JPH06283286A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To prevent a striation in simple constitution without deteriorating efficiency or the like. CONSTITUTION:On-duty between switching elements Q1 and Q2 in an inverter circuit 4 is set and controlled in asymmetry by a switching ratio control means 5. Thereby, a waveform of voltage impressed upon a discharge lamp 3 is formed substantially as an asymmetric waveform between a positive and a negative, and a striation is prevented on the similar principle in the case of a DC bias system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device provided with a half-bridge type or full-bridge type inverter circuit.

[0002]

2. Description of the Related Art Generally, there are various types of discharge lamp lighting devices, and one of the typical ones supplies high-frequency AC power to a discharge lamp by alternately turning on and off a pair of switching elements. There is a system provided with a half-bridge type inverter circuit that keeps lighting by doing so.

Here, it is known that when a discharge lamp containing an inert gas having a large atomic weight such as argon is lit by alternating current, a phenomenon in which a striped pattern appears on the tube wall (hereinafter referred to as "striation") occurs. ing. Although the cause of such striations is not clear, it is likely to occur especially when the lamp ambient temperature is low or during dimming lighting, and causes discomfort such as flicker.

As measures for reducing or preventing such striations, for example, Japanese Patent Publication No. 2-1199.
As disclosed in Japanese Patent Laid-Open No. 5 and Japanese Patent Application Laid-Open No. 57-118396, there is a direct current superimposing method in which a direct current bias is applied to a lamp current for a discharge lamp that is lit by alternating current. Further, as disclosed in Japanese Patent Laid-Open No. 3-156891,
For example, there is a discharge lamp in which a direct current converting means is connected in parallel with a diode and an impedance element such as a resistor to make the alternating lamp current asymmetric between positive and negative.

Although these measures actually cause striations, the stripes move at high speed due to the DC electric field due to the DC bias or the positive / negative asymmetry, so that it is visually equivalent to the fact that the striations do not occur. It can be done.

[0006]

However, these striation countermeasures require a direct current power source, a direct current converting means, etc., which complicates the circuit configuration. In addition, for example, since power loss due to resistance in the DC conversion means is large and efficiency is reduced, or since a diode is connected in parallel to both ends of a discharge lamp to which a large starting voltage is applied, a diode having a large withstand voltage is required. However, there is a drawback that the shape becomes large.

[0007]

According to a first aspect of the present invention, there is provided an inverter circuit having an LC resonance circuit connected to a discharge lamp and having at least a pair of switching elements which are alternately turned on and off. In the electric lamp lighting device, switching ratio control means for setting and controlling the on-duty between the switching elements asymmetrically is provided.

According to the second aspect of the invention, the inverter circuit has an operating frequency variably controlled according to the level of the dimming signal.

In this case, according to the third aspect of the present invention, level switching means for determining the level of the dimming signal is provided, and the switching ratio for asymmetrically setting and controlling the on-duty between the switching elements only when dimming below a certain level. It was used as a control means.

On the other hand, in the invention described in claim 4, claim 1
In the invention described above, the temperature detection means for detecting the temperature in the vicinity of the discharge lamp is provided, and the switching ratio control means for setting and controlling the on-duty between the switching elements asymmetrically is provided only when the detected temperature is equal to or lower than the predetermined temperature.

In these inventions, in the invention described in claim 5, the asymmetric ratio to be set and controlled is a preset constant value, and in the invention described in claim 6, the asymmetric ratio to be set and controlled is variable.

In this case, in the invention according to claim 7, in the invention according to claim 5 or 6, the asymmetric ratio to be set and controlled is within the range of 7: 3 to 8: 2.

Further, in the invention described in claim 8, in the invention described in claim 1, the switching ratio control means for increasing / decreasing the asymmetry ratio according to the level of the dimming signal is used.

[0014]

In the first aspect of the invention, since the on-duty between the switching elements in the inverter circuit is asymmetrically set and controlled by the switching ratio control means, the voltage waveform applied to the discharge lamp is also a substantially positive / negative asymmetrical waveform. Therefore, the peak voltage is different between positive and negative in terms of high frequency, and striation is prevented as in the case of the conventional DC bias method. In particular, it is only necessary to control the on-duty, there is no need to add a DC power supply or DC conversion means, and it is possible to implement a striation countermeasure that is simple and has little power loss.

Particularly, in the invention described in claim 2, since the invention is applied to the one having the inverter circuit having the dimming function in which the operating frequency is variably controlled according to the level of the dimming signal, striation is likely to occur. With a dimming function, striation can be effectively prevented.

