TWI421839B - Balancing transforming circuit for cold cathode fluorescent lamps - Google Patents

Description

Balance circuit of cold cathode tube

The invention relates to a balancing circuit of a cold cathode tube, in particular to a balancing circuit of a cold cathode tube which can perform current balancing on a secondary side coil of a transformer.

In a liquid crystal display (LCD), a Cold Cathode Fluorescent Lamp (CCFL) is used as a light source of a backlight module, and is driven by a driver circuit of an inverter. Due to the ever-increasing size of liquid crystal display panels, a single CCFL cold cathode tube has been unable to provide proper illumination brightness, requiring two or more CCFL cold cathode tubes. In a liquid crystal display panel using a plurality of cold cathode tubes, in order to ensure uniform brightness of the liquid crystal display panel, it is necessary to adjust the current flowing through each of the CCFL cold cathode tubes at any time so as to flow through each of the CCFL cold cathode tubes. The electric current is equal. However, the parasitic parameters (parasitic resistance or parasitic capacitance) of each CCFL cold cathode tube are different, so it is difficult to maintain the uniformity of the impedance of each CCFL cold cathode tube, and the impedance of each CCFL cold cathode tube is inconsistent. It will cause different currents to flow through each of the cold cathode tubes, so that each cold cathode tube has a different brightness.

Therefore, how to provide a mechanism for balancing the current of each cold cathode tube to maintain the current flowing through each of the cold cathode tubes substantially or to control each cold cathode tube, thereby producing the desired illumination effect on the liquid crystal display panel. At the same time, reducing electronic control and power conversion equipment to achieve a reduction in system cost will be a problem currently being solved. The current design focuses on the change of the drive circuit type, and the tube current of different cold cathode tubes is balanced by the drive circuit, such as the Republic of China patent TW573441. However, this design can only balance a pair of cold cathode tubes at a time, and there is still a problem of tube current imbalance between cold cathode tubes between different pairs. For the above balancing circuit, U.S. Patent Publications US20050093471 and US20050093472 use a single closed loop to simultaneously balance the currents of all cold cathode tubes. In this circuit, all cold cathode tubes are connected to the secondary side of the same transformer, if cold As the number of cathode tubes increases, the load on the transformer will also increase, which must be achieved with a high-load transformer.

The cold cathode tube balance circuit of the cold cathode tube can only balance the pair of cold cathode tubes. For the balance of multiple cold cathode tubes, the balance effect is still poor. In view of the above problems, the present invention provides a balance circuit for a cold cathode tube for balancing the currents of a plurality of cold cathode tubes such that the brightness of each of the cold cathode tubes tends to be uniform.

In order to achieve the above object, the present invention discloses a balanced circuit for a cold cathode tube, which is applied to a driving system of a plurality of cold cathode tubes, wherein the balance circuit of the cold cathode tube comprises a transformer circuit, a secondary balance circuit and a cold. Cathode tube balancing circuit.

The transformer circuit comprises a plurality of parallel transformers, each transformer having a primary side coil and a secondary side coil, wherein the primary side coils are respectively connected to a power source for receiving a power input to convert the voltage, Side coil output.

The secondary balance circuit is connected to the transformer circuit, and includes a plurality of first induction coils and an induction circuit, wherein each of the first induction coils is respectively connected to the secondary side of each transformer in the transformer circuit. The inductive loop is a closed loop, and has a plurality of balance coils, and the balance coils are respectively balanced with the first induction coils, so that the secondary side outputs of the transformers tend to be uniform.

The cold cathode tube balance circuit has a complex array balance coil group, wherein each balance coil group is a second induction coil that is paired and in which magnetic lines of force sense each other. In each of the balance coils, one end of each of the second induction coils is simultaneously connected to the first balance coil in the secondary side balance loop, and each set of balance coil sets respectively corresponds to one first induction coil. The other ends of the second induction coil are respectively connected to the high voltage end of a cold cathode tube, so that the pair of cold cathode tubes receive the power supply of the pair of second induction coils. The tube currents of the pair of cold cathode tubes tend to be balanced by mutual sensing of the paired second induction coils. Moreover, the secondary side outputs of the foregoing transformers also tend to be uniform, so that the currents of the different pairs of cold cathode tubes can also be made uniform, so that the tube currents of the plurality of cold cathode tubes are balanced to obtain uniform brightness. Moreover, each transformer only supplies a current required for a pair of cold cathode tubes, so that the load of the transformer can be reduced.

The effect of the invention is that the secondary side coil output of the transformer is first balanced by the secondary side balancing circuit, and the tube current of the pair of cold cathode tubes is balanced by the second induction coil. This design allows each transformer to only support the output of a pair of cold cathode tubes, thereby reducing its load and ensuring that different pairs of cold cathode tubes have the same tube current for consistent brightness.

