CN100489606C - Lamp tube driving circuit - Google Patents

Abstract

A lamp driving circuit is used for driving a plurality of lamps. A plurality of lamps are used in the backlight assembly. The backlight assembly is used for providing a light source required by the liquid crystal display to display images. The lamps are electrically connected with a coil respectively. The coils have the same number of windings and the same magnetic circuit, so that the current flowing through the lamp tubes is balanced.

Description

Lamp drive circuit

technical field

The invention relates to a liquid crystal display, and in particular to a lamp driving circuit for balancing lamp current.

Background technique

A liquid crystal display usually uses a set of driving circuits 100 to drive a light tube. The light tube is used in the backlight assembly of the liquid crystal display to provide the light source required for the liquid crystal display to display images. As shown in FIG. 1 , it is a schematic diagram of a conventional lamp driving circuit. A set of driving circuits 100 includes a DC power supply DC, a switch 102 and a transformer 104 . The switching switch 102 is used to switch the DC voltage output by the DC power supply DC into an AC voltage to the transformer 104 so that the transformer 104 can generate an AC voltage level required to drive the lamp 106 accordingly.

However, as the size of liquid crystal displays continues to increase, such as large-sized LCD TVs, the brightness required by the backlight components must also increase accordingly in order to maintain the image quality of the picture. Therefore, in order to improve the luminance of the backlight assembly, in addition to using longer lamp tubes, a plurality of lamp tubes must be used to achieve the desired brightness.

Therefore, in order to reduce the cost required for driving multiple lamp tubes, the conventional approach is often to let the above-mentioned set of driving circuits 100 drive multiple lamp tubes. For example, as shown in FIG. 2 , it is a schematic diagram of another example of a conventional lamp driving circuit. By electrically connecting a plurality of lamp tubes 106(1)-106(N) in parallel to reduce the number of transformers 104 and switches 102 used, thereby reducing costs, N is a positive integer.

However, although the above method can reduce the cost, it is limited by the characteristics of the lamp tubes 106 , that is, the impedances of each lamp tube 106 are different from each other, so that the current flowing through each lamp tube 106 is different. As a result, the luminance of each lamp tube 106 will be different, which will result in uneven luminance of the backlight assembly and degrade the image quality displayed by the liquid crystal display. Therefore, how to solve the problem of unbalanced maintenance cost and current when driving multiple lamps is an urgent issue in the industry.

Contents of the invention

In view of this, the object of the present invention is to provide a lamp driving circuit for driving multiple lamps and balancing the currents flowing through these lamps. In this way, the light source provided by the backlight assembly to the liquid crystal display panel will be more uniform, and the current balance between the lamp tubes will make the service life of the lamp tubes longer.

According to the object of the present invention, a lamp driving circuit is provided for driving a first lamp and a second lamp. The lamp driving circuit includes a power supply circuit and at least one balancing circuit. The power supply circuit provides an AC voltage. The balance circuit is used for receiving the AC voltage and driving the first lamp and the second lamp. The balance circuit at least includes a first winding and a second winding. One end of the first winding is used for receiving AC voltage. The other end of the first winding outputs the first current to the first lamp tube. One end of the second winding is used to receive the AC voltage, and the other end of the second winding outputs a second current to the second lamp tube. The voltage across the first winding corresponds to the voltage across the second winding.

In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, a preferred embodiment is specifically cited below and described in detail in conjunction with the accompanying drawings:

Description of drawings

FIG. 1 is a schematic diagram of a conventional lamp driving circuit.

FIG. 2 is a schematic diagram of another example of a conventional lamp driving circuit.

FIG. 3 is a schematic diagram of a liquid crystal display.

FIG. 4A is a schematic diagram of an example of a lamp driving circuit according to the first embodiment of the present invention.

4B is a schematic diagram of another example of the lamp driving circuit according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram of an example of a balancing circuit.

FIG. 6 is a schematic diagram of a second example of a balancing circuit.

FIG. 7 is a schematic diagram of a third example of a balancing circuit.

FIG. 8 is a schematic diagram of a fourth example of a balancing circuit.

FIG. 9 is a schematic diagram of a fifth example of a balancing circuit.

FIG. 10 is a schematic diagram of a sixth example of a balancing circuit.

FIG. 11 is a schematic diagram of an example of a feedback circuit configured in a lamp driving circuit.

FIG. 12 is a schematic diagram of a lamp driving circuit according to a second embodiment of the present invention.

FIG. 13 is a schematic diagram of an example of a balancing circuit.

Fig. 14 is a schematic diagram of a second example of a balancing circuit.

Fig. 15 is a schematic diagram of a third example of a balancing circuit.

