LCD devices are commonly used as displays for compact electronic apparatuses, because they provide good quality images with little power consumption and are very thin. The liquid crystal material in an LCD device does not emit light. The liquid crystal material must be lit by a light source to clearly and sharply display text and images. Thus, a backlight module is generally needed for an LCD device. The backlight module usually uses cold cathode fluorescent lamps (CCFLs) as light sources. Due to the lamps needed to be driven by an alternating current high voltage, the backlight module using the lamps as its light source needs a backlight driving circuit which can convert a direct current voltage to an alternating current voltage to drive the lamps.
Referring to FIG. 5, one such backlight driving circuit 100 includes a brightness controller 110, a pulse width modulation (PWM) circuit 150, an inverter 160, and a lamp 170 electrically connected in series. The backlight driving circuit 100 is used to drive the lamp 170 and adjust a brightness thereof.
When a user sends a brightness adjusting signal to the brightness controller 110 via on-screen display keys (not shown) disposed on a frame of an LCD device using the backlight driving circuit 100, the brightness controller 110 outputs a control signal to the PWM circuit 150. The PWM circuit 150 receives the control signal and outputs a pulse signal to the inverter 160. The pulse signal has a duty ratio according to the control signal. The inverter 160 receives the pulse signal and generates an alternating current voltage to drive the lamp 170. The brightness of the lamp 170 changes according to the duty ratio. The larger the duty ratio is, the brighter the lamp 170 is.
For energy saving and contrast improving, new technology for adjusting the brightness of backlight has been developed, such as dynamic backlight control (DBC) technology. By using the DBC technology, the brightness of backlight can be adjusted dynamically according to display images. The DBC technology is desired to be employed to reduce backlight power consumption while maintaining image fidelity and quality. However, the backlight driving circuit 100 can adjust the brightness of the lamp 170 only by the user via the brightness controller 110. Thus, the backlight driving circuit 100 lacks compatibility with other backlight control technology.
Therefore, an improved backlight driving circuit is desired to overcome the above-described deficiencies.