WO2007055289A1

WO2007055289A1 - Fluorescent lamp operation device

Info

Publication number: WO2007055289A1
Application number: PCT/JP2006/322389
Authority: WO
Inventors: Guo-Hua Wang
Original assignee: Nitta Corporation
Priority date: 2005-11-14
Filing date: 2006-11-09
Publication date: 2007-05-18
Also published as: TW200726321A; JPWO2007055289A1; EP1951006A4; EP1951006A1

Abstract

A fluorescent lamp operation device includes: a polarity switching circuit (5) for performing polarity switching with a low frequency (f) not greater than 20 kHz on DC input; a plurality of fluorescent lamps (71, …, 7n) connected to the output line of the polarity switching circuit (5); a uniform flow circuit (6) formed by constant current circuits (61, …, 6n) connected to the other end of the fluorescent lamps (71, …, 7n) and having a transistor for supplying identical current to the respective fluorescent lamps (71, …, 7n). Since the fluorescent lamps are turned on with a low frequency (f) not greater than 20 kHz, they are hardly affected by stray capacitance. The fluorescent lamps (71, …, 7n) can be arranged near a chassis (8) of a display device and it is possible to prolong wiring.

Description

Specification

Fluorescent lamp lighting device

Technical field

[0001] The present invention relates to a fluorescent lamp lighting device capable of simultaneously lighting a plurality of fluorescent lamps.

Background art

A cold cathode tube (Cold Cathode Fluorescent Tube), which is a type of fluorescent lamp, is used as a backlight of various display devices such as a liquid crystal display device. Conventionally, a high-frequency AC lighting method using an inverter has been adopted for driving the cold cathode tube.

FIG. 15 is a circuit diagram showing a conventional high-frequency AC lighting device. This high-frequency AC lighting device includes an inverter circuit 21 for supplying high-frequency AC power of several tens of kHz, a main transformer 31, and a plurality of cold cathodes connected at one end to the output line of the main transformer 31. A tube 70 and a current equalizing circuit 601 that is connected to the other ends of the plurality of cold cathode tubes 70 and has a plurality of transformer forces for flowing an equal current to each of the cold cathode tubes 70 are provided.

[0003] FIG. 16 shows waveforms of respective parts of the high-frequency lighting device of FIG. (A) in Fig. 16 shows the DC input voltage input to inverter 2. FIG. 16 (b) shows the output voltage of the inverter 2, that is, the primary voltage waveform of the main transformer 31. FIG. (C) in Fig. 16 shows the waveform of the high-frequency voltage on the secondary side of the main transformer 31.

Patent Document 1: JP 2000-294391 A

Disclosure of the invention

Problems to be solved by the invention

[0004] In such a high-frequency lighting device, since the current-dividing circuit 601 includes a plurality of transformers, the size thereof is increasing.

In addition, in the conventional high-frequency AC lighting device, the main transformer 31 accounts for the largest proportion in terms of the overall dimensions and price, and thus the miniaturization of the main transformer 31 is also desired.

In addition, since stray capacitance exists between the fluorescent lamp and the surrounding chassis, when the fluorescent lamp is turned on with a high frequency AC power supply of several tens of kilohertz, the high frequency current flows through the stray capacitance. There is a problem if the efficiency during lighting decreases.

[0005] An object of the present invention is to provide a fluorescent lamp lighting device that can use a small current-balance circuit, can efficiently light a fluorescent lamp, and can be made compact as a whole.

Means for solving the problem

[0006] The fluorescent lamp lighting device according to the present invention performs polarity switching at a predetermined frequency (D with respect to a DC input, thereby switching the polarity switching circuit that outputs the predetermined frequency (β low-frequency driving voltage). A plurality of fluorescent lamps having one end connected to the output line of the polarity switching circuit, and a transistor connected to the other end of the plurality of fluorescent lamps for flowing an equal current to each fluorescent lamp. And a current equalizing circuit having a constant current circuit force.

[0007] With this fluorescent lamp lighting device, since the current equalizing circuit is a constant current circuit including a transistor, the current equalizing circuit can be reduced in size. Therefore, the overall size of the high-frequency AC lighting device can be reduced.

Since the current equalizing circuit has a constant current circuit power including a transistor, when the driving frequency of the fluorescent lamp is as high as before, the loss tends to increase and the amount of generated heat tends to increase. Therefore, the frequency (£) of the polarity switching circuit is preferably as low as possible, exceeding ζ, and not more than 10 kHz. It is more preferable if it exceeds OHz and 1 kHz or less.

