CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-053313, filed on Mar. 2, 2007, the entire contents of which are incorporated herein by reference.
TECHNICAL FIELD
The present invention is related to a multi-discharge tube lighting apparatus capable of driving a plurality of discharge tube units with a reduced number of current balancing transformers.
BACKGROUND
In a liquid crystal display apparatus such as a liquid crystal display television using a plurality of discharge tubes in a single panel of a liquid crystal screen, it is necessary to illuminate the entire liquid crystal screens in uniform luminance from the discharge tubes. If the plurality of discharge tubes are lighted (turned ON) in different current values, an illumination failure such as unequal luminance gradations may occur. FIG. 10 shows a multi-discharge tube lighting apparatus for applying AC high voltages (alternating high voltages) to one terminal of each of a plurality of discharge tubes so as to balance currents flowing through the respective discharge tube. As shown in FIG. 10, the multi-discharge tube lighting apparatus includes: 3 sets of discharge tube units 1 to 3; an AC power supply 10; transformers T1 to T3; another transformer T4; and still another transformer T5. Each of the three discharge tube units 1 to 3 includes: a first discharge tube 1a and a first winding 1b, which are series-connected to each other; and a second discharge tube 2a and a second winding 2b, which are series-connected to each other. One terminal of each of the first discharge tubes 1a and each of the second discharge tubes 2a is connected to the AC power supply 10 via a capacitor 20. In each of the transformers T1 to T3, the first winding 1b is electromagnetically coupled to the second winding 2b. In the transformer T4, a first winding 1b is electromagnetically coupled to a second winding 2b, where the first winding 1b is connected to both the first winding 1b and the second winding 2b of the transformer T1, and the second winding 2b is connected to the first winding 1b and the second winding 2b of the transformer T2. In the transformer T5, a first winding 1b is electromagnetically coupled to a second winding 2b, where the first winding 1b is connected between the first and second windings 1b, 2b of the transformer T4 and the ground, and the second winding 2b is connected between the first and second windings 1b, 2b of the transformer T3 and the ground. The current flowing through the discharge tube 1a and the current flowing through the discharge tube 2a of the first discharge tube unit 1 which is connected between the AC power supply 10 and the ground via the capacitors 20 and the transformer T1 is balanced by the first winding 1b and the second winding 2b of the transformer T1, so that the same current flows through the discharge tubes 1a and 2a. The total current of the two discharge tubes, i.e., the first discharge tube 1a and the second discharge tube 2a, flows through a junction point between the first winding 1b and the second winding 2b of the transformer T1.
Similarly, the current flowing through the discharge tube 1a and the discharge tube 2a of the second discharge tube unit 2 connected between the AC power supply 10 and the ground via the capacitors 20 and the transformer T2 is balanced by the first winding 1b and the second winding 2b of the transformer T2, so that the same current flows through the first discharge tube 1a and the second discharge tube 2a. The total current of two discharge tubes, i.e., the first discharge tube 1a and the second discharge tube 2a, flows through a junction point between the first winding 1b and the second winding 2b of the transformer T2.
Similarly, the current flowing through the discharge tube 1a and the discharge tube 2a of the third discharge tube unit 3 connected between the AC power supply 10 and the ground via the capacitors 20 and the transformer T3 is balanced by the first winding 1b and the second winding 2b of the transformer T3, so that the same current flows through the first discharge tube 1a and the second discharge tube 2a. The total current of two discharge tubes, i.e., the first discharge tube 1a and the second discharge tube 2a, flows through a junction point between the first winding 1b and the second winding 2b of the transformer T3.
The junction point between the first winding 1b and the second winding 2b of the transformer T1 is connected to the first winding 1b of the transformer T4, and the junction point between the first winding 1b and the second winding 2b of the transformer T2 is connected to the second winding 2b of the transformer T4. Therefore, the current flowing through the first discharge tube unit 1 and the second discharge tube unit 2 is balanced by the transformer T4, so that the same current flows through the first discharge tube unit 1 and the second discharge tube 2. The total current of the four discharge tubes, i.e., the discharge tubes of the first discharge tube unit 1 and the second discharge tube unit 2, flows through the junction between the first winding 1b and the second winding 2b of the transformer T4. The current of two discharge tubes, i.e., the third discharge tube unit 3, flows through the junction between the first winding 1b and the second winding 2b of the transformer T3.
