1. Field of the Invention
The present invention relates to an inverter circuit for driving a lamp and a backlight module using the same, and more particularly, relates to an inverter circuit utilizing current control mode to drive the lamp.
2. Description of Related Art
With great advance in the techniques of electro-optical and semiconductor devices, flat panel displays, such as liquid crystal displays (LCD), have enjoyed burgeoning development and flourished in recent year. Due to the numerous advantages of the LCD, such as low power consumption, free of radiation, and high space utilization, the LCD has become the main stream in the market. An LCD includes a liquid crystal display panel and a backlight module. The liquid crystal display panel has no capacity of emitting light by itself so that the backlight module is arranged below the liquid crystal display panel to provide the surface light source for the liquid crystal display panel so as to perform the display function.
Generally, a cold cathode fluorescent lamp (CCFL) is often used in the backlight module for providing a backlight. An inverter circuit is needed to generate a driving signal with alternating current (AC) to drive the CCFL.
The transformer 140 and the capacitors C1 and C2 converts the said square wave signal into a quasi-sine wave signal to drive the CCFL 160. Since the luminance of the CCFL 160 is determined according to the amount of current flowing through the CCFL 160, the voltage detector 150 detects a current flowing through the CCFL 160 and converts the current signal into a voltage signal as a feedback signal fb. Hence, the pulse width modulator 120 adjusts the pulse widths of the control signals CON1 through CON4 according to the feedback signal fb for a purpose of steadily adjusting the luminance of the CCFL 160.
Nevertheless, the bridge DC/AC converter 130 of the said inverter circuit 100 uses too many electrical components, e.g. switches S1 through S4, and the incorrect operation of the switches S1 through S4 may cause the inverter circuit 100 failing to drive the CCFL 160. For example, the switches S1 and S2 are conducted simultaneously. Besides, the conventional inverter circuit 100 often utilizes voltage control mode to drive the CCFL 160. The feedback signal fb generated by the voltage detector 150 is utilized to adjust the control signals CON1 through CON4. However, the pulse width modulator 120 can not immediately adjust the pulse widths of the control signals CON1 through CON4 by utilizing such outer loop feedback path. Hence, the factories and stores are giving many efforts to solve the above-mentioned problems.
Accordingly, the present invention provides an inverter circuit of driving a lamp and a backlight module using the same that can efficiently drive the lamp and steadily strike the lamp by utilizing current control mode.
An inverter circuit for driving a lamp is provided in the present invention. The inverter circuit includes a switching unit, a first capacitor, a transformer, a signal generation module, and a first detecting module. The switching unit has a control terminal receiving the PWM signal for controlling the conductivity of the switching unit, and has a first current terminal and a second current terminal parallel connected to the first capacitor. The transformer has a primary winding coupled to the first voltage and the first current terminal of the switching unit, and has a secondary winding coupled to a second voltage and a lamp. The transformer provides a driving signal with alternating current to the lamp. The signal generation module generates a pulse width modulation (PWM) signal according to the first voltage, wherein a duty cycle of the PWM signal is determined by a feedback signal according to the lamp and a sensed signal. The first detecting module is coupled between the second current terminal of the switching unit and the signal generation module for generating the sensed signal according to the flowing current of the switching unit.
The foregoing inverter circuit further includes a second detecting module in one embodiment of the present invention. The second detecting module is coupled between the lamp and the signal generation module. The second generates the feedback signal according to the flowing current of the lamp.
A backlight module is provided in the present invention. The backlight module includes a lamp and an inverter circuit. The inverter circuit is coupled to the lamp, which provides a light source as a backlight, and is used for driving the lamp. The inverter circuit includes a switching unit, a first capacitor, a transformer, a signal generation module, and a first detecting module. The switching unit has a control terminal receiving the PWM signal for controlling the conductivity of the switching unit, and has a first current terminal and a second current terminal parallel connected to the first capacitor. The transformer has a primary winding coupled to the first voltage and the first current terminal of the switching unit, and has a secondary winding coupled to a second voltage and the lamp. The transformer generates a driving signal with alternating current to the lamp. The signal generation module generates a PWM signal according to the first voltage, wherein a duty cycle of the PWM signal is determined by a feedback signal according to the lamp and a sensed signal. The first detecting module is coupled between the second current terminal of the switching unit and the signal generation module. The first detecting module generates the sensed signal according to the flowing current of the switching unit.
