel may be damaged by the cold-cathode tube, or may be short-circuited between the ballast capacitor output side and the ground, and may be subjected to the electrical stress of the transformer primary winding part due to the short-circuit. However, even if a failure occurs in the circuit, a voltage obtained by converting the tube current of the cold-cathode tube, in which the other failure does not occur, into a voltage is input to the control IC 43, so that the discharge tube lighting circuit continues the lighting operation. There is a risk that the malfunction will increase.

On the other hand, the discharge tube lighting device of the first embodiment
If at least one of the two cold cathode tubes 7 and 8 connected in parallel to the secondary winding of the transformer 105 has a failure, the discharge tube abnormality detection circuit 51 forcibly sets the potential of the node N3 to GND, When the control IC 43 stops the lighting control operation, the cold cathode tubes 7 and 8 can be turned off. That is, the discharge tube abnormality detection circuit 51, the control IC
If at least one of the cold-cathode tubes 7 and 8 causes a failure due to the discharge tube lighting protection unit including the tube current detection resistors 43 and 43 and the rectifier capacitors 19 and 20,
The cold cathode tubes 7, 8 can be quickly turned off.

Therefore, as in the conventional configuration, the control IC
In this case, it is possible to prevent a voltage and a current that are higher than normal from flowing continuously for a long time when the control region is exceeded, thereby effectively preventing component deterioration due to component stress and solving the above-described problem. .

<Embodiment 2> FIG. 3 is a circuit diagram showing a configuration of a discharge tube lighting device according to Embodiment 2 of the present invention. As shown in the figure, NPN bipolar transistors 39 and 31 shown in FIG.
To constitute the discharge tube abnormality detection circuit 52.
That is, the drains of the N-channel FETs 37 and 38 are commonly connected to the node N3, the sources are commonly grounded, and the gates are connected to the collectors of the NPN bipolar transistors 28 and 29, respectively.

The other structure is the same as that of the first embodiment shown in FIG. Even when the discharge tube lighting device is configured as in the second embodiment shown in FIG. 3, the same effect as in the first embodiment can be obtained.

<Third Embodiment> FIG. 4 is a circuit diagram showing a configuration of a discharge tube lighting device according to a third embodiment of the present invention. As shown in the figure, a discharge tube abnormality detection circuit 53 is configured by replacing the NPN bipolar transistors 39 and 31 shown in FIG. That is, the anodes of the thyristors 39 and 40 are commonly connected to the node N3, the cathodes are commonly grounded, and the gates are connected to the collectors of the PN bipolar transistors 28 and 29, respectively. Other configurations are the same as those of the first embodiment shown in FIG. Even with the configuration as in the third embodiment, the same effect as in the first embodiment can be obtained.

In the discharge tube lighting device of the third embodiment, when at least one of the cold-cathode tubes 7 and 8 has a problem, the thyristor 39 or the thyristor 40 is in a conductive state. When the control IC 43 stops the lighting control operation, the cold cathode tubes 7 and 8 can be turned off.

The thyristors 39, 40 latch once they become conductive (the operation is continued) and maintain the conductive state until the power is turned on again. In this respect, the discharge tube lighting device according to the third embodiment is superior to the first embodiment in that the problem of relighting by mistake can be avoided.

<Fourth Embodiment> FIG. 5 is a circuit diagram showing a configuration of a discharge tube lighting device according to a fourth embodiment of the present invention. As shown in the drawing, the NPN bipolar transistors 39 and 31 shown in FIG. 1 are replaced by diodes 45 and 46 to constitute a discharge tube abnormality detection circuit 54, and a discharge tube lighting circuit control block 35 includes a SW (switch). 44 are added.

That is, the driving power supply 48 of the control IC 43
Are connected to the control IC 43 via the SW (switch) 44, the anodes of the diodes 45 and 46 are connected to the collectors of the NPN bipolar transistors 28 and 29, respectively, and the cathodes are commonly connected to the node N4 (OR connection).
Is done. Then, the abnormality detection signal S54 obtained from the node N4 is applied to the control input C of the SW44. SW44
Turns off when the abnormality detection signal S54 is "H",
It turns on when it is "L".

