JP2002134292A - Lighting equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lighting equipment for cathode-ray tubes, which can carry out direct-current lighting without degrading life of the cathode-ray tube by making influence of floating capacity into the minimum, and preventing generating of a cataphoresis phenomenon. SOLUTION: The lighting circuit for carrying out direct-current lighting, consists of the cathode-ray tube DL, the direct-current power supply, which generates the voltage, which can maintain lighting of the cathode-ray tube DL, and switching elements Q3 and Q4, which change the output voltage from the direct-current power supply to plus and minus on the basis of zero with a predetermined cycle and the like. The voltage impressed to one electrode of the cathode-ray tube DL is changed to the polarity of plus or minus on the basis of zero, and the electrode of another side is set as a value near zero or zero. By this, the polarity can be reversed with a predetermined cycle, without switching directly the voltage impressed to the cathode-ray tube DL with physical switches, such as a semiconductor switching element, a relay, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique effectively applied to a lighting device for suppressing cataphoresis that occurs when a cathode ray tube is lit by direct current.

[0002]

2. Description of the Related Art As a technique studied by the present inventor, the following techniques shown in FIGS. 8, 9 and 10 studied by the present inventor can be considered for a cathode-ray tube lighting device. 8 is a configuration diagram showing a lighting circuit for high-frequency lighting, FIG. 9 is a configuration diagram showing a lighting circuit for DC lighting,
FIG. 10 is an explanatory diagram showing the polarity of the voltage applied to the cathode tube in DC lighting.

As shown in FIG. 8, in the configuration of a lighting circuit for high-frequency lighting, a voltage resonance circuit of switching elements Q1 and Q2 constituted by a push-pull has a resonance frequency of one of a resonance capacitor C1 and a step-up transformer T1. It is determined by the secondary side inductance and the like. Each of the switching elements Q1 and Q2 is turned on by a current flowing from the starting resistor R1 or R2, and the step-up transformer T1 is turned off using saturation. As a result, the switching elements Q1 and Q2 are turned on alternately by self-excited oscillation. The DC voltage DC1 is input to the primary side of the step-up transformer T1, and a voltage substantially boosted by the turns ratio is output to the secondary side of the step-up transformer T1. Step-up transformer T
The output voltage on the secondary side of 1 is substantially sinusoidal with a half-wave being a positive pole and a half-wave being a negative pole depending on the winding direction of the winding, and the balance of the waveforms of the positive pole and the negative pole is almost the same, that is, a DC component is superimposed. Will not be. This voltage is supplied to the cathode tube DL via the capacitor of the current limiting element of C2.

As shown in FIG. 9, in a lighting circuit for DC lighting, it is assumed that the DC voltage DC1 applied to the cathode tube DL is a voltage capable of maintaining the lighting of the cathode tube DL. Since the direction of the current flowing through the cathode tube DL is constant, the mercury ions in the cathode tube DL are biased to the cathode electrode and a cataphoresis phenomenon occurs. Therefore, the switching control circuit SS1 applies the mercury ions to the cathode tube DL at a predetermined cycle. The polarity of the voltage to be changed is switched by the changeover switches SW1 to SW4.

In such DC lighting, the polarity of the voltage applied to the cathode tube DL when the polarity is switched is as shown in FIG.
It will be like 0. As a technique relating to this, there is a technique described in, for example, JP-A-9-27392 or JP-A-5-121189.

[0006]

The inventors of the present invention have studied the technologies of the lighting circuit for high-frequency lighting and the lighting circuit for DC lighting as described above. became.

For example, in a lighting circuit for high-frequency lighting, the lighting circuit, the wiring between the cathode tubes and the stray capacitance of a nearby conductor such as a housing to be mounted, and the stray capacitance of a nearby conductor such as a cathode tube and a reflector cause the following problems. There are problems such as flickering and non-lighting, an increase in the output voltage of the step-up transformer, and an increase in the size of circuit components including the step-up transformer. Problems such as deterioration or destruction of the insulation system due to capacitive coupling with a nearby conductor are considered. Can be

In a lighting circuit for DC lighting,
It is necessary to switch the high voltage applied to the cathode tube by a physical switch such as a semiconductor switching element or a relay, and the mercury is affected by differences including circuit component size, inclination of both electrodes in the cathode tube, and structural variations. Since it can be inferred that the ion acceleration is different, it is considered that the DC component is integrated in the polarity inversion at a predetermined cycle, the mercury ion distribution in the cathode tube becomes non-uniform, and the cataphoresis phenomenon occurs.