The junction point between the first winding 1b and the second winding 2b of the transformer T4 is connected to the first winding 1b of the transformer T5, and the junction point between the first winding 1b and the second winding 2b of the transformer T3 is connected to the second winding 2b of the transformer T5. As a consequence, the current flowing through 4 pieces of the discharge tubes flows through the first winding 1b of the transformer T5, whereas the current flowing through 2 pieces of the discharge tubes flows through the second winding 2b of the transformer T5, so that a turn ratio of the first winding 1b to the second winding 2b is set to such a value obtained by multiplying the flowing current by an inverse number. For instance, the current for the 4 discharge tubes flows through the first winding 1b of the transformer T5, whereas the current for the 2 discharge tubes flows through the second winding 2b thereof. As a result, a ratio of the current becomes a relationship of 2:1. As a consequence, assuming now that a turn number of the first winding 1b of the transformer T5 is equal to 1, a turn ratio of the first winding 1b to the second winding 2b of the transformer T5 is set to be 1:2, namely, a turn number of this second winding 2b is set to 2. Any of these transformers T1 to T5 have an effect capable of averaging and balancing the current flowing through the respective discharge tubes 1a and 2a.
A multi-discharge tube lighting apparatus shown in FIG. 11 has a configuration that the capacitors 20 are omitted from the above-described multi-discharge tube lighting apparatus shown in FIG. 10. Another multi-discharge tube lighting apparatus shown in FIG. 12 has a configuration that the transformers T1 to T5 are omitted from the above-explained multi-discharging tube lighting apparatus, the first discharge tube 1a and the second discharge tube 2a of each of the first to third discharge tube units 1 to 3 are directly connected to each other to have a U-shape. Although the first discharge tube 1a and the second discharge tube 2a of each of the discharge tube units 1 to 3 are connected to one terminal and the other terminal of an AC power supply 10 which generates AC voltages having opposite phases to each other, this multi-discharge tube lighting apparatus of FIG. 12 cannot average and balance the current flowing through the respective discharge tube units 1 to 3. FIG. 13 shows another multi-discharge tube lighting apparatus. In the multi-discharge tube lighting, series-connected first and second windings 1b, 2b connected to each of the discharge tubes 1a and 2a are connected to a common line 4. The first winding 1b of the first discharge tube 1a of the first discharge tube unit 1 is electromagnetically coupled to the second winding 2b of the second discharge tube 2a of the third discharge tube unit 3 connected via the common line 4 to the first winding 1b of the second discharge tube 2a of the third discharge tube unit 3. Each of the first windings 1b of the second and subsequent discharge tube 2a of the first discharge tube unit 1 is electromagnetically coupled to the second winding 2b which is connected to the pre-staged discharge tube. That is, conversely, each of the second windings 2b is electromagnetically coupled to the first winding 1b connected to the post-staged discharge tube. FIG. 14 shows a configuration of another multi-discharge tube lighting apparatus in which the capacitors 20 shown in the lighting apparatus of FIG. 13 are omitted.
FIG. 15 shows another multi-discharge tube lighting apparatus. In the multi-discharge tube lighting apparatus, a first discharge tube 1a and a second discharge tube 2a of each of first to third discharge tube units 1 to 3 are respectively connected to one terminal and the other terminal of an AC power supply 10. A second winding 2b connected to the first discharge tube 1a of the first discharge tube unit 1 is electromagnetically coupled to a first winding 1b connected to the second discharge tube 2a of the first discharge tube unit 1, and this second winding 2b is connected to a common line 4. The first winding 1b connected to the second discharge tube 2a of the first discharge tube unit 1 is series-connected to a second winding 2b electromagnetically coupled to a first winding 1b connected to the first discharge tube 1a of the second discharge tube unit 2, and this second winding 2b is connected to the common line 4. Accordingly, FIG. 15 shows such an arrangement that a series circuit of the first winding 1b and the second winding 2b is connected between the common line 4 and the discharge tubes 1a and 2a of each of the first to third discharge tube units 1, 2, 3; each of the first windings 1b thereof is electromagnetically coupled to the second winding 2b of the pre-staged discharge tube, that is, each of the second windings 2b is electromagnetically coupled to the first winding 1b of the post-staged discharge tube. FIG. 16 shows another multi-discharge tube lighting apparatus in which the capacitors 20 shown in the lighting apparatus of FIG. 15 have been omitted. The multi-discharge tube lighting apparatus shown in FIG. 13 to FIG. 16 can average and balance the current in a similar manner to those shown in FIG. 10 and FIG. 11. The discharge tube lighting apparatuses capable of averaging and balancing the current in the above-explained manners is disclosed in, for instance, JP-A-2004-335443.
