JP2008171741A - Discharge lamp lighting device and lighting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a stable light control up to a low flux of light such that the optical output ratio to the rated lighting may become several % without causing flickering and turning off, even in the case of light control of a discharge lamp having a high lamp impedance. <P>SOLUTION: The frequency of an inverter 2 is variably controlled by a control circuit 4 by receiving a detection output of a starting detection circuit 6, and a first period in which a high lamp voltage capable of starting a discharge lamp La is output, a second period in which a lamp voltage capable of maintaining lighting of the discharge lamp La is output, and a third period in which the discharge lamp La is turned off are repeated at a cycle in which the changes of optical output are hardly perceived by human eyes. Control is made so that in a frequency f1 of the first period, when starting of the discharge lamp La is confirmed by the starting detection circuit 6, it is immediately switched over to the frequency f2 of the second period, and after completing the second period, the operation of the inverter is moved to the third period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device for lighting and dimming a discharge lamp with high frequency power using a separately excited inverter, and a lighting fixture using the same.

  As a conventional technique for dimming control of a discharge lamp to a low luminous flux, there is a dimming system disclosed in Japanese Patent Publication No. 6-77479. In this method, a period of a first frequency for generating a high-frequency voltage sufficient for starting the discharge lamp and a period of a second frequency in which a current substantially flows through the discharge lamp (can maintain lighting) are alternately and periodically. By repeatedly changing the second frequency, the dimming and lighting can be stably performed without disappearing even if the light is dimmed to a low luminous flux.

Further, there is a burst dimming method as a dimming method of a cold cathode discharge lamp used as a backlight of a liquid crystal display or the like. In this method, the cold cathode discharge lamp is dimmed by intermittently stopping the oscillation of the inverter and blinking the lamp at a cycle that cannot be recognized by human eyes.
Japanese Patent Publication No. 6-77479

  However, the conventional method has a drawback that flickering is likely to occur in a lamp having a high lamp voltage (high impedance). This is because a high-impedance lamp has a limited range in which the current substantially flows (can be maintained in lighting) at the second frequency. In order to avoid flicker, it is necessary to raise the level of the dimming lower limit, and dimming to a low luminous flux is impossible.

  FIG. 13A shows a lamp current waveform when dimming a lamp having a low lamp voltage (low impedance) by the conventional method. In this case, dimming is performed by lighting with a high luminous flux during the period of the first frequency f1, and lighting with a low luminous flux during the period of the second frequency f2.

  FIG. 13B shows a lamp current waveform when a lamp having a high lamp voltage (high impedance) is dimmed by the conventional method. In the conventional example, the dimming level is changed by changing the frequency of the second frequency f2. However, in a lamp with a high lamp voltage (high impedance), the first dimming level is adjusted during dimming as shown in FIG. Since the extinction occurs in the period of the frequency of 2, the magnitude of the lamp current varies for each period. This is because the timing at which the disappearance occurs in the period of the second frequency f2 is different for each period. This causes flickering.

  Even if the lamp generates a voltage that reliably starts the lamp in the period of the first frequency f1, depending on the low ambient temperature of the lamp or the gas pressure in the bulb, it may be regenerated as shown in FIG. Since the timing of ignition is also different for each period, it causes further flickering. If the frequency f1 is further brought closer to the no-load resonance frequency f0 and the voltage applied to both ends of the lamp is increased, it becomes easier to start, but the light output (lamp current) increases after lighting, resulting in flashing. Dimming down to a low luminous flux is impossible.

  On the other hand, in the burst dimming method that intermittently stops the oscillation of the inverter, when the inverter that turns on the discharge lamp is also used as the supply source of the preheating current, the preheating current is not periodically supplied to the filament. . For this reason, a so-called cold start is performed while the filament is not heated enough to emit thermoelectrons, which has a significant adverse effect on the lamp life. In other words, repeated extinction causes stress on the filament, leading to deterioration of the lamp life.