Accordingly, an object of the present invention is to provide a lighting device for a cathode tube capable of minimizing the influence of stray capacitance, preventing the occurrence of a cataphoresis phenomenon, and performing DC lighting without deteriorating the life of the cathode tube. Things.

[0010]

According to the present invention, in order to achieve the above object, a DC power supply for generating a voltage capable of maintaining lighting of a cathode tube, and a cathode connected to one electrode of the cathode tube, The present invention is characterized in that the output voltage of the DC power supply is applied in a predetermined cycle while switching between plus and minus with reference to zero without directly switching the high voltage applied to the tube.

In this configuration, during a period in which a DC voltage is output based on zero at a predetermined cycle, a voltage obtained by inverting the polarity of the output DC voltage with respect to zero for a short period of time. , At different periods.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. In all the drawings for describing the embodiments, the same members are denoted by the same reference numerals, and the repeated description thereof will be omitted.

(Embodiment 1) FIG. 1 is a block diagram showing a lighting circuit for DC lighting according to Embodiment 1 of the present invention.
FIG. 3 is a configuration diagram showing a filter circuit using a center tap type transformer in the lighting circuit of the present embodiment, and FIG. 3 is a waveform diagram showing a voltage waveform applied to a cathode ray tube.

First, the configuration of an example of a lighting circuit for DC lighting according to the present embodiment will be described with reference to FIG.

The lighting circuit of the present embodiment has a circuit configuration for, for example, DC lighting, and includes a cathode tube DL, switching elements Q3 to Q5, resistors R2 to R6, a transformer T
2, T3, capacitors C3 to C6, diodes D1 to D
5, DC voltage DC2, coils L1 to L3, changeover switches SW5 and SW6, comparator Comp1, reference voltage Ref1, drive circuits Drv1, Drv2, oscillators OSC1, OSC2, duty control circuit Cntl1,
Cntl2, a timer circuit Tmr1, and the like.

In the configuration of the lighting circuit, the cathode tube DL
, Each component functions as a DC power supply that generates a voltage that can maintain the lighting of the cathode tube DL, and switches the output voltage of this DC power supply between plus and minus with a predetermined period based on zero. The means for applying to one electrode of the cathode tube DL comprises switching elements Q3 and Q4, and these switching elements Q3 and Q4 are not simultaneously turned on by the operations of the changeover switches SW5 and SW6.

Next, the operation of this embodiment will be described with reference to FIG.
The operation of the lighting circuit will now be described with reference to FIGS.

First, the changeover switch SW5 is turned on. Thereby, switching is started by the switching element Q3. Since the switching element Q4 is turned off by the changeover switch SW6, the current flows only in the direction of the switching element Q3. Switching is performed via the drive circuit DRV2, and the switching frequency is determined by the oscillator OSC2.

A high voltage corresponding to the turns ratio is generated on the secondary side of the transformer T2. However, since a pulsating flow is generated, a stray capacitance is generated in the cycle of the pulsating flow, and it can be visually recognized as flickering. Smoothing is performed by the coils L2 and L3 and the capacitor C6.

The back electromotive force generated when the switching element is turned off is inserted into diodes D2 and D3, a capacitor C3, and a resistor R2 which constitute a snubber circuit for protection of the switching element.

In the circuit on the secondary side of the transformer T2, the capacitor C5 and the resistor R6 are inserted as a filter circuit. Although the filter circuit is composed of L, C and R in FIG. 1, a method of smoothing with a coil L4 and a capacitor C7 using a transformer T4 grounded at a center tap as shown in FIG. 2 may be used. The diodes D6 and D7 are for preventing reverse current.