In the third aspect of the present invention, more practically, the on-duty between the switching elements is set and controlled asymmetrically only when the dimming signal level is equal to or lower than a certain level, so striation occurs. The effect can be exerted only in an easy situation, and particularly in a situation in which the occurrence of striation is not a problem, lighting control can be performed with the on-duty symmetrical as usual.

Further, according to the invention of claim 4, the on-duty between the switching elements is set asymmetrically only when the temperature in the vicinity of the discharge lamp is a low temperature below a predetermined temperature, so that striation is likely to occur. Only in the situation where the occurrence of striation is not a problem, the lighting control can be performed with the on-duty symmetrical as usual.

According to the fifth aspect of the present invention, the asymmetric ratio is set to a constant value set in advance. Therefore, the ratio switching means is not required, which is simple.

In the invention according to claim 6, since the asymmetry ratio is made variable, the ratio difference is made larger as the dimming level becomes smaller, or the ratio difference becomes larger as the temperature becomes lower. Fine grain control can be performed according to the level at which ation is likely to occur.

In the invention according to claim 7, since the specific value of the asymmetry ratio is set to 7: 3 or more, the striation prevention effect can be secured, and since it is set to 8: 2 or less, the ON width is long. The current flowing through the other switching element does not approach the phase advance and the design is not difficult.

Further, in the invention of claim 8,
Since the asymmetry ratio is increased or decreased according to the level of the dimming signal, it is possible to control dimming while preventing striation.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. First, as a basic configuration, a pair of switching elements (FET = field effect transistor) Q ₁ and Q ₂ are connected in series to the DC power source 1, and a choke L is provided at both ends of one switching element Q _2. LC series resonance circuit with ₀ and capacitor C ₁ (LC resonance circuit)
A discharge lamp 3 is connected in parallel with 2 and the capacitor C ₁ . The connection point of the switching elements Q ₁ and Q ₂ and the L
Between the C series resonance circuit 2 and the DC cut capacitor C ₀
Are connected. Here, the switching element Q
_A well-known half-bridge type inverter circuit 4 is composed of ₁ , Q ₂ and LC series resonance circuit 2, and discharges high-frequency AC power accompanying the alternating on / off oscillation operation of the switching elements Q ₁ , Q _2. By putting it in No. 3, lighting is maintained.

Here, the switching elements Q ₁ and Q _{2 are}
Under the control of the drive control circuit 5, is ON / OFF controlled at a high speed at a predetermined operating frequency.
In this embodiment, the drive control circuit 5 is configured to also function as a switching ratio control means, and the on-duty between the pair of switching elements Q ₁ and Q ₂ is set to be asymmetric. That is, in the case of a normal inverter circuit, the pair of switching elements are set so that the on-duty is 5: 5 and symmetrical, but in the present embodiment, for example, as shown in FIGS. In addition, the ON width on the switching element Q ₁ side is set asymmetrically so as to be longer than the ON width on the switching element Q ₂ side.

With such a configuration, the currents I _Q1 and I _Q2 as shown in (c) and (d) of the drawing flow through the switching elements Q ₁ and Q ₂ in accordance with the on-duty. As a result, the lamp voltage V _L applied across the discharge lamp 3 is
Since the DC component is cut by the cut capacitor C ₁ , a positive / negative asymmetric waveform is obtained as shown in FIG.
Therefore, the lamp current I _L also has a positive / negative asymmetric waveform corresponding to this, as shown in FIG. In other words, even when viewed from a high frequency, the peak values are different depending on whether it is positive or negative, so that the stripes move at high speed as in the conventional DC bias method, and striation can be visually prevented.

According to this embodiment, since the on-duty of the switching elements Q ₁ and Q ₂ may be set asymmetrically to prevent striation, it is not necessary to provide a DC power supply or a DC conversion means as in the conventional case. In addition, it can be easily configured and does not involve power loss.

By the way, according to an experiment conducted by the present inventor, the degree of asymmetry (on-width ratio) is 7: 3 to.
It was proved to be appropriate to set the ratio within the range of 8: 2. That is, when the asymmetry ratio is 7: 3 or less, the effect on striation is hardly recognized. Further, when the asymmetry ratio is 8: 2 or more, as can be seen from the current waveform shown in FIG. 2, the current I _Q1 flowing in the switching element Q ₁ having a longer ON width approaches a phase advance, so designing is performed. Because it becomes difficult.