[0008] In this way, by making the frequency (£) of the polarity switching circuit lower than before, the lighting device of the fluorescent lamp has the effect of stray capacitance between the fluorescent lamp or its wiring and the chassis (ground potential). Less affected. For this reason, the fluorescent lamp can be directly attached to the chassis of the display device, and the wiring can be extended longer. By directly attaching the fluorescent lamp to the chassis, the thickness of the display device can be reduced. If the wiring can be extended for a long time, a display device with a large screen can be easily manufactured.

[0009] In addition, fluorescent lamp direct current (OHz) lighting has been attempted in the past! If DC lighting is used, the effect of floating capacity is eliminated. However, when the fluorescent lamp is turned on by direct current, the mercury in the fluorescent lamp moves due to the electric field, and a “dark edge phenomenon” occurs in which the anode direction becomes darker with time. In addition, a “sputtering phenomenon” occurs in which only one electrode is worn. For this reason, the screen brightness cannot be made uniform.

[0010] Therefore, the present invention provides advantages and subordinates of direct current lighting by using low frequency lighting as described above. It is possible to provide a fluorescent lamp lighting device having the advantages of conventional high-frequency lighting. If the frequency of the polarity switching circuit is set so that the frequency (fl) at the start of lighting of the fluorescent lamp is set to be higher than the frequency (ί) during lighting, the start of lighting of the fluorescent lamp becomes easier. This is because when starting lighting at a low frequency (β, especially when the outside air temperature is low, it may be difficult to start lighting. Therefore, if the fluorescent lamp is started at a high frequency (fl) only at the time of starting lighting, it will be difficult even at low temperatures. It is possible to start lighting easily.After starting lighting, switching to low frequency (D) makes it possible to make a fluorescent lamp lighting device that is not affected by stray capacitance.

[0011] The time (T) for controlling the frequency to be higher than the predetermined frequency (£) may be a time necessary for starting the fluorescent lamp. It is desirable to set according to the outside temperature conditions. For example, 1 to 10 seconds.

In addition, a configuration in which a high-frequency voltage having a higher frequency (12) is superimposed on a low-frequency driving voltage that changes the frequency (D is changed. That is, the predetermined frequency is applied to the fluorescent lamp.

(A high frequency voltage superposition circuit for superposing a high frequency voltage having a frequency (β) higher than D on the low frequency drive voltage is further provided.

[0012] With this configuration, when the fluorescent lamp is turned on, the fluorescent lamp is turned on using the high-frequency voltage superimposed by the high-frequency voltage superimposing circuit. After starting lighting, lighting can be continued using the low frequency drive voltage output from the polarity switching circuit. Even during this lighting, if the high-frequency current superimposed by the high-frequency voltage superposition circuit continues to flow S and the amplitude of the high-frequency voltage is set smaller than the amplitude of the low-frequency drive voltage, the fluorescent lamp or its wiring This is a problem because it is less affected by stray capacitance with the chassis. Of course, you can turn off the high-frequency voltage superimposing circuit and turn on the high-frequency current during lighting.

[0013] As the high-frequency voltage superimposing circuit, a high-frequency superimposing transformer having a high-frequency power source connected to the primary side and capable of extracting a high-frequency voltage from the secondary side may be used. The use of a high-frequency superimposed transformer has the advantage that it can be easily insulated between the fluorescent lamp and the high-frequency power source. An intermediate tap is provided on the secondary side of the high-frequency superimposing transformer, the output line of the polarity switching circuit is connected to the intermediate tap, the plurality of fluorescent lamps are divided into two groups, and the two One end of the fluorescent lamp belonging to each group is attached to both ends of the secondary side wire. Each may be connected. In this way, the high frequency superimposing transformer can be further reduced by / J.

[0014] The secondary side winding of the high-frequency superimposing transformer is connected to one output line of the polarity switching circuit through one capacitor and connected to the other output line of the polarity switching circuit through another capacitor. It may be configured. In this way, the high-frequency superimposing transformer can be made smaller, and both ends of the fluorescent lamp can be balancedly lit using the same-phase low-frequency driving voltage, so that uneven brightness can be further eliminated.

[0015] An LC resonance circuit having an inductor connected in series and a capacitor connected in parallel may be connected between the polarity switching circuit and the plurality of fluorescent lamps. As a result, a high-frequency voltage can be generated by self-excitation from a low-frequency drive voltage.

