JP2010146967A - Lighting device, luminaire and backlight device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive lighting device with high efficiency, which can light a lamp stably even in a state of a less lamp current and high lamp voltage in a lighting circuit for lighting a fluorescent lamp or the like. <P>SOLUTION: The lighting device uses both of a feedback controller FB1 for controlling a frequency setting signal Frq of an inverter circuit so that a current corresponding to an input current of the inverter circuit or the lamp current becomes a certain value, and a feed forward controller FF1 for detecting an input voltage of the inverter circuit or an input voltage of a smoothing circuit, and correcting a pulse width signal Dty1 for setting an on time or an opening/closing phase of a switch element of the inverter circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lighting device for lighting a lamp using an inverter circuit, and a lighting fixture and a backlight device using the lighting device.

  For example, in a backlight device used for a liquid crystal display device or the like, an image is generally displayed using light obtained by lighting a plurality of fluorescent lamps such as cold cathode lamps. An inverter circuit is generally used for the lighting circuit of this type of fluorescent lamp. By turning on the fluorescent lamp at a high frequency with an inverter circuit, the luminous efficiency of the fluorescent lamp is improved, and electronic components such as a transformer can be miniaturized.

  However, with the spread of liquid crystal display devices, further improvement in the efficiency of devices has been demanded, and increasing the efficiency of backlight devices that consume most of the power of liquid crystal display devices has become an important issue. . To meet this demand, lighting devices have been devised to reduce the switching loss of the inverter circuit using a zero voltage switching method, etc., or to increase the DC power source input to the inverter circuit to reduce the transformer loss. ing.

  However, in the backlight device of the liquid crystal display device, the power conversion efficiency of the lighting circuit is lower than that of the lighting circuit for general illumination. The reason is that it is necessary to stabilize the power supply for suppressing flickering more than the lighting circuit for general lighting, and an insulating circuit is necessary from the viewpoint of noise and safety.

  With regard to flickering, if the liquid crystal display device is used like a television, the image is updated as needed, so it is not noticeable.However, when a still image is displayed, the flickering of the fluorescent lamp that is the light source is flickering as it is. It appears as a problem. Another reason why flicker is likely to be a problem is interference with the image update frequency of the liquid crystal display panel. This is because the frequency of the commercial power supply is 50 Hz or 60 Hz, and the image update frequency is also a frequency close to that (60 Hz to 120 Hz), so that frequency interference due to light fluctuation is likely to occur.

  For example, when the commercial power supply is 50 Hz, a ripple voltage of 100 Hz is generated in the DC voltage input to the inverter circuit. If the lamp is turned on by an inverter circuit without removing this ripple voltage, the light will fluctuate with a frequency component of 100 Hz. For example, the fluctuation range of the ripple voltage of the inverter circuit for general lighting is 10% or less of the average value. Even if you look directly at this light, you will hardly see any flicker. This is because the frequency of light change is as high as 100 Hz. However, flickering occurs in the light that has passed through the liquid crystal filter. In other words, if 100 Hz light is modulated by the liquid crystal filter at an image update frequency of 60 Hz, fluctuations in frequency components of 60 Hz and 100 Hz are mixed in the light, and a frequency difference component of 100 Hz-60 Hz = 40 Hz is generated. This is felt as flicker. Although there are individual differences, if the frequency of light fluctuation is 50 Hz or less, flicker will be felt even if there is a fluctuation of about several percent. Therefore, the flicker of the ripple voltage 10% becomes a large flicker when the frequency is 40 Hz.

  Therefore, a general liquid crystal display device includes a stabilized power supply circuit that removes a ripple voltage of a DC power supply caused by a commercial power supply. Since the circuit loss occurs, the conversion efficiency to light decreases.

  One possible method for improving the efficiency of the lighting circuit and reducing flickering is to add a power supply ripple elimination function to the inverter circuit. For example, the lamp current may be feedback controlled. If feedback control is performed, the lamp current becomes constant, and light fluctuations due to ripple voltage can be eliminated. It is also possible to eliminate various fluctuations such as a change in lamp characteristics due to temperature and a change in lamp voltage due to a nearby conductor.