The present embodiment is not limited to the configuration shown in FIG. 1, but may be, for example, a circuit configuration having the LC series resonance circuit 6 as the LC resonance circuit as shown in FIG.
As shown in FIG. 2B, two DC cut capacitors C
_{The same} can be applied to a circuit configuration having ₁₁ and C ₁₂ (the same applies to the following embodiments). Furthermore, with regard the switching elements Q _1, Q ₂ parts, not limited to using the FET, for example, as shown in FIG. 4, the diode D _1,
Alternatively, switching elements Q ₃ and Q ₄ represented by a transistor in which D ₂ is connected in parallel may be used (this point also applies to the following embodiments).

By the way, Japanese Patent Publication No. 3-78759 discloses that dimming is performed by making the ON widths of a pair of half-bridge connected switching elements asymmetrical, but striation prevention is described. Is not mentioned at all. Therefore, in particular, the asymmetric ratio is not related to the range of the asymmetric ratio effective for preventing striation as described above,
For example, in the region where the asymmetry ratio is extremely small, striation cannot be prevented even though dimming control can be performed.

Next, a second embodiment of the present invention will be described with reference to FIGS. The same parts as those shown in the above-mentioned embodiments are designated by the same reference numerals (the same applies to the following embodiments). This embodiment is applied to a lighting device having a dimming function, and variably controls the on / off operating frequency of the switching elements Q ₁ and Q _{2 in} the inverter circuit 4 according to the level of the dimming signal. The drive control circuit 7 is also used as the switching ratio control means.

In such a structure, at the time of all light (dimming level 100%), as shown in FIG. 6 (a), the switching element is switched by the drive signal whose on-duty is asymmetrical as in the case of the above embodiment. Q _1, Q ₂ performs on-off control has been turned alternately operated. This allows
All-light lighting with striation prevented is performed.

However, during dimming, the drive control circuit 7 raises the operating frequency of the switching elements Q ₁ and Q ₂ of the inverter circuit 4 to a higher frequency than during full light. The deeper (smaller) the dimming level is, the higher the frequency becomes. Also at this time, these switching elements Q ₁ ,
The on-duty of Q ₂ remains asymmetric as shown in FIG. 6B, and the dimming lighting is performed with the striation prevented.

Incidentally, the above-mentioned Japanese Patent Publication No. 3-78759.
According to the gazette, it is stated that the ON width of a pair of switching elements is asymmetrical for dimming, but it is performed under the condition that the operating frequency of the inverter circuit is constant, and the dimming signal is adjusted according to the level. There is no mention of preventing striation by always making the on-duty asymmetric under the condition that the operating frequency is variably controlled.

Next, a third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, an on-duty serving as a switching ratio control means is provided separately from the original frequency control circuit 8 which variably controls the on / off operating frequencies of the switching elements Q ₁ and Q ₂ according to the level of the dimming signal. The switching circuit 9 is provided, and the on-duty switching circuit 9 is selectively operated by the judgment output of the level judgment means 10 for detecting the level of the dimming signal. The on-duty switching circuit 9 is normally set to drive the switching elements Q ₁ and Q ₂ at a symmetrical ratio of on-duty of 5: 5, but when the dimming signal level is below a certain level. The switching elements Q ₁ and Q ₂ are driven with an on-duty as an asymmetric ratio.

Therefore, in the case of the present embodiment, when all lights are lit or dimming lights of a certain level or more are lit, the switching elements Q ₁ and Q ₂ are symmetrical with on-duty of 5: 5, as shown in FIG. 8A. In this state, drive control is performed at the operating frequency determined by the frequency control circuit 8. Then, during deep dimming lighting in which the dimming level is below a certain level, the operation of the on-duty switching circuit 9 is switched by the judgment output from the level judging means 10, and the switching element Q
The on-duty of ₁ and Q ₂ has an asymmetric ratio as shown in FIG. At the same time, the frequency control circuit 8 raises the frequency to an operating frequency suitable for the dimming level.
This enables dimming lighting in which striation is prevented. Since striations are apt to cause striations during dimming, particularly during deep dimming below a certain level, the switching element Q ₁ , only when the striations are likely to occur, as in the present embodiment.
It is effective to drive Q ₂ asymmetrically.