The DC power supply circuit for generating the DC input may include a main transformer for converting an AC voltage and a rectifier circuit for rectifying the output of the main transformer. By setting the power ratio of the main transformer, a desired DC voltage necessary for lighting the fluorescent lamp can be obtained.

If the rectifier circuit is a voltage doubler rectifier circuit, the voltage can be increased by the voltage doubler rectifier circuit, so that the burden of the step-up ratio on the main transformer can be reduced. Therefore, the power ratio of the main transformer can be reduced, which is advantageous for downsizing the main transformer.

The AC voltage supplied to the main transformer is preferably generated by an inverter that obtains a high-frequency output of a predetermined frequency from DC. As a result, the high frequency generated by the inverter can be set to a high frequency advantageous for improving the conversion efficiency of the main transformer. In general, the higher the frequency of the transformer, the higher the conversion efficiency. Thus, the number of main transformers can be reduced, and the main transformer can be made sufficiently small.

[0017] In the conventional high-frequency AC lighting device shown in Fig. 15, the main transformer can be made smaller by increasing the frequency of the inverter, but if the frequency is increased, the effect of stray capacitance between the fluorescent lamp and the chassis is increased. Will grow bigger. When the stray capacitance increases, the wiring distance cannot be increased, and the arrangement of fluorescent lamps in the device is restricted. In addition, the reactive current increases, the illuminance of the fluorescent lamp decreases, and it becomes difficult to make the screen brightness uniform.

[0018] Thus, conventionally, the frequency of the inverter is adjusted to a frequency that is convenient for the main transformer! I couldn't raise it.

However, in the present invention, the high frequency output from the inverter is converted to direct current by the rectifier circuit and supplied to the fluorescent lamp via the polarity switching circuit. That is, the frequency of the inverter and the driving frequency of the fluorescent lamp can be set separately. Therefore, the frequency of the inverter can be set to a sufficiently high frequency that is advantageous for improving the conversion efficiency of the main transformer. As a result, the main transformer can be easily downsized and the driving frequency f of the fluorescent lamp can be lowered as described above, so that the fluorescent lamp and its wiring can be affected by stray capacitance. Disappear.

[0019] The above-described or other advantages, features, and effects of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

Brief Description of Drawings

FIG. 1 is a circuit diagram of a fluorescent lamp lighting device according to the present invention.

FIG. 2 is a graph showing waveforms at various parts of the lighting device of FIG.

[Fig. 3] This is a graph showing how the frequency fl is set to a faster frequency fl only at the start of lighting of the fluorescent lamp and is switched to the frequency f which is turned on and slow.

[Fig. 4] This is a graph showing how the frequency fl is set to a faster frequency fl only at the start of lighting of the fluorescent lamp and is switched to the slower frequency f.

FIG. 5 is a circuit diagram of a fluorescent lamp lighting device according to the present invention in which a high-frequency voltage superposition circuit is provided between the polarity switching circuit 5 and the plurality of cold cathode tubes 71.

FIG. 6B is a waveform diagram showing an output voltage waveform of the polarity switching circuit 5.

[Fig. 6] is a waveform diagram showing the output voltage waveform after the high frequency voltage is superimposed by the high frequency voltage superimposing circuit.

FIG. 7 is a specific circuit diagram of the high-frequency power source 9 including two transistors Ql and Q2.

FIG. 8 is a circuit diagram of a fluorescent lamp lighting device of the present invention provided with a high-frequency voltage superposition circuit according to a modification.

FIG. 9 is a circuit diagram of a fluorescent lamp lighting device of the present invention provided with a high-frequency voltage superposition circuit according to still another modification.

FIG. 10 is a circuit diagram of a fluorescent lamp lighting device using a self-excited high-frequency power supply superposition circuit. FIG. 11A is a diagram showing an output voltage waveform of the polarity switching circuit 5.

FIG. 11B is a diagram showing an output voltage waveform after a high frequency voltage is superimposed.

FIG. 12 is a circuit diagram of a main part of a transformerless lighting device in which the main transformer 3 is omitted.

FIG. 13 is a main part circuit diagram showing a configuration in which the inverter circuit 2 and the main transformer 3 are omitted, and the inverter circuit and the transformer of the device 10 in which the lighting device is incorporated are diverted.

FIG. 14 is a circuit diagram showing another example of a current equalization circuit.

FIG. 15 is a circuit diagram showing a conventional high-frequency AC lighting device.

FIG. 16 is a graph showing waveforms at various parts of the high-frequency lighting device of FIG.