Fig. 16 is a schematic diagram of a fourth example of a balancing circuit.

Fig. 17 is a schematic diagram of a fifth example of a balancing circuit.

Fig. 18 is a schematic diagram of a sixth example of a balancing circuit.

Fig. 19 is a schematic diagram of a seventh example of a balancing circuit.

Fig. 20 is a schematic diagram of an eighth example of a balancing circuit.

Fig. 21 is a schematic diagram of a ninth example of a balancing circuit.

Fig. 22 is a schematic diagram of a tenth example of a balancing circuit.

FIG. 23 is a schematic diagram of an example of a feedback circuit configured in a lamp driving circuit.

Detailed ways

The invention provides a lamp tube driving circuit, which is used to drive multiple lamp tubes. Multiple light tubes are used in the backlight assembly. The backlight assembly is used to provide the light source required for the liquid crystal display to display images. By electrically connecting the lamp tubes with a coil, the coils have the same number of windings and the same magnetic circuit, so that the current flowing through the lamp tubes can be balanced. In this way, the light source provided by the backlight assembly to the liquid crystal display panel will be more uniform, and the current balance between the lamp tubes will further prolong the service life of the lamp tubes.

Please refer to FIG. 3 , which is a schematic diagram of a liquid crystal display. The liquid crystal display 200 includes a lamp driving circuit 202 and a backlight assembly 204 . The lamp driving circuit 202 is used to drive a plurality of lamps 206(1)-206(N), where N is a positive integer. A plurality of light tubes 206 ( 1 )- 206 (N) are used in the backlight assembly 204 to enable the backlight assembly 204 to provide the light source required by the liquid crystal display 200 for displaying images. The lamp driving circuit 202 includes, for example, a power supply circuit 208 and a balancing circuit 210 . The power supply circuit 208 is used to provide an AC voltage AC. The balance circuit 210 is used to receive the AC voltage AC and drive a plurality of lamp tubes 206(1)-206(N) accordingly, and maintain the balance of the current flowing through these lamp tubes 206(1)-206(N). The present invention will be further described below with two embodiments.

first embodiment

Take driving two light tubes, that is, the first light tube 206 ( 1 ) and the second light tube 206 ( 2 ) and a balancing circuit 210 as an example for illustration. Please refer to FIG. 4A , which is a schematic diagram of an example of the lamp driving circuit 202 according to the first embodiment of the present invention. The power supply circuit 208 includes, for example, a transformer TS, a DC power supply DC and a switch 212 . The transformer TS has a primary winding P and a secondary winding S. The primary side coil P receives the AC voltage AC1 provided by the liquid crystal display 200 , for example. The switch 212 is used to switch the DC voltage output by the DC power source DC into an AC voltage AC1 to the transformer TS, so that the transformer TS can generate the voltage needed to drive the first lamp 206(1) and the second lamp 206(2). AC voltage level, that is, AC voltage AC2. Wherein, the AC voltage AC1 received by the transformer TS can not only be generated by the above-mentioned DC power supply DC and the switch 212, but also can be directly provided by the commercial power, such as AC110, through the energy converter to convert the required AC voltage AC1. In this embodiment, the source of the AC voltage AC1 received by the transformer TS is not limited, as long as the AC voltage level ( AC voltage AC2) can be.

Please refer to FIG. 5 , which is a schematic diagram of an example of the balancing circuit 210 . Take the architecture shown in FIG. 4A as an example. The balance circuit 210 includes a first coil (1) and a second coil (2). One end of the first coil ( 1 ) is used to receive the AC voltage AC2 , and the other end outputs the first current I1 to the first lamp 206 ( 1 ). One end of the second winding coil ( 2 ) is used to receive the AC voltage AC2 , and the other end outputs the second current I2 to the second lamp tube 206 ( 2 ). The first coil (1) and the second coil (2) are co-wound on the same core (1), and the first coil (1) and the second coil (2) have substantially the same number of windings . Therefore, the cross-voltage of the first winding coil (1) corresponds to the cross-voltage of the second winding coil (2), that is, the driving current is induced by the same magnetic circuit method induced by the first winding coil (1) and the second winding coil (2). I1 is almost the same as I2. In this way, the luminance of the first light tube 206(1) and the second light tube 206(2) can be almost the same, and finally the luminance of the backlight assembly can be more uniform. Moreover, the balance between the currents I1 and I2 will further prolong the service life of the lamp tubes 206(1) and 206(2).

