1. Technical Field
Embodiments of the present disclosure relates to backlight driving systems, and particularly to a backlight driving system to drive a plurality of lamps.
2. Description of Related Art
Discharge lamps, such as cold cathode fluorescent lamps (CCFLs), are used as backlights for liquid crystal display (LCD) panels. Normally, the CCFLs are driven by electrical signals provided by inverter circuits.
In a large-size LCD panel, such as an LCD TV, two or more lamps are employed to provide sufficient brightness to meet practical requirements. However, currents flowing through the lamps may be unbalanced due to different characteristics of the lamps. Thus, brightness of the large-size LCD panel may not be uniform.
Additionally, any faults or abnormalities in the lamps will affect the entire LCD panel. For example, as lamps age, uniformity of current flow or other electrical characteristics may deteriorate. As more lamps are employed in a LCD panel, faults or abnormalities in any one lamp may be difficult to detect.
Many aspects of the embodiments can be better understood with references to the following drawings, wherein like numerals depict like parts, and wherein:
Referring to
The current balance module 110 comprises a plurality of first balance transformers Tb. In one embodiment, each of the plurality of first balance transformers Tb comprises a high voltage winding N1 and a low voltage winding N2, where both the high voltage winding N1 and the low voltage winding N2 comprise a first end and a second end. The high voltage winding N1 of each first balance transformer Tb is connected between one end of a lamp 140 and the inverter circuit 100. The low voltage windings N2 of the plurality of first balance transformers Tb are connected in series. The second end of the low voltage winding N2 of a first one of the plurality of first balance transformers Tb is connected to the first end of the low voltage winding N2 of a second one of the plurality of first balance transformers Tb. The second end of the low voltage winding N2 of the second one of the plurality of first balance transformers Tb is connected to the first end of the low voltage winding N2 of a third one of the plurality of first balance transformers Tb, and so on through to the second end of the low voltage winding N2 of a last but one of the plurality of first balance transformers Tb is connected to the first end of the low voltage winding N2 of a last one of the plurality of first balance transformers Tb. Because the low voltage windings N2 of the plurality of first balance transformers Tb are connected in series, currents flowing through the low voltage windings N2 of the plurality of first balance transformers Tb are about equal. If the plurality of first balance transformers Tb are the same, the currents flowing through the high voltage windings N1 of the plurality of first balance transformers Tb are also about equal. Thus, the currents flowing through the plurality of lamps 140 are balanced by the current balance module 110.
In one embodiment, one end of the plurality of lamps 140 receives the electrical signals, and the other end thereof is grounded. In alternative embodiments, one end of the plurality of lamps 140 receives the high positive voltage signals, and the other end thereof receives the negative voltage signals.
The feedback module 120 comprises a feedback transformer Tf and a feedback circuit 1200. In one embodiment, the feedback transformer Tf comprises a primary winding W1 and a secondary winding W2. The primary winding W1 of the feedback transformer Tf is connected in series with the low voltage windings N2 of the plurality of first balance transformers Tb to detect the currents flowing through the plurality of lamps 140 and to generate a feedback signal to the inverter module 100 accordingly. Namely, the primary winding of the feedback transformer Tf comprises a first end connected to the first end of the low voltage winding N2 of the first one of the plurality of first balance transformers Tb, and a second end connected to the second end of the low voltage winding N2 of the last one of the plurality of first balance transformers Tb, forming a closed loop. The secondary winding W2 of the feedback transformers is connected to the feedback circuit 1200. The feedback circuit 1200 receives voltage variations of the feedback transformer Tf that indicate current variations of the plurality of lamps 140, and generates a feedback signal accordingly, to the inverter module 100, to regulate the currents flowing through the plurality of lamps 140.
The open-lamp protection module 130 comprises a detection coil L and an open-lamp protection detection circuit 1300. The detection coil L is wrapped around the feedback transformer Tf with one end grounded and the other end connected to the open-lamp protection detection circuit 1300. The detection coil L detects the voltage variations of the feedback transformer Tf consistently, and provides feedback to the open-lamp protection detection circuit 1300. Then, the open-lamp protection detection circuit 1300 generates the detection signal (for example, a voltage signal) accordingly to the inverter circuit 100. The inverter module 100 determines one or more of the plurality of lamps 140 are faulty according to the detection signal, and stops providing the electrical signals to the plurality of lamps 140.
Each of the plurality of second balance transformers Tb′ comprises a high voltage winding N1′ and a low voltage winding N2′, and both the high voltage winding N1′ and the low voltage winding N2′ comprise a first end and a second end. The high voltage winding N1′ of each second balance transformers Tb′ is connected between the other end of a lamp 140 and the inverter circuit 100. The low voltage windings N2′ of the plurality of second balance transformers Tb′ are connected in series with those of the plurality of first balance transformers Tb. The second end of the low voltage winding N2′ of a first one of the plurality of second balance transformers Tb′ is connected to the first end of the low voltage winding N2′ of a second one of the plurality of second balance transformers Tb′. The second end of the low voltage winding N2′ of the second one of the plurality of second balance transformers Tb′ is connected to the first end of the low voltage winding N2 of a third one of the plurality of second balance transformers Tb′, so on through to the second end of the low voltage winding N2′ of the last but one of the plurality of first balance transformers Tb′ is connected to the first end of the low voltage winding N2′ of a last one of the plurality of first balance transformers Tb′. The first end of the low voltage winding N2′ of the first one of the plurality of second balance transformers Tb′ is connected to the first end of the low voltage winding N2 of the first one of the plurality of first balance transformers Tb. The low voltage windings N2′ of the plurality of second balance transformers Tb′, the low voltage winding N2 of the first balance Tb and the primary winding W1 of the feedback transformer Tf are connected in series to form a closed loop collectively. The second end of the low voltage winding N2′ of the last one of the plurality of second balance transformers Tb′ is connected to the first end of the primary winding W1 of the feedback transformer Tf. The second end of the primary winding W1 of the feedback transformer Tf is connected to the second end of the low voltage winding N2 of the last one of the first balance transformer Tb. In one embodiment, one end of the plurality of lamps 140 receives the high positive voltage signal and the other end thereof receives the high negative voltage signal.
It should be noted that the current balance circuit 310 as shown in
It is apparent that the present disclosure provides a backlight driving system operable to balance currents flowing through the plurality of lamps 140, and to determine if one or more of the plurality of lamps 140 are faulty by detecting the current variations of the plurality of lamps 140, and to stop to providing the electrical signals to the plurality of lamps 140.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various modifications, alterations and changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
Number | Date | Country | Kind |
---|---|---|---|
2009 2 0129516 | Jan 2009 | CN | national |
Number | Name | Date | Kind |
---|---|---|---|
6459216 | Tsai | Oct 2002 | B1 |
7719211 | Kuo et al. | May 2010 | B2 |
7764024 | Cheng et al. | Jul 2010 | B2 |
Number | Date | Country |
---|---|---|
1254155 | Apr 2006 | CN |
1770946 | May 2006 | CN |
Number | Date | Country | |
---|---|---|---|
20100181920 A1 | Jul 2010 | US |