Explanation of symbols

[0021] 1, \ 'High-frequency voltage superposition circuit

2 Inverter

3 Main transformer

4 double voltage rectifier circuit

5 Polarity switching circuit

6 Current equalizing circuit

61 · · 6η Constant current circuit

71 · · 7η Cold cathode tube

8 Chassis

9 High frequency power supply

10 Equipment

12 Voltage superimposing transformer

51 Control circuit

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

This lighting device includes an inverter 2 that converts DC input into AC, a main transformer 3 that boosts the AC voltage from the inverter 2, and a voltage doubler that doubles and rectifies the AC voltage output from the main transformer 3. A rectifier circuit 4, a polarity switching circuit 5 for switching the polarity of the rectified DC voltage, The output lines (e) and (n) of the polarity switching circuit 5 are connected to the other (n) cold cathode tubes 71 · 7n connected to D and to the other ends of the plurality of cold cathode tubes 71 · 7n. Each cold-cathode tube 71... 7 n is equipped with a current equalizing circuit 6 for supplying a current and the like U.

[0023] The operation of this apparatus will be described. First, the DC input is converted to an AC frequency optimum for the main transformer 3 by switching the switching transistor included in the inverter 2. This “optimal AC frequency for the main transformer 3” is a frequency at which sufficient conversion efficiency is obtained for the main transformer 3, and is usually several tens of kHz to several hundreds of kHz. If the frequency force is lower than this range, the main transformer 3 needs to be enlarged, and the entire device becomes large and heavy. If the frequency is higher than this range, the influence of the parallel capacitance generated inside the main transformer 3 becomes large, resonance occurs, and conversion efficiency decreases.

Next, the AC voltage is boosted at a predetermined step-up ratio by the main transformer 3 having a predetermined number of turns and a turn ratio. Further, the voltage doubler rectifier circuit 4 performs rectification and boosting. As a result, it is possible to obtain a DC voltage necessary for lighting the cold cathode tubes 71. The “DC voltage required for lighting the cold cathode tube 71... 7η” is about 1000 V to 2000 V.

This DC voltage is converted into AC by turning on / off the switching transistor of the polarity switching circuit 5. The control circuit 51 controls on / off of the switching transistor. The control circuit 51 controls the age of each switching transistor by supplying an on / off signal to the gate of each switching transistor.

[0025] The range of the frequency f of the on / off signal may be more than OHz and 20 kHz or less. If possible, more than OHz and less than 10kHz is more preferable, more preferably more than OHz and less than 1kHz. The current equalizing circuit 6 is an electronic circuit (constant current circuit, ぅ) 61 ', 6n that obtains a constant current using the current flowing between the collector emitters of the transistors, depending on the number of cold cathode tubes 71 ··· 7n. I have. Each cold cathode tube 71 ··· 7η and each constant current circuit 61 ··· 6η are connected in series with each other. This series of cold cathode tubes 71 ··· 7η and constant current circuits 61 ··· 6η (the number of cold cathode tubes 71 ··· 7η) is equal to the two output lines (e), ( Connected to D.

As shown in FIG. 1, the transistors of the constant current circuits 61... 6η are connected in force parallel to the ηρη type and the ρηρ type. Explaining the ηρη type, a resistor R is connected between the emitter and ground. It is. The bases of the transistors are connected to each other in common. This common base voltage is expressed as Vb. Since the voltage Vb that is almost equal to the voltage Vb is common to each transistor, the voltage across the resistor R is almost equal in each constant current circuit 61 ··· 6η. For this reason, the current flowing in each direction of each constant current circuit 61... 6η in one direction (from the collector of the ηρη type transistor to the emitter) is almost equal, and a constant current is obtained. The current flowing in the reverse direction (the emitter force of the ρηρ transistor is also the collector direction) is equalized by the same action of the ρηρ transistor, and a constant current is obtained.

[0027] As described above, the constant current circuit 61 ··· 6η including the transistor realizes a constant current, so that it is smaller than the current equalization circuit 601 using a plurality of transformers as in the past. Light weight can be achieved.