  As another method, it is conceivable to perform feedforward control. If the output of the inverter circuit is increased or decreased according to the ripple voltage, the control circuit can be configured on the non-insulated primary side, and the design of the control circuit is easy. Further, since the ripple voltage is generated relatively stably, it is suitable for feedforward control. Various methods have been proposed for feedforward control of the discharge lamp lighting device.

In Patent Document 1 (Japanese Patent Laid-Open No. 2002-330591), an input voltage of an inverter circuit is detected, and a drive frequency of a switch element or a switch-on time ratio is changed so as to suppress a lamp current change due to a change in the input voltage. Techniques for making them disclosed are disclosed.
JP 2002-330591 A

  Not only the light source of a liquid crystal display device but also a discharge lamp is dimmed. Since dimming can prevent wasteful energy consumption, it is an important function of the lighting device. When dimming a low-pressure arc discharge lamp such as a fluorescent lamp, the lamp voltage increases in inverse proportion to the lamp current. That is, when the lamp current is decreased, the lamp voltage increases. Therefore, it is necessary to design a lighting device for dimming a discharge lamp so that stable lamp discharge is maintained even if the lamp voltage increases during dimming.

  In a fluorescent lamp, frequency dimming is generally performed using an LC resonance circuit. This is a method of controlling the lamp current mainly using the impedance change of the inductor of the LC resonance circuit. During dimming, the operating frequency of the inverter circuit is increased to increase the impedance of the inductor. As a result, the lamp current decreases.

  If dimming is performed in this way, the output impedance of the inverter circuit increases in accordance with the rise in lamp voltage, so that the constant current characteristic can be maintained. There is also a technique for performing dimming over a wider range by combining this frequency dimming with feedback control. For example, if constant current feedback control and frequency dimming are used in combination, it is possible to perform lighting that suppresses power supply fluctuations and lamp characteristic fluctuations while performing dimming.

  However, a cold cathode fluorescent lamp used in a liquid crystal display device has a higher lamp voltage than a hot cathode fluorescent lamp used in general illumination. This is because the arc tube is long and the inner diameter of the arc tube is small. Such dimming that increases or decreases the current of the lamp becomes difficult. That is, the design cannot be made so that the output impedance of the inverter circuit is sufficiently larger than the equivalent impedance of the lamp under various dimming conditions. In such a situation, a measure is taken such as increasing the gain of feedback control to the extent that the constant impedance is insufficient due to the output impedance.

  However, when the oscillation frequency is changed by feedback control, the lamp current is controlled in a stable direction, but there is a problem that feedback control oscillates. For example, in an inverter circuit using a constant current characteristic by an inductor, when the lamp current is increased by lowering the frequency and lowering the output impedance because the lamp current is small, the constant current characteristic deteriorates due to the decrease in the output impedance. The discharge becomes unstable and flickering occurs.

  Thus, it is likely that problems such as oscillation can be solved if feedforward control is used easily instead of feedback control, but the setting of control parameters in various dimming states becomes complicated and design is difficult. Therefore, it is not realistic.

  The present invention has been made to solve such problems of the prior art, and in a lighting circuit for lighting a fluorescent lamp or the like, the lamp is stably lit even in a state where the lamp current is low and the voltage is high, and the cost is low. An object is to provide a highly efficient lighting device.

  In order to solve the above-mentioned problem, the invention of claim 1, as shown in FIG. 1, rectifier DB for rectifying commercial power supply Vin, and at least one smoothing circuit for smoothing the output of rectifier DB (power factor improvement) Circuit PFC), an inverter circuit having switching elements Q1 and Q2 for inputting the output of the smoothing circuit and outputting a high frequency voltage, and an impedance element (between the output of the inverter circuit and a lamp Lamp1 as a load) Inductor Lr1), frequency setting means (frequency setting signal Frq) for setting the drive frequency of the inverter circuit, and the frequency setting circuit so that the current corresponding to the input current or lamp current of the inverter circuit becomes a constant value. The feedback circuit to be controlled (feedback controller FB1) and the switching element of the inverter circuit turned on A pulse width setting means (pulse width signal Dty1) for controlling the interval or open / close phase, and a control signal for detecting the input voltage of the inverter circuit or the input voltage of the smoothing circuit and correcting the output of the inverter circuit. A feedforward circuit (feedforward controller FF1) for supplying the means is provided.

