JP2007220562A - Discharge lamp lighting device, lighting apparatus, backlight device for liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device capable of lighting in order or light-controlling in order a plurality of discharge lamps with a small number of circuit components. <P>SOLUTION: The discharge lamp lighting device has a plurality of load circuits A1, A2, A3, A4, to which a discharge lamp is connected, connected in series, and is provided with a plurality of switching elements Q1, Q3, Q5, Q7 on high potential side which respectively connect both ends of each load circuit A1, A3, A5, A7 to the positive electrode of DC power supply Vdc, a plurality of switching elements Q2, Q4, Q6, Q8 on low potential side which respectively connect both ends of respective load circuits A1, A2, A3, A4 to the negative electrode of the DC power supply Vdc, and a control circuit 5 which controls respective switching elements Q1-Q8 so that high frequency current may flow into at least one load circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device, a lighting fixture using the same, and a backlight device for liquid crystal display.

  2. Description of the Related Art Conventionally, liquid crystal display devices with a backlight device have been widely used as image display devices for personal computers and flat-screen televisions. In this type of liquid crystal display device, when high-speed moving image display is attempted, the response time of the liquid crystal is slow, so that a tailing phenomenon due to an afterimage occurs and display quality is deteriorated.

  Therefore, as disclosed in Patent Document 1 and Patent Document 2, a light emitting unit having a plurality of light emitting regions is arranged on the back surface of the liquid crystal display unit, and the timing for increasing the light emission intensity of each light emitting region is synchronized with the vertical synchronization signal. After the data has been written to the pixels of the liquid crystal display, it is controlled to increase the light emission intensity when the liquid crystal responds, thereby making the progress of the optical response of the liquid crystal less noticeable. A technique for preventing the deterioration of display quality is known.

  FIG. 16 shows a schematic configuration of a conventional liquid crystal display device. The liquid crystal panel 10 includes a gate driver 11 that drives scanning lines and a source driver 12 that drives signal lines, and the liquid crystal panel control circuit 13 writes luminance information of a video signal to each pixel. A plurality of discharge lamps 14 are arranged on the back surface of the liquid crystal panel 10 at substantially equal intervals, and each discharge lamp 14 is turned on by the output of the corresponding inverter 15. The inverter control circuit 16 controls the output of the inverter 15 so that the discharge lamps 14 are sequentially turned on (or sequentially dimmed) in synchronization with the vertical synchronization signal.

  Patent Document 1 or 2 does not disclose a specific configuration of the inverter, but one inverter is used for one lamp. As the inverter, a known full bridge circuit (FIG. 17A) or a half bridge circuit (FIG. 17B) can be used.

  In the full bridge circuit of FIG. 17A, switching elements Q1 and Q4 are on, switching elements Q2 and Q3 are off, switching elements Q1 and Q4 are off, and switching elements Q2 and Q3 are on. Is used to turn on the discharge lamp La1 at high frequency via the resonance circuit of the inductor L1 and the capacitor C1.

In the half-bridge circuit of FIG. 17B, the switching elements Q1 and Q2 are alternately turned on and off at a high frequency, thereby supplying a high-frequency voltage to the resonance circuit of the inductor L1 and the capacitor C1 via the DC cut capacitor Cc. The discharge lamp La1 is lit at a high frequency by a resonance action.
JP-A-11-202286 JP 2002-72988 A

  In the case of the conventional example of FIG. 16, the tailing phenomenon of the liquid crystal display device is suppressed by sequentially lighting (or sequentially dimming) the discharge lamps by the outputs of a plurality of inverters individually provided for each discharge lamp. However, since one inverter is used for one lamp, it causes an increase in size and cost of the apparatus.

  As an example of a circuit used as an inverter, when the full bridge circuit of FIG. 17A is used, the switching element needs to be four times as many as the number of lamps, and the switching element driving circuit is also four times as many as the number of lamps. This is necessary and causes an increase in cost. When the half-bridge circuit of FIG. 17B is used, the total number of switching elements and drive circuits is halved compared to the case of using the full-bridge circuit of FIG. 17A, but is applied to both ends of the load circuit. Since the voltage to be supplied is about half that of the DC power supply Vdc, the power supply utilization efficiency is poor. Further, the DC cut capacitor Cc is required, and there are disadvantages that the number of parts is large, miniaturization is difficult, and the cost is high.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a discharge lamp lighting device capable of sequentially lighting or dimming a plurality of discharge lamps with a small number of circuit components. There is to do.

  In the present invention, in order to solve the above problem, as shown in FIG. 1, a plurality of load circuits A1, A2, A3, A4 to which discharge lamps are connected are connected in series, and each load circuit A1 is connected. , A2, A3, A4, a plurality of switching elements Q1, Q3, Q5, Q7 on the high potential side connecting both ends of the DC power supply Vdc to each other, and both ends of each load circuit A1, A2, A3, A4 connected to the DC power supply A plurality of low-potential-side switching elements Q2, Q4, Q6, and Q8 that are respectively connected to the negative electrode of Vdc, and a control circuit 5 that controls the switching elements Q1 to Q8 so that a high-frequency current flows through at least one load circuit. It is characterized by comprising.

  According to the present invention, compared to the case where a full-bridge inverter is used individually for each discharge lamp, a plurality of discharge lamps can be lit at a high frequency with about half of the switching elements. Can be reduced in size and cost. In addition, compared to the case where a half-bridge inverter is used for each discharge lamp, the applied voltage to the load circuit including the discharge lamp can be increased, so that the use efficiency of the DC power source is increased and a large-capacity capacitor is used. There is also an advantage that becomes unnecessary.