(A) in FIG. 2 shows the DC input voltage input to the inverter 2. Fig. 2 (b) shows the waveform of the output voltage of the inverter 2, that is, the primary side voltage of the main transformer. (C) in Fig. 2 shows the waveform of the secondary side voltage of the main transformer 3. The secondary side voltage of the main transformer 3 is boosted according to the turn ratio of the main transformer 3 with respect to the primary side voltage of the main transformer 3. (D) of FIG. 2 is an output waveform of the voltage doubler rectifier circuit 4. This output voltage rises further than the secondary voltage of the main transformer 3, and at the same time is rectified into a pulsating current. (E) in Fig. 2 shows the output waveform of polarity switching circuit 5. The polarity switching circuit 5 switches the DC output rectified into a pulsating flow so that it is alternately positive and negative. This switched output current force is supplied to each cold-cathode tube 71.

[0028] It is preferable to set the switching frequency of the polarity switching circuit 5 to be faster only at the start of lighting, and this will be described. In the above, the range of the switching frequency f of the polarity switching circuit 5 is set to a frequency fl (fl≥f) that is faster only at the start of lighting when it exceeds 20 Hz and below 20 kHz. The frequency may be switched to a slower frequency f within the range of 20 kHz exceeding OHz.

FIG. 2 (e) shows an example in which the on / off frequency of the control circuit 51 is set to a faster frequency fl only at the start of lighting, and after switching on, the frequency is switched to the frequency f.

Fig. 3 is a graph showing the relationship between time and frequency. And after a predetermined time τ, the frequency f is switched to a slower frequency f. For example, fl = lkHz at the start of lighting, and f = 120Hz, which is slower after lighting. The predetermined time T is set according to the outside air temperature, but is set to about 1 to 10 seconds at room temperature. When starting in a low temperature environment, set a longer time. When using in a high temperature environment, set a shorter time.

[0030] Further, as shown in Fig. 4, the frequency fl may be set to be faster only at the start of lighting, and the frequency fl may be gradually decreased and converged to the frequency f as the predetermined time T elapses from the start of lighting. . The setting range of the predetermined time T is almost the same as the case of FIG.

Thus, if the switching frequency of the polarity switching circuit 5 is increased only at the start of lighting, the wiring connected to the cold cathode tubes 7 1, 7n and the cold cathode tubes 71 7n and the shank that supports the cold cathode tubes 71 7n Using the stray capacitance between the 8 This is particularly advantageous for starting at low temperatures.

[0031] With the configuration of the lighting device of the present invention as described above, a plurality of cold-cathode tubes 71 ··· 7η can be lit at a low frequency with a frequency f.

Here, “low frequency lighting” means lighting while switching the direct current by the polarity switching circuit 5 at a lower frequency f than in the prior art. As mentioned above, the range of the low frequency f is over 0 Hz and below 20 kHz. Preferably it exceeds OHz and is 10 kHz or less, more preferably it exceeds OHz and is 1 kHz or less.

[0032] Conventionally, the cold-cathode tube 71 · · 7n with a current of such a low frequency f as compared with the cold-cathode tube 71 · · By lighting 7η, the cold cathode tube 71 · 7η and the influence of stray capacitance generated between the wiring connected to 7η and the chassis 8 can be reduced, and the screen brightness uniformity is close to ideal! It can be a thing. The effect of maintaining the uniformity of the screen brightness is more advantageous as the switching frequency f of the polarity switching circuit 5 is lower.

[0033] In addition, since the main transformer 3 can be driven at a high frequency unrelated to the switching frequency f of the polarity switching circuit 5, the size of the main transformer 3 can be reduced.

Therefore, if the lighting device is used for a backlight of a liquid crystal display device or the like, the entire lighting device can be made small. In addition, by floating the cold cathode tube using low frequency, Since the influence of the quantity can be reduced, the cold cathode tube and the chassis supporting it can be brought to infinity. Therefore, the thickness of the liquid crystal display device can be reduced.

Next, a circuit example in which a high frequency voltage superposition circuit for superposing a high frequency voltage having a frequency f 2 higher than the low frequency f on the low frequency drive voltage will be described.

When superimposing the voltage at frequency f2, the voltage at frequency f2 is superimposed on the voltage at frequency f for the entire duration of lighting, not just at the start of lighting.

Fig. 5 shows a circuit diagram of a fluorescent lamp lighting device in which an inductor Ll, a capacitor Cl, a high-frequency power source 9 and a voltage superimposing transformer 12 are provided between the polarity switching circuit 5 and a plurality of cold-cathode tubes 71 ··· 7η. It is. The inductor Ll, capacitor Cl, high frequency power source 9 and voltage superimposing transformer 12 constitute a high frequency voltage superimposing circuit 1.