  According to a second aspect of the present invention, in the first aspect of the present invention, as shown in FIG. 1, the smoothing circuit (power factor correction circuit PFC) includes means for controlling the output voltage to be substantially constant (output voltage feedback circuit CTR1). The feedforward circuit (feedforward controller FF1) controls the switch-on duty ratio of the inverter circuit in a range of 30% to 50%.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, as shown in FIG. 5, the pulse width setting means supplies predetermined values Adj1 to Adj3 to the output of the feedforward circuit (feedforward controller FF1). Adjustment means for adding (adders ADD1 to ADD3) is provided, and the switch element of the inverter circuit is controlled by the output of the adjustment means.

  According to a fourth aspect of the present invention, in the first or second aspect of the invention, the feedforward circuit increases the gain in accordance with a set value of the pulse width setting means, as shown in FIGS. And

  According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the feedback circuit includes a low-pass filter, and as shown in FIG. 4, the closed circuit gain becomes 1 at a frequency equal to or lower than twice the frequency of the commercial power supply. It has the point.

  According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, as shown in FIG. 1, the smoothing circuit (power factor correction circuit PFC) is a DC voltage detector (resistors Ra1 and Ra2) that detects the output voltage VDC. The feedforward circuit (feedforward controller FF1) detects the output of the DC voltage detector and corrects the output of the inverter circuit.

A seventh aspect of the invention is a lighting fixture including the lighting device according to the first to sixth aspects.
The invention of claim 8 is a backlight device provided with the lighting device of claims 1 to 6 (FIG. 8).

  According to the present invention, the on-time or the open / close phase of the switching element of the inverter circuit is feedforward controlled in accordance with the power supply fluctuation, and the oscillation frequency of the inverter circuit is feedback controlled in accordance with the lamp current. The output light flicker can be reduced, the power supply can be easily stabilized, and the circuit efficiency can be improved.

  In order to clarify the above and other objects, features, and advantages of the present invention, embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 shows a lighting circuit according to Embodiment 1 of the present invention. The lighting circuit includes a rectifier circuit DB that rectifies the commercial power supply Vin, and a power factor correction circuit PFC that boosts and smoothes the output of the rectifier circuit DB. The power factor correction circuit PFC includes an output voltage feedback circuit CTR1. That is, the output voltage VDC is divided by the series circuit of the resistors Ra1 and Ra2, and the ON time of the switch element Q0 is controlled so that the voltage becomes a predetermined value. This power factor correction circuit PFC is a well-known step-up chopper circuit including an inductor L0, a diode D0, a smoothing capacitor C0, and a switch element Q0. The switch element Q0 is on / off controlled at a frequency sufficiently higher than the commercial AC frequency, and the DC voltage VDC obtained by boosting the output voltage of the rectifier circuit DB is charged in the smoothing capacitor C0.

  The output voltage of the power factor correction circuit PFC is supplied to a push-pull inverter circuit including semiconductor switch elements Q1 and Q2, a drive circuit DRV thereof, and a transformer Tr1 with an intermediate tap. The drive circuit DRV alternately turns on / off the semiconductor switch elements Q1, Q2 according to the output of the pulse width modulator PWM1. A series circuit of an inductor Lr1 and a fluorescent lamp Lamp1 is connected between the secondary winding outputs of the transformer Tr1 with an intermediate tap. A capacitor Cr1 is connected between the terminals of the fluorescent lamp Lamp1. The high-frequency rectangular wave output of the push-pull inverter circuit is shaped by a series circuit of an inductor Lr1 and a capacitor Cr1, and power is supplied to the fluorescent lamp Lamp1.

  This circuit includes a feedback circuit that controls the input current of the push-pull inverter circuit to be constant. That is, the input current of the inverter circuit is detected by the current detection circuit DET1, and the output is input as a comparison value of the feedback controller FB1. Further, the target value signal Aim from the dimmer Dim1 is input to the feedback controller FB1. The feedback controller FB1 sends the frequency setting signal Frq to the pulse width modulator PWM1 so that the comparison value matches the target value Aim. The feedback controller FB1 is composed of, for example, an operational amplifier having an integration circuit as a feedback impedance. The pulse width modulator PWM1 is composed of a switching regulator control IC (for example, TL494), and can control the frequency and the pulse width.