In the discharge tube lighting device according to the fourth embodiment, when at least one of the cold cathode tubes 7 and 8 has a problem, the diode 45 or the diode 46 is turned on, and the diode 45 or the diode 46 is supplied to the control input C of the SW 44. Abnormality detection signal S
Since the signal 54 goes to the “H” level, the SW 44 is turned off. As a result, the driving power supply 48 is not supplied to the control IC 43, and the control IC 43 stops its control operation and releases the lighting circuit block 42 from the control of the control IC 43.

On the other hand, since the P-channel FET 101 of the lighting circuit block 42 is of the enhancement type, the P-channel FET 101 is in the off state under the release state under the control of the control IC 43 to which the control signal S43 is not output. Therefore, since the lighting operation by the lighting circuit block 42 is stopped, the cold cathode tubes 7 and 8 can be turned off.

<Fifth Embodiment> FIG. 5 is a circuit diagram showing a configuration of a discharge tube lighting device according to a fifth embodiment of the present invention. As shown in the drawing, the NPN bipolar transistors 30 and 31 shown in FIG. 1 are removed to form a discharge tube abnormality detection circuit 55, and a SW (switch) 44 is added in the discharge tube lighting circuit control block 35. And a microcomputer 41 are further added.

That is, the driving power supply 48 of the control IC 43
Are connected to the control IC 43 via the SW (switch) 44, and the microcomputer 41 is connected to the NPN bipolar transistor 2
The potentials obtained from the collectors 8 and 29 are determined by the abnormality detection signal S.
55a and S55b.

The microcomputer 41 determines whether the abnormality detection signals S55a, S55
When at least one of the potentials 55b becomes the power supply voltage Vcc, the control signal C of "H" is input to the control input C of the SW 44.
41, and outputs an "L" control signal S41 to the control input C of the SW 44 at other times.

In the discharge tube lighting device according to the fifth embodiment, when a failure occurs in at least one of the cold cathode tubes 7 and 8, N
An abnormality detection signal S55a or S55 which is the collector potential of the PN bipolar transistor 28 or 29.
When b becomes the power supply voltage Vcc, the microcomputer 41 outputs the control signal S41 of “H” to the control input C of the SW 44, so that the SW 44 is turned off. As a result, the cold cathode tubes 7 and 8 can be turned off in the same manner as in the fourth embodiment.

<Others> In the first to fifth embodiments, the case where two discharge lamps are controlled has been described as an example. However, not only two lamps but also three or more discharge tubes may be controlled. Of course, it is applicable. In this case, when a defect occurs in any of the three or more discharge tubes, the defect is detected using any of the methods of Embodiments 1 to 5, and
The discharge tube is configured to be turned off.

[0077]

As described above, in the discharge tube lighting device according to the first aspect of the present invention, the plurality of discharge tubes are protected by the discharge tube lighting protection unit based on the plurality of tube currents flowing through each of the plurality of discharge tubes. Judge each normal / abnormal,
By forcibly stopping the lighting operation of the lighting circuit unit when any abnormality of the plurality of discharge tubes is detected, if an abnormality occurs in at least one of the plurality of discharge tubes, the plurality of discharge tubes can be turned off. .

The discharge tube abnormality detecting section in the discharge tube lighting device according to the second aspect determines whether each of the plurality of discharge tubes is normal or abnormal based on a plurality of detected voltages obtained by current / voltage conversion of a plurality of tube currents. By outputting the discharge tube abnormality detection signal, it is possible to forcibly stop the lighting operation by the lighting circuit unit by the lighting circuit control unit when any of the plurality of discharge tubes is detected as abnormal.

The lighting circuit control unit in the discharge tube lighting device according to claim 3 can control the operation content of the lighting operation by the lighting circuit unit based on the feedback voltage in a normal state in which the feedback voltage does not indicate an abnormal state. .