In addition, the first winding coil ( 1 ) and the second winding coil ( 2 ) can achieve a better balance effect by means of impedance matching. Please refer to FIG. 6 , which is a schematic diagram of a second example of the balancing circuit 210 . The balance circuit 210 further includes a matching inductor L, a first capacitor C1 and a second capacitor C2. The other end of the first winding coil (1) is coupled to one end of the inductor L via the first capacitor Cl. The other end of the second winding coil (2) is coupled to the other end of the inductor L via the second capacitor C2. That is to say, the balancing circuit 210 can also achieve a better current balancing effect by selecting appropriate impedance values of the inductor L and the capacitors C1 and C2 .

Please refer to FIG. 7 , which is a schematic diagram of a third example of the balancing circuit 210 . Likewise, the architecture shown in FIG. 4A is taken as an example. The balance circuit 210 further includes a second core (2), a third coil (3) and a fourth coil (4). The number of turns of the first winding coil (1), the second winding coil (2), the third winding coil (3) and the fourth winding coil (4) are all the same. The third coil (3) and the first coil (1) are wound on the first core (1). And the third winding coil (3) and the fourth winding coil (4) form a closed loop. The fourth coil (4) and the second coil (2) are co-wound on the second core (2). Also by means of a common magnetic circuit, that is, the first winding coil (1) and the second winding coil (1) use a common magnetic circuit to induce the same voltage to the first winding coil (1) and the third winding coil (3). And the third winding coil (3) and the fourth winding coil (4) form the same loop and have the same number of coil turns, so the third winding coil (3) and the fourth winding coil (4) have the same cross voltage. Finally, the second winding coil ( 2 ) and the fourth winding coil ( 4 ) also use a common magnetic circuit to induce the same voltage to the second winding coil ( 2 ) and the fourth winding coil ( 4 ). Eventually, the first current I1 and the second current I2 will automatically reach a balance.

Similarly, please refer to FIG. 8 , which is a schematic diagram of a fourth example of the balancing circuit 210 . Instead, a balance circuit 210 is used to drive three lamp tubes. The balance circuit 210 also includes a second core (2), a third core (3), a third coil (3), a fourth coil (4), a fifth coil (5) and a sixth coil ( 6). The number of turns of the third winding coil (3), the fourth winding coil (4), the fifth winding coil (5) and the sixth winding coil (6) are all the same. The third coil (3) and the first coil (1) are wound on the first core (1). The fourth coil (4) and the fifth coil (5) are co-wound on the second core (2). The second coil (2) and the sixth coil (6) are co-wound on the third core (3). The third winding coil (3), the fifth winding coil (5) and the sixth winding coil (6) form a closed loop. One end of the first winding coil (1), the second winding coil (2) and the fourth winding coil (1) are all used to receive the second AC voltage AC2, and the other ends output the first current I1, the second current I2 and the second current I2 respectively. third current I3. Like the principle described in FIG. 7 , the first current I1 , the second current I2 and the third current I3 will automatically reach a balance. So far, in summary, under the capacity of the transformer TS, the balance circuit 210 can drive more than three lamp tubes 206, that is, each lamp tube 206 is connected to a corresponding coil (for example, in FIG. 8 ). The first winding coil (1), the second winding coil (2) and the fourth winding coil (4)) are connected in series. And these corresponding windings coil (1), coil (2) and coil (4) are each associated with a corresponding winding coil (for example, the third winding coil (3), the fifth winding coil (5) and the first winding coil in FIG. 8 The six coils (6) are wound on the same core and make these coils coil(3), coil(5) and coil(6) form a closed loop, and finally make the current flowing through these lamp tubes 206 reach a balance.

Moreover, a capacitor can be connected across the output ends of the balance circuit 210 to achieve a better current balance effect. As shown in FIG. 9 , it is a schematic diagram of a fifth example of the balancing circuit 210 . FIG. 9 takes the architecture shown in FIG. 7 as an example, and the balancing circuit 210 further includes a third capacitor C3. The third capacitor C3 is connected across the output terminal of the balancing circuit 210 . Alternatively, please refer to FIG. 10 , which is a schematic diagram of a sixth example of the balancing circuit 210 . FIG. 10 takes the architecture shown in FIG. 8 as an example, and the balancing circuit 210 further includes a fourth capacitor C4 and a fifth capacitor C5 . The fourth capacitor C4 is connected across the input ends of the light tubes 206(1) and 206(2). The fifth capacitor C5 is connected across the input ends of the lamp tubes 206(2) and 206(3). In addition, the capacitors C3 , C4 and C5 can be divided into two capacitors, for example, the third capacitor C3 can be divided into capacitors C3 ( 1 ) and C3 ( 2 ). In addition, one ends of the capacitors C4 ( 1 ), C4 ( 2 ), C5 ( 1 ) and C5 ( 2 ) are respectively coupled to the corresponding output ends, and the other ends thereof are respectively coupled to the ground voltage.