  Separately, if an inverter dedicated to filament preheating is provided, it is possible to supply a preheating current, but this is not practical because the cost increases and the shape of the ballast increases.

  As a lamp having a high lamp voltage or high starting voltage (high impedance), a compact fluorescent lamp can be mentioned. The difference between a compact fluorescent lamp and a straight tube lamp, which is a typical straight tube, is that the outer diameter of the arc tube is small and that the arc tube is bent several times to obtain a compact shape. is there. This is because the brightness of the fluorescent lamp is mainly determined by the length of the arc tube (discharge path), and the longer the arc tube, the brighter and the higher the output the fluorescent lamp becomes. This is because it is necessary to reduce the outer diameter of the arc tube and bend it a plurality of times.

  However, by making the arc tube thin and long, it becomes difficult for current to flow, and as a result, the lamp voltage increases. Therefore, if the arc tube is made thin and long, the impedance of the lamp is increased.

  Table 1 shows the straight tube fluorescent lamp FHF32 and compact fluorescent lamps FHT32, FHT42 arc tube outer diameter and length, rated lamp voltage and current, and when the light output ratio relative to the rated lighting is 5%. Indicates lamp voltage.

  The dimming method as in the conventional example is effective in the FHT 32, and the ballast for low luminous flux dimming with a dimming ratio of 5% with respect to the rated output uses the technology of the conventional example (Japanese Patent Publication No. 6-77479). And it is actually commercialized. However, the dimming method as in the conventional example does not work effectively for compact lamps such as FHT32 and FHT42, and flickering occurs.

  The present invention has been made in view of the above points, and even in a discharge lamp having a high lamp voltage (lamp impedance), the light output ratio relative to the rated lighting is several percent without causing flickering or extinction. It is an object of the present invention to provide a low-beam dimming ballast that realizes dimming to such a low luminous flux, and in particular, in a hot cathode discharge lamp, does not cause deterioration of the lamp life.

  According to the present invention, in order to solve the above problems, as shown in FIG. 1, an inverter 2 that converts a DC voltage Vdc into a high-frequency voltage, and an inductor L2 and a capacitor C2 that are supplied with the high-frequency voltage from the inverter 2 A load circuit 3 to which the discharge lamp La can be connected, a start detection circuit 6 for detecting the start of the discharge lamp La, and the operation of the inverter 2 in a first period and a second period. A discharge lamp lighting device for low luminous flux dimming, comprising a control circuit 4 for periodically and repeatedly switching in a third period, and dimming the discharge lamp La by changing each period. As shown in FIG. 3, the frequency f1 in the first period is a frequency that generates a voltage sufficient for starting the discharge lamp La, and the frequency f2 in the second period is arc discharge to the discharge lamp La. Weed The frequency of generating a voltage that can be generated, and during the third period, the inverter 2 is operated to generate a voltage that is so low that arc discharge cannot be maintained in the discharge lamp La, and the start detection circuit 6 When the start of the discharge lamp La is confirmed at the frequency f1 in the period, the operation of the control circuit 4 is immediately changed to the frequency f2 in the second period, and the control circuit 4 performs the operation after the second period ends. In the period in which the operation of the inverter is shifted to the third period and the control circuit 4 repeats the first period, the second period, and the third period alternately, the change in the light output of the discharge lamp La It is characterized by a repetition period that cannot be recognized by the eyes.

  According to the present invention, the first period for outputting a high lamp voltage capable of starting the discharge lamp, the second period for outputting the lamp voltage capable of maintaining the lighting of the discharge lamp, and the third period for extinguishing the discharge lamp. When the start of the discharge lamp is confirmed by the start detection circuit at the frequency of the first period, the period is immediately switched to the frequency of the second period. Since the operation of the inverter is shifted to the third period after the second period is over, even when the discharge lamp having a long arc tube and a high lamp impedance is dimmed, There is no flickering of the light output due to a shift in the timing of extinction or the timing of re-ignition, and stable light control can be achieved deeply.