(Embodiment 1)
FIG. 1 is a circuit diagram of Embodiment 1 of the present invention. In this example, a basic circuit configuration (FIGS. 1 and 2) will be described, and a control operation (FIG. 3) that enables sequential lighting of each lamp using this circuit configuration will be described.

  First, the circuit configuration of FIG. 1 will be described. In parallel with DC power supply Vdc, a series circuit of switching elements Q1 and Q2, a series circuit of switching elements Q3 and Q4, a series circuit of switching elements Q5 and Q6, and a series circuit of switching elements Q7 and Q8 are connected. Switching elements Q1, Q3, Q5, Q7 are high potential side switching elements connected to the positive side of DC power supply Vdc, and switching elements Q2, Q4, Q6, Q8 are low potential side connected to the negative side of DC power supply Vdc. Switching element. The high-potential side switching element and the low-potential side switching element connected in series between the positive electrode and the negative electrode of the DC power supply Vdc are not simultaneously controlled to be turned on.

  A load circuit A1 including a discharge lamp is connected between the connection point of the switching elements Q1, Q2 and the connection point of the switching elements Q3, Q4. A load circuit A2 including a discharge lamp is connected between the connection point of the switching elements Q3 and Q4 and the connection point of the switching elements Q5 and Q6. A load circuit A3 including a discharge lamp is connected between the connection point of the switching elements Q5 and Q6 and the connection point of the switching elements Q7 and Q8. A load circuit A4 including a discharge lamp is connected between the connection point of the switching elements Q7 and Q8 and the connection point of the switching elements Q1 and Q2. As a result, the load circuits A1, A2, A3, and A4 are connected in series in a ring shape as a whole.

  Load circuits A1 and A2 share switching elements Q3 and Q4, load circuits A2 and A3 share switching elements Q5 and Q6, and load circuits A3 and A4 share switching elements Q7 and Q8. The load circuits A4 and A1 share the switching elements Q1 and Q2.

  Each of the switching elements Q1 to Q8 is turned on / off at a high frequency by a drive signal from the control circuit 5, and supplies power to the discharge lamps in the load circuits A1 to A4.

  FIG. 2 shows a configuration example of the load circuit A1. In this example, the load circuit A1 includes a discharge lamp La1 made of a hot cathode fluorescent lamp having a pair of filament electrodes and an LC resonance circuit. The LC resonance circuit includes an inductor L1 connected in series with the discharge lamp La1 and a capacitor C1 connected in parallel between terminals on the filament electrode of the discharge lamp La1 that are not connected to the switching circuit. It is well known that the preheating, starting, lighting or dimming operations of the discharge lamp La1 are appropriately performed by controlling the high frequency supplied from the switching circuit to the LC resonance circuit. The other load circuits A2, A3, and A4 are assumed to have the same configuration as the load circuit A1 shown in FIG.

  FIG. 3 shows the driving signals of the respective switching elements Q1 to Q8 with respect to the vertical synchronizing signal whose cycle is Tv, and the lamp lighting state. The horizontal axis is time. Note that lamps La1 to La4 in the figure indicate lamps included in the load circuits A1 to A4, respectively.

The detailed operation of this example will be described below with reference to FIG.
In the period of t1, the operation of turning on the switching elements Q1, Q4 and turning off the switching elements Q2, Q3 and the operation of turning off the switching elements Q1, Q4 and turning on the switching elements Q2, Q3 are alternately repeated at a high frequency. Only lights up.

  In the period of t2, the switching elements Q3 and Q6 are turned off, the switching elements Q4 and Q5 are turned on, and the switching elements Q3 and Q6 are turned on and the switching elements Q4 and Q5 are turned off alternately at a high frequency. Only lights up.

  During the period t3, the switching elements Q5 and Q8 are turned on, the switching elements Q6 and Q7 are turned off, and the switching elements Q5 and Q8 are turned off and the switching elements Q6 and Q7 are turned on alternately and repeatedly at a high frequency. Only lights up.

  During the period of t4, the switching elements Q7 and Q2 are turned off, the switching elements Q1 and Q8 are turned on, and the switching elements Q7 and Q2 are turned on and the switching elements Q1 and Q8 are turned off alternately at a high frequency. Only lights up.

  Thereafter, the same control as in the period of t1 is repeated again. As described above, by switching the switching elements Q1 to Q8, the lamps La1 to La4 of the load circuits A1 to A4 are sequentially turned on one by one. For example, when used for a backlight of a liquid crystal display device In addition, the tailing phenomenon can be suppressed.

  If limited to the period t1, the basic circuit operation is the same as that of the full-bridge inverter shown in the conventional example (FIG. 17A), but in the control example of FIG. The series circuit of Q2 combines the lamps La1 and La4, the series circuit of the switching elements Q3 and Q4 uses the lamps La1 and La2, etc. The use efficiency of the switching element is increased. Therefore, the total number of switching elements is eight, which is half of the total number of switching elements operated by an independent full bridge inverter.

  In addition, compared with the half-bridge inverter shown in the conventional example (FIG. 17B), the total number of switching elements is the same, but when the inverter is operated, both ends of the load circuits A1 to A4 are Since a high voltage of each DC power supply Vdc is applied, the power supply utilization efficiency is higher than that of the half-bridge inverter. In addition, since the DC cutting capacitor can be omitted, the number of parts can be further reduced, and the size and cost can be reduced.