In a lighting apparatus for lighting a large number of discharge tubes, current flowing through at least one discharge tube in a single discharge tube unit can be balanced. However, in order to balance the current with respect to discharge tubes of other discharge tube units, it is necessary to provide transformers for balancing the current. As a consequence, in the above-described discharge tube lighting apparatus containing two discharge tubes in each discharge tube unit, a plurality of transformers are necessarily required, the total number of which is equal to twice number of the discharge tube units or equal to the number calculated by subtracting 1 from the twice number of the total number of the discharge tube units. As a result, costs of the discharge tube lighting apparatus may be increased.
SUMMARY
Accordingly, one aspect of the invention has an object to provide a multi discharge tube lighting apparatus with reduced number of transformers capable of balancing currents flowing through a plurality of discharge tubes.
According to a first aspect of the invention, there is provided a multi-discharge tube lighting apparatus connectable to a power source comprising a first output terminal and a second output terminal respectively outputting voltages of opposite phases, the lighting apparatus comprising: first to n-th discharge tube units where n represents an integer of two or more, each of which has a first end connected to the first output terminal and a second end connected to the second output terminal and comprises at least one discharge tube, a first winding, and a second winding, which are connected in series between a first end and a second end, wherein the first winding of the first discharge tube unit is electromagnetically coupled via a transformer to the second winding of the n-th discharge tube unit, and wherein the first windings of the second and subsequent discharge tube units are electromagnetically coupled via transformers to the second windings of the previous discharge tube units, respectively.
According to a second aspect of the invention, there is provided a multi-discharge tube lighting apparatus connectable to a power source comprising a first output terminal and a second output terminal respectively outputting voltages of opposite phases, the lighting apparatus comprising: a first discharge tube unit and a second discharge tube unit connected in parallel with respect to the power source, each of the first discharge tube unit and the second discharge tube unit comprising at least one discharge tube, a first winding and a second winding, wherein the second winding of the first discharge tube unit is electromagnetically coupled to the first winding of the second discharge tube unit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an electric circuit diagram for showing a multi-discharge tube lighting apparatus according to a first embodiment of the present invention;
FIG. 2 is an electric circuit diagram for representing a multi-discharge tube lighting apparatus according to a second embodiment of the present invention, in which capacitors are omitted from the first embodiment of FIG. 1;
FIG. 3 is an electric circuit diagram for showing a multi-discharge tube lighting apparatus according to a third embodiment of the present invention, in which the connecting sequence of the circuit elements provided in the discharge tubes unit is changed;
FIG. 4 is an electric circuit diagram for representing a multi-discharge tube lighting apparatus according to a fourth embodiment of the present invention, in which capacitors are omitted from the third embodiment of FIG. 3;
FIG. 5 is an electric circuit diagram for showing a multi-discharge tube lighting apparatus according to a fifth embodiment of the present invention, in which the arrangements of the transformers are changed;
FIG. 6 is an electric circuit diagram for showing a multi-discharge tube lighting apparatus according to a sixth embodiment of the present invention, in which a current detecting resistor is provided;
FIG. 7 is an electric circuit diagram for showing a multi-discharge tube lighting apparatus according to a seventh embodiment of the present invention, in which current detecting means made by a current transformer is provided;
FIG. 8 is an electric circuit diagram for showing a multi-discharge tube lighting apparatus according to an eighth embodiment of the present invention, in which a voltage detecting resistor is provided;
FIG. 9 is an electric circuit diagram for representing a multi-discharge tube lighting apparatus according to a ninth embodiment of the present invention, which employs a U-shaped discharge tube;
FIG. 10 is the circuit diagram for showing the first conventional example of the multi-discharge tube lighting apparatus;
FIG. 11 is the circuit diagram for indicating the second conventional example which is manufactured by omitting the capacitors from the circuit of FIG. 10;
FIG. 12 is the circuit diagram for showing the third conventional example of the multi-discharge tube lighting apparatus;
FIG. 13 is the circuit diagram for indicating the fourth conventional example which is manufactured by changing the connecting structure of the transformers;
FIG. 14 is the circuit diagram for indicating the fifth conventional example which is manufactured by omitting the capacitors from the circuit of FIG. 13;
FIG. 15 is the circuit diagram for indicating the sixth conventional example which is manufactured by reducing a total number of the transformers from the circuit of FIG. 13; and
FIG. 16 is the circuit diagram for indicating the seventh conventional example which is manufactured by omitting the capacitors from the circuit of FIG. 15.