(Embodiment 1)
FIG. 1 is a circuit diagram of Embodiment 1 of the present invention. This circuit includes a DC power source 1 having a constant output voltage, an inverter 2 connected to the output terminal of the DC power source 1, a load circuit 3 including a resonance circuit connected to the output terminal of the inverter 2 and a discharge lamp La, an inverter 2 includes a control circuit 4 that controls the output of No. 2, a dimmer 5 that provides a dimming signal to the control circuit 4, and a start detection circuit 6 that detects the start of the discharge lamp La.

  The DC power supply 1 uses a step-up chopper, and as shown in the figure, includes an AC power supply Vs, a diode bridge DB1, an inductor L1, a diode D1, a smoothing capacitor C1, and a switching element Q1. The output terminal of the control circuit 7 that drives the switching element Q1 is connected to Q1. The chopper output Vdc can be made constant or variable by the operation of the step-up chopper. In the present embodiment, the chopper output Vdc operates so as to be constant regardless of the load.

  The inverter 2 has a series circuit of switching elements Q2 and Q3 connected in parallel to the output of the DC power supply 1, and a DC cut capacitor Cd is connected between the connection point of the switching elements Q2 and Q3 and the inductor L2. The switching elements Q2 and Q3 are driven by the control circuit 4 at a high frequency. The control circuit 4 is a PWM-IC and can change the switching frequency and on-duty of the switching elements Q2 and Q3.

  In response to the dimming signal from the dimmer 5, the control circuit 4 changes the switching frequency of the switching elements Q1, Q2 to turn on and dimm the discharge lamp La.

  The start detection circuit 6 detects the DC component of the lamp voltage. When the DC level of the lamp voltage becomes lower than a predetermined value, the start detection circuit 6 determines that the discharge lamp La has started, outputs an H signal to the control circuit 4, and outputs an inverter. Change the frequency. The start detection circuit 6 is not limited to the illustrated configuration, and any configuration may be used as long as it can detect that the discharge lamp La has started.

  The basic operation will be described below. FIG. 2 shows the lamp current waveform and the inverter frequency during dimming in this embodiment. During dimming, the control circuit 4 periodically and alternately switches the switching elements Q1 and Q2 of the inverter 2 during the first period, the second period, and the third period, and changes each period to change the discharge lamp. Dimming La.

  FIG. 3 shows the frequency characteristics of the resonance system in this embodiment. The frequency f1 in the first period is a frequency close to the no-load resonance frequency f0 of the resonance circuit, and generates a voltage at both ends of the discharge lamp La sufficient to start the discharge lamp La. The frequency f2 in the second period is a frequency in a range in which a current substantially flows through the discharge lamp (lighting can be maintained), and the discharge lamp is in a dimmed state. In the third period, the oscillation of the inverter 2 is stopped and the discharge lamp La is completely turned off.

  Actually, since the impedance of the discharge lamp La increases as dimming proceeds, the natural vibration frequency fz at the time of lighting approaches the no-load resonance frequency f0. Therefore, the lighting characteristics in FIG. 3 resemble the curve of the no-load resonance frequency as the dimming progresses (as the frequency increases), but here, for the sake of simplification of explanation, along the lighting curve, Assume that lamp power is decreasing.

  Here, the period in which the first period, the second period, and the third period are alternately repeated is several hundred Hz to several kHz, and the change in brightness due to the change in the light output of the discharge lamp La It is a level that cannot be recognized by the eyes.

  In the conventional example, the operation of the inverter 2 is close to the no-load resonance frequency f0, the period of the frequency f1 at which a voltage sufficient to start the discharge lamp La is generated at both ends of the discharge lamp La, and the oscillation stop (operation stop). Since only the period is repeated, flickering occurs due to variations in lamp start timing in each cycle as shown in FIG. 13C depending on the lamp state such as at low temperatures.

  In this embodiment, when the start of the lamp is detected at the frequency f1 in the first period, the inverter frequency is immediately changed to the frequency f2 in the second period. Since the frequency f2 in the second period is a frequency that can reliably maintain lighting, the frequency f1 does not turn off and is higher than the frequency f1 in the first period. The illuminance is lower than the hour.