  Also provided is a feedforward controller FF1 that receives the divided voltages of the resistors Ra1 and Ra2 of the power factor correction circuit PFC and supplies the pulse width signal Dty to the pulse width modulator PWM1 so as to cancel the power supply fluctuation. Thus, the cost of the voltage detection circuit can be reduced by sharing the detection voltage of the power factor correction circuit PFC (the divided voltage of the resistors Ra1 and Ra2) as the input signal of the feedforward controller FF1. In addition, the power consumption of the voltage detection circuit can be reduced.

  The operation state of this embodiment is shown in FIG. In FIG. 2, the output voltage VDC of the power factor correction circuit PFC, the pulse width signal Dty that is the output voltage of the feedforward controller FF1, the target value Aim that is the output of the dimmer Dim1, and the feedback controller FB1 A frequency setting signal Frq, which is a control output, and a lamp current Ila are shown.

  The output voltage VDC of the power factor correction circuit PFC includes a so-called ripple voltage whose voltage varies periodically as shown in FIG. The ripple voltage can be reduced by increasing the capacitance of the smoothing capacitor C0 in the power factor correction circuit PFC, but it is difficult in principle to make the ripple voltage zero. Further, the ripple voltage changes due to the deterioration of the smoothing capacitor C0. This ripple voltage causes a periodic power change in a load circuit such as a lamp, which becomes a problem. Therefore, it is necessary to stabilize the voltage separately by a DC-DC converter or the like, but power loss due to the DC-DC converter occurs.

  Therefore, in the present embodiment, control for output correction of the ripple voltage is performed by the inverter circuit. The feedforward controller FF1 corrects the output of the inverter circuit to decrease when the output voltage VDC of the power factor correction circuit PFC is high, and increases the output of the inverter circuit when the output voltage VDC of the power factor improvement circuit PFC is low. It is corrected as follows. That is, when the output voltage VDC of the power factor correction circuit PFC is high, the pulse width signal Dty as a correction signal is lowered, and when the output voltage VDC of the power factor improvement circuit PFC is low, the pulse width signal Dty as a correction signal is high. To do. In proportion to the pulse width signal Dty, the pulse width modulator PWM1 increases or decreases the switching time of the semiconductor switch elements Q1 and Q2.

  In a general design power factor correction circuit, the ripple voltage component of the DC voltage fluctuates about ± 5% of the DC average voltage value. Furthermore, the DC voltage fluctuates by about ± 10% due to the influence of load fluctuation, input voltage, and element variation. Furthermore, a dead time with a duty ratio of about 3 to 5% is required so that the semiconductor switch elements Q1 and Q2 of the inverter circuit do not turn on at the same time. Therefore, the switch-on time of the pulse width modulator PWM1 may be designed to be in the range of 30% to 45% with the maximum on-duty ratio being 50%.

  Furthermore, depending on the design of the power factor correction circuit PFC, it is possible to design the DC voltage change width as described above, and in that case, the change width of the switch-on time can be reduced, thereby improving the power conversion efficiency of the inverter circuit. it can.

  The dimmer Dim1 sets the target value Aim of the lamp current in the feedback controller FB1. The feedback controller FB1 calculates the frequency setting signal Frq according to the target value Aim. In this embodiment, since the lamp current is increased or decreased by changing the impedance of the inductor Lr1, the frequency setting signal Frq is increased to decrease the lamp current, the operating frequency of the inverter circuit is increased, and the lamp current is increased. Is increased, the frequency setting signal Frq is lowered to lower the operating frequency of the inverter circuit.

  As a result, as shown in FIG. 2, the lamp current Ila increases or decreases in accordance with the output signal Aim of the dimmer Dim1. Further, since the switching time is changed according to the power supply ripple by the feedforward controller FF1 independently of the operating frequency, the flickering of the lamp can be reduced.

  In the circuit of the present embodiment, optimum control can be realized by combining feedforward control and feedback control. Hereinafter, characteristics of each control will be described.