The detailed features and advantages of the present invention are set forth in the Detailed Description of the Detailed Description of the <RTIgt; </ RTI> <RTIgt; </ RTI> </ RTI> </ RTI> <RTIgt; The objects and advantages associated with the present invention can be readily understood by those skilled in the art.

Please refer to FIG. 1 , which is a circuit diagram of a balance circuit of a cold cathode tube according to a first embodiment of the present invention, which includes a transformer circuit 10 , a secondary balance circuit 20 , and a cold cathode tube balance circuit. 30.

The transformer circuit 10 includes a plurality of transformers 11 connected in parallel. For convenience of description, the present embodiment will be described with only two transformers 11. The two transformers 11 are connected in parallel to a power source S1 for receiving a power input to convert the voltage. Each of the transformers 11 has a primary side coil 11a and a secondary side coil 11b, wherein the number of winding turns of the primary side coil 11a of each transformer 11 is the same, and the secondary side coil 11b of each transformer 11 also has the same winding. The number is such that each transformer 11 has similar electrical characteristics.

The secondary balance circuit 20 includes a plurality of first induction coils 21 and an induction loop 22, and the number of the first induction coils 21 corresponds to the number of the transformers 11. In this embodiment, the secondary balance circuit 20 has two first induction coils 21 to correspond to the two transformers 11, respectively. The two first induction coils 21 are respectively connected to the secondary side coil 11b of the transformer 11 corresponding thereto to receive the voltage output after the transformer 11 converts the power source S1. The inductive loop 22 has a plurality of series connected balance coils 221 to form a closed current loop. The number of balance coils 22 is equal to or greater than the number of the first induction coils 21. In the present embodiment, the inductive loop 22 has two balance coils 221 to correspond to the number of the first induction coils 21. Each of the balance coils 221 generates magnetic line induction with the different first induction coils 21, so that the currents of the two first induction coils 21 tend to be uniform, thereby balancing the output of the secondary side coil 11b of each transformer 11.

Therefore, when the two transformers 11 convert the power source S1 into the currents I11, I12, the first induction coil 21 can pass through the inductive loop 22, so that the currents I11, I12 are balanced with each other and tend to be uniform.

The cold cathode tube balance circuit 30 has a complex array balance coil group 31, the number of which corresponds to the number of the first induction coils 21. In the present embodiment, the cold cathode tube balance circuit 30 has two balance coil groups 31, which are respectively connected to Each of the first induction coils 21 is for supplying power to the pair of cold cathode tubes 40.

Each of the balance coil sets 31 includes a second induction coil 311 that is paired and in which magnetic lines of force sense each other. In each set of balanced coil sets 31, the second induction coils 311 are connected in parallel, one end of which is simultaneously connected to the same first induction coil 21 in the secondary side balance circuit 20, and each set of balance coil sets 31 respectively Corresponding to a first induction coil 21. The other ends of the second induction coil 311 are respectively connected to the high voltage end of a cold cathode tube 40, and the low voltage ends of the cold cathode tubes 40 are grounded, so that the pair of cold cathode tubes 40 receive the pair of second induction coils 311. Supply power. The tube currents of the pair of cold cathode tubes 40 tend to be balanced by mutual sensing of the pair of second induction coils 311.

The present invention cross forces the current twice to make the tube current of the cold cathode tube 40 tend to be uniform. It first passes through the secondary side balance circuit 20, forcing the output of the secondary side coil 11b of the transformer 11 to be balanced. Then, when the transformers 11 are output to the pair of cold cathode tubes 40, the tube currents of the same pair of cold cathode tubes 40 are further forced to balance each other. That is, the tube current of the cold cathode tube 40 in the same pair can be balanced, and the secondary side coil 11b of the transformer 11 is also balanced, so that the tube currents of the different pairs of the cold cathode tubes 40 can also be balanced, thereby balancing all The tube current of the cold cathode tube 40 is such that its brightness tends to be uniform.

Please refer to FIG. 2, which is a circuit diagram of a cold cathode tube balancing circuit according to a second embodiment of the present invention. The second embodiment is applied to the driving system of the cold cathode tube, and the circuit diagram of the second embodiment is different from the circuit diagram of the first embodiment in that the sensing circuit 22 has a plurality of balancing coils 221, and each of the balancing coils 21 has The first circuit and the feedback coil 23 are mutually inductive, and the change of the voltage and current of the feedback coil 23 is detected by the feedback circuit, so that the current change in the induction circuit 22 can be known, thereby indirectly estimating the secondary side of each transformer 11. The current output from the coil 11b is used as feedback control to adjust the output of the power source S1 at any time to change the tube current of the cold cathode tube 40.