  As described above, in the present embodiment, by providing the start detection circuit 6 and the period of the frequency f2, even if the lamp start timing varies as shown in FIG. Absent. This is because the period of the frequency f1 (the frequency that is close to the no-load resonance frequency f0 and generates a certain amount of light output after lighting) for the entire first, second, and third periods is small.

  Further, since the frequency f2 in the second period is a frequency within a range in which lighting can be reliably maintained, the disappearance occurs in the second period, and the flicker as shown in FIG. 13B does not occur. When changing the dimming level, as shown in FIGS. 2A and 2B, the second period (lighting time at frequency f2) is changed, or the frequency f2 (lamp in the second period) is changed. The current Ila) may be changed.

  Furthermore, since the period of oscillation stoppage (zero light output) is provided in the third period, the light can be adjusted more deeply and stably than the conventional example (Japanese Patent Publication No. 6-77479).

  In the present embodiment, the DC component of the lamp voltage is detected, and when the DC level of the lamp voltage becomes lower than a predetermined value, it is determined that the lamp has started, and the second frequency f2 is a frequency at which the inverter frequency can be immediately maintained. It is changing to. The DC component of the lamp voltage increases as the lamp impedance increases (when dimming), but also occurs in half-wave discharge at the end of the lamp life. Normally, at the end of the lamp life, the emitter (electron emitting material) of the lamp electrode decreases, leading to disconnection. Since the decrease in the emitter of the lamp filament does not occur evenly in both filaments, a half-wave discharge always occurs. Therefore, the start detection circuit 6 has an advantage that it can also be used as the end of life detection circuit.

(Embodiment 2)
FIG. 4 shows a circuit diagram of the second embodiment. The difference between the present embodiment and the previous embodiment is that the inverter does not stop in the third period, and the inverter frequency f3 is a frequency that generates a high-frequency voltage that is low enough that the lamp current does not flow. It is characterized by a frequency that turns off. Further, a preheating transformer Tf connected in parallel with the inverter 2 is provided. Capacitors Cf1 and Cf2 are connected to the secondary side of the preheating transformer Tf, and the filament of the discharge lamp La is connected via the capacitors Cf1 and Cf2. ing.

  FIG. 5 shows the lamp current waveform and the inverter frequency in this embodiment. In this embodiment, since the inverter 2 does not stop and continues to operate during the third period of the inverter operation, a sufficient preheating current is supplied from the preheating transformer Tf to the lamp filament. Since the frequency f3 in the third period is higher than the frequencies f1 and f2 in the first and second periods, the impedance of the capacitors Cf1 and Cf2 on the secondary side of the preheating transformer Tf is reduced, and the preheating current is increased. It is to do.

  Here, the amount of preheating current in the period of the frequency f3 is a preheating current that can supply energy necessary for emitting thermoelectrons from the filament to the filament. For example, it is set to be equal to or higher than the absolute minimum preheating current value required for emitting thermoelectrons when the preheating time is sufficiently long as defined by JIS. Further, in order to prevent the cathode from being damaged due to excessive evaporation of the emitter, it is set to be equal to or less than the maximum preheating current defined by JIS. As a result, even when the discharge lamp La is turned off, a sufficient preheating current is supplied to the filament, and even when the discharge lamp La is re-ignited, thermionic electrons can be emitted. There is no deterioration.

  In the previous embodiment, since the inverter 2 is stopped in the third period, it is not possible to share the inverter that turns on and dimmes the discharge lamp as the supply source of the preheating current. In general ballasts, an inverter that supplies high-frequency power to the discharge lamp and an inverter that supplies pre-heating current to the filament are used in common, so the pre-heating current that is supplied to the filament when the inverter that supplies high-frequency power to the discharge lamp stops. Will also stop. There is no problem with a cold cathode discharge lamp, but with a hot cathode discharge lamp, it is necessary to provide a separate dedicated inverter for filament preheating. In that case, it is possible to supply a preheating current, but this is not practical because the cost increases and the shape of the ballast increases.