When the switching element Q3 is on,
The voltage applied to one electrode VL1 of the cathode tube DL is shown in FIG.
The DC voltage on the positive side is set with reference to zero such as the time Tm1. The voltage of the other electrode VL2 of the cathode tube DL is zero or a value close to zero.

However, if this state continues for a long time, the cathode tube DL
Since the direction of the discharge current in the inside is constant, mercury ions are non-uniformly present in the tube, and the light emission of the cathode tube DL causes a cataphoresis phenomenon due to one side.

To prevent the above phenomenon, a timer circuit T
At a predetermined time set by mr1, the switch control circuit C
At trl2, the changeover switch SW5 is turned off, and at the same time, the changeover switch SW6 is turned on. Timer circuit Tmr
1 starts re-counting after the timer ends. Thus, switching is started by the switching element Q4.

Since the switching element Q3 is turned off by the changeover switch SW5, the current flows only in the direction of the switching element Q4. At this time, the voltage applied to one electrode VL1 of the cathode tube DL is a DC voltage on the negative side with respect to zero shown at time Tm2 in FIG. The voltage of the other electrode VL2 of the cathode tube DL is zero or a value close to zero. These operations are repeated by switching the operations of the switch control circuit Ctrl2 and the switches SW5 and SW6 at a predetermined cycle set in the timer circuit Tmr1.

As shown in FIG. 3, in order to prevent DC voltage from being superimposed, the time during which each of the switching elements Q3 and Q4 is turned on is assumed to be approximately Tm1２Tm2, and is substantially the same as the voltage value E1 ≒ E2. I do.

In FIG. 1, the current flowing through the cathode tube DL uses a current transformer T3 using the tertiary winding of the transformer T2, and the current flowing through the current transformer T3 is monitored by the voltage across the current monitoring resistor R5. , D5 and the voltage smoothed by the capacitor C4 are divided by the resistors R3 and R4, compared with the reference voltage Ref1 by the comparator Comp1, and the duty control circuit Cntl1 controls the step-down type chopper circuit switching element Q5 via the drive circuit Drv1. I do. Thereby, the transformer T2
Increase or decrease the voltage input to the primary side of. Note that D1 is a flywheel diode, and L1 is a choke coil.

Thus, the current flowing through the cathode tube DL is operated at a constant current. The switching frequency is determined by the oscillator OSC
Determined by 1.

Therefore, according to the present embodiment, the two switching elements Q3 and Q4 are separately driven while the driving circuit is a push-pull type comparator circuit, and the driving time is controlled to thereby control the cathode tube DL. One electrode VL
The voltage applied to the cathode tube DL is directly changed to a semiconductor switching element or a relay by switching the voltage applied to 1 to positive or negative polarity with reference to zero and setting the other electrode VL2 to zero or a value close to zero. The polarity can be inverted at a predetermined cycle without switching with a physical switch or the like.

(Embodiment 2) FIG. 4 is a block diagram showing a lighting circuit for DC lighting according to Embodiment 2 of the present invention.
6 is a waveform diagram showing waveforms of various parts of the lighting circuit of the present embodiment, and FIG. 7 is a waveform diagram showing a voltage waveform applied to the cathode tube.

First, the configuration of an example of a lighting circuit for DC lighting according to the present embodiment will be described with reference to FIG. The basic configuration of the lighting circuit of the present embodiment is the same as the configuration of the first embodiment shown in FIG.
4 is switched at a different cycle, thereby providing a circuit configuration for extending the switching cycle of each element.

That is, the lighting circuit of the present embodiment comprises a cathode tube DL, switching elements Q3 to Q5, resistors R2 to R5.
6, transformers T2 and T3, capacitors C3 to C6, diodes D1 to D5, DC voltage DC2, coils L1 to L
3, changeover switches SW7 to SW10, comparator Comp1, reference voltage Ref1, drive circuit Drv
1, Drv3, Drv4, oscillators OSC1, OSC3,
The circuit includes duty control circuits Cntl1 and Cntl3, a timer circuit Tmr2, AND circuits AND1 and AND2, a NOT circuit NOT1, a counter circuit Cnt1, and the like. The filter circuit of the secondary circuit of the transformer T2 may be a system using a transformer T4 grounded by a center tap as shown in FIG.

