Abstract:
A system for driving a lamp module ( 13 ) includes a converter ( 11 ), a driving circuit ( 12 ), and a pulse width modulation (PWM) controller ( 14 ). The lamp module includes a plurality of lamps. The converter converts a received voltage to a direct current (DC) voltage. The driving circuit converts the DC voltage to an alternating current (AC) voltage. The PWM controller is connected between the converter and the lamp module, for regulating the DC voltages outputted from the converter according to current flowing through the lamps of the lamp module. In one embodiment, the system includes a bus inverter controller. The bus inverter controller is connected between the driving circuit and the lamp module, for regulating a working frequency thereof and controlling the AC voltage outputted from the driving circuit when the lamps are turned on. The system has a reduced number of PWM controllers and a relatively low cost.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to systems for driving plural or multiple lamps, and particularly to a system typically used for driving plural or multiple lamps of a backlight module of a liquid crystal display (LCD).  
         [0003]     2. Related Art  
         [0004]     Generally, a discharge lamp used as a light source of a liquid crystal display (LCD) panel has a terminal voltage characteristic that varies according to the frequency of alternating current applied to the discharge lamp. The discharge lamp also exhibits a negative impedance characteristic whereby the impedance decreases upon an increase in input power. A circuit for driving the discharge lamp can for example be an inverter. The circuit should be configured with a controllable alternating current power supply and a feedback loop, for monitoring the current flowing through the lamp to ensure stable operation and to regulate the load as well.  
         [0005]     A conventional system for driving plural lamps normally requires two pulse width modulation (PWM) controllers.  FIG. 5  is a block diagram of a conventional system for driving plural lamps. The system comprises a converter  1 , a bridge driving circuit  2 , a lamp module  3 , a PWM controller  4 , and a bridge controller  5 . The converter  1  converts a received direct current (DC) voltage or alternating current (AC) voltage to a DC voltage. The bridge circuit  2  converts the DC voltage received from the converter  1  to an AC voltage. The AC voltage is used for igniting lamps in the lamp module  3 . The PWM controller  4  receives the DC voltage outputted from the converter  1 , and generates a feedback signal to control the converter  1  to output a fixed DC voltage. The bridge controller  5  is another PWM controller, which is connected between the lamp module  3  and the bridge driving circuit  2 . The bridge controller  5  is used for controlling the bridge driving circuit  2 , in order to regulate current flowing through the lamp module  3 .  
         [0006]     Thus, the conventional system for driving plural lamps uses two PWM controllers. The two PWM controllers respectively receive different feedback signals to control the system. One is used for regulating current flowing through the discharge lamps, and the other is used for fixing the DC voltage outputted from the converter  1 . A PWM controller is expensive, especially a PWM controller used for driving a multi-lamp module. Therefore the cost of the conventional driving system requiring two of the PWM controllers is inevitably high.  
         [0007]     It is desired to provide a system for driving plural or multiple lamps such as those of an LCD, the system having a reduced number of PWM controllers and a relatively low cost.  
       SUMMARY  
       [0008]     Certain embodiments of the invention provide a system for driving a lamp module, the system comprising a converter, a driving circuit, and a pulse width modulation (PWM) controller. The lamp module comprises a plurality of lamps. The converter converts a received voltage to a direct current (DC) voltage. The driving circuit converts the DC voltage to an alternating current (AC) voltage. The PWM controller is connected between the converter and the lamp module, for regulating the DC voltages outputted from the converter according to current flowing through the lamps of the lamp module. The system further comprises a bus inverter controller. The bus inverter controller is connected between the driving circuit and the lamp module, for regulating a working frequency thereof and controlling the AC voltage outputted from the driving circuit when the lamps are turned on.  
         [0009]     Certain other embodiments of the invention provide a system for driving lamp modules, the system comprising a plurality of converters, a plurality of driving circuits and a multi-phase PWM controller. Each lamp module comprises a plurality of lamps. The converters convert received voltages to DC voltages. The driving circuits convert the DC voltages to AC voltages. The multi-phase PWM controller is connected between the converters and the lamp modules, for regulating the DC voltages outputted from the converters according to currents flowing through the lamp modules. The system further comprises a bus inverter controller. The bus inverter controller is connected between the driving circuits and the lamp modules, for regulating a working frequency of the bus inverter controller and controlling the AC voltages outputted from the driving circuits when the lamps are turned on.  
