JPH06203983A - Lighting device for plural discharge lamps - Google Patents

Abstract

PURPOSE:To compensate the dispersion in luminance or difference in deterioration of respective discharge lamps and illuminate the whole surface with uniform brightness. CONSTITUTION:A DC power source DC and a transistor Q1 driven by an inverter controller 1 are connected on the primary side of a transformer T1. A series circuit of a plurality of cold cathode discharge tubes CFL1-CFL3 with transistors Q2-Q4 is connected in parallel on the secondary side of the transformer T1. Monostable multivibrators MS1-MS3 for driving the transistors Q2-Q4 are triggered in the order by the output of a decoder 17. The ON times of MS1-MS3 are set by variable resistors RV1-RV3 according to the luminances of the respective discharge tubes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device for a plurality of discharge lamps, and more particularly to a lighting device for a plurality of discharge lamps used as a light source for a backlight of a liquid crystal (LCD) display device.

[0002]

2. Description of the Related Art In a backlight type LCD display device, a multi-lamp lighting system has come to be adopted as the screen becomes larger, and further, discharge lamps having different lengths according to the aspect ratio of the screen. It has become necessary to consolidate.

FIG. 4 is a circuit diagram of a lighting device used for this type of application. As shown in the figure, in the conventional example,
One end on the primary side of the transformer T1 is connected to the DC power supply DC, and the other end is connected to the collector of the driver transistor Q1 driven by an oscillator (not shown).
Further, a capacitor C is provided at one end of the transformer T1 on the secondary side.
Cold cathode discharge tubes CFL1, CFL via 1, C2, C3
2, CFL3 are connected in parallel, and the other end of the secondary side of the transformer T1 is grounded.

[0004]

In the above-mentioned conventional lighting system, the brightness of the entire discharge lamp can be adjusted by controlling the oscillator that supplies the inverter input, but the brightness of each discharge lamp is individually adjusted. I couldn't do that. Therefore, when there is a variation in the brightness of each discharge lamp, the variation appears on the screen and the display quality is significantly degraded. Further, in the conventional lighting method, since discharge lamps having different lengths cannot be lit in parallel, it is necessary to prepare an oscillator, a driver transistor and a transformer for each discharge lamp. Therefore, it is difficult to respond to downsizing of the device and the device becomes very expensive.

Therefore, the object of the present invention is to
In a method of driving a plurality of discharge lamps in parallel by using a single inverter (power supply), the brightness of each discharge lamp can be adjusted independently. Then, according to the present invention, it is possible to compensate for the variation in the luminance between the discharge lamps, enable the mixed mounting of the discharge lamps having different lengths, and improve the display quality of the display device.

[0006]

In order to achieve the above-mentioned object, the present invention provides a lighting device for a plurality of discharge lamps in which a plurality of discharge lamps are connected in parallel to the output side of the inverter. A plurality of discharge lamps having one end connected, a switching element connected to the other end of each discharge lamp, and at least one open switching element among the switching elements are formed, and the opening is performed. There is provided a lighting device for a plurality of discharge lamps, comprising: a control unit that sequentially closes at least one of the switching elements at a predetermined timing.

[0007]

In the lighting device for a plurality of discharge lamps according to the present invention, the plurality of discharge lamps are driven in a time division manner by one inverter, and the lighting period of each discharge lamp can be adjusted independently for each discharge lamp. I am trying.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a circuit connection diagram showing the principle of the present invention. In the present invention, a plurality of cold cathode discharge tubes CFL
, One end of each of CFL2, CFL3, ... Is connected to the secondary side of the transformer T1, and the other end of each cold cathode discharge tube is connected through a transistor Q2, Q3, Q4 ,. It is grounded. The inverter controller 1 drives the driver transistor Q1 and also drives the transistors Q2, Q3, Q.
4 ... are sequentially turned on (closed) or shut off (opened). This inverter controller 1 makes at least one open switching element among the switching elements, and controls at least one of the open switching elements to be sequentially replaced at a predetermined timing to be closed. However, the internal structure and detailed operation will be described later.