In the discharge tube lighting device according to the fourth aspect, the discharge tube abnormality detecting section can set the level of the abnormality detection signal by turning on / off the switching element based on the presence or absence of any abnormality in the plurality of discharge tubes. .

In the discharge tube lighting device according to the fifth aspect, once the thyristor is turned on, the thyristor is kept on until the power is turned on again. Can be reliably avoided.

In the discharge tube lighting device according to the sixth aspect, the operation of the lighting circuit control unit is stopped when an abnormality is detected in any of the plurality of discharge tubes, thereby releasing the lighting circuit unit from the control of the lighting circuit control unit. Thus, the plurality of discharge tubes can be turned off.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a discharge tube lighting device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an internal configuration of a control IC of FIG.

FIG. 3 is a circuit diagram showing a configuration of a discharge tube lighting device according to a second embodiment.

FIG. 4 is a circuit diagram showing a configuration of a discharge tube lighting device according to a third embodiment.

FIG. 5 is a circuit diagram showing a configuration of a discharge tube lighting device according to a fourth embodiment.

FIG. 6 is a circuit diagram showing a configuration of a discharge tube lighting device according to a fifth embodiment.

FIG. 7 is a circuit diagram showing a conventional discharge tube lighting device.

[Explanation of symbols]

22 to 27 resistors, 28 to 31 NPN bipolar transistors, 37, 38 N-channel FETs, 39, 40
Thyristor, 41 microcomputer, 43 control IC 43, 4
4 SW (switch), 45, 46 diode, 51
~ 55 Discharge tube abnormality detection circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K072 AA01 AB02 BA03 BA05 BC03 EA02 EB07 GA01 GA02 GB14 GC02 HA02 3K098 CC12 CC40 DD20 DD21 DD35 DD43 EE18 EE37 FF04

Claims (6)

[Claims] A plurality of discharge tubes; a lighting circuit unit for performing a lighting operation of lighting the plurality of discharge tubes collectively by using a transformer; and a plurality of tube currents flowing through each of the plurality of discharge tubes. Determining whether each of the plurality of discharge tubes is normal or abnormal;
A discharge tube lighting device comprising: a discharge tube lighting protection unit for forcibly stopping the lighting operation by the lighting circuit unit when an abnormality is detected in any of the plurality of discharge tubes. 2. The discharge tube lighting device according to claim 1, wherein the discharge tube lighting protection unit includes: a current / voltage conversion unit that converts the plurality of tube currents into a plurality of detection voltages; A discharge tube abnormality detection unit that determines a normal / abnormal state of each of the plurality of discharge tubes based on the voltage, and outputs a discharge tube abnormality detection signal indicating an abnormal state when any abnormality of the plurality of discharge tubes is detected; A lighting circuit control unit for receiving the discharge tube abnormality detection signal and forcibly stopping the lighting operation by the lighting circuit unit when the discharge tube abnormality detection signal indicates an abnormal state. 3. The discharge tube lighting device according to claim 2, wherein the lighting circuit control unit receives the plurality of detection voltages as a feedback voltage, and performs the lighting operation of the lighting circuit unit based on the feedback voltage. The discharge tube abnormality detection unit has a function of controlling an operation content, and the discharge tube abnormality detection unit sets the feedback voltage to a level instructing an abnormal state when any of the plurality of discharge tubes is detected, and the discharge tube abnormality detection signal is Discharge tube lighting device including feedback voltage. 4. The discharge tube lighting device according to claim 2, wherein the discharge tube abnormality detection section has a switching element, and the switching element detects any abnormality of the plurality of discharge tubes. A discharge tube lighting device, wherein the abnormality detection signal is set to a predetermined level indicating an abnormal state by turning on the LED. 5. The discharge tube lighting device according to claim 4, wherein the switching element includes a thyristor. 6. The discharge tube lighting device according to claim 2, wherein the lighting circuit unit performs the lighting operation under the control of the lighting circuit control unit, and is released from the control of the lighting circuit control unit. Then, the lighting circuit control unit stops execution of the lighting operation, and the lighting circuit control unit stops its own operation when the abnormality detection signal indicates an abnormal state.