         [0010]     Other advantages and novel features will be drawn from the following detailed description of preferred embodiments of the present invention with the attached drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a block diagram of a first embodiment of a system for driving plural lamps in accordance with the present invention;  
         [0012]      FIG. 2  is a block diagram of a second embodiment of a system for driving plural lamps in accordance with the present invention;  
         [0013]      FIG. 3  is a block diagram of a third embodiment of a system for driving plural lamps in accordance with the present invention;  
         [0014]      FIG. 4  is a block diagram of a fourth embodiment of a system for driving plural lamps in accordance with the present invention; and  
         [0015]      FIG. 5  is a block diagram of a conventional system for driving plural lamps. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0016]      FIG. 1  is a block diagram of a first embodiment of a system for driving plural lamps in accordance with the present invention. The system comprises an alternating current/direct current (AC/DC) converter  11 , a driving circuit  12 , a lamp module  13 , a pulse width modulation (PWM) controller  14 , and a bus inverter controller  15 . The lamp module  13  comprises a plurality of lamps.  
         [0017]     The AC/DC converter  11  receives an AC voltage from an AC power source (not shown) to convert the AC voltage to a DC voltage. The driving circuit  12  is electrically connected to the AC/DC converter  11  to convert the DC voltage to an AC voltage.  
         [0018]     In the first embodiment, the driving circuit  12  may be a half-bridge circuit, a full-bridge circuit, a pull-push circuit or a royer circuit.  
         [0019]     The lamp module  13  is electrically connected to the driving circuit  12 , for receiving the AC voltage provided by the driving circuit  12 . The AC voltage is used for lighting the lamps in the lamp module  13 .  
         [0020]     The bus inverter controller  15  is electrically connected between the lamp module  13  and the driving circuit  12 , for lighting the lamp module  13 . When the lamps in the lamp module  13  are being turned on, a high AC voltage is needed to drive the lamps. Once the lamps are turned on, a stable AC voltage is needed to drive the lamps. Correspondingly, a working frequency of the bus inverter controller  15  can be changed if the lamps are being turned on, and the working frequency becomes stable once the lamps are turned on. Therefore, when the lamps in the lamp module  13  are being turned on, the lamp module  13 , the bus inverter controller  15 , and the driving circuit  12  form a loop, in which no current flows through the lamp module  13 , and the bus inverter controller  15  increases the working frequency thereof to control the driving circuit  12  to output a higher AC voltage for lighting the lamp module  13 . Once the lamps in the lamp module  13  are turned on, current flows through the lamp module  13 , and the working frequency of the bus inverter controller  15  is dropped to a preset value. The preset value is a stable working frequency of the bus inverter controller  15 .  
         [0021]     The PWM controller  14  is electrically connected between the lamp module  13  and the AC/DC converter  11 , for generating a control signal sent to the AC/DC converter  11  according to a feedback current outputted from the lamp module  13 . The AC/DC converter  11  changes DC voltage outputted therefrom based on the control signal, thereby changing a brightness of the lamps in the lamp module  13  via the driving circuit  12 . In the first embodiment, the DC voltage outputted from the AC/DC converter  11  is variable. Therefore, when the lamps in the lamp module  13  are turned on and the brightnesses thereof are uneven, the lamp module  13 , the PWM controller  14  and the AC/DC converter  11  form a loop, and the DC voltage outputted from the AD/DC converter  11  is changed according to the feedback current flowing through the loop.  
         [0022]     In an alternative embodiment, when the lamps in the lamp module  13  are being turned on, the driving circuit  12  is controlled to output a higher AC voltage via the PWM controller  14  and the AC/DC converter  11 , instead of via the bus inverter controller  15 .  