Further, a fourth embodiment of the present invention will be described with reference to FIGS. 9 and 10. In the present embodiment, in consideration of the fact that striation is likely to occur when the temperature in the vicinity of the discharge lamp 3 is low, temperature detection is performed by taking in temperature information from the temperature sensor 11 arranged in the vicinity of the discharge lamp 3 and detecting the temperature. Means 12
10, the on-duty switching circuit 9 is switched by the detection signal from the temperature detecting means 12 only when the temperature is lower than the predetermined temperature Tc as shown in FIG.
The on-duty ratios of ₁ and Q ₂ are set to have an asymmetric ratio. This prevents striations from occurring at low temperatures.

In the present embodiment, the frequency control circuit 8 is provided, and the present invention is applied to a structure in which the operating frequency is variably controlled according to a dimming signal, but the same applies to a device without a dimming function. Applicable to

Further, a fifth embodiment of the present invention will be described with reference to FIG. In the above-described embodiment, the on-duty asymmetry ratio of the switching elements Q ₁ and Q ₂ is always constant, but in the present embodiment, as shown in FIG. Up to, the asymmetry ratio is continuously variable according to the dimming level. That is, as the dimming level becomes deeper, the asymmetry ratio is set to be larger, which corresponds to the easiness of striation, so that effective striation prevention is performed. FIG. 11B shows a case where the temperature is controlled by the neighborhood temperature as shown in FIG.
In the following low temperature range, the asymmetry ratio is continuously variable as the temperature becomes lower.

By the way, based on both the information of the level of the dimming signal and the temperature near the discharge lamp 3, the switching element Q
_When controlling the on-duty asymmetry of ₁ and Q ₂ ,
Controlled according to the more demanding conditions. For example, if the on-duty ratio determined by the temperature is 55:45 and the on-duty ratio determined by the dimming level is 60:40 at a certain temperature and a certain dimming level, the conditions are more severe. Is controlled as an asymmetric ratio. This surely prevents the occurrence of striations.

A sixth embodiment of the present invention will be described with reference to FIGS. 12 and 13. In the present embodiment, for example, in the configuration shown in FIG. 1, the dimming signal is input to the drive control circuit 5, and the on-duty of the switching elements Q ₁ and Q ₂ is changed according to the level of the dimming signal. The asymmetry ratio of is increased or decreased to perform dimming.
Here, as shown in FIG. 12A, the on-duty of the switching elements Q ₁ and Q ₂ has already been set asymmetrical at the time of full light, and at the time of dimming, as shown in FIG. Is to be changed so as to increase. That is, the switching elements Q ₁ and Q _{2 have} already been activated from the time of full light.
The on-duty of the lamp voltage is set to be asymmetrical. By increasing the asymmetrical ratio as the dimming level decreases, the positive / negative asymmetry of the lamp voltage V _L becomes large as shown in FIG. Since the average power is reduced, dimming lighting is possible. As a result, it is possible to easily realize dimming at an arbitrary level while preventing striation from the full light without changing the operating frequency.

Incidentally, the above-mentioned Japanese Patent Publication No. 3-78759.
According to the publication, it is stated that dimming is performed with the ON widths of the pair of switching elements being asymmetrical, but the ON widths of the pair of switching elements are symmetric at full light, and striation measures are not considered. Is.

In each of the above-described embodiments, the on /
The example of the half-bridge type inverter circuit 4 including the pair of switching elements Q ₁ and Q ₂ controlled to be turned off has been described, but the invention is not limited to this, and for example, as shown in FIG. 14, four switching elements Q _{5 to} Q _{8 are used.} The present invention can be similarly applied to a full bridge type inverter 13 using That is, between the switching elements Q _5, Q ₆ of the pair, each may be asymmetrical on-duty between the switching elements Q _7, Q _8. Here, the capacitor C ₃ and the transformer 14 are connected between the middle points of the full bridge, and the discharge lamp 3 is connected to the secondary side of the transformer 14 via the LC series resonance circuit 2.

[0042]

According to the first aspect of the present invention, since the on-duty between the switching elements in the inverter circuit is asymmetrically set and controlled by the switching ratio control means, the voltage waveform applied to the discharge lamp is also controlled. Since it has a substantially positive / negative asymmetrical waveform and the peak voltage differs depending on whether it is positive or negative even at high frequencies, it is possible to prevent striation as in the case of the conventional DC bias method. A striation countermeasure can be realized as a simple one with less power loss, without the need for adding a charging means.