Next, in terms of feedback. The aforementioned lamp driving circuit 202 also includes a feedback circuit 214 . The feedback circuit 214 is used to output a feedback signal (FeedbackSignal) FSi according to the electrical signal required to drive the lamp 206 . The lamp driving circuit 202 adjusts the duty cycle of the switch 212 according to the feedback signal FSi, so that the lamp 206 can achieve a desired brightness and keep it stable. Please refer to FIG. 11 , which is a schematic diagram of an example of a feedback circuit configured in a lamp driving circuit. In the balance circuit 210, part of the coils form a closed loop, such as the structure disclosed in FIG. 7 and FIG. For example, the feedback circuit 214 can obtain the required electrical signal from the loop formed by the third winding coil (3) and the fourth winding coil (4), that is, the third winding coil (3) and the fourth winding coil (4) The voltage difference between them is used to output the corresponding feedback signal FSi to achieve the above purpose. The feedback circuit 214 includes a full/half-wave rectification circuit 216 and a filter 218 . The full/half-wave rectification circuit 216 is used to rectify the above-mentioned voltage difference and output it to the filter 218, so that the filter 218 can filter the noise accordingly to obtain the feedback signal FSi.

Next, please refer to FIG. 4B , which is a schematic diagram of another example of the lamp driving circuit 202 according to the first embodiment of the present invention. The above-mentioned one balancing circuit 210 driving multiple lamp tubes is taken as an example for illustration. Of course, the lamp driving circuit 202 also includes another balancing circuit, that is, the original first balancing circuit 210(1) and a second balancing circuit 210(2). Both the first balancing circuit 210(1) and the second balancing circuit 210(2) may have the structures shown in FIGS. 5-10 above. Each balancing circuit 210 drives a corresponding number of lamps. FIG. 4B is an example of the structure of the balancing circuit 210 shown in FIG. 8 . A set of drivers, ie, the lamp driving circuit 202, can drive six lamps 206(1)-206(N) at a time and simultaneously solve the problem of current imbalance, so as to reduce the cost of driving multiple lamps.

Among them, special attention should be paid to the winding impedance. There is a certain correspondence between each winding coil and the impedance of the lamp tube. It is known from the experiment that when the impedance of the winding is much larger than the impedance of the lamp tube, the better the balance effect is. However, considering that the greater the winding impedance, the greater the wasted power. Therefore, the winding impedance must be at least greater than 1/5 of the lamp impedance in order to achieve a certain current balance effect.

second embodiment

Different from the first embodiment, the structure of the balanced circuit in the second embodiment is changed to a dual-terminal input, that is, it has two input terminals, the first input terminal IN(1) and the second input terminal IN(2). Please refer to FIG. 12 , which is a schematic diagram of a lamp driving circuit 202' according to a second embodiment of the present invention. The liquid crystal display 200' includes a lamp driving circuit 202' and a backlight assembly 204' as described above. The lamp driving circuit 202' also includes a power supply circuit 208' and a balancing circuit 210'. It should be noted that the power supply circuit 208' includes two primary coils P1 and P2 and two secondary coils S1 and S2. The two primary side coils P1 and P2 both receive the first AC voltage AC1'. Like the first embodiment, the first AC voltage AC1' is generated by means of a DC power supply and a switch, or directly converted from the mains AC110 volts by an energy converter to provide the required AC voltage. The DC power supply and the switching switch are not shown in the figure any more. The two secondary side coils S1 and S2 are connected in series, and their common points can be connected to ground voltage (GND) or floating (floating), for example, as shown in Figure 12, the common points of the secondary side coils S1 and S2 are coupled Connect to the ground voltage to make the voltages of the first input terminal IN(1) and the second input terminal IN(2) have the same polarity. Both ends of the secondary coil S1 and S2 are connected in parallel with capacitors CT1 and CT2 respectively, that is, both ends of the secondary coil S1 are connected in parallel with the capacitor CT1 , and both ends of the secondary coil S2 are connected in parallel with the capacitor CT2 . The two secondary coils S1 and S2 respectively output the second AC voltages AC2'(1) and AC2'(2) to the two input terminals IN(1) and IN(2) of the balancing circuit 210'. The balance circuit 210' is used to receive the second AC voltage AC2'(1) and AC2'(2) and drive a plurality of lamp tubes 206(1)-206(N) accordingly, and let the lamp tubes 206(1) ) ~ 206 (N) current balance, N is a positive integer.