DESCRIPTION OF THE EMBODIMENT
A description will now be made of various embodiments of multi-discharge tube lighting apparatuses according to the present invention with reference to FIG. 1 to FIG. 9. It should be noted that the same reference numerals shown in FIG. 10 to FIG. 16 will be employed as those for denoting the similar structural elements represented in FIG. 1 to FIG. 9, and descriptions thereof will be omitted.
As shown in FIG. 1, a multi-discharge tube lighting apparatus, according to a first embodiment of the present invention, includes n sets of discharge tube units 1 to n (where “n” represents: an integer of two or more; and the total number of the discharge tube units), which is connectable to an AC power supply 10. Each of these discharge tube units 1 to n contains a first discharge tube 1a, a first winding 1b, a second winding 2b, and a second discharge tube 2a, which are connected in series. The AC power supply 10 generates alternating voltages having opposite phases to each other from a first output terminal 10a and a second output terminal 10b of the AC power supply 10, and a potential at a ground terminal 10c thereof is defined as a reference potential. The first output terminal 10a and the second output terminal 10b are respectively connected to one end and the other end of each of the discharge tube units 1 to n via respective capacitors 20. Each of these discharge tube units 1 to n includes series-connected first discharge tube 1a having a straight shape and a second discharge tube 2a having a straight shape so as to form a pseudo U shape. The first winding 1b of the first discharge tube unit 1 is electromagnetically coupled via a transformer “Tn=m” (where, “m” represents the total number of the transformers) to the second winding 2b of the n-th discharge tube unit n; the first winding 1b of the second discharge tube unit 2 is electromagnetically coupled via a transformer T1 to the second winding 2b of the first discharge tube unit 1; and third and succeeding discharge tube units 3 to n are arranged in a similar manner as to the second discharge tube unit. Accordingly, the respective first windings 1b of the second and succeeding-numbered discharge tube units are electromagnetically coupled via the transformers T2 to Tn−1 to the second windings 2b of the respective preceding-numbered discharge tube units.
Also, the second winding 2b of the second discharge tube unit 2 is electromagnetically coupled via the transformer T2 to the first winding 1b of the third discharge tube unit 3, and the third and succeeding-numbered discharge tube units are arranged in a similar manner. Accordingly, the respective second windings 2b of the second and succeeding-numbered discharge tube units are electromagnetically coupled via the transformers T2 to Tn−1 to the first windings 1b of the third and succeeding-numbered discharge units respectively. It should be noted that the transformers T1 to Tn are tightly coupled transformers whose turn ratios are 1:1. As described above, in the first embodiment of the present invention, the first windings 1b and the second windings 2b as to the adjacent discharge tube units and the first and n-th discharge tube units are electromagnetically coupled via the transformers T1 to Tn to each other. As a result, a total number of the transformers is reduced, as compared with those of the multi-discharge tube lighting apparatus described in the background art, the multi-discharge tube lighting apparatus of the first embodiment can be made compact, and the manufacturing cost thereof can be reduced. Also, since the transformers averaging the current flowing through the respective discharge tube units 1 to n are connected, when the multi-discharge tube lighting apparatus is activated, electromotive force is produced in a transformer connected to a discharge tube which has not yet been turned ON, and therefore, a voltage to be applied to the discharge tube which has not yet been turned ON is increased, so that this discharge tube can be readily turned ON. Also, since the total number of the transformers is reduced, as compared with that of the multi-discharge tube lighting apparatus described in the background art, the multi-discharge tube lighting apparatus of the first embodiment can be made compact so as to be assembled to various sorts of electronic appliances, and furthermore, can be manufactured in lower cost.