  In this example, the case where the number of series circuits of the switching elements is four has been described. However, the number of series circuits may be any number as long as there are three or more. In particular, if there are 2N switching circuit series circuits (N is an integer equal to or greater than 2), 2N load circuits can be connected in series in a ring shape, eliminating the series circuit of switching elements that are not shared. The sharing effect of the switching elements is increased.

  In the circuit example of FIG. 1, power MOSFETs are used as the switching elements Q1 to Q8. However, other semiconductor switching elements such as transistors and IGBTs may be used.

  Further, the load circuit is not limited to the configuration shown in FIG. 2. For example, in FIG. 2, a capacitor preheating system that supplies a preheating current via the resonance capacitor C1 is used. However, the secondary winding of the inductor L1 is used. For example, a winding preheating method for supplying a preheating current may be adopted. Alternatively, a plurality of discharge lamps may be connected in series or in parallel in one load circuit. Further, a transformer type in which a primary winding of a step-up transformer is connected to a location where the load circuit of FIG. 1 is connected, and power is supplied from the secondary winding of the step-up transformer to the discharge lamp may be used.

  Further, as an example of a discharge lamp, a hot cathode type is described, but a cold cathode type or an external electrode type discharge lamp may be used.

  When the discharge lamp lighting device of the present embodiment is applied to a backlight device of a liquid crystal display device, the lighting device capable of suppressing the tailing phenomenon can be configured with a small number of parts, and downsizing and cost reduction are possible.

(Embodiment 2) (Batch lighting)
FIG. 4 is a waveform diagram for explaining the operation of the second embodiment of the present invention. In this example, an operation when all the lights are turned on or off at once will be described. The circuit configuration is the same as in FIGS.

  As shown in FIG. 4, the switching elements Q1, Q4, Q5, Q8 are turned on, the switching elements Q2, Q3, Q6, Q7 are turned off, the switching elements Q1, Q4, Q5, Q8 are turned off, the switching elements Q2, By repeating the operation of turning on Q3, Q6, and Q7 alternately at a high frequency, all the discharge lamps La1 to La4 are turned on (ON). Further, all the switching elements Q1 to Q8 are turned off, so that all the discharge lamps La1 to La4 are turned off (off).

  This example is effective when, for example, all the lamps are to be turned on at the time of start-up, or when the control circuit 5 is turned off by cutting off only the drive signal while energized, as in the standby mode. . In the standby mode, it can be turned on at an arbitrary timing from the state in which all the lamps are off regardless of the charging time of the control power source or the like.

  Note that when all the lights are turned on at the time of start-up, it is possible to use a change in the frequency of the LC resonance as used in a general inverter. That is, at the time of preheating, by setting the frequency of the drive signal of each switching element Q1 to Q8 to a frequency sufficiently higher than the resonance frequency of the resonance circuit, a sufficient preheating current is supplied to each filament of the discharge lamp. By lowering the frequency of the drive signal so as to approach the resonance frequency of the resonance circuit, a high voltage due to LC resonance is applied to both ends of the discharge lamp to start. At the time of lighting, the frequency of the drive signal is set so that an appropriate lamp current flows through the discharge lamp.

  According to the present embodiment, all lamps can be turned on and off with simple control. Moreover, since the on / off timings of the switching elements are synchronized for all the lamps, light interference between the lamps can be suppressed.

(Embodiment 3) (Two lights are turned on sequentially)
FIG. 5 is a waveform diagram for explaining the operation of the third embodiment of the present invention. The circuit configuration is the same as in FIGS. FIG. 5 shows the driving signals of the respective switching elements Q1 to Q8 with respect to the vertical synchronizing signal whose cycle is Tv, and the lamp lighting state. The horizontal axis is time. Note that lamps La1 to La4 in the figure indicate lamps included in the load circuits A1 to A4, respectively.

In this example, a control operation in the case of sequentially lighting two lights at a time will be described.
In the period between t1 and t2, the switching elements Q1, Q4, Q5 are turned on, the switching elements Q2, Q3, Q6 are turned off, the switching elements Q1, Q4, Q5 are turned off, and the switching elements Q2, Q3, Q6 are turned on. The operation is alternately repeated at a high frequency, and the lamps La1 and La2 are turned on.

In the period between t3 and t4, the switching elements Q5, Q8, Q1 are turned on, the switching elements Q6, Q7, Q2 are turned off, the switching elements Q5, Q8, Q1 are turned off, and the switching elements Q6, Q7, Q2 are turned on. The operation is alternately repeated at a high frequency, and the lamps La3 and La4 are lit.
Thereafter, the same control as in the period of t1 and t2 is repeated again.

As in this example, if the on / off of the three arms is controlled at the same time, it is possible to sequentially turn on two lights at a time.
As can be seen from the first and third embodiments, the adjacent M arms (M is an integer of 2 or more) are simultaneously turned on / off, and one of the arms at both ends is included after a certain period of time. In addition, by repeating ON / OFF control of the adjacent M arms, it is possible to light up sequentially while simultaneously lighting M-1 lamps. Can be turned on sequentially.