Firstly, the case of driving two lamps, that is, the first lamp 206(1) and the second lamp 206(2) will be described. Please refer to FIG. 13 , which is a schematic diagram of an example of a balancing circuit 210'. The balance circuit 210' includes a first coil'(1) and a second coil'(2). One terminal (first input terminal IN(1)) of the first coil'(1) is used to receive the AC voltage AC2'(1), and the other terminal outputs the first current I1' to the first lamp 206(1). One end of the second coil'(2) (the first input end IN(2)) is used to receive the AC voltage AC2'(2), and the other end outputs the second current I2' to the second lamp tube 206(2). The first winding coil'(1) and the second winding coil'(2) are co-wound on the core'(1), and the first winding coil'(1) and the second winding coil'(2) have the same winding thread count. As with the above-mentioned balance principle, the luminance of the first light tube 206(1) and the second light tube 206(2) will be almost the same, and finally the luminance of the backlight assembly will be more uniform. Moreover, the balance between the currents I1' and I2' will further prolong the service life of the first lamp tube 206(1) and the second lamp tube 206(2).

Wherein, a capacitor C3' may also be connected across the two output terminals of the balancing circuit 210' shown in FIG. 13 to achieve a better current balancing effect. Please refer to FIG. 14 , which is a schematic diagram of a second example of the balancing circuit 210'. Alternatively, please refer to FIG. 15 , which is a schematic diagram of a third example of the balancing circuit 210'. The capacitor C3' between the two output terminals of the balancing circuit 210' can also be divided into two capacitors, for example, the capacitor C3'(1) and the capacitor C3'(2), and one end of the capacitor C3'(1) and the capacitor C3'(2) respectively are coupled to the corresponding output terminals, and the other terminals are both coupled to the ground voltage.

In addition, like the first embodiment, the first winding coil'(1) and the second winding coil'(2) can achieve a better current balance effect by means of impedance matching. Please refer to FIG. 16 , which is a schematic diagram of a fourth example of the balancing circuit 210'. The balancing circuit 210' also includes an inductor L', a first capacitor C1' and a second capacitor C2'. The other end of the first winding coil'(1) is coupled to one end of the inductor L' via the first capacitor C1'. The other end of the second winding coil' (2) is coupled to the other end of the inductor L' via the second capacitor C2'. The balancing circuit 210' outputs the first current I1 and the second current I2 respectively at both ends of the inductor L'.

Please refer to FIG. 17 , which is a schematic diagram of a fifth example of the balancing circuit 210'. Similarly, take the structure of driving two lamps as an example. The balance circuit 210' also includes a second core'(2), a third coil'(3) and a fourth coil'(4). The number of turns of the first winding coil'(1), the second winding coil'(2), the third winding coil'(3) and the fourth winding coil'(4) are all the same. The third winding coil'(3) and the first winding coil'(1) are wound on the first core'(1) together. And the third winding coil'(3) and the fourth winding coil'(4) form a closed loop. The fourth winding coil' (4) and the second winding coil' (2) are wound on the second core (2). Also with the help of the common magnetic circuit, that is, the first winding coil'(1) and the second winding coil'(1) use the common magnetic circuit to make the first winding coil'(1) and the third winding coil'(3) induce the same voltage. And the third winding coil'(3) and the fourth winding coil'(4) form the same loop and have the same number of coil turns, so the third winding coil'(3) and the fourth winding coil'(4) have the same across pressure. Finally, the second winding coil'(2) and the fourth winding coil'(4) also use the common magnetic circuit to induce the same voltage to the second winding coil'(2) and the fourth winding coil'(4). Finally, the first winding coil'(1) outputs the first current I1' to the first lamp tube 206(1) and the second winding coil'(2) outputs the second current to the first lamp tube 206(2) I2 will be automatically balanced.

Under the architecture shown in FIG. 17 , the output terminal of the balancing circuit 210' can also be connected across a capacitor C3'' as described above, as shown in FIG. 18 , which is a schematic diagram of a sixth example of the balancing circuit 210'. The balancing circuit 210' also includes a capacitor C3''. Alternatively, the capacitor C3'' can also be divided into two capacitors C3''(1) and C3''(2), as shown in FIG. 19 , which is a schematic diagram of a seventh example of the balancing circuit 210'. One ends of the two capacitors C3''(1) and C3''(2) are respectively coupled to the corresponding output ends, and the other ends are both coupled to the ground voltage.

