This application claims priority to and the benefit of Chinese Patent Application No. 200910059430.X, filed May 26, 2009, which is incorporated herein by reference in its entirety.
This disclosure relates generally to a driver circuit for a LCD backlight, and more particularly, to a dual ended driver circuit for a LCD backlight.
Lamps in large LCD panel backlight applications are very long. In order to get high luminance uniformity, the lamps are driven at both ends (referred to also as dual ended driven). To maximize the life of the lamps, the lamps need to be driven by pure sine waveforms at both ends. Any DC component or harmonic would cause some of the gases to accumulate at one end of the tube and create an irreversible light gradient, so that one end of the tube is brighter than the other, which will significantly shorten the lamp life. In addition, to maximize the efficiency, the drive signals for the dual ends should be 180° phase shifted. The synchronization and symmetry of the drive signals is important. Any mismatch will influence reliability and efficiency.
The first output stage circuit O1 and the second output stage circuit O2 may comprise one or more output stages. The topology of the output stage may be full-bridge, half-bridge, or push-pull.
The output signals provided by the first transformer set T1 and the second transformer T2 are drive signals used to drive the two ends of the lamp set, so as to provide backlight to the LCD panel. In addition, the first transformer set T1 provides a lamp feedback signal FB1 to the control chip IC1 and the second transformer set T2 provides a lamp feedback signal FB2 to the control chip IC2.
As illustrated above, circuit 50 uses two control chips to drive the lamp set. It synchronizes the drive signals through the synchronous signal SY. However, the synchronous signal SY is sensitive and easily corrupted. Thus, the drive signals at either end may not have good symmetry. In addition, the duty cycle and frequency may differ at the two ends due to different control ICs with different lamp feedback signals.
In the description that follows, the scope of the term “an embodiment” is not to be limited as to mean more than one embodiment, bur rather, the scope may include one embodiment, more than one embodiment, or perhaps all embodiments.
Specifically, circuit 100 comprises the master board B1 and the slave board B2. The master board B1 is coupled to one end of a lamp set to provide a first drive signal. The slave board B2 is coupled to the other end of the lamp set to provide a second drive signal. The master board B1 further comprises a first output stage circuit O1, for receiving the control signal and providing a first amplified signal, and a first transformer set T1, coupled to the first output stage circuit O1, for receiving the first amplified signal and providing a first output driven signal. The slave board B2 comprises a second output stage circuit O2, for receiving the control signal and providing a second amplified signal and a second transformer set T2, coupled to the second output stage circuit O2, for receiving the second amplified signal and providing a second output driven signal. The first output driven signal provided by the first transformer set T1 is the first driven signal, which is sent to the first end of the lamp set. The second output driven signal provided by the second transformer set T2 is the second driven signal, which is sent to the second end of the lamp set.
In one embodiment, the first output stage circuit O1 and the second output stage circuit O2 comprises one or more output stages, which could be full-bridge, half-bridge, and push-pull.
In one embodiment, the first driven circuit D1 in the master board B1 of circuit 200 is integrated into the control chip IC. In addition, the first driven circuit D1 and the second driven circuit D2 comprise one or more drivers.
When circuit 200 is on operation, the first drive circuit D1 receives the control signal provided by the control chip IC, and outputs the first switch driven signal. The first output stage circuit O1 receives the first switch drive signal, and provides a first amplified signal. The first transformer set T1 receives the first amplified signal, and provides a first output drive signal to one end of the lamp set.
In the slave board B2, the second drive circuit D2 receives the control signal provided by the control chip IC, and outputs the second switch drive signal. The second output stage circuit O2 receives the second switch drive signal, and provides a second amplified signal. The second transformer set T2 receives the second amplified signal, and provides a second output drive signal to the other end of the lamp set.
As illustrated above, circuit 100/200 drives the lamp set to provide backlight to the LCD by adopting only a single control chip. Accordingly, no synchronous signal is needed. In addition, the output signals of the first transformer set T1 and the second transformer set T2 are fed back to the control chip IC, so as to get the output drive signals modulated. The 180° phase shift could be realized by accurately controlling the ON/OFF of switches in the first output stage circuit O1 and the second output stage circuit O2, or by setting the dotted terminals of the first transformer set T1 and the second transformer set T2. The control signal could also be set to realize the 180° phase shift. As a result, the synchronization and the symmetry of the driven signals are realized.
This written description uses examples to disclose the invention, including the best mode, and also to enable a person skilled in the art to make and use the invention. The patentable scope of the invention may include other examples that occur to those skilled in the art.
Number | Date | Country | Kind |
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200910059430.X | May 2009 | CN | national |