The inductor L1 is connected in series between the polarity switching circuit 5 and the cold cathode tubes 71... 7η, and prevents the superimposed high-frequency current from flowing back to the polarity switching circuit 5. Capacitor C1 is provided to prevent short circuit of the low frequency drive voltage. The voltage superimposing transformer 12 includes a primary side wire T1 and a secondary side wire T2, and a high frequency power source 9 is connected to the primary side wire T1. The frequency of the high frequency power supply 9 is written as “f 2”. The frequency f2 is preferably set to about 5 to 50 times the low frequency f. For example, if f = 100Hz, f2 = 500Hz ~ 5kHz

FIG. 6A shows an output voltage waveform of the polarity switching circuit 5. This waveform is the same as (e) in Fig. 2, but the pulsating flow is omitted. Figure 6B shows the output voltage waveform on which the high-frequency voltage of frequency f2 is superimposed by the high-frequency voltage superposition circuit 1.

Here, the amplitude relationship will be described. Assuming that the amplitude of the output voltage of the polarity switching circuit 5 is “a” and the amplitude of the high-frequency voltage of the frequency f2 is “b”, it is desirable that b is about 0.1 to 0.5 times a. 0. If it is lower than 1 times, the effect of superimposing the high frequency f2 will be diminished, and it will be the same as starting with only the low frequency f. If it is higher than 5 times, the power loss during lighting increases due to the stray capacitance.

[0037] Since the high-frequency voltage of frequency f2 is superimposed on the output voltage waveform of the polarity switching circuit 5, the high-frequency voltage is used to start the cold cathode tube 71 · 7η. It can be done easily. This is particularly effective for starting lighting at low temperatures. Also, by adjusting the amplitude “b” of the high-frequency voltage at the frequency f2, the brightness of the cold-cathode tube 71 •• 7n being lit can be controlled. The larger “b”, the brighter the sound, and the smaller “b”, the more B sound.

[0038] The brightness of the cold cathode tube 71 ··· 7η being lit can be adjusted by selecting the value of the frequency f2. In other words, if there is a leakage magnetic field (1 eakage magbetic flux) of the secondary winding Τ2 of the voltage superimposing transformer 12, the cold cathode tube 71 7n can be darkened by increasing the frequency f2, and the frequency f 2 If the value is lowered, the cold cathode tube 71 ··· 7η can be brightened. On the other hand, if there is no leakage magnetic field of secondary side wire Τ2, the cold cathode tube 71 · 7η can be brightened by increasing the frequency f 2 and cold cathode tube 71 · 7η by reducing the frequency f 2 Can be darkened.

FIG. 7 is a specific circuit diagram of the high-frequency power source 9 described so far. The high frequency power supply 9 is a circuit in which two transistors Ql and Q2 are connected in series, and an AC switching circuit 11 that alternately outputs a high voltage and a low voltage at a frequency f2 is connected to the bases of the transistors Ql and Q2. . When the AC switching circuit 11 outputs a high voltage, the transistor Q1 is turned on, and the primary side wire T1 is charged from the power source F through the capacitor C3. When the AC switching circuit 11 outputs a low voltage, the transistor Q2 is turned on, and the current charged in the primary side wire T1 discharges the capacitor C3. In this way, a high-frequency current can flow through the primary winding T1.

Next, a modified example of the high-frequency voltage superimposing circuit 1 will be described with reference to FIGS.

In FIG. 8, a transformer having a tapped secondary side wire T2 is used as the voltage superimposing transformer 12, and the output line (e) of the polarity switching circuit 5 is connected to this tap. Divide multiple cold-cathode tubes into two groups, connect the cold-cathode tubes in parallel in each group, and connect the cold-cathode tube connection ends to the ends (g) and (h) of the secondary side wire T2. It is a figure which shows the circuit structure connected respectively. The cold cathode tubes belonging to one group are indicated as 71, 72 ···, and the cold cathode tubes belonging to the other group are indicated as 81, 82 ···. A high-frequency power source 9 is connected to the primary winding T1 of the voltage superimposing transformer 12 as in FIG. The frequency f2 of the high frequency power supply 9 is set to about 5 to 50 times the low frequency f.