Next, the situation of driving four lamp tubes, that is, the first lamp tube 206(1), the second lamp tube 206(2), the third lamp tube 206(3) and the fourth lamp tube 206(4) will be described. . Please refer to FIG. 20 , which is a schematic diagram of an eighth example of the balancing circuit 210'. The balance circuit 210' also includes 4 cores and 8 coils. The four cores are: the first core'(1), the second core'(2), the third core'(3) and the fourth core'(4). The 8 winding coils are respectively: the first winding coil'(1) and the second winding coil'(2), the third winding coil'(3), the fourth winding coil'(4), and the fifth winding coil'(5), sixth coil'(6), seventh coil'(7) and eighth coil'(8). The coil turns of the winding coil' (1) to the winding coil' (8) are all the same. Moreover, the first winding coil'(1) and the third winding coil'(3) are wound on the first core'(1), and the fourth winding coil'(4) and the fifth winding coil'(5) are Wound on the second core'(2), the sixth coil'(6) and the second coil'(2) are wound on the third core'(3), the seventh coil'(7) It is wound on the fourth core '(4) together with the eighth winding coil'(8). The first winding coil'(1) and the eighth winding coil'(8) form a closed loop. The fifth winding coil' (5) and the sixth winding coil' (6) form another closed loop.

One end of the first coil'(1) and the fourth coil'(4) receive the second AC voltage AC2(1), and the other end outputs the first current I1' and the third current I3' respectively. The first current I1' is used to drive the first lamp 206(1). The third current I3' is used to drive the third lamp 206(3). One end of the second coil'(2) and the seventh coil'(7) receive the second AC voltage AC2(2), and the other end outputs the second current I2' and the fourth current I4' respectively. The second current I2 is used to drive the second lamp 206(2). The fourth current I4' is used to drive the fourth lamp 206(4). With the above structure, the currents I1 - I4 of the four lamp tubes 206 can be balanced.

Wherein, a capacitor can also be connected across the output terminals of the balancing circuit 210' respectively. For example, as shown in FIG. 21 , it is a schematic diagram of a ninth example of a balancing circuit 210'. That is, a capacitor C4' is connected across the two output ends of the balance circuit 210' output current I1' and I3', and another capacitor C5' is connected across the two output ends of the balance circuit 210' output current I2' and I4'. Alternatively, as shown in FIG. 22, which is a schematic diagram of a tenth example of a balancing circuit 210'. Each of the capacitors C4' and C5' is divided into two capacitors. For example, the capacitor C4' is divided into two capacitors C4'(1) and C4'(2). One end of the capacitors C4'(1) and C4'(2) are respectively coupled to the corresponding output terminals, and the other ends are both coupled to the ground. Voltage. Similarly, the capacitor C5' can also adopt this method. By connecting a capacitor across the output terminals of the balancing circuit 210', a better current balancing effect can be achieved.

Next, on the feedback side of the circuit. Please refer to FIG. 23 , which is a schematic diagram of an example of the feedback circuit configured in the lamp driving circuit 202'. The lamp driving circuit 202' also includes a feedback circuit 214'. As mentioned above, the feedback circuit 214' is used to output a feedback signal (Feedback Signal) FSi' according to the electrical signal required to drive the lamp 206. The lamp driving circuit 202' adjusts the duty cycle of the switch 212 according to the feedback signal FSi, so that the lamp 206 can achieve a desired brightness and maintain stability. Because in the balance circuit 210', part of the winding coil' forms a closed loop, for example, at least one closed loop is formed in the structures disclosed in FIGS. 17 to 20 . The required electrical signals are obtained from these closed loops to be converted into feedback signals FSi'. For example, as shown in Figure 23, the feedback circuit 214' can obtain the required electrical signal from the loop formed by the third winding coil'(3) and the fourth winding coil'(4) in Figure 17, that is, the third winding coil The voltage difference between '(3) and the fourth winding coil'(4) is used to output a corresponding feedback signal FSi' to achieve the above purpose.

Wherein, special attention should be paid to it, as described in the last paragraph of the first embodiment. in terms of winding impedance. There is a certain correspondence between each winding coil and the impedance of the lamp tube. It is known from the experiment that when the impedance of the winding is much larger than the impedance of the lamp tube, the better the balance effect is. However, considering that the greater the winding impedance, the greater the wasted power. Therefore, the winding impedance must be at least greater than 1/5 of the lamp impedance in order to achieve a certain current balance effect.

For the lamp driving circuit disclosed in the above-mentioned embodiments of the present invention, no matter whether the balanced circuit is single-ended or double-ended input or the type of transformer used for step-up/step-down transformers, for example, the transformer can be one or multiple transformers can be connected in parallel, etc. A transformer is effectively formed by electrically connecting (in series) the multiple lamp tubes to be driven with a coil (coil), and these coils have the same number of windings and the same magnetic circuit to allow the current to flow through these lamps The current in the tube is balanced. In this way, the light source provided by the backlight assembly to the liquid crystal display panel will be more uniform, and the current balance between the lamp tubes will make the service life of the lamp tubes longer.