  Although not shown in the waveform diagram, the periods in which the lamps La1 and La2 are lit, the periods in which the lamps La2 and La3 are lit, the periods in which the lamps La3 and La4 are lit, and the periods in which the lamps La4 and La1 are lit are sequentially switched. You may control to.

(Embodiment 4) (Sequential dimming with two lamps)
FIG. 6 is a waveform diagram for explaining the operation of the fourth embodiment of the present invention. The circuit configuration is the same as in FIGS. In FIG. 6, the driving signal of each switching element Q1-Q8 with respect to the vertical synchronizing signal whose period is Tv, and the lighting state of the lamp are shown. Full indicates a full lighting state, and Dim indicates a dimming lighting state.

  In this example, a description will be given of a control operation in which dimming is performed sequentially so that two lamps become brighter and the other two lights become darker from period t1 to period t4 without turning off any lamp. Basically, the lighting frequency of all the lamps La1 to La4 is set to the frequency fd at the time of full lighting.

  In the period t1, only the switching elements Q1 and Q2 are turned on / off alternately at a dimming frequency of 2 × fd, so that the lamps La4 and La1 are dimmed and the lamps La2 and La3 are all lit.

  In the period t2, only the switching elements Q3 and Q4 are turned on / off alternately at a dimming frequency of 2 × fd, whereby the lamps La1 and La2 are dimmed and the lamps La3 and La4 are all lit.

  In the period t3, only the switching elements Q5 and Q6 are alternately turned on / off at a dimming frequency of 2 × fd, so that the lamps La2 and La3 are dimmed and the lamps La4 and La1 are fully lit.

  In the period t4, only the switching elements Q7 and Q8 are alternately turned on / off at a dimming frequency of 2 × fd, whereby the lamps La3 and La4 are dimmed and the lamps La1 and La2 are all lit.

  Thereafter, the control from the period t1 is repeated again. By synchronizing the frequency fd in the fully lit state and the frequency 2 × fd in the dimming lit state, it is possible to control the dimming sequentially with a simple frequency dividing circuit. Therefore, compared with a conventional sequential dimming method realized by separate inverters, simple control is sufficient, and for example, special control for synchronization between control ICs is not required.

  If this control is used, it is not necessary to turn off the lamp over the entire period from t1 to t4. For this reason, a starting voltage for starting the lamp from the off state to the on state is applied, for example, with a fluorescent lamp having a hot cathode. There is no need to do this, only switching control of the operating frequency is required, and the stress of the switching element is reduced.

  It should be noted that the frequencies in the fully lit state and the dimming lighting state may be an integral multiple, for example, the dimming frequency may be three times the fd with respect to the frequency fd in the fully lit state.

  In this example, the case of four lamps has been described, but it goes without saying that even if the number of lamps is large, the dimming control can be performed sequentially.

  Also in the above-described third embodiment (FIG. 5), the drive signals of the switching elements Q7 and Q8 are not stopped in the periods t1 and t2, but the frequency fd of the drive signals of the other switching elements Q1 to Q6 is not stopped. If an integral multiple of the drive signal is supplied, the extinguished lamps La3 and La4 can be brought into the dimming lighting state, and similarly, the drive signals of the switching elements Q3 and Q4 are stopped in the periods t3 and t4. Instead, if a drive signal that is an integral multiple of the frequency fd of the drive signals of the other switching elements Q1, Q2, Q5 to Q6 is supplied, the extinguished lamps La1 and La2 can be brought into a dimming lighting state.

(Embodiment 5) (One lamp is turned off)
FIG. 7 is a waveform diagram for explaining the operation of the fifth embodiment of the present invention. The circuit configuration is the same as in FIGS. FIG. 7 also shows the driving signals of the respective switching elements Q1 to Q8 with respect to the vertical synchronization signal whose cycle is Tv, and the lamp lighting state. The horizontal axis is time. Lamps La1 to La4 in the figure indicate lamps included in the load circuits A1 to A4, respectively.

  In this example, a description will be given of a control operation in the case where lighting is sequentially performed while only one lamp is turned off.

  7 is different from FIG. 3 in that the state of the switching element in the period t1 is always off. That is, the difference is that all the switching elements Q1 to Q4 are turned off in the period t1 during which the lamp La1 is turned on in FIG.

  By controlling in this way, for example, when an abnormality is detected in the lamp by a detection circuit (not shown), the other lamps can be continuously turned on with only one lamp turned off. By controlling in this way, it is possible to notify the user without reducing the illuminance around the position of the abnormal lamp as much as possible.

  Here, the control example in which only the lamp La1 is turned off has been described, but in FIG. 3, the switching signals corresponding to the arbitrary lamps are all turned off during the lighting period of the lamp, so that the remaining lamps are sequentially turned on. Needless to say, it is possible to turn off only an arbitrary lamp while the lighting is maintained.

  Unlike the conventional example shown in FIG. 17, for example, in this circuit, even when only one lamp is turned off, the switching element connected to the lamp is not turned off for the entire period. It is characterized by being used for lighting.

(Embodiment 6) (Sequential start)
FIG. 8 is a waveform diagram for explaining the operation of the sixth embodiment of the present invention. The circuit configuration is the same as in FIGS. In FIG. 8, the driving signals of the switching elements Q1 to Q8 and the lamp lighting state are shown. The horizontal axis is time. Lamps La1 to La4 in the figure indicate lamps included in the load circuits A1 to A4, respectively.