[0041] According to this circuit, the low frequency voltage output from the polarity switching circuit 5 is divided by the tap force. Then, both end (g) and (h) forces of the secondary side winding T2 also go out to each group, and the cold cathode tubes of each group are driven to light. The low-frequency voltage output from the polarity switching circuit 5 has the same phase at both ends (g) and (h) of the secondary winding T2. The high-frequency voltage output from the high-frequency power supply 9 starts lighting the cold cathode tubes of each group in opposite phases from both ends of the secondary winding T2. That is, the high-frequency voltage output from the high-frequency power source 9 is in opposite phase at both ends (g) and (h) of the secondary side winding T2. This circuit eliminates the need for capacitor C1 as in the circuit of FIG. In addition, since the secondary winding T2 having a center tap is used, the core demagnetization due to the direct current is offset. Therefore, the saturation of the core is reduced, and a small transformer with a small core can be used.

[0042] Fig. 9 shows that the output line of the polarity switching circuit 5 is connected to the capacitors CI and C 2 connected in series with each other, and the intermediate connection point of the capacitors CI and C2 (the voltage superimposing transformer 12 is connected to 0, An example of a circuit for supplying a starting high-frequency voltage to the cold cathode tubes 71... 7n from the superposed transformer 12 through the capacitors CI and C2 is shown.

According to this circuit, the high-frequency voltage output from the high-frequency power source 9 starts lighting the cold cathode tubes 71... 7n from the secondary side wire T2 through the capacitors CI and C2. The values of the capacitors C1 and C2 may be equal to each other (C1 = C2) or may be different (C1 ≠ C2). Further, either one of the capacitors CI and C2 may be omitted. In other words, C1 is short-circuited, or C2 is short-circuited!

[0043] In this circuit, particularly when the values of the capacitors CI and C2 are close to each other, high-frequency voltages appear on both lines (e) and (h) on the output side of the polarity switching circuit 5, respectively. It has almost the same potential and the same phase. In other words, high-frequency voltages of almost the same potential and phase can be applied from both ends of each cold-cathode tube, and these high-frequency currents are all transmitted through the cold-cathode tube 71 ··· 7η and wiring connected to it. Will flow to 8. Therefore, it is possible to eliminate uneven brightness that may occur in the cold cathode tube 71. Moreover, a small transformer having a small core can be used.

Next, another circuit example of the lighting device of the present invention will be described. The high-frequency voltage superposition circuit 1 described so far in FIGS. 5 to 9 is a separately-excited circuit using a high-frequency power source 9. However, the resonant circuit of the capacitor C and the inductor L is connected to both lines (e) and (D on the output side of the polarity switching circuit 5. It is also possible to employ a self-excited circuit that oscillates a high-frequency voltage. Fig. 10 is a circuit diagram of a fluorescent lamp lighting device using a self-excited high-frequency voltage superimposing circuit 1 '.

[0045] An inductor L is connected in series between the polarity switching circuit 5 and the cold-cathode tubes 71 ··· 7n, and a capacitor C is connected in parallel to the ground. Since the inductor L and the capacitor C oscillate, the relationship between L and C should satisfy 2 π ί2 = ΐΖ (LC).

Figure 11 を shows the output voltage waveform of polarity switching circuit 5 when no LC resonant circuit is present. This waveform is the same as in Figure 6A. Figure 11B shows the output voltage waveform with the high frequency voltage superimposed by the LC resonant circuit. When the low-frequency output waveform switches from negative to positive or positive and negative due to the LC resonance circuit, the oscillation output appears and gradually attenuates.

[0046] Since the high-frequency voltage is superimposed on the output voltage waveform of the polarity switching circuit 5 in this way, it is possible to easily start the lighting by using this high-frequency voltage for starting the cold cathode tube 71 ··· 7η. Can do.

The capacitor C may be composed of a cold cathode tube 71... 7η and a floating capacity between the wiring and the chassis 8.

Hereinafter, a circuit modification example of the fluorescent lamp lighting device will be described.

FIG. 12 is a circuit diagram of a main part of a transformerless lighting device in which the main transformer 3 is omitted. In this circuit, an AC voltage is directly obtained from a DC input by a resonant circuit ^ using a coil and a transistor. The AC voltage obtained by the resonant circuit is about 10 times the DC input, for example 240V, and the frequency is 200kHz. The AC voltage is passed through the voltage doubler rectifier circuit 4 to obtain a predetermined voltage, for example, a DC voltage of 1500V. The configuration subsequent to the voltage doubler rectifier circuit 4 is the same as that shown in FIGS.

[0048] With this configuration, the main transformer 3 can be eliminated, and thus the lighting device can be further reduced in size.

