Patent Application
20080030454
Referring to
Referring to
The AND gate 210 has a first input end 211, a second input end 212, and an output end 213. The first input end 211 is the first signal input end of the backlight driving circuit 20, and the second input end 212 is the second signal input end of the backlight driving circuit 20.
The first transistor 240 is a N-Channel enhancement mode metal-oxide-semiconductor field-effect transistor (N-MOSFET), having a gate electrode 241 connected to the output end 213 of the AND gate 210 through the follower 220, a source electrode 242 connected to the signal output terminal 280, a drain electrode 243 connected to the first power supply 260.
The second transistor 250 is a N-Channel enhancement mode metal-oxide-semiconductor field-effect transistor (N-MOSFET), having a gate electrode 251 connected to the output end 213 of the AND gate 210 through the reverser 230, a source electrode 252 connected to the ground, a drain electrode 253 connected to the signal output terminal 280.
The follower 220 has a first positive power supply terminal 221 and a first negative power supply terminal 222. The first positive power supply terminal 221 is connected to the second power supply 270 through the diode 200, and the first negative power supply terminal 222 is connected to the signal output terminal 280. The reverser 230 has a second positive power supply terminal 231 and a second negative power supply terminal 232. The second positive power supply terminal 231 is connected to the second power supply 270, and the second negative power supply terminal 232 is connected to the ground.
The diode 200 is connected to the first positive power supply terminal 221 through its cathode, and is connected to the second power supply 270 through its anode. The capacitor 290 is connected between the first negative power supply 222 and the first positive power supply 221.
The AND gate 210 can be 74AC08. The follower can be 74ALS1035. The reverser can be 74AC05. The diode 200 can be BZX55-C18. The first and the second transistors 240, 250 can be D13N03TL. The capacitance of the capacitor 290 is 0.1 uF.
In operation, when the first input end 211 of the AND gate 210 receives a low-level voltage signal, the AND gate 210 outputs a low-level signal all the time, and the reverser 230 outputs a high-level signal all the time, which turns on the second transistor 250. Thus, the signal output terminal 280 is connected to the ground through the drain electrode 253 and the source electrode 252 of the second transistor 250. Therefore, the backlight driving circuit 10 can not effectively work.
When the first input end 211 of the AND gate 210 receives a high-level voltage signal, the output signal of the AND gate 211 changes following the change of the input signal of the second input end 212. If the input signal of the second input end 212 is invariable, one of the first and the second transistors 240, 250 keeps on-state. If the first transistor 240 turns on all along, the signal output terminal 280 is connected to the first power supply 260 through the first transistor 240. If the second transistor 250 turns on all along, the signal output terminal 280 is connected to the ground through the second transistor 250. Thus, the signal output terminal 280 is connected to the first power supply 260 all the time or is connected to the ground all the time. Therefore, the backlight driving circuit 20 can not effectively work.
When the first input end 211 of the AND gate 210 receives a high-level voltage signal, and the second input end 212 receives a pulse signal, the first and the second transistors 240, 250 turn on alternately. Thus, the signal output terminal 280 alternately outputs high-level and low-level signals. The backlight driving circuit 20 can realize effective works.
When the second input end 212 receives a high-level signal, the AND gate 210 outputs a high-level voltage signal. The follower 220 and the reversers 230 respectively output a high-level voltage signal and a low-level voltage signal. The high-level voltage signal is the voltage signal of the first positive power supply terminal 221 of the follower 220, i.e. the voltage difference between the second power supply terminal 270 and the breakover voltage drop of the diode 200, equals to 10.3V. Thus, the first transistor 240 turns on, and the second transistor 250 turns off. The signal output terminal 280 is connected to the first power supply 260 through the first transistor 240 and outputs a 18V high-level voltage signal. At the same time, the 18V high-level voltage is output to a low-level end of the follower 220. Because the voltages at two ends of the capacitor 290 can not jump, the voltage of the first positive power supply terminal 221 of the follower 220 is improved to 28.3V. At the same time, the diode 200 turns off, and the follower 220 outputs a 28.3V high-level voltage signal. The first transistor 240 continuously turns on and the signal output terminal 280 outputs a 18V high-level voltage.
When the second input end 212 receives a low-level signal, the AND gate 210 outputs a low-level voltage signal. The reverser 230 outputs a 11V low-level voltage signal to the gate electrode 251 of the second transistor 250. Thus, the second transistor 250 turns on. The signal output terminal 280 is connected to the ground through the second transistor 250 and outputs a 0V low-level voltage signal. At the same time, the 0V low-level voltage signal is output to a low voltage end of the first transistor 240. Because the voltages of the two ends of the capacitor 290 can not jump, the voltage of the first positive power supply 221 of the follower 220 is lowered to 10.3V. Because the follower 220 outputs a 0V low-level voltage signal, the second transistor 250 keeps turning off, and the signal output terminal 280 keeps being connected to the ground through the second transistor 250.
Therefore, when the first input end 211 receives a high-level signal, and the second input end 212 receives a pulse signal, the backlight driving circuit 20 can periodically output high-level and low level voltage signals.
Comparing to the conventional technology, the backlight driving circuit 20 of the liquid crystal display 2 utilizes the first transistor 240, the capacitor 290 and the follower 220, and N-MOSFET first transistor 240 to realize a good backlight controlling. Because the voltages at two ends of the capacitor 290 can not jump, the voltage of the first positive power supply terminal 221 of the follower 220 can be higher than that of the source electrode 242 of the first transistor 240. Thus, the voltage of the gate electrode 241 is higher than that of the source electrode 242, and the first transistor 240 turns on. Because the N-MOSFET transistor has a low internal resistance, generally is 0.01 ohm. Therefore, the energy consummation is lower and the transferred heat by the consummating energy is lower. Moreover, the first transistor 240 can keep a low operation temperature, which assures a good operation stability of the backlight driving circuit 20. In addition, the cost of the N-MOSFET is low, which also lower the cost of the backlight driving circuit 20.
The backlight driving circuit 20 can also have some modifications, such as the first and the second transistor 240, 250 can be a N-channel depletion metal-oxide-semiconductor field-effect transistors.
The first positive power supply terminal 221 of the follower 220 can be connected to the first power supply 260 through the diode 200, i.e. the cathode of the diode 200 is connected to the positive power supply terminal 221 of the follower, and the anode of the diode 200 is connected to the first power supply 260.
The second power supply 231 of the reverser 230 can be connected to the first power supply 260.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 95128629 | Aug 2006 | TW | national |