  First, feedforward control is suitable for disturbances that can be predicted in advance. As described above, even if the power factor correction circuit PFC is used, a ripple voltage is generated in the DC voltage VDC. However, it can be said that the ripple voltage is a stable disturbance. That is, the fluctuation occurs with a fixed period and with a stable amplitude. Feed forward control is suitable for such a predictable disturbance. Therefore, the switching time of the semiconductor switch elements Q1 and Q2 is controlled by feedforward so as to cancel the power supply voltage fluctuation in the inverter circuit. By adjusting the switching time according to the ripple voltage, the input voltage can be equivalently brought close to a constant voltage.

  Here, if the response characteristic of the feedforward control is designed to have a sufficient response in the vicinity of twice the frequency of the power supply frequency, it is advantageous because malfunction can be prevented. For example, if the frequency of the commercial power supply is 60 Hz, a ripple voltage of 120 Hz is generated.

  On the other hand, the feedback control operates so as to suppress lamp temperature characteristics, variations, and aging. Since these variables are difficult to predict, feedback control is suitable. In this embodiment, the increase / decrease of the lamp current is feedback controlled so that the input current is constant, and the power supplied to the lamp is controlled to be constant.

  As described above, in the present embodiment, the feedforward control and the feedback control are independently controlled with different input signals and output signals, so that the power supplied to the lamp is finally controlled to be constant. That is, the switch-on time constitutes a control system that suppresses the influence of power supply fluctuations, and the switching frequency constitutes a control system that corrects the lamp output, so that the output impedance of the inverter circuit is stably controlled. Therefore, stable lamp lighting is possible even in a dimming state where the equivalent impedance of the lamp is high. Further, since the insulation circuit can be easily configured, insulation and ripple voltage can be regulated only by the inverter circuit, and both high efficiency and suppression of flicker, which are the objects of the present invention, can be achieved at low cost.

  In the present embodiment, the push-pull type is exemplified as the configuration of the inverter circuit, but the same control is possible with a half-bridge type or a full-bulge type. In particular, in the full bridge type, power control can be performed by switching phase control, so that the use efficiency of the switch element can be increased, and the primary voltage of the transformer can be increased compared to the half bridge type, and the use efficiency of the transformer. Therefore, it is effective for downsizing the circuit.

  In the present embodiment, the lighting circuit of the discharge lamp is exemplified, but the same effect can be obtained even when the frequency of the inverter circuit is varied to adjust the amount of power to the load light source. The load light source can be applied to a light source having a positive load characteristic such as an LED.

  If this embodiment is used, the lighting device which can suppress the light fluctuation resulting from a commercial power supply and can supply electric power to a lamp with high efficiency can be provided at low cost.

(Embodiment 2)
FIG. 3 shows a lighting circuit according to the second embodiment of the present invention. The lighting circuit includes a rectifier circuit DB that rectifies the commercial power supply Vin, and a power factor correction circuit PFC that boosts and smoothes the output of the rectifier circuit DB. The power factor correction circuit PFC includes an output voltage feedback circuit CTR1. The output voltage VDC of the power factor correction circuit PFC is supplied to a push-pull inverter circuit including semiconductor switch elements Q1 and Q2, a driving circuit DRV11 thereof, and a transformer Tr1 with an intermediate tap.

  The drive circuit DRV11 has an insulating structure inside, and the semiconductor switch elements Q1 and Q2 are alternately turned ON / OFF according to the output of the pulse width modulator PWM11 connected to the insulated primary side. A series circuit of an inductor Lr1 and a fluorescent lamp Lamp1 is connected between the outputs of the secondary winding of the transformer Tr1 with an intermediate tap. The high-frequency rectangular output of the push-pull inverter circuit is supplied to the fluorescent lamp Lamp1 via the inductor Lr1.

  Further, a feedback circuit for controlling the lamp current to be constant is provided. That is, the current flowing through the lamp Lamp1 is detected by the current detection circuit DET1, and the detection signal is input as a comparison value for the feedback controller FB1. The target value signal Aim from the dimmer Dim1 is input to the feedback controller FB1. The feedback controller FB1 sends the frequency setting signal Frq to the pulse width modulator PWM11 so that the comparison value matches the target value Aim.