FIG. 13 is a diagram showing a configuration in which the inverter circuit 2 and the main transformer 3 are omitted and the inverter circuit 2 and the main transformer 3 of a device (for example, a television receiver) 10 in which the lighting device is incorporated are omitted. It is a partial circuit diagram. AC voltage is obtained from the secondary winding of the power transformer of the device 10, and it is passed through the voltage doubler rectifier circuit 4 to boost and rectify. With this configuration, Cold cathode tube 71 · · 7n dedicated inverter 2 and transformer are not required, so the entire device can be downsized.

FIG. 14 is a circuit diagram showing another example of the current-equalizing circuit. In this current equalization circuit, a circuit 6a for flowing a constant current in one direction and a circuit 6b for flowing in the other direction are separated from each other and installed on both sides of the cold cathode tube. The operation of each constant current circuit 6a, 6b is the same as described with reference to FIG. According to this current equalization circuit, all npn transistors can be used, which is advantageous in terms of cost.

Although the embodiments of the present invention have been described so far, it is needless to say that the present invention is not limited to the above-described embodiments. For example, the output of the main transformer 3 is rectified and boosted by the voltage doubler rectifier circuit 4. However, boosting and rectification may be separated, boosting may be performed by the main transformer, and rectification may be performed by a simple rectifier circuit that is not doubled. In addition, the circuit example of the current sharing circuit is not limited to that shown in FIGS. 1 and 14, and any constant current circuit using a transistor may be used. Further, the present invention is not limited to the cold cathode tube used in the above embodiment, and can be applied to general fluorescent lamps.

Claims

The scope of the claims

[1] By switching the polarity at a predetermined frequency (D with respect to the DC input, the predetermined frequency (a polarity switching circuit that outputs a low-frequency driving voltage of D,

A plurality of fluorescent lamps connected at one end to an output line of the polarity switching circuit;

A fluorescent lamp lighting device comprising: a current equalizing circuit including a constant current circuit including a transistor, connected to the other ends of the plurality of fluorescent lamps, and configured to flow an equal current to each fluorescent lamp.

2. The fluorescent lamp lighting device according to claim 1, wherein a frequency (£) of the polarity switching circuit is a frequency exceeding OHz and not more than 10 kHz.

[3] The frequency (£) of the polarity switching circuit is a frequency exceeding OHz and 1 kHz or less.

2. A fluorescent lamp lighting device according to 2.

[4] The frequency of the polarity switching circuit (having a control circuit for controlling D;

2. The fluorescent lamp lighting device according to claim 1, wherein the control circuit controls the frequency at the start of lighting of the fluorescent lamp so as to be higher than the predetermined frequency (£).

5. The fluorescent lamp lighting device according to claim 4, wherein time (T) for the control circuit to control the frequency to be higher than the predetermined frequency (1) is 1 second to 10 seconds.

[6] The high-frequency voltage superimposing circuit for superimposing a high-frequency voltage having a frequency (12) higher than the predetermined frequency (1) on the low-frequency driving voltage having the frequency (£) is further provided. The fluorescent lamp lighting device described.

7. The fluorescent lamp lighting device according to claim 6, wherein the high-frequency voltage superimposing circuit includes a high-frequency superimposing transformer to which a high-frequency power source having a frequency (12) is connected on the primary side and capable of taking out a high-frequency voltage from the secondary side. .

[8] The intermediate side tap of the high-frequency superimposing transformer is provided with an intermediate tap, the output line of the polarity switching circuit is connected to the intermediate tap, and the plurality of fluorescent lamps are divided into two groups. 8. The fluorescent lamp lighting device according to claim 7, wherein one end of a fluorescent lamp belonging to each group is connected to both ends of the secondary side winding.

[9] The secondary side winding of the high-frequency superimposing transformer is connected to one output line of the polarity switching circuit through one capacitor and through the other capacitor to the polarity switching circuit. 8. The fluorescent lamp lighting device according to claim 7, wherein the fluorescent lamp lighting device is connected to the other output line.

[10] An LC resonance circuit having an inductor connected in series and a capacitor connected in parallel is connected between the polarity switching circuit and the plurality of fluorescent lamps, and the resonance frequency of the LC resonance circuit is 2. The fluorescent lamp lighting device according to claim 1, wherein the predetermined frequency (higher than D! Is a frequency).

[11] A DC power supply circuit for generating the DC input is further provided,

The DC power supply circuit has a main transformer for converting AC voltage and a voltage doubler rectifier circuit for rectifying the output of the main transformer, and the AC voltage supplied to the main transformer is a direct current. 2. The fluorescent lamp lighting device according to claim 1, wherein the lighting device is generated by an inverter for obtaining a high-frequency output from the lamp.