In this example, a case where the lamps La1 to La4 are sequentially started will be described.
In the period from a1 to a2, the operation of turning on the switching elements Q1 and Q4 and turning off the switching elements Q2 and Q3 and the operation of turning off the switching elements Q1 and Q4 and turning on the switching elements Q2 and Q3 are repeated at a high frequency. Lights up.

  More specifically, during preheating, a sufficient preheating current is supplied to the filament of the lamp La1 by setting the frequency of the drive signal of each switching element Q1 to Q4 to a frequency sufficiently higher than the resonance frequency of the resonance circuit. At the time of starting, by reducing the frequency of the drive signal so as to approach the resonance frequency at the time of no load of the load circuit A1, a high voltage due to no load resonance is applied to both ends of the lamp La1, thereby starting the lamp La1. After the lighting, the frequency of the drive signal of the switching elements Q1 to Q4 is set high so that the lamp La1 is in a dimming state, so that the next lamp La2 is started.

  During the period from a2 to a3, the switching elements Q1 to Q4 are operated, and the switching elements Q5 and Q6 are further turned on and off at a high frequency to light the lamp La2. That is, the switching elements Q1, Q4, and Q5 are turned on, the switching elements Q2, Q3, and Q6 are turned off, and the switching elements Q1, Q4, and Q5 are turned off and the switching elements Q2, Q3, and Q6 are turned on at high frequencies. In addition to the lamp La1, the lamp La2 is also turned on.

  More specifically, the frequency of the drive signal of the switching elements Q1 to Q6 is set sufficiently higher than the resonance frequency of the resonance circuit so that the lamp La1 is dimmed, and a preheating current is passed through the filament of the lamp La2. . Next, by reducing the frequency of the drive signal so as to approach the resonance frequency of the load circuit A2 when there is no load, a high voltage due to no-load resonance is applied to both ends of the lamp La2, thereby starting the lamp La2. At this time, since the lamp La1 has already been started, the resonance frequency when the load circuit A1 is lit is lower than the resonance frequency when there is no load, and an excessive voltage is not applied to the lamp La1. After the lamp La2 is turned on, the frequency of the drive signal for the switching elements Q1 to Q6 is set high so that the lamps La1 and La2 are in a dimming state to prepare for the next start of the lamps La3 and La4.

  During the period from a3 to a4, the switching elements Q1 to Q6 are operated and the switching elements Q7 and Q8 are further turned on and off at a high frequency to light the lamps La3 and La4. That is, the switching elements Q1, Q4, Q5, and Q8 are turned on, the switching elements Q2, Q3, Q6, and Q7 are turned off, the switching elements Q1, Q4, Q5, and Q8 are turned off, and the switching elements Q2, Q3, Q6, and Q7 are turned off. Is turned on at a high frequency to turn on the lamps La3 and La4 in addition to the lamps La1 and La2.

  More specifically, the frequency of the drive signals of the switching elements Q1 to Q8 is set sufficiently higher than the resonance frequency of the resonance circuit so that the lamps La1 and La2 are dimmed, and the filaments of the lamps La3 and La4 Apply preheating current. Next, by reducing the frequency of the drive signal so as to approach the resonance frequency at the time of no load of the load circuits A3, A4, a high voltage due to no load resonance is applied to both ends of the lamps La3, La4, and the lamps La3, La4. Start. At this time, since the lamps La1 and La2 are already started, the resonance frequency when the load circuits A1 and A2 are turned on is lower than the resonance frequency when no load is applied, and an excessive voltage is applied to the lamps La1 and La2. It will never be done. After the lamps La3 and La4 are turned on, the frequency of the drive signal for the switching elements Q1 to Q8 is set so that the current at the time of lighting is supplied to the lamps La1 to La4.

  By controlling in this way, it is possible to sequentially delay the peak of power input to start the lamp in time, and lower the peak value of input power compared to the case where all lamps are started at once. Can be suppressed. However, since the inverter arm is also used, the last two lights are started simultaneously.

  According to the present embodiment, by distributing the input power at the time of starting the lamp, the stress on the input power supply of the inverter can be reduced, and for example, the smoothing capacitor can be downsized.

  In each of the embodiments described so far, the input power source of the inverter has been described as the DC power source Vdc. However, the present invention is not limited to this. For example, a commercial AC power source Vs as shown in FIG. The voltage may be boosted at. As is well known about the configuration and operation of the step-up chopper circuit, a series circuit of an inductor L and a switching element Q is connected to the output of a diode bridge circuit DB for full-wave rectifying the commercial AC power supply Vs, and a diode is connected to both ends of the switching element Q. A smoothing capacitor C is connected via D, and the DC voltage obtained by boosting the rectified output voltage of the diode bridge circuit DB is charged to the smoothing capacitor C by turning on and off the switching element Q at a high frequency. Is done.

  FIG. 10 is a circuit diagram showing a generalized configuration of the inverter according to the present invention in the case of n load circuits (n is an even number). When the number n of load circuits is an even number, as shown in FIG. 10, the load circuits A1 to A (n) can be connected in series as a whole, so two series circuits of all switching elements are provided. Since the load circuit can be shared and the series circuit of the switching elements that are not shared can be eliminated, the switching element sharing effect is enhanced. If n is an odd number, the load circuit A (n) in FIG. 10 may be removed.