  Also provided is a feedforward controller FF1 that receives the secondary winding voltage of the choke transformer L1 of the power factor correction circuit PFC and supplies the pulse width signal Dty1 to the pulse width modulator PWM11 so that the lamp current becomes constant. . Since a voltage corresponding to the input voltage of the power factor correction circuit PFC is generated in the choke transformer L1, fluctuations in the ripple voltage can be detected and can be used for feedforward control. In addition, the broken line which shows an insulation part has shown that the power supply side and the load side are insulated from this, and the core of each transformer is independent.

  In the present embodiment, feedback control design will be described. As described above, the feedback control operates so as to suppress the temperature characteristics, variations, and aging of the lamp. Since these variables are difficult to predict, feedback control is suitable. However, if feedforward control and feedback control are performed simultaneously, the lighting control may become unstable. As a result, there is a problem that the lamp flickers.

  In order to solve this problem, the responsiveness of feedback control is appropriately set. In the present embodiment, the feedback control is a control that suppresses the temperature characteristics, variations, and aging of the lamp, so there is no problem even if the response speed of the control is designed to be relatively slow. Therefore, the feedback control may be designed so as not to respond in the frequency region where the feedforward control mainly operates. That is, a low-pass filter is provided in the feedback loop, and the feedback circuit is designed so that the feedback gain becomes 1 (0 dB) in a band twice the commercial power supply frequency.

  FIG. 4 is an explanatory diagram showing an example of the design, and shows changes in gain with respect to the frequency of feedforward control and feedback control. From the figure, it can be seen that the feedforward control has a characteristic of reducing the gain with the frequency fc1 as a pole, and the feedback control has a characteristic of reducing the gain with the frequency fc2 as a pole. The gain of feedback control is 1 (0 dB) at the frequency fc1.

  Here, the frequency fc1 is set to twice the commercial power supply frequency. That is, when the commercial power supply frequency is 50 Hz, the frequency fc1 is 100 Hz. The feedback control is set not to respond at this frequency fc1. In this way, unstable operation of feedback control due to power supply ripple can be prevented.

  By the way, at the frequency lower than the frequency fc2 in this gain characteristic, the gains of both the feedforward control and the feedback control are maximized, but this is not a problem. This is because the only disturbance factor that is actually subject to feedback control is the variation in power supply ripple and DC voltage. That is, constant voltage control is effective for the output voltage VDC of the power factor correction circuit PFC below the commercial power supply frequency. The variation in DC voltage is due to a shift in the control command value of the power factor correction circuit PFC, and is not a periodic variation. Therefore, the lamp does not flicker in response to the feedback control. If periodic voltage fluctuations that cannot be stabilized by the power factor correction circuit PFC occur, the cut-off frequency fc2 may be set lower.

  If this embodiment is used, the lighting device which can suppress the light fluctuation resulting from a commercial power supply and can supply electric power to a lamp with high efficiency can be provided at low cost.

(Embodiment 3)
FIG. 5 shows a lighting circuit according to Embodiment 3 of the present invention. The lighting circuit rectifies the commercial power supply Vin, outputs the DC voltage VDC by smoothing the output of the rectifier DB, and inputs the output of the power factor correction circuit PFC to output a high-frequency voltage. Inverter circuits INV1 to INV3 and ballast elements Z1 to Z3 connected to the outputs of the inverter circuits INV1 to INV3 are provided. The lamps Lamp1 to Lamp3 are connected to inverter circuits INV1 to INV3 via ballast elements Z1 to Z3, respectively. Each inverter circuit INV1 to INV3 is operated by pulse width modulators PWM1 to PWM3.

  The oscillation frequency of the pulse width modulators PWM1 to PWM3 is determined by the feedback controller FB1. Further, the ON duty (switch ON time) of the pulse width modulators PWM1 to PWM3 is individually determined by the outputs of the adders ADD1 to ADD3. The adders ADD1 to ADD3 perform an operation of adding the output of the feedforward controller FF1 and the adjustment values Adj1 to Adj3 corresponding to the respective adders ADD1 to ADD3.

  In this embodiment, it is possible to solve flickering and unevenness that occur when a plurality of lamps Lamp1 to Lamp3 are turned on at the same frequency. The ballast elements Z1 to Z3 for stabilizing the lamp current of the lighting circuit have element variations, which affect the lamp current variations. The ballast elements Z1 to Z3 often use reactance elements such as inductors or capacitors in order to reduce losses. In order to correct variations in lamp current due to variations in the elements, a deviation is provided in the operating frequency of the inverter circuit. Adjustments are generally made. However, this frequency correction has a problem of voltage interference due to a frequency difference. That is, when the lamps are lit by a plurality of inverter circuits, voltage interference occurs between the lamps due to the frequency difference of the inverter circuits, and the lamp current changes and flickers.