In summary, although the present invention has been disclosed as above with many preferred embodiments, it is not intended to limit the present invention. Any person familiar with the art, without departing from the spirit and scope of the present invention, can make various Therefore, the scope of protection of the present invention should be defined by the appended claims of the application.

Claims (31)

1. A lamp driving circuit for driving a first lamp and a second lamp, the lamp driving circuit comprising: a power supply circuit for providing an alternating voltage; and At least one balance circuit is used to receive the AC voltage and drive the first lamp and the second lamp accordingly. The balance circuit at least includes: a first winding, one end of the first winding is used to receive the AC voltage, and the other end of the first winding outputs a first current to the first lamp tube; and A second winding, one end of the second winding is used to receive the AC voltage, and the other end of the second winding outputs a second current to the second lamp tube; Wherein, the cross voltage of the first winding corresponds to the cross voltage of the second winding. 2. The lamp driving circuit according to claim 1, wherein the balancing circuit further comprises: An iron core, on which both the first winding and the second winding are wound, and the number of turns of the first winding is equal to the number of turns of the second winding. 3. The lamp driving circuit as claimed in claim 2, wherein the impedance of the first winding corresponds to the impedance of the first lamp, and the impedance of the second winding corresponds to the impedance of the second lamp. 4. The lamp driving circuit according to claim 2, wherein the balancing circuit further comprises: a first inductance; a first capacitor, the other end of the first winding is coupled to one end of the first inductor via the first capacitor; and A second capacitor, the other end of the second winding is coupled to the other end of the first inductor via the second capacitor. 5. The lamp driving circuit according to claim 1, wherein the number of turns of the first winding is equal to the number of turns of the second winding, and the balancing circuit further comprises: a first iron core; a second iron core; a third winding, the number of turns of the third winding is equal to the number of turns of the first winding, and the third winding is wound on the first core together with the first winding; and A fourth winding, the third winding and the fourth winding form a closed loop, the number of turns of the fourth winding is equal to the number of turns of the first winding, and the fourth winding and the second winding are co-wound on on the second core. 6. The lamp driving circuit according to claim 5, wherein the balancing circuit further comprises: A capacitor is coupled between the other end of the first winding and the other end of the second winding. 7. The lamp driving circuit according to claim 5, wherein the balancing circuit further comprises: a first capacitor, the other end of the first winding is coupled to a fixed voltage via the first capacitor; and A second capacitor, the other end of the second winding is coupled to the fixed voltage via the second capacitor. 8. The lamp driving circuit according to claim 5, further comprising: a feedback circuit, outputting a feedback signal according to a voltage difference between one end of the third winding and one end of the fourth winding; Wherein, the power supply circuit outputs the AC voltage according to the feedback signal. 9. The lamp driving circuit according to claim 8, wherein the feedback circuit comprises: a full-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 10. The lamp driving circuit according to claim 8, wherein the feedback circuit comprises: a half-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 11. The lamp driving circuit as claimed in claim 1, characterized in that it is also used to drive a third lamp, and the balancing circuit further comprises: a first iron core; a second iron core; a third iron core; a third winding, the number of turns of the third winding is equal to the number of turns of the first winding, and the third winding is wound on the first core together with the first winding; A fourth winding, one end of the fourth winding is used to receive the AC voltage, the other end of the fourth winding outputs a third current to the third lamp, the number of turns of the fourth winding is equal to that of the first winding the number of coil turns; a fifth winding, the number of turns of the fifth winding is equal to the number of turns of the fourth winding, and the fifth winding and the fourth winding are wound on the second core; and a sixth winding, the number of turns of the sixth winding is equal to the number of turns of the second winding, and the sixth winding and the second winding are wound on the third core; Wherein, the third winding, the fifth winding and the sixth winding form a closed loop, and the number of turns of the first winding is substantially equal to the number of turns of the second winding. 12. The lamp driving circuit according to claim 11, wherein the balancing circuit further comprises: a first capacitor coupled to the other end of the first winding and the other end of the fourth winding; and A second capacitor is coupled to the other end of the fourth winding and the other end of the second winding. 13. The lamp driving circuit according to claim 11, further comprising: a feedback circuit, outputting a feedback signal according to a voltage difference between one end of the third winding and one end of the sixth winding; Wherein, the power supply circuit outputs the AC voltage according to the feedback signal. 