Next, the operation of the present embodiment will be described with reference to FIG.
The operation of the lighting circuit will now be described with reference to FIGS. 5, 6, and 7.

First, the changeover switches SW7 and SW9 are turned on, and the changeover switches SW8 and SW10 are turned off. Although the switching elements Q3 and Q4 are pulse-driven, they need to be driven and controlled because they cannot be turned on at the same time due to the circuit configuration. As a simple example, an N-ary up counter Cnt1 is used. FIG. 5 is a waveform example of each part in the circuit configuration of FIG.

Oscillator OSC3 whose frequency can be set arbitrarily
From the rising edge of n1 oscillation signals a generated at
The signal up to the two rising edges is output as a signal b. Signal b
The signal c is obtained by processing the signal a and the signal a in the AND circuit AND1. The switching element Q4 is operated by the drive circuit Drv4 by the signal c.

At the same time, a signal d obtained by processing the signal b by the NOT circuit NOT1 and a signal e obtained by processing the signal a by the AND circuit AND2. The switching element Q4 is operated by the signal e via the drive circuit Drv3.
The count number n1 at this time is an arbitrary value including zero, and it is assumed that the counter restarts after the count is completed.

If a 2 ⁿ -ary counter or a combination is used, the value of ⁿ 2 can be any value including zero. As a result, the switching elements Q3 and Q4 are driven without being turned on at the same time, and the voltage applied to one electrode VL1 of the cathode tube DL becomes a DC voltage on the positive side with respect to zero at time Tm3 in FIG. At Tm4, a voltage on the minus side is applied for a short time with respect to zero at a predetermined cycle. The voltage of the other electrode VL2 of the cathode tube DL is zero or a value close to zero.

The ON time of each of the switching elements Q3 and Q4 is set to Tm3> Tm4, and Tm3 is made sufficiently long.
If Tm3 can be secured for a sufficiently long time, DC drive is performed substantially, and generation of stray capacitance can be suppressed. In addition, it is assumed that the voltage value E3 ≒ E4 is almost the same.

However, since the cataphoresis phenomenon occurs with the lapse of time because Tm3 ≠ Tm4 in this state, these operations are performed by the switch control circuit Ctrl3 in the switch control circuit Ctrl3 at the predetermined cycle set in the timer circuit Tmr2. Is turned off, and the changeover switches SW8 and SW10 are turned on. After the switching, the signals for driving the switching elements Q3 and Q4 are reversed, so that the waveform becomes as shown in FIG. 6, and the voltage VL1 applied to the cathode tube DL is inverted with reference to zero.

Of course, the time during which each of the switching elements Q3 and Q4 is turned on is Tm3> Tm4, and Tm3 is made sufficiently long. If Tm3 can be secured for a sufficiently long time, DC drive is performed substantially, and generation of stray capacitance can be suppressed. In addition, it is assumed that the voltage value E3 ≒ E4 is almost the same.

For example, VL1 shown in FIG.
The upper diagram shows the waveform in the circuit configuration of FIG. 1 in the first embodiment, and the lower diagram shows the waveform in the circuit configuration of FIG. 4 in the present embodiment. The waveform in the circuit configuration of FIG. 4 can suppress the occurrence of the cataphoresis phenomenon by applying a voltage whose polarity is inverted for a short time to the cathode tube DL. That is, the polarity inversion time can be extended by Tm6−Tm5 minutes by using two kinds of the applied voltage cycle of f1 and f2.

Therefore, according to the present embodiment, similarly to the first embodiment, the voltage applied to the cathode tube DL is directly
The polarity can be inverted at a predetermined cycle without switching by a physical switch such as a semiconductor switching element or a relay. In this embodiment, the polarity is inverted by applying a voltage whose polarity is inverted for a short time to the cathode tube DL. Since the time can be extended, the acceleration of the occurrence of the cataphoresis phenomenon can be suppressed.

The present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the scope of the present invention. For example, the present invention is not limited to the circuit configuration as shown in FIGS. 1, 2 and 4, and switches at least one electrode of the cathode tube between plus and minus with a predetermined period based on zero as a reference. Any configuration that can apply the voltage may be used.