  In addition, when the lamp goes out during the third period, there is a case where only the vicinity of the filaments at both ends of the lamp becomes slightly bright although it is not substantially in the lighting state. Such a discharge state is in a glow discharge region as indicated by a one-dot chain line in FIG. 6 in terms of lamp VI characteristics, and is a region exhibiting positive characteristics in which the lamp voltage and the lamp current are in a proportional relationship. In this region, the lamp is in a very unstable discharge state, and from a lighting state of the entire arc tube to a light-off state where only the vicinity of the filaments at both ends of the lamp is slightly bright due to a slight disturbance factor. Therefore, the entire lamp is not lit, and the illuminance is very low, so that it cannot be used as illumination in actual use.

  However, in general, since this state is a state in which thermionic electrons can be sufficiently emitted from the filament, the lamp starting voltage is lower than the state where the lamp is completely extinguished. Therefore, as shown in FIG. 7, the frequency f1 in the first period may be farther than the no-load resonance frequency f0 compared to the previous embodiments, and the flash at the start of the lamp can be kept low. Since the filament is not completely extinguished, the filament is in a heated state, and the stress on the filament can be kept low even if the frequencies f1, f2, and f3 are alternately repeated periodically.

  Even if the desired preheating current cannot be supplied in the third period due to the design constraints of the preheating circuit, the deterioration of the lamp life can be suppressed.

  As described above, in the present embodiment, by providing the third period in which the lamp current does not flow substantially without stopping the inverter, the starting voltage at the time of re-ignition is suppressed to a low level. The flash just after starting can be suppressed. Further, since the preheating current supply source also serves as an inverter for lighting and dimming the discharge lamp, it is not necessary to provide a separate preheating inverter, and the cost and parts area can be reduced.

(Embodiment 3)
FIG. 8 shows a circuit diagram of Embodiment 3 of the present invention. The difference from the previous embodiments is that a series resonance circuit of a capacitor and an inductor is provided in the secondary winding of the preheating transformer Tf.

  FIG. 9 shows changes in the preheating current If and the lamp current Ila during dimming according to the present embodiment. FIG. 10 shows changes in the preheating current If and the lamp current Ila in the embodiments so far.

  In the embodiments so far, as shown in FIG. 10, in the third period having the frequency f3, the preheating current that can emit the thermal electrons is supplied to the filament. However, in the frequencies f1 and f2 other than the frequency f3, Since the inverter frequency changes, the filament preheating current amount also changes. This is because the impedance of the capacitors Cf1 and Cf2 on the secondary side of the preheating transformer changes due to the change in frequency. Since the frequencies f1 and f2 in the first and second periods are lower than the frequency f3 in the third period, the impedances of the capacitors Cf1 and Cf2 increase, and the amount of preheating current decreases. In such a state where the increase / decrease of the preheating current is transiently repeated, the heating state of the filament of the discharge lamp La changes abruptly, which may affect the lamp life and stable dimming.

  Therefore, in the present embodiment, as shown in FIG. 9, the preheating currents in the period of the first frequency f1, the period of the second frequency f2, and the period of the third frequency f3 are substantially equal. As shown in FIG. 8, a series resonance circuit of an inductor Lf1 and a capacitor Cf1 and a series resonance circuit of an inductor Lf2 and a capacitor Cf2 are provided on the secondary side of the preheating transformer Tf, and the secondary side of the preheating transformer Tf. As shown in FIG. 11, the resonance frequency fs of the series resonance circuit is set to a frequency much higher than the no-load resonance frequency f0, and even if the inverter operating frequency is repeatedly changed to the frequencies f1 and f2, the preheating transformer Tf This is because the output of is almost unchanged.

  As a result, even when the lamp repeatedly blinks at a cycle that cannot be recognized by the human eye, the lamp characteristic change due to the transient change in preheating current can be eliminated, and stable and deep light control can be performed.