(Embodiment 7) (Feedback control)
FIG. 11 is a circuit diagram of Embodiment 7 of the present invention. In this example, a detection circuit 6 surrounded by a dotted line detects a load current, and an output adjustment signal is given to the control circuit 5 via a feedback circuit 7 also surrounded by a dotted line, thereby arbitrarily setting a reference voltage. The feedback control of the load current is performed so that the command value defined by Vk is obtained.

  A low resistance R1 for current detection is inserted between the source electrode of the switching element Q2 on the low potential side and the negative electrode of the DC power supply Vdc, and the combined current flowing through the load circuit A4 and the load circuit A1 is detected.

  A low resistance R2 for current detection is inserted between the source electrode of the switching element Q4 on the low potential side and the negative electrode of the DC power supply Vdc, and the combined current flowing through the load circuit A1 and the load circuit A2 is detected.

  A low resistance R3 for current detection is inserted between the source electrode of the switching element Q6 on the low potential side and the negative electrode of the DC power supply Vdc, and the combined current flowing through the load circuit A2 and the load circuit A3 is detected.

  A low resistance R4 for current detection is inserted between the source electrode of the switching element Q8 on the low potential side and the negative electrode of the DC power supply Vdc, and the combined current flowing through the load circuit A3 and the load circuit A4 is detected.

  The non-ground side terminals of the current detection resistors R1, R2, R3, and R4 are connected to the anode terminals of the diodes D1 to D4. The cathode terminals of the diodes D1 to D4 are connected to the inverting input terminal (− side terminal) of the operational amplifier OP via resistors Rd and Ri. A capacitor Cd is connected between the connection point of the resistors Rd and Ri and the ground. A reference voltage Vk is connected between the non-inverting input terminal (+ side terminal) of the operational amplifier OP and the ground. A capacitor Cf is connected between the output terminal of the operational amplifier OP and the inverting input terminal (− terminal). An output signal of the operational amplifier OP is input to the control circuit 5.

  The control circuit 5 adjusts the load current flowing through the load circuits A1 to A4 by variably controlling the operating frequency or on time width (on duty) of the switching elements Q1 to Q8 using the output signal of the operational amplifier OP as an output adjustment signal. Is possible.

  When the control circuit 5 controls each of the switching elements Q1 to Q8 as shown in the waveform diagram of FIG. 5, a current corresponding to two lamps according to the period flows through the switching elements Q4 and Q8 on the low potential side. However, because of the sequential lighting, an averaged DC voltage appears on the capacitor Cd. Feedback control is performed so that the voltage value of the capacitor Cd converges to the reference voltage Vk by comparing the DC voltage with the reference voltage Vk and passing through an integration circuit constituted by the operational amplifier OP. By controlling in this way, since it is not necessary to control for each lamp, the configuration of the control unit can be simplified.

  Further, when the control circuit 5 controls each of the switching elements Q1 to Q8 as shown in the waveform diagram of FIG. 4, the switching elements Q2, Q4, Q6, and Q8 on the low potential side are respectively connected to lamps for the collective lighting. Although the current for two lamps flows, since the representative value of the load current is detected by the OR circuit composed of the diodes D1 to D4, it is not necessary to control each lamp, and the configuration of the control unit is simple. Can be

  Further, when the control circuit 5 controls the switching elements Q1 to Q8 as shown in the waveform diagram of FIG. 3, the low-potential side switching elements Q2, Q4, Q6, and Q8 include one lamp corresponding to the period. However, because of the sequential lighting, an averaged DC voltage appears in the capacitor Cd. Therefore, it is possible to control the load current to be constant with the configuration of FIG. 11 in any case of sequential lighting of two lights, batch lighting of four lights, and sequential lighting of one lamp. .

  As described above, according to the configuration of this example, the feedback control is realized by detecting the combined current flowing through the shared switching element, so that individual feedback control for each discharge lamp is not required. Easy to control when lit. In addition, the circuit configuration for feedback control can be simplified, and downsizing and cost reduction are possible.

(Embodiment 8) (Abnormal protection)
FIG. 12 shows a main circuit configuration according to the eighth embodiment of the present invention. In the lighting device shown in FIG. 11, the comparison circuit 8 shown in FIG. The structure of the other parts is the same as in FIG. In this example, abnormality detection of the load circuits A1 to A4 is performed by the current flowing through the switching elements Q2, Q4, Q6, and Q8 on the low potential side.

  In the comparison circuit 8 of FIG. 12, the cathode terminals of the diodes D1 to D4 in FIG. 11 are connected to the comparison input terminal a, and are connected from the comparison input terminal a to the negative terminal of the comparator CP via the resistor Ra. A reference voltage Va is connected between the positive terminal of CP and the ground. The output of the comparator CP becomes an input signal to the control circuit 5 in FIG.

  In this circuit, when the voltage at the comparison input terminal a becomes higher than the reference voltage Va, the output of the comparator CP becomes low level. During normal lighting, if the voltage at the comparison input terminal a is set to be smaller than the reference voltage Va, the output of the comparator CP is normally at a high level. At this time, the control circuit 5 performs a normal lighting operation.

  Next, at the time of an abnormality in which an excessive current flows through the lamp, the output of the comparator CP becomes a low level. In response to the change in the output level of the comparator CP, the control circuit 5 can notify the user of the lamp abnormality by stopping the switching operation or setting the dimming mode. Or when using together with a liquid crystal panel, you may display that it is abnormal on a liquid crystal screen.