In particular, according to the second aspect of the invention, since the invention is applied to the one having the inverter circuit having the dimming function in which the operating frequency is variably controlled according to the level of the dimming signal, striation occurs. With an easy dimming function, striation can be effectively prevented.

According to the third aspect of the invention, more practically, the on-duty between the switching elements is asymmetrically set and controlled only when the dimming signal level is below a certain level. The effect can be exerted only under the situation where the occurrence of the striation is likely to occur, and particularly under the situation where the occurrence of the striation is not a problem, the lighting control can be performed with the on-duty symmetrical as usual.

Further, according to the invention described in claim 4, since the on-duty between the switching elements is set asymmetrically only when the temperature in the vicinity of the discharge lamp is a low temperature below a predetermined temperature, striation is likely to occur. In the situation where the occurrence of striation does not pose a problem, the lighting control can be performed with the on-duty symmetrical as usual.

According to the fifth aspect of the present invention, the asymmetric ratio is set to a preset constant value, so that the ratio switching means is not required and the structure becomes simple.

According to the sixth aspect of the invention, since the asymmetric ratio is variable, the smaller the dimming level is, the larger the ratio difference is, or the lower the temperature is, the larger the ratio difference is. Fine grain control can be performed according to the level at which striation is likely to occur.

According to the invention described in claim 7, since the specific value of the asymmetry ratio is set to 7: 3 or more, the striation prevention effect can be secured, and the ratio is set to 8: 2 or less. There is no inconvenience that it becomes difficult to design because the current flowing through the longer switching element approaches the phase advance.

Further, according to the invention described in claim 8, since the asymmetry ratio is increased or decreased according to the level of the dimming signal, it is possible to control the dimming while preventing the striation from the full light. Becomes

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing the operation.

FIG. 3 is a circuit diagram showing a modified example of the basic configuration.

FIG. 4 is a configuration diagram showing a modified example of a switching element portion.

FIG. 5 is a circuit diagram showing a second embodiment of the present invention.

FIG. 6 is a waveform diagram showing the operation.

FIG. 7 is a circuit diagram showing a third embodiment of the present invention.

FIG. 8 is a waveform diagram showing the operation.

FIG. 9 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 10 is a characteristic diagram showing the control characteristic.

FIG. 11 is a characteristic diagram showing a control characteristic of the fifth embodiment of the present invention.

FIG. 12 is a waveform diagram showing a sixth embodiment of the present invention.

FIG. 13 (a) is a lamp voltage waveform diagram during deep dimming,
(B) is a waveform diagram showing a part of it in an enlarged manner.

FIG. 14 is a circuit diagram showing a modification of the full-bridge type configuration.

[Explanation of symbols]

2 LC resonance circuit 3 discharge lamp 4 inverter circuit 5 switching ratio control means 6 LC resonance circuit 7 switching ratio control means 9 switching ratio control means 10 level determination unit 12 temperature detecting means Q ₁ to Q ₈ switching elements 13 inverter circuit

Claims (8)

[Claims] 1. A discharge lamp lighting device comprising an inverter circuit having an LC resonance circuit connected to a discharge lamp and having at least a pair of switching elements which are alternately on / off controlled, wherein an on-duty between the switching elements. The discharge lamp lighting device is provided with a switching ratio control means for setting and controlling asymmetrically. 2. The discharge lamp lighting device according to claim 1, wherein the inverter circuit is an inverter circuit whose operating frequency is variably controlled according to the level of a dimming signal. 3. A switching ratio control means for providing a level determination means for determining the level of the dimming signal and asymmetrically setting and controlling the on-duty between the switching elements only when dimming below a certain level. Claim 2
The discharge lamp lighting device described. 4. A switching ratio control means for providing a temperature detection means for detecting the temperature in the vicinity of the discharge lamp and for controlling the on-duty between switching elements asymmetrically only when the detected temperature is equal to or lower than a predetermined temperature. The discharge lamp lighting device according to claim 1. 5. The discharge lamp lighting device according to claim 1, 2, 3 or 4, wherein the asymmetric ratio to be set and controlled is a preset constant value. 6. The discharge lamp lighting device according to claim 1, wherein the asymmetric ratio to be set and controlled is variable. 7. The asymmetric ratio for setting and control is 7: 3 to 8:
The discharge lamp lighting device according to claim 5 or 6, wherein the discharge lamp lighting device is within the range of 2. 8. The discharge lamp lighting device according to claim 1, further comprising switching ratio control means for increasing / decreasing the asymmetry ratio according to the level of the dimming signal.