  As described above, if this embodiment is used, the filament preheating current does not change when the lamp is turned off or on, so that the lamp life is not further deteriorated compared to the previous embodiments, and the light can be adjusted stably. Can be obtained.

(Embodiment 4)
FIG. 12 shows a downlight lighting apparatus including the discharge lamp lighting device according to any one of the above-described embodiments and a discharge lamp whose lighting / dimming operation is controlled by the discharge lamp lighting device. The lamp body 31 is equipped with a high-frequency lighting dedicated compact type lamp such as FHT42 / 32, and is lit and dimmed by a lighting device housed in the fixture case 32.

It is a circuit diagram which shows the structure of Embodiment 1 of this invention. It is a wave form diagram which shows operation | movement of Embodiment 1 of this invention. It is a characteristic view which shows the resonance characteristic of Embodiment 1 of this invention. It is a circuit diagram which shows the structure of Embodiment 2 of this invention. It is a wave form diagram which shows operation | movement of Embodiment 2 of this invention. It is a characteristic view which shows the lamp | ramp characteristic of Embodiment 2 of this invention. It is a characteristic view which shows the resonance characteristic of Embodiment 2 of this invention. It is a circuit diagram which shows the structure of Embodiment 3 of this invention. It is a wave form diagram which shows the lamp current and preheating current of Embodiment 3 of this invention. It is a wave form diagram which shows the lamp current and preheating current of Embodiment 1, 2 of this invention. It is a characteristic view which shows the resonance characteristic of Embodiment 3 of this invention. It is a figure which shows the structure of the lighting fixture of Embodiment 4 of this invention, (a) is a top view, (b) is a side view. It is a wave form diagram which shows operation | movement of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power source 2 Inverter 3 Load circuit 4 Control circuit 5 Dimmer 6 Start detection circuit La Discharge lamp

Claims (7)

An inverter that converts a DC voltage into a high-frequency voltage;
A load circuit to which a high frequency voltage is supplied from an inverter, including a resonance circuit including an inductor and a capacitor, to which a discharge lamp can be connected;
A start detection circuit for detecting the start of the discharge lamp;
A control circuit that periodically and alternately switches the operation of the inverter in a first period, a second period, and a third period;
A discharge lamp lighting device for dimming a low luminous flux by dimming a discharge lamp by changing each period,
The frequency of the first period is a frequency that generates a voltage sufficient for starting the discharge lamp,
The frequency of the second period is a frequency for generating a voltage capable of maintaining arc discharge in the discharge lamp,
In the third period, the inverter is operated to generate a voltage so low that arc discharge cannot be maintained in the discharge lamp,
The start detection circuit changes the operation of the control circuit to the frequency of the second period immediately after the start of the discharge lamp is confirmed at the frequency of the first period,
The control circuit shifts the operation of the inverter to the third period after the second period ends, and the control circuit repeats the first period, the second period, and the third period alternately. The discharge lamp lighting device is characterized in that the change in the light output of the discharge lamp is a repetitive cycle that cannot be recognized by human eyes. The discharge lamp lighting device according to claim 1, wherein the discharge lamp is a hot cathode discharge lamp, and a preheating current is supplied to the discharge lamp electrode in the third period. 3. The discharge lamp lighting device according to claim 2, wherein the inverter for lighting and dimming the discharge lamp is used as a supply source for supplying the preheating current. 4. The discharge lamp lighting device according to claim 2, wherein the preheating current is a preheating current amount capable of supplying energy necessary for emitting thermal electrons to the discharge lamp electrode. The discharge lamp lighting device according to any one of claims 2 to 4, wherein all of the preheating current amounts in the first, second, and third periods are the same preheating current. The start detection circuit detects a DC voltage component of the discharge lamp voltage, and detects that the discharge lamp has started when the DC voltage component is equal to or less than a predetermined value. The discharge lamp lighting device described. A lighting fixture comprising: the discharge lamp lighting device according to any one of claims 1 to 6; and a discharge lamp whose lighting operation is controlled by the discharge lamp lighting device.

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