  Therefore, in the present embodiment, the operation frequency of each of the inverter circuits INV1 to INV3 is controlled to be constant, and an adjustment circuit is individually provided for the switch-on time, thereby avoiding flicker due to voltage interference and reducing lamp current variation. It is. For example, when the lamp current increases by 5% due to variations in the ballast element Z1, the on-time of the switch element of the inverter circuit INV1 is shortened by about 5% of the standard by the adjustment value Adj1. That is, if the standard is an on time with a duty of 40%, the adjustment value Adj1 may be set so that the duty is around 38%. Adjustment values Adj1 to Adj3 can be easily set at the time of product adjustment using a semi-fixed resistor or a trimming resistor. It is also possible to perform self-adjustment during use using digital storage means. Further, if the switching elements of the inverter circuits INV1 to INV3 are PWM controlled using the timer function of the microprocessor, the control circuit can be greatly simplified. That is, since high-speed calculation is not required for the feedback control unit FB1 and the feedforward control unit FF1, many inverter circuits INV1 to INV3 can be controlled simultaneously by one microprocessor.

  By using this embodiment, even in a lighting circuit for lighting a large number of lamps at once, a lighting device capable of suppressing light fluctuation caused by a commercial power supply and supplying power to the lamp with high efficiency can be provided at low cost. .

(Embodiment 4)
FIG. 6 shows a lighting circuit according to a fourth embodiment of the present invention. The lighting circuit rectifies the commercial power supply Vin, outputs the DC voltage VDC by smoothing the output of the rectifier DB, and inputs the output of the power factor correction circuit PFC to output a high-frequency voltage. An inverter circuit INV1 and a ballast element Z1 connected to the output of the inverter circuit INV1 are provided. The discharge lamp Lamp1 is connected to the output of the inverter circuit INV1 via the ballast element Z1. The inverter circuit INV1 is operated by the pulse width modulator PWM1.

  The oscillation frequency of the pulse width modulator PWM1 is determined by the feedback controller FB1. The on-duty (switch ON time) of the pulse width modulator PWM1 is determined by the output of the adder ADD1. The adder ADD1 performs an operation of adding the output of the feedforward controller FF1 and the signal of the sweep generator Swp.

  FIG. 7 shows the operation of this embodiment. FIG. 7 shows from the top the time variation of the output voltage VDC of the power factor correction circuit PFC, the duty control signal Dty1 of the pulse width modulator PWM1, the signal output of the sweep generator Swp, and the current flowing through the lamp Lamp1. The sweep generator Swp periodically generates a trapezoidal voltage. That is, the voltage is gradually increased from time t1 to t2, maintained at t2 to t3, and gradually decreased from t3 to t4. The operation similar to the period from t1 to t5 is repeated after time t5.

  The signal output of the sweep generator Swp and the signal of the feedforward controller FF1 are added to generate the duty control signal Dty1 of the pulse width modulator PWM1 as shown in the figure. Based on the duty control signal Dty1 of the pulse width modulator PWM1, the inverter circuit INV1 controls the ON time of the switch element. As a result, the lighting current of the lamp Lamp1 is also so-called burst lighting in which the current is periodically generated with a slope.

  The period from time t1 to t2 is a period for starting the lamp by increasing the output voltage of the inverter circuit INV1. Times t3 to t4 are periods in which the output voltage of the inverter circuit INV1 is lowered to turn off the lamp.

  This embodiment has an effect of reducing light fluctuations in the starting part and the extinguishing part of the lamp in burst lighting control. When the lamp output is high, the lighting period such as the period t2 to t3 is long, the influence of light fluctuations at the starting part and the extinguishing part of the lamp is small, and the problem that the light fluctuates hardly occurs. However, in the deep dimming state in which the periods t2 to t3 are shortened, the ratio of light in the starting part and the extinguishing part is increased. Therefore, there is a problem that the light fluctuates due to the lamp voltage change in the starting part and the extinguishing part due to the fluctuation of the input voltage of the inverter circuit.