  In addition, by connecting the input terminal of the feedback circuit 7 described in FIG. 11 and the input terminal of the comparison circuit 8 in FIG. 12 in parallel, one detection circuit 6 can be used for both feedback control and abnormality detection control. It doesn't matter.

  As described above, according to the configuration of this example, since the protection at the time of abnormality is realized by detecting the combined current flowing in the shared switching element, individual abnormality detection for each discharge lamp is unnecessary. Therefore, protection in the event of an abnormality can be easily performed. In addition, the circuit configuration for abnormality protection can be simplified, and the size and cost can be reduced. Further, when the seventh and eighth embodiments are combined, one detection circuit can be used for both feedback control of load current and protection in case of abnormality, so the number of parts is reduced, and further downsizing and cost reduction can be achieved.

(Embodiment 9) (Both sides arrangement)
FIG. 13 shows a circuit configuration of the ninth embodiment of the present invention. FIG. 14 is a schematic configuration diagram of a lighting fixture or a liquid crystal display backlight device according to the present embodiment. In this example, when the lighting device described in each of the above-described embodiments is incorporated in a lighting fixture, a backlight device for liquid crystal display, or the like, the circuit, particularly the wiring of the path from the switching element to the lamp is as short as possible. A configuration arranged as described above will be described.

  FIG. 13 is a diagram in which FIG. 1 and FIG. 2 are combined. The combination of the switching elements Q1 and Q2, the inductor L1, and the capacitor C1 surrounded by a one-dot chain line is the arm 1, and similarly, the switching surrounded by the one-dot chain line. The arm 2 is a combination of the elements Q3 and Q4, the inductor L2, and the capacitor C2. The arm 3 and the arm 4 have the same configuration, but detailed illustration is omitted. In the figure, A1 and A2 surrounded by dotted lines indicate load circuits including the discharge lamp of FIG.

  After defining the arms 1 to 4 as described above, each circuit is divided into both sides of the light source unit C by dividing the substrate A of the arms 1 and 3 and the substrate B of the arms 2 and 4 as shown in FIG. Arrange. Here, the light source part C has shown the light emission part, for example of the lighting fixture or the backlight apparatus for liquid crystal displays.

  The discharge lamps La1 to La4 connected to the load circuits A1 to A4 are all straight tube lamps, and the discharge lamps of the two load circuits sharing the switching element are arranged side by side so as to be adjacent to each other. Switching elements shared between the electric lamps are alternately arranged on one end side and the other end side in the longitudinal direction of the discharge lamp.

  In the case of the lamp La1, the terminals a, b, c, and d in FIG. 13 correspond to a, b, c, and d in FIG. Therefore, since the wiring from the switching elements Q1 and Q2 in the circuit is supplied from the arm 1 to the lamp La1 and is routed to the arm 2 without returning to the arm 1 again, the wiring length can be shortened. However, for the terminal D on the capacitor C1 side, the wiring returns to the arm 1. However, the influence of the wiring length on the resonance system is larger for the terminals A and C. The terminals C and D on the capacitor C1 side are larger. The impact of is minor. Of the circuits distributed on both sides of the light source C, the ground line GND needs to be shared.

  According to this example, since the wiring can be shortened, the cost becomes low, and the wiring length of the circuit including the switching element is short, so that noise resistance can be increased.

(Embodiment 10) (one side arrangement)
FIG. 15 is a schematic configuration diagram of a lighting fixture or a liquid crystal display backlight device according to Embodiment 10 of the present invention. In this example, a configuration in which the circuit board is arranged to be as small as possible when the lighting device described in each of the above-described embodiments is incorporated in a lighting fixture, a backlight device for liquid crystal display, or the like will be described. . The circuit diagram is the same as FIG.

  Also in this example, each of the lamps La1 to La4 is a straight tube lamp. The straight tube lamps are arranged in parallel so that the longitudinal directions thereof are substantially parallel, and the arms 1 to 4 connected to the respective lamps La1 to La4 are arranged on one end side in the longitudinal direction of the straight tube lamps. Features. By arranging in this way, all the circuits are arranged on one side of the light source unit C, so that the substrate A of the arms 1 to 4 can be shared, and the circuit becomes small.

  Moreover, according to this Embodiment, the direction of the electric current which flows into the mutually adjacent lamp | ramp can be comprised oppositely. For example, when the current flowing through the lamps La1 and La3 flows from the left to the right in the figure, the current flowing through the lamps La2 and La4 can flow from the right to the left in the figure. Even when bright and dark portions occur at both ends of the light, the brightness uniformity at both ends can be averaged.

  According to this example, since the circuits can be collected in one place, the substrate can be reduced in size. In addition, the brightness uniformity of the light source unit can be maintained high.

  In the above description, an example in which the discharge lamp lighting device of the present invention is used as a backlight device for liquid crystal display has been described, but it may also be used as a backlight device for signboard lights, advertising lights, emergency lights, guide lights, traffic signs, etc. You may use it for a general indoor or outdoor lighting fixture. In short, the present invention can be applied regardless of the form of the appliance as long as it is a lighting fixture that lights a plurality of discharge lamps mounted on the appliance main body using a lighting device built in the appliance main body.

