JPH0335800B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a discharge lamp lighting device that has a plurality of discharge paths and sequentially switches the discharge paths to achieve one function.

[Background Art] The present inventor previously filed an application (Japanese Patent Application No. 131593/1982) proposing the above-mentioned discharge lamp.
FIG. 4 shows an example of such a discharge lamp, in which a discharge space airtightly formed by an outer bulb 1 and a stem 2 is bent into a U-shape, and a red and a
Three inner tubes 3R, 3G, and 3B coated with phosphors that emit green and blue light are provided.
One end of each of R, 3G, and 3B is hermetically fixed around the anode 4 by glass welding, and the other end is opened near the cathode 5 coated with an electron radioactive material. Furthermore, several Torr of rare gas and a small amount of mercury are sealed inside the outer tube 1.

Fig. 5 is a circuit diagram showing the basic configuration for lighting such a discharge lamp, in which a closed circuit is constructed of a DC power source Vs, a discharge path selection switch SW, and a current limiting resistor R. By controlling, the light emission of each inner tube 3R, 3G, 3B is time-divided, and the emission color is controlled by changing the mutual light emission time ratio. For example, as shown in Fig. 6, three arc tubes move within a constant period T of about 10 ms.
In other words, the inner tubes 3R, 3G, which emit red, green, and blue light,
By dividing the light emitting period into 3B and changing the mutual ratio, it appears that each arc tube is emitting light at the same time with the _intensity of _the set _ratio . If set like this, each light will emit white, yellow, and purple light, allowing for variable color control.

However, in such a discharge lamp lighting device, when switching the discharge path, an instantaneous current pause or decrease period occurs, and in order to realize stable switching lighting operation, the power supply voltage must be made sufficiently large relative to the lamp voltage. According to experiments, a power supply voltage of 5 to 7 times the lamp voltage was required. Therefore, the power loss in the current limiting resistor R becomes extremely large, and the circuit efficiency becomes extremely low.

Therefore, the following method can be considered to improve this problem. Figure 7 shows the basic configuration of such a system, in which a DC power supply Vs, a discharge path selection switch SW, a discharge lamp FL having multiple discharge paths, and an impedance consisting of a resistor R and an inductance L are connected in series. This is to form a closed circuit.

FIG. 8 shows the circuit diagram, in which the discharge path changeover switch SW is connected to three transistors Tr ₁ ,
Consists of Tr ₂ and Tr ₃ , and each transistor
Tr ₁ , Tr ₂ , and Tr ₃ are controlled by a control circuit C. The power supply Vs is composed of a control power supply Vs ₁ and a main circuit power supply Vs ₂ connected in series, and the transistors Tr ₁ , Tr ₂ and Tr ₃ constitute a switch means.

With this configuration, at the moment when the discharge path is switched (for example, at the moment when the inner tube 3R that emits red light is switched to the inner tube 3G that emits green light),
When the current attempts to decrease, a kick voltage is generated in the inductance L connected in series, and is applied to the discharge lamp FL in a superimposed manner with the power supply voltage. Therefore,
Tube voltage V (discharge lamp FL and each transistor Tr ₁ , Tr ₂ ,
As shown in FIG. 9d, the voltage across the series circuit of Tr ₃ produces a pulse-like high voltage Vl every time the discharge path is switched. In addition, FIGS. 9a to 9c show the control circuit C.
This figure shows a state in which each transistor Tr ₁ , Tr ₂ , and Tr ₃ is turned on in a time-division manner.
is the transistor Tr ₁ (red), and b is the transistor
Tr ₂ (green), and c in the figure shows the state of the transistor Tr ₃ (blue).

In this way, the necessary high voltage is supplied by the inductance L at the moment the discharge path is switched, so it is possible to maintain sufficiently stable operation by making the power supply voltage slightly higher than the effective value of the tube voltage. . According to experiments, the required power supply voltage is 2 times the tube voltage.
It was possible to reduce the amount by more than double. Although the power supply voltage has now been reduced, a high-voltage pulse is still required at the moment of switching the discharge path, and transistors Tr ₁ , Tr ₂ , and Tr ₃ must be able to withstand such a high-voltage pulse. The use of such expensive transistors poses a major problem in terms of circuit cost.

Therefore, a conventional example shown in FIG. 10 solves this problem. That is, it is generally known that if the electrodes of a discharge lamp (fluorescent lamp) are heated in advance, the discharge lamp can be started or restarted with a relatively low applied voltage. This conventional example utilizes such characteristics to reduce the high voltage pulse required when switching the discharge path. As shown in FIG. 10, the basic configuration is the same as that in FIG. 8. This conventional example is characterized in that a resistor r is connected between the emitter and collector of the transistor _Tr1 .

That is, when the transistor _Tr1 is on, current is naturally supplied to the discharge path (inner tube) 3R, but by appropriately selecting the value of the resistor r, the transistor
Even after Tr ₁ is turned off, a certain amount of discharge current (minor current) flows into the discharge path 3R via the resistor r.
That is, in the previous conventional example, the current flowing into the common cathode 5 was once zero for a very short time at the moment when the discharge path was switched, but in this conventional example,
The preheating current continues to flow through the common cathode 5 through the discharge path 3R by the resistor r. Therefore,
By constantly supplying a preheating current to the common cathode 5 of the discharge lamp FL to heat it, it is possible to reduce the high voltage pulse that must be applied when switching the discharge path, and the withstand voltage required for the transistor is also reduced. Become. Note that the resistor r through which the preheating current flows is a transistor.
Not only when added to Tr ₁ , but also when adding transistor Tr ₂
Alternatively, the same effect can be obtained even when it is added to any one of the transistors _Tr3 . Further, the value of the preheating current is set as a value equivalent to the so-called preheating current of the discharge lamp.