14. The lamp driving circuit according to claim 13, wherein the feedback circuit comprises: a full-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 15. The lamp driving circuit according to claim 13, wherein the feedback circuit comprises: a half-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 16. The lamp driving circuit according to claim 1, wherein the AC voltage further comprises a first AC voltage and a second AC voltage, one end of the first winding is used to receive the first AC voltage, to output the first current to the first lamp at the other end of the first winding, and to receive the second AC voltage at one end of the second winding to output the second current at the other end of the second winding to the second lamp. 17. The lamp driving circuit according to claim 16, wherein the balancing circuit further comprises: an iron core, the first winding and the second winding are wound on the same iron core, and the coil turns of the first winding The number is equal to the number of coil turns of the second winding. 18. The lamp driving circuit as claimed in claim 17, wherein the impedance of the first winding corresponds to the impedance of the first lamp, and the impedance of the second winding corresponds to the impedance of the second lamp. 19. The lamp driving circuit according to claim 17, wherein the balancing circuit further comprises: a first inductance; a first capacitor, the other end of the first winding is coupled to one end of the first inductor via the first capacitor; and A second capacitor, the other end of the second winding is coupled to the other end of the first inductor via the second capacitor. 20. The lamp driving circuit according to claim 16, wherein the balancing circuit further comprises: a first iron core; a second iron core; a third winding, the number of turns of the third winding is equal to the number of turns of the first winding, and the third winding is wound on the first core together with the first winding; and A fourth winding, the third winding and the fourth winding form a closed loop, the number of turns of the fourth winding is equal to the number of turns of the first winding, and the fourth winding is co-wound with the second winding on the second core. Wherein, the number of turns of the first winding is equal to the number of turns of the second winding. 21. The lamp driving circuit according to claim 20, wherein the balancing circuit further comprises: A capacitor is coupled to the other end of the first winding and the other end of the second winding. 22. The lamp driving circuit according to claim 20, wherein the balancing circuit further comprises: a first capacitor, the other end of the first winding is coupled to a fixed voltage via the first capacitor; and A second capacitor, the other end of the second winding is coupled to the fixed voltage via the second capacitor. 23. The lamp driving circuit according to claim 20, further comprising: A feedback circuit outputs a feedback signal according to a voltage difference between one end of the third winding and one end of the fourth winding. 24. The lamp driving circuit according to claim 23, wherein the feedback circuit comprises: a full-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 25. The lamp driving circuit according to claim 23, wherein the feedback circuit comprises: a half-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 26. The lamp driving circuit according to claim 16, further used to drive a third lamp and a fourth lamp, the balancing circuit further comprising: a first iron core; a second iron core; a third iron core; a fourth iron core; a third winding, the number of turns of the third winding is equal to the number of turns of the first winding, and the third winding is wound on the first core together with the first winding; A fourth winding, one end of the fourth winding is used to receive the first AC voltage, the other end of the fourth winding outputs a third current to the third lamp, the number of turns of the fourth winding is equal to that of the first The number of coil turns of a winding; a fifth winding, the number of turns of the fifth winding is equal to the number of turns of the fourth winding, and the fifth winding and the fourth winding are wound on the second core; A sixth winding, the sixth winding and the fifth winding form a closed loop, the number of turns of the sixth winding is equal to the number of turns of the fifth winding, and the sixth winding is wound with the second winding on the third core; A seventh winding, one end of the seventh winding is used to receive the second AC voltage, the other end of the seventh winding outputs a fourth current to the fourth lamp, the number of turns of the seventh winding is equal to that of the first the number of coil turns of the secondary winding; and An eighth winding, the eighth winding and the third winding form a closed loop, the number of turns of the eighth winding is equal to the number of turns of the seventh winding, and the eighth winding and the seventh winding are co-wound on the fourth core; Wherein, the number of turns of the first winding is equal to the number of turns of the second winding. 27. The lamp driving circuit according to claim 26, wherein the balancing circuit further comprises: a first capacitor coupled to the other end of the first winding and the other end of the fourth winding; and A second capacitor is coupled to the other end of the second winding and the other end of the seventh winding. 28. The lamp driving circuit according to claim 26, further comprising: A feedback circuit outputs a feedback signal according to a voltage difference between one end of the third winding and one end of the eighth winding. 29. The lamp driving circuit according to claim 28, wherein the feedback circuit comprises: a full-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 30. The lamp driving circuit according to claim 28, wherein the feedback circuit comprises: a half-wave rectification circuit, used to rectify the voltage difference and output it; and A filter is used to filter noise from the rectified voltage difference to obtain the feedback signal. 31. The lamp driving circuit according to claim 1, wherein the power supply circuit comprises: At least one transformer is used to output the AC voltage.

Images