FIG. 2A is a waveform diagram of the voltage VB applied to the bases of the transistors Q2, Q3 and Q4 which are switching elements, and FIG. 2B shows the cold cathode discharge tube CFL1 accordingly. 6 is a waveform diagram of a current IC that flows to CFL3. FIG. The transistors Q2, Q3, Q4 are sequentially closed and controlled by the inverter controller 1. At that time, the length from the conduction start time point S of these transistors to the conduction end time point, that is, the transistor Q2,
The times t2, t3 and t4 when Q3 and Q4 are closed are controlled so that the brightness of the cold cathode discharge tubes connected to them is equal to each other. That is, each transistor is controlled to be turned on for a long time when the brightness of the discharge lamp connected to the transistor is lower than the standard, and to be conducted for a short time when the brightness is higher than the standard. As a result, each discharge lamp can be controlled so as to have a constant brightness regardless of the variation in the original brightness and the length of the dimension.
When this lighting method is applied to, for example, a lighting device of an LCD display device, it is possible to obtain a screen with uniform brightness over the entire screen. Note that these transistors are subjected to conduction / interruption control in a short cycle that cannot be visually recognized by human eyes, and the switching speed thereof is 1/2.
It should be shorter than about 0 seconds.

FIG. 3 is a circuit connection diagram of a discharge lamp lighting device showing an embodiment of the present invention. In the figure, R1 and R
2 is a resistor, C1 and C2 are capacitors, and D1 and D2 are diodes. Further, in the inverter controller 1, 11 is an operational amplifier that monitors the DC voltage obtained by tapping down the output of the transformer T1, compares this value with the output value of the reference voltage source 15, and determines the difference voltage between them. Is output. Reference numeral 14 is a triangular wave oscillator, which generates a triangular wave which is a basis for determining the width of the driver transistor Q1 to be turned on. Reference numeral 15 is a reference voltage source. Reference numeral 12 is a comparator, which is an inverter controller 1
The abnormal voltage is not applied to the case of and its potential is "0".
Then, the triangular wave oscillated from the triangular wave oscillator 14 that exceeds the threshold value output from the operational amplifier 11 is passed.
That is, the lower the potential at the point e for monitoring the output voltage of the transformer T1 is than the voltage of the reference voltage source 15, the larger the width of the triangular wave to be passed. 13 is a reference voltage source 15
Of the triangular wave oscillator 14, that is, the output signal of the comparator 12 is passed, and when the output of the reference voltage source 15 is "0", the triangular wave oscillator 1 is generated.
4, a gate circuit for interrupting the output signal of 4, a frequency counter 16 for dividing the output frequency of the gate circuit 13 into 1/10, a decoder 17, MS1, MS2, MS3 for monostable multivibrators, RV1, RV2, RV3 Is a variable resistor for adjusting the on-time of each of the monostable multivibrators.

Next, the circuit operation of the embodiment shown in FIG. 3 will be described. First, assuming that the drive transistor Q1 is repeatedly turned on and off at high speed, the transformer T
On the secondary side of 1, a sine wave according to the on / off of the drive transistor Q1 is induced, and this output is the capacitor C1.
After passing through and rectifying with diode D1, cold cathode discharge tube C
It is applied to one end of FL1, CFL2, CFL3. Then, the signals from the inverter controller 1 sequentially turn on the transistors Q1, Q2 and Q3 to sequentially light these cold cathode discharge tubes.

Here, when the output voltage of the transformer T1 becomes low, the period in which the driver transistor Q1 is turned on becomes long, and it works to increase the output voltage of the transformer T1. Conversely, when the output voltage of the transformer T1 becomes high, the driver The period for turning on the transistor Q1 is shortened to work to lower the output voltage of the transformer T1.

The output signal of the comparator 13 is divided by the frequency counter 16 into a frequency of 1/10. In the monostable multivibrators MS1, MS2, MS3, the count value of the frequency counter 16 is set to 3 in advance.
When the two values are sequentially reached, they are sequentially triggered via the decoder 17. Monostable multivibrator MS
1, MS2, MS3 on time is cold cathode discharge tube CFL
In order to adjust the brightness of CFL1, CFL2, and CFL3, they are independently adjusted by the variable resistors RV1, RV2, and RV3.

In the above-mentioned embodiment, only one cold cathode discharge tube is sequentially turned on, and the brightness of each cold cathode discharge tube is adjusted independently. However, the present invention is not limited to this, and, for example, a transformer. , A plurality of cold cathode discharge tubes are connected in parallel, only one of them is turned off, and the turned off cold cathode discharge tubes are sequentially moved. An example in which such a plurality of cold cathode discharge tubes are divided into a plurality of groups and each group is sequentially turned on is also included. Such a change substantially changes the circuit configuration of the inverter controller 1. It can be realized without.