The present invention can be widely applied to all devices using a cold cathode tube as a light source of an LCD backlight, such as a notebook personal computer.

[0045]

According to the present invention, DC lighting of a cathode ray tube is
The voltage polarity is inverted without directly switching the DC voltage applied to the cathode ray tube, and there is an effect that the life of the cathode ray tube is not affected. In particular, by accelerating the polarity inversion time by applying a voltage whose polarity is inverted for a short time to the cathode ray tube, it is possible to suppress the acceleration of the occurrence of the cataphoresis phenomenon. Further, by realizing DC lighting, there is an effect that a margin in supply power can be provided without being affected by stray capacitance. As a result, it is possible to provide a cathode-ray tube lighting device capable of minimizing the influence of stray capacitance, preventing the occurrence of the cataphoresis phenomenon, and performing DC lighting without deteriorating the life of the cathode-ray tube.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a lighting circuit for DC lighting according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a filter circuit using a center tap type transformer in the lighting circuit according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram showing a voltage waveform applied to a cathode tube in the lighting circuit according to the first embodiment of the present invention.

FIG. 4 is a configuration diagram showing a lighting circuit for DC lighting according to a second embodiment of the present invention.

FIG. 5 is a waveform chart showing waveforms at various parts of a lighting circuit according to Embodiment 2 of the present invention.

FIG. 6 is a waveform chart showing waveforms of respective parts of the lighting circuit according to the second embodiment of the present invention.

FIG. 7 is a waveform diagram showing a waveform of a voltage applied to a cathode tube in the lighting circuit according to the second embodiment of the present invention.

FIG. 8 is a configuration diagram showing a lighting circuit for high-frequency lighting which is a premise of the present invention.

FIG. 9 is a configuration diagram showing a lighting circuit for DC lighting which is a premise of the present invention.

FIG. 10 is an explanatory diagram showing the polarity of a voltage applied to a cathode tube in DC lighting as a premise of the present invention.

[Explanation of symbols]

DL: cathode tube DL, Q1 to Q5: switching element, R
1 to R6: resistance, T1 to T4: transformer, C1 to C7 ...
Capacitors, D1 to D7 ... diodes, DC1, DC2
... DC voltage, L1 to L4 ... Coil, SW1 to SW10 ...
Changeover switch, Comp1, comparator, Ref
1: Reference voltage, Drv1 to Drv4: Drive circuit, O
SC1 to OSC3 ... oscillator, Cntl1 to Cntl3 ...
Duty control circuit, Tmr1, Tmr2 ... timer circuit, AND1, AND2 ... AND circuit, NOT1 ... NO
T circuit, Cnt1 ... counter circuit, SS1 ... switching control circuit.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshiaki Fujie 810 Shimoimaizumi, Ebina-shi, Kanagawa F-term in the Internet Platform Division, Hitachi, Ltd. 3K072 AA01 AC01 AC11 BA03 BB01 BC01 BC02 BC03 CA01 GA02 GB14 3K082 AA34 AA59 AA76 BA04 BA24 BA33 BA53 BD04 BD28 BE06 5H007 AA06 BB03 CA02 CB06 CC12 DA05 DB01 DC02

Claims (3)

[Claims] A cathode tube; a DC power supply for generating a voltage capable of maintaining lighting of the cathode tube; and a cathode while switching the voltage of the DC power supply between plus and minus with a predetermined period based on zero. A lighting device comprising: means for applying a voltage to one electrode of a tube. 2. The lighting device according to claim 1, wherein, during the period in which the DC voltage is output based on zero in the predetermined cycle, the output DC voltage is based on zero. A lighting device comprising: means for applying a voltage whose polarity has been inverted for a short period of time at another cycle. 3. The lighting device according to claim 1, wherein the DC voltage applied to the cathode tube is not directly switched by a physical switch such as a semiconductor switching element or a relay, and one of the cathode tubes is switched. A lighting device comprising means for indirectly switching a DC voltage applied to an electrode to plus or minus on the basis of zero.