The multi-discharge tube lighting apparatus shown in FIG. 1 according to the first embodiment of the present invention may be modified in various manners. For instance, as shown in FIG. 2, the capacitors 20 (shown in FIG. 1) connected between the respective discharge tubes 1a, 2a, and the AC power supply 10 may be omitted. Also, in FIG. 1, each set of the discharge tube units 1 to n is arranged in such a sequential manner that the first discharge tube 1a, the first winding 1b, the second winding 2b, and the second discharge tube 2a are connected via the capacitor 20 to the AC power supply 10. Alternatively, this connecting sequence may be properly changed. For example, as shown in FIG. 3, each set of the discharge tube units 1 to n may be arranged in such a sequential manner that the first winding 1b, the first discharge tube 1a, the second discharge tube 2a, and the second winding 2b are connected via the capacitor 20 to the AC power supply 10. In the above-described case, as shown in FIG. 4, the capacitors 20 may be omitted. Also, as shown in FIG. 5, the multi-discharge tube lighting apparatus may further include a transformer Tm=n+1 including a first winding 1b and a second winding 2b. The second winding 2b of the transformer Tn+1 forms a pair with a first winding 1b of a first discharge tube unit 1. The first winding 1b of the transformer Tn+1 forms a pair with a second winding 2b connected to a second discharge tube 2a of an n-th discharge tube unit n. The first and second windings 1b, 2b of the transformer Tn+1 are connected by a connection line 5. Accordingly, the first winding 1b of the first discharge tube unit 1 is electromagnetically coupled to the second winding 2b of the n-th discharge tube unit n via the transformers Tn, Tn+1.
The turn ratio of the first winding 1b to the second winding 2b as to the transformer Tn and the transformer Tn+1 may be changed from 1:1, depending upon use condition. For instance, a turn ratio of the first winding 1b to the second winding 2b as to the transformer Tn may be selected to be 0.1:1, whereas a turn ratio of the first winding 1b to the second winding 2b as to the transformer Tn+1 may be selected to be 1:0.1, namely, turn ratios of such transformers which are connected to each other may be changed in the same ratio. When a turn ratio is decreased, a voltage produced on the connection line 5 is lowered, so that an adverse influence caused from the connection line 5 to an external unit may be reduced, or an adverse influence given from the external unit to a winding may be reduced. When a winding ratio is increased, a voltage produced on the connection line 5 is increased, since a current is decreased, an adverse influence caused by electromagnetic indications may be reduced.
Alternatively, as shown in FIG. 6, a current detecting resistor 6 serving as an example of a current detecting unit may be provided in at lease one of the first to n-th discharge tube units 1 to n. In the illustrated example, the current detecting resistor 6 is series-connected to the first winding 1b and the second winding 2b of the first discharge tube unit 1. One end of the current detecting resistor 6 is connected to the ground, so that a value of a current flowing through the first discharge tube 1a and the second discharge tube 2a of the first discharge tube unit 1 is detected by this current detecting resistor 6. As a result, values of currents flowing through all of discharging tubes 1a and 2a can be detected, which enables various sorts of controls (for instance, current value controls) to be performed with respect to the multi-discharge tube lighting apparatus based on the detected current values. FIG. 7 represents an example in which the current detecting resistor 6 is connected to the first discharge tube unit 1 via a current detecting transformer provided between the first winding 1b and the second winding 2b of the first discharge tube unit 1. Also, as shown in FIG. 8, a voltage detecting resistor 7 serving as an example of a voltage detecting unit may be connected to any terminal of a first winding 1b and a second winding 2b of any one of n sets of the above-explained discharge tube units, so that a value of a voltage applied to the first discharge tube 1a and the second discharge tube 2a may be detected by this voltage detecting resistor 7. For instance, the voltage detecting resistor 7 is connected between the ground and a junction point between the first winding 1b and the first discharge tube 1a of the first discharge tube unit 1, so that various sorts of controls (for example, voltage value control) can be performed with respect to the multi-discharge tube lighting apparatus in response to a detected voltage value, and a failure of a discharge tube and dismounting of a discharge tube can be detected by the above-described voltage detecting unit. Also, the above-described current detections and voltage detections can be performed by low cost and easy structures. Furthermore, as shown in FIG. 9, each of discharge tube units 1 to n may include a U-shaped discharge tube.
The embodiments of the present invention can be especially advantageously embodied in such a multi-discharge tube lighting apparatus which includes a plurality of discharge tube units having at least a pseudo single U-shaped discharge tube among plural discharge tubes, and in which currents flowing through the respective discharge tubes are balanced by transformers.
Since the total number of the transformers is reduced, the multi-discharge tube lighting apparatus can be made compact and manufactured in low cost, and the reduced-sized multi-discharge tube lighting apparatus can be assembled in various electronic devices.
Patent Grant
7825608