FIG. 4 is a circuit connection diagram showing a second embodiment of the present invention. In the embodiment described in FIGS. 1 to 3 above, only half-wave current can flow from the transformer T1 to the cold cathode discharge tubes CFL1 to CFL3, and the efficiency is poor.
In this embodiment, full-wave current can be passed through the cold cathode discharge tubes CFL1 to CFL3. That is, the cold cathode discharge tube C
NPN transistor and PN between FL1-CFL3 and ground
A circuit in which a P-transistor is connected in parallel is inserted. From the Q terminal of the monostable multivibrator MS1 to MS3 to N
A signal is applied to the base of the PN transistor, and a signal is applied from the inverted Q terminal to the base of the PNP transistor. In the inverted Q signal, "1" (plus potential) and "0" (0 volt) alternately appear, and the PNP transistor cannot be switching-controlled by this signal. Therefore, a level shifter LV is inserted between the base of the PNP transistor and the inverted Q terminal of the monostable multivibrator, and (-Vb) obtained at the connection point of the diode D2 and the capacitor C2 is applied to the level shifter LV. Then, when the inverted Q signal is "1", -Vb is applied to the base of the PNP transistor. The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In the circuit shown in FIG. 4, when the decoder 17 selects the monostable multivibrator MS1 and applies a trigger pulse to the monostable multivibrator MS1, the Q terminal is "1" at the timing when a current flows in the direction of the arrow on the secondary side of the transformer T1. ",
Cold cathode discharge tube CFL with NPN transistor turned on
1 is turned on, the inverted Q terminal becomes "1" at the timing when a current flows in the direction opposite to the arrow on the secondary side of the transformer T1, the PNP transistor is turned on, and the cold cathode discharge tube CFL1 is turned on again. When a current flows in the reverse direction of the secondary side of the transformer T1, the cold cathode discharge tube lights up. The timing of inverting the Q terminal and the inverted Q terminal of the monostable multivibrator MS1 is adjusted by the variable resistor RV1.

[0017]

As described above, the lighting apparatus for a plurality of discharge lamps according to the present invention has a plurality of discharge lamps connected in parallel to the output of the inverter and sets the lighting start time and the extinction time independently of each other. Since each discharge lamp is lit in a time-division manner as described above, according to the present invention, it is possible to obtain illumination of uniform brightness by compensating for variations in the brightness of each discharge lamp and differences in the degree of deterioration. be able to. Further, since it becomes possible to mount the discharge lamps having different lengths together by preparing only one inverter, it is possible to contribute to downsizing of the device and cost reduction.

[Brief description of drawings]

FIG. 1 is a circuit connection diagram for explaining the principle of the present invention.

FIG. 2 is a voltage and current waveform diagram for explaining the operation of the device of FIG.

FIG. 3 is a circuit connection diagram for explaining an embodiment of the present invention.

FIG. 4 is a circuit connection diagram for explaining a second embodiment of the present invention.

FIG. 5 is a circuit connection diagram of a conventional example.

[Explanation of symbols]

 1 Inverter Controller 11 Operational Amplifier 12 Comparator 13 Gate Circuit 14 Triangular Wave Oscillator 15 Reference Voltage Source 16 Frequency Counter 17 Decoder C1, C2, C3 Capacitor CFL1-CFL3 Cold Cathode Discharge Tube D1, D2 Diode MS1, MS2, MS3 Monostable Multivibrator Q1 Driver Transistors Q2-Q4 Control transistors R1, R2 Resistances RV1, RV2, RV3 Variable resistors

Claims (4)

[Claims] 1. A lighting device for a plurality of discharge lamps, wherein a plurality of discharge lamps are connected in parallel to the output side of an inverter, wherein a plurality of discharge lamps each having one end connected to the output side of said inverter, and each of said discharge lamps are provided. A switching element connected to the other end of the switching element and at least one of the switching elements that are opened, and at least one of the opened switching elements is sequentially replaced at a predetermined timing. A lighting device for a plurality of discharge lamps, comprising: a control means for closing. 2. The lighting device for a plurality of discharge lamps according to claim 1, wherein the time taken for each of the closed switching elements to open and close is shorter than at least 1/20 second. 3. The lighting device for a plurality of discharge lamps according to claim 1 or 2, wherein there is only one switching element that is closed, and the switching elements that are closed are sequentially replaced. . 4. The closed switching element is a set of a plurality of switching elements, and the set of closed switching elements is sequentially replaced. Lighting device for multiple discharge lamps.