  Therefore, in the present embodiment, the gain Gain of the feedforward controller FF1 is changed according to the signal of the sweep generator Swp. That is, when the duty control signal Dty1 is small, the gain of the feedforward control is decreased, and the gain of the feedforward control is gradually increased as the level of the duty control signal Dty1 increases. By doing so, it is possible to suppress variations in the output voltage of the inverter circuit due to fluctuations in the input voltage of the inverter circuit even during the sweep.

  By using this embodiment, even in a lighting circuit that performs deep dimming, it is possible to provide a lighting device that can suppress light fluctuation caused by a commercial power supply and can supply power to a lamp with high efficiency at low cost.

(Embodiment 5)
FIG. 8 is an exploded perspective view showing a schematic configuration of a liquid crystal display device using the lighting device of the present invention. A backlight device is disposed on the back surface (directly below) of the liquid crystal panel LCP. The backlight device includes a housing 22, a reflector 23 installed thereon, a plurality of discharge lamps Lamp1 to Lamp4, and an upper portion thereof. It comprises an installed diffusion plate 25 and an optical sheet 26 such as a prism sheet. In addition, a lamp lighting device 21 for lighting the discharge lamps Lamp1 to Lamp4 is installed on the back surface of the housing 22. The reflector 23 effectively directs the irradiation light of each of the discharge lamps Lamp1 to Lamp4 toward the front surface. The diffusion plate 25 has a function of diffusing the light from the discharge lamps Lamp1 to Lamp4 and the reflection plate 23 to average the brightness distribution of the illumination light to the front surface.

  Needless to say, the use of the lighting device of the present invention is not limited to a backlight device of a liquid crystal display device, and can be mounted on a general lighting fixture.

It is a circuit diagram of Embodiment 1 of the present invention. It is operation | movement explanatory drawing of Embodiment 1 of this invention. It is a circuit diagram of Embodiment 2 of the present invention. It is operation | movement explanatory drawing of Embodiment 2 of this invention. It is a circuit diagram of Embodiment 3 of the present invention. It is a circuit diagram of Embodiment 4 of the present invention. It is operation | movement explanatory drawing of Embodiment 4 of this invention. It is a disassembled perspective view which shows schematic structure of the liquid crystal display device using the lighting device of this invention.

Explanation of symbols

FF1 feedforward controller FB1 feedback controller

Claims (8)

A rectifier for rectifying a commercial power supply; at least one smoothing circuit for smoothing an output of the rectifier; an inverter circuit having a switch element for inputting an output of the smoothing circuit and outputting a high-frequency voltage; and an output of the inverter circuit; An impedance element inserted between lamps as a load; frequency setting means for setting a drive frequency of the inverter circuit; and the frequency so that a current corresponding to an input current or a lamp current of the inverter circuit becomes a constant value. A feedback circuit for controlling the setting means; a pulse width setting means for setting an ON time or a switching phase of the switching element of the inverter circuit; and an input voltage of the inverter circuit or an input voltage of the smoothing circuit to detect the inverter circuit. A feed signal for supplying a control signal for correcting the output to the pulse width setting means. Lighting device characterized in that it comprises a chromatography de circuit. 2. The smoothing circuit includes means for controlling the output voltage to be substantially constant, and the feedforward circuit controls a switch-on duty ratio of the inverter circuit in a range of 30% to 50%. Lighting device. 3. The pulse width setting means includes adjustment means for adding a predetermined value to the output of the feedforward circuit, and controls the switch element of the inverter circuit according to the output of the adjustment means. Lighting device. The lighting device according to claim 1, wherein the feedforward circuit increases a gain according to a set value of the pulse width setting unit. The lighting device according to any one of claims 1 to 4, wherein the feedback circuit includes a low-pass filter, and has a point that a closed circuit gain becomes 1 at a frequency equal to or less than twice a frequency of a commercial power source. The smoothing circuit includes a DC voltage detector that detects an output voltage, and the feedforward circuit detects an output of the DC voltage detector and corrects an output of the inverter circuit. The lighting device according to any one of 5. The lighting fixture provided with the lighting device in any one of Claims 1-6. The backlight apparatus provided with the lighting device in any one of Claims 1-6.

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