However, in the conventional example shown in Fig. 10, since a preheating current is constantly flowing through one of the discharge paths contributing to light emission, some light emission from that discharge path always remains, resulting in mixed color light. There was a problem that this resulted in a decrease in color purity.

[Object of the Invention] The present invention has been provided in view of the above-mentioned points, and has the purpose of reducing the high voltage pulse required when switching the discharge path, lowering the withstand voltage required of the transistor, and reducing the cost of the circuit. The object of the present invention is, of course, to provide a discharge lamp lighting device that does not cause a decrease in the color purity of mixed color light even if a minute current is constantly passed through the electrodes.

[Disclosure of the Invention] (Structure) The present invention includes a switching means that uses a switching transistor to switch the discharge current flowing from a power source to a plurality of discharge paths each emitting light of a different color, and a control circuit that controls the switching means in a time-division manner. A current supply means is provided for constantly supplying a minute current to the electrode through a path that does not contribute to the light emission of the discharge path.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
Figure 1 shows the circuit diagram. In this embodiment, unlike the case shown in FIG. 10, a fourth switching transistor Tr ₄ of PNP type which is turned on and off by the control circuit C as shown in FIG. 1 is added. Collector of ₄ discharge lamps FL
_A resistor r is connected between the emitter and the collector of the transistor _Tr4 . Then, according to a signal from the control circuit C, the transistors Tr ₁ , Tr ₂ ,
Tr ₃ and Tr ₄ are repeatedly turned on and off in time series. Here, when the transistor Tr ₄ is on, a preheating current is naturally supplied, and even when it is off, the preheating current continues to flow through the resistor r. According to such an operation, not only the breakdown voltage of the transistor is reduced for the same reason as the conventional example described above, but also the preheating current is constantly flowing to the cathode 5 through a path that does not contribute to light emission. A decrease in the color purity of the emitted light color is also avoided. Note that the resistors r, _r1 , etc. constitute a current supply means.

FIG. 2 shows another embodiment, in which a fourth anode 6 that does not contribute to light emission is added to the discharge lamp FL. That is, the resistance r
A transistor connected between emitter and collector
The collector of Tr ₄ is connected to the anode 6 via a resistor r ₁ . Even with such a system, it is possible to obtain the same effects as the embodiment shown in FIG. 1 above.

In addition, FIG. 3 shows another embodiment of the discharge lamp FL,
The open ends of the inner tubes 3R, 3G, and 3B are arranged in the opening 8 of the cathode chamber 7 covering the cathode 5,
Similarly to the above, the preheating current is supplied by the resistor r. Further, instead of a single discharge lamp consisting of a plurality of discharge paths, a plurality of discharge lamps may form a plurality of discharge paths.

[Effects of the Invention] As described above, the present invention includes a switching means that uses a switching transistor to switch a discharge current flowing from a power source to a plurality of discharge paths each emitting light of a different color;
It is equipped with a control circuit for time-divisionally controlling this switching means, and is provided with a current supply means that constantly flows a minute current through the electrode through a path that does not contribute to the light emission of the discharge path. By constantly passing a small current through a path that does not contribute to the light emission of the discharge path, the electrodes of the discharge path are heated and there is no need to generate more high-voltage pulses than necessary. It is possible to reduce the high-voltage pulses required at times, thereby reducing the withstand voltage required for switching transistors, reducing the cost of the circuit, and reducing the discharge path that contributes to light emission. Unlike in the past, where a minute current was always flowing through one of the paths, a minute current is always flowing through a path that does not contribute to light emission, so some light emission from the discharge path does not always remain, and mixed color light is generated. This has the effect of not causing a decrease in color purity.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a circuit diagram of another embodiment of the same as above, Fig. 3 is a sectional view of another embodiment of the same discharge lamp, and Figs. 4 a and b. are a perspective view and a plan view of the discharge lamp, FIG. 5 is a circuit diagram of the conventional example, FIG. 6 is a time chart of the same as above, FIG. 7 is a circuit diagram of another conventional example, and FIG. 8 is a circuit diagram of the same as above, FIG. 9 is a time chart similar to the above, and FIG. 10 is a circuit diagram of another conventional example. 3R, 3G, 3B are inner tubes, 4 is an anode, 5 is a cathode, 6 is an anode, FL is a discharge lamp, C is a control circuit, Tr ₁
~Tr ₃ indicates a switching transistor.

Claims (1)

[Claims] 1 Equipped with a switching means that uses a switching transistor to switch the discharge current flowing from a power source to a plurality of discharge paths each emitting light of a different color, and a control circuit that controls this switching means in a time-division manner, and the light emission of the discharge path is 1. A discharge lamp lighting device characterized by comprising a current supply means for constantly flowing a minute current through an electrode through a path that does not cause the current to flow through the electrode.