Referring to Fig. 3, there is provided a circuit diagram of a cold cathode tube balancing circuit of a third embodiment of the present invention. The third embodiment is applied to the driving system of the cold cathode tube, and the greatest difference from the circuit diagram of the second embodiment is that in the secondary side balancing circuit 20, the two first induction coils 21 are integrally wound on the same magnetic core. Corresponding to the same balance coil 221 in the inductive loop 22, the secondary side coil 11b of the balance transformer 11 is forced to output. The other balance coil 221 of the induction circuit 22 can be used to sense the mutual feedback coil 23 and detect the output of the secondary side coil 11b for feedback control.

The balance circuit of the cold cathode tube provided by the present invention balances the output of the secondary side coil 11b of the transformer by the secondary side balance circuit 20, and balances the tube current of the pair of cold cathode tubes 40 through the second induction coil 311. . This design allows each transformer 11 to only have to bear the output of a pair of cold cathode tubes 40, thereby reducing its load, and ensuring that different pairs of cold cathode tubes 40 have the same tube current for consistent brightness. In addition, the secondary side balance circuit 20 can detect the output of the secondary side 11b through the feedback coil 23 through the magnetic line induction method, and does not need to directly or indirectly detect the current supply circuit of the cold cathode tube 40. The circuit can reduce the influence of the feedback detection circuit on the tube current of the cold cathode tube 40.

Although the present invention has been disclosed above in the foregoing embodiments, it is not intended to limit the invention. It is within the scope of the invention to be modified and modified without departing from the spirit and scope of the invention. Please refer to the attached patent application for the scope of protection defined by the present invention.

10. . . Transformer circuit

11. . . transformer

11a. . . Primary side coil

11b. . . Secondary side coil

20. . . Secondary balance circuit

twenty one. . . First induction coil

twenty two. . . Inductive loop

221. . . Balance coil

twenty three. . . Feedback coil

30. . . Cold cathode tube balance circuit

31. . . Current balancing coil set

311. . . Second induction coil

40. . . Cold cathode tube

S1. . . power supply

I11, I12. . . Current

1 is a circuit diagram of a first embodiment of a balanced circuit for a cold cathode tube according to the present invention; FIG. 2 is a circuit diagram of a second embodiment of a balanced circuit for providing a cold cathode tube according to the present invention; and FIG. 3 is a view of the present invention. A circuit diagram of a third embodiment of a balancing circuit for a cold cathode tube is provided.

10. . . Transformer circuit

11. . . transformer

11a. . . Primary side coil

11b. . . Secondary side coil

20. . . Secondary balance circuit

twenty one. . . First induction coil

twenty two. . . Inductive loop

221. . . Balance coil

30. . . Cold cathode tube balance circuit

31. . . Current balancing coil set

311. . . Second induction coil

40. . . Cold cathode tube

S1. . . power supply

I11, I12. . . Current

Claims (5)

A balance circuit of a cold cathode tube, a plurality of parallel transformers, each of the transformers has a primary side coil and a secondary side coil, wherein each of the primary side coils is connected to a power source for receiving a power input, The switching voltage is outputted by each of the secondary side coils; a plurality of first induction coils, each of the first induction coils being respectively connected to one of the secondary side coils; a closed induction loop, and the first sensing The coil generates magnetic line sensing; and the complex array balancing coil set, each of the balancing coil sets includes a second inductive coil that is paired and in which the magnetic lines of force sense each other, wherein in each of the sets of the balanced coil sets, one end of each of the second inductive coils The system is connected to one of the first induction coils at the same time, and the other ends of the second induction coils are respectively connected to the high voltage end of a cold cathode tube. The balance circuit of the cold cathode tube according to claim 1, wherein the induction circuit has a plurality of balance coils connected in series, and each of the balance coils generates magnetic line induction with one of the first induction coils. The balance circuit of the cold cathode tube according to claim 1, further comprising a feedback coil, wherein the induction circuit generates a magnetic line induction to detect a current change of the induction circuit, thereby indirectly estimating each The current output from the secondary side coil of the transformer. The balance circuit of the cold cathode tube according to claim 3, wherein the induction circuit has a plurality of balance coils connected in series, wherein one of the balance coils and the feedback coil generate magnetic line induction with each other, and the rest The balance coils respectively generate magnetic line inductance with one of the first induction coils. The balance circuit of the cold cathode tube according to claim 3, wherein the induction circuit has at least one balance coil, and the first induction coils jointly generate magnetic line induction with the balance coil.