It is a circuit diagram of Embodiment 1 of the present invention. It is a circuit diagram which shows the structure of the load circuit 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 wave form diagram which shows the operation | movement of Embodiment 2 of this invention. It is a wave form diagram which shows the operation | movement of Embodiment 3 of this invention. It is a wave form diagram which shows the operation | movement of Embodiment 4 of this invention. It is a wave form diagram which shows the operation | movement of Embodiment 5 of this invention. It is a wave form diagram which shows the operation | movement of Embodiment 6 of this invention. It is a circuit diagram which shows the structure which actualized DC power supply of Embodiment 1-6 of this invention. It is a circuit diagram which generalizes and shows the structure of Embodiment 1-6 of this invention. It is a circuit diagram of Embodiment 7 of the present invention. It is a circuit diagram which shows the principal part structure of Embodiment 8 of this invention. It is a circuit diagram of Embodiment 9 of the present invention. It is a schematic block diagram for demonstrating the circuit arrangement | positioning of Embodiment 9 of this invention. It is a schematic block diagram for demonstrating the circuit arrangement | positioning of Embodiment 10 of this invention. It is a block circuit diagram which shows schematic structure of the conventional liquid crystal display device. It is a circuit diagram of the conventional inverter.

Explanation of symbols

Q1-Q8 Switching element A1-A4 Load circuit 5 Control circuit Vdc DC power supply La1-La4 Discharge lamp

Claims (13)

A plurality of load circuits connected to the discharge lamp are connected in series, a plurality of switching elements on the high potential side connecting both ends of each load circuit to the positive electrode of the DC power supply, and both ends of each load circuit connected to the negative electrode of the DC power supply A discharge lamp lighting device comprising: a plurality of low-potential-side switching elements respectively connected to each other, and a control circuit that controls each switching element so that a high-frequency current flows through at least one load circuit. 2. The control circuit according to claim 1, wherein the control circuit controls each switching element so that a high-frequency current flows through one of the two load circuits sharing the high-potential side switching element and the low-potential side switching element. The operation of controlling each switching element so that a high-frequency current flows through the other load circuit is sequentially repeated for each load circuit sharing the high-potential side switching element and the low-potential side switching element. A discharge lamp lighting device that is controlled so that a high-frequency current flows sequentially. The control circuit according to claim 1, wherein the control circuit performs an operation of controlling each switching element so that a high-frequency current flows simultaneously through two load circuits sharing the switching element on the high potential side and the switching element on the low potential side. A discharge lamp lighting device characterized by controlling so that a high-frequency current sequentially flows through each load circuit by sequentially repeating each load circuit sharing the switching element and the low-potential side switching element. 2. The discharge lamp lighting device according to claim 1, wherein the control circuit controls each switching element so that a high-frequency current flows through all the load circuits simultaneously. The control circuit according to claim 1, wherein when an abnormality is detected in any of the load circuits, the control circuit controls each switching element so that a high-frequency current does not flow through the load circuit. A discharge lamp lighting device. 5. The load circuit according to claim 4, wherein the load circuit includes a resonance circuit that supplies a resonance voltage to the discharge lamp, and when the discharge lamp is started, the control circuit reduces the frequency of the high-frequency current flowing through the load circuit in a direction that approaches the resonance frequency of the resonance circuit. The discharge lamp lighting device characterized by making it. 6. The discharge lamp of one of the load circuits according to claim 1, wherein, when the discharge lamp is started, the control circuit is one of the two load circuits sharing the high-potential side switching element and the low-potential side switching element. After switching each switching element to start, the operation to control each switching element to start the discharge lamp of the other load circuit is shared by the switching element on the high potential side and the switching element on the low potential side. A discharge lamp lighting device characterized by sequentially starting the discharge lamps of each load circuit by sequentially repeating each load circuit. 8. The detection circuit according to claim 1, wherein the two load circuits sharing the high-potential side switching element and the low-potential side switching element detect the combined current flowing in the shared switching element, and the detection A discharge lamp lighting device comprising: a feedback circuit that provides an output adjustment signal to a control circuit so as to change a switching frequency or an on-time width of a switching element in a direction in which a detection value of the circuit converges to a target value. 9. The detection circuit for detecting a combined current flowing in a shared switching element for the two load circuits sharing the high-potential side switching element and the low-potential side switching element according to claim 1, and the detection A discharge lamp lighting device comprising: a comparison circuit that provides a protection signal to the control circuit so as to stop or suppress high-frequency output to the load circuit when the detected value of the circuit exceeds a reference value for abnormality determination . In any one of Claims 1-9, the discharge lamp connected to each load circuit is a straight tube | pipe type lamp, and two load circuits which share a high potential side switching element and a low potential side switching element are used. The discharge lamps are juxtaposed so as to be adjacent to each other, and the high-potential side switching element and the low-potential side switching element shared between the adjacent discharge lamps are one end side and the other end side in the longitudinal direction of the discharge lamp. Discharge lamp lighting device characterized by being arranged alternately. The discharge lamp connected to each load circuit according to any one of claims 1 to 9 is a straight tube lamp, and the straight tube lamps are arranged in parallel so that their longitudinal directions are substantially parallel to each other. The discharge lamp lighting device, wherein the element is arranged on one end side in the longitudinal direction of the straight tube lamp. The lighting fixture which makes the discharge lamp lighting device in any one of Claims 1-11 built in a fixture main body, and makes the several discharge lamp with which a fixture main body is mounted | worn with the said discharge lamp lighting device. A backlight device for a liquid crystal display, comprising the discharge lamp lighting device according to claim 1, wherein the liquid crystal panel is illuminated from the back surface by a plurality of discharge lamps that are lit by the discharge lamp lighting device.

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