The present invention provides an inverter circuit and a backlight module that utilize current control mode to drive a lamp. As known, the transformer included in the inverter circuit generates the driving signal with AC to drive the lamp according to the signal variation of its primary winding. The sensed signal is generated according to the flowing current of the switching unit and is utilized to control the duty cycle of the PWM signal. When the sensed signal reaches a presetting value, the PWM signal controls the switching unit to be turn off for avoiding over-current and thus increasing the switching efficiency of the switching unit. The feedback path of the sensed signal is an inner closed loop so that not only can immediately adjust the PWM signal, but also the lamp can be driven more efficiently and can be struck steadily.
In order to make the features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A primary winding of the transformer 230 is coupled to a first voltage Vin (e.g. a DC voltage) and the first current terminal of the switching unit 230, and a secondary winding of the transformer 230 is coupled to the lamp 210 and a second voltage (i.e. the ground voltage GND herein). According to a signal variation of its primary winding, the transformer 230 generates a driving signal DR with alternating current to drive the lamp 210. The first detecting module 250 is coupled between the second current terminal of the switching unit 230 for generating a sensed signal FS according to the flowing current of the switching unit 230. The second detecting module 240 is coupled between the lamp 210 and the signal generation module 220 for generating a feedback signal FB according to the flowing current of the lamp 210. The signal generation module 220 generates the pulse width modulation (PWM) signal F3 according to the first voltage Vin, wherein a duty cycle of the PWM signal F3 is determined by the feedback signal FB and the sensed signal FS. The following describes the operation of the inverter circuit 200 in detail.
Referring to
When the PWM signal F3 changes from logic low level (“0”) to logic high level (“1”), the transistor N1 is conducted. The conducted transistor N1 provides a shortest path that current can pass through. Hence, the first source/drain (i.e. the node A) voltage of the transistor N1 decreases to about 0V, and the second source/drain (i.e. the node B) voltage of the transistor N1 tends to increase linearly. In the embodiment, the resistor unit 252 included in the first detecting module 250 converts the flowing current of the switching unit 230 into the voltage signal, i.e. the sensed signal FS, and feedbacks the sensed signal FS to the signal generation module 220 for controlling the duty cycle of the PWM signal F3. When the sensed signal FS reaches to a presetting value EA_out, the PWM signal F3 immediately changes from logic high (“1”) to logic low (“0”) for turning off the transistor N1. The feedback path of the sensed signal FS is inner closed loop and the current control mode is utilized herein.
It is noted that the secondary winding of the transformer 230 induces the signal variation of the primary winding, and generates the driving signal DR with AC through the switching of the switching unit 230. Referring to
The following describes how to control the duty cycle of the PWM signal F3 via the sensed signal FS and the feedback signal FB.
Referring
In summary, the said embodiments can generate the driving signal DR with AC to drive the lamp 210 by controlling the switching unit 230 to be turn on/off. The flowing current of the lamp 210 is converted to the feedback signal FB in voltage via the second detecting module 240. Utilizing the feedback signal FB to control the duty cycle of the PWM signal F3 can adjust the flowing current of the lamp 210, and it is so called the voltage control mode. In the said embodiments, the first detecting module 250 is connected to the second current terminal of the switching unit 230 for detecting the flowing current of the switching unit 230 and thereby generating the sensed signal FS. When the sensed signal FS reaches the output of the error amplifier 222a, i.e. the first error signal F1, the signal generation module 250 can immediately turn off the switching unit 230 to avoid the over-current and increase the switching efficiency of the switching unit 230. Since the sensed signal FS can responds the flowing current of the switching unit 230, utilizing the sensed signal FS to control the duty cycle of the PWM signal F3 is called current control mode.
Though the present invention has been disclosed above by the preferred embodiments, they are not intended to limit the present invention. Anybody skilled in the art can make some modifications and variations without departing from the spirit and scope of the present invention. Therefore, the protecting range of the present invention falls in the appended claims.
Number | Name | Date | Kind |
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20060001385 | Lee | Jan 2006 | A1 |
20070126372 | Huang et al. | Jun 2007 | A1 |
Number | Date | Country | |
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20090237346 A1 | Sep 2009 | US |