         [0023]      FIG. 2  is a block diagram of a second embodiment of a system for plural lamps in accordance with the present invention. The circuit structure shown in  FIG. 2  is substantially the same as that of the  FIG. 1 , except that the circuit has a DC/DC converter  11 ′ instead of an AC/DC converter  11 . Thus, a detailed description of other elements of the system is omitted herefrom. The DC/DC converter  11 ′ in  FIG. 2  is used for receiving a DC voltage from a DC power source (not shown).  
         [0024]     When there are a plurality of lamp modules in the system and the driving circuit  12  cannot supply sufficient power, the invention provides other embodiments as follows.  
         [0025]      FIG. 3  is a block diagram of a third embodiment of a system for driving plural lamps in accordance with the present invention. The system comprises a plurality of AC/DC converters  11 ,  21 , . . . , N 1 , a plurality of driving circuits  12 ,  22 , . . . , N 2 , a plurality of lamp modules  13 ,  23 , . . . , N 3 , a multi-phase PWM controller  14 ′, and a bus inverter controller  15 .  
         [0026]     In the third embodiment, each of the driving circuits  12 ,  22 , . . . , N 2  may be a half-bridge circuit, a full-bridge circuit, a pull-push circuit or a royer circuit.  
         [0027]     The AC/DC converters  11 ,  21 , . . . , N 1 , the driving circuits  12 ,  22 , . . . , N 2 , and the lamp modules  13 ,  23 , . . . , N 3  have similar connections to those of the AC/DC converter  11 , the driving circuit  12  and the lamp module  13  as shown in  FIG. 1 .  
         [0028]     The multi-phase PWM controller  14 ′ is electrically connected between the AC/DC converters  11 ,  21 , . . . , N 1  and the lamp modules  13 ,  23 , . . . , N 3 . The bus inverter controller  15  is electrically connected between the driving circuits  12 ,  22 , . . . , N 2  and the lamp modules  13 ,  23 , . . . , N 3 .  
         [0029]     The multi-phase PWM controller  14 ′ generates control signals to control corresponding AC/DC converters  11 ,  21 , . . . , N 1  according to different preset periods. The AC/DC converters  11 ,  21 , . . . , N 1  correspondingly receive AC voltages from an AC power source (not shown) according to the control signals in corresponding preset periods.  
         [0030]     In a first preset period, the multi-phase PWM controller  14 ′ controls the AC/DC converter  11  to receive the AC voltage from the AC power source. The AC/DC converter  11  converts the AC voltage to the DC voltage. The driving circuit  12  converts the DC voltage generated by the AC/DC converter  11  to the AC voltage, in order to light up the lamps in the lamp module  13 . Similarly, when the lamps in the lamp module  13  are being turned on, and there is no current flowing through the lamps in the lamp module  13 , the bus inverter controller  15  increases the working frequency thereof, and controls the driving circuit  12  to output a higher AC voltage for lighting the lamp module  13 . Once the lamps in the lamp module  13  are turned on, the working frequency of the bus inverter controller  15  is dropped to a stable frequency.  
         [0031]     When the lamps in the lamp module  13  are turned on in a first preset period, correspondingly, in an Nth (N=2, 3 . . . ) preset period, the multi-phase PWM controller  14 ′ controls the AC/DC controller N 1  (N=2, 3 . . . ) to receive an AC voltage from the AC power source. The AC/DC controller N 1  (N=2, 3 . . . ) converts the AC voltage received to a DC voltage. The driving circuit N 2  (N=2, 3 . . . ) converts the DC voltage to an AC signal, in order to turn on the lamps in the lamp module N 3  (N=2, 3 . . . ). Similarly, when the lamps in the lamp module N 3  (N=2, 3 . . . ) are being turned on, and there is no current flowing through the lamps in the lamp module N 3  (N=2, 3 . . . ), the bus inverter controller  15  increases the working frequency thereof, and controls the driving circuit N 2  (N=2, 3 . . . ) to output a higher AC voltage for lighting the lamp module N 3  (N=2, 3 . . . ).  
         [0032]     When the lamps in the lamp modules  13 ,  23 , . . . , N 3  are turned on, however, the brightnesses of the lamps are uneven. The multi-phase PWM controller  14 ′ regulates the DC voltage outputted from the AC/DC converter  11 ,  21 , . . . , N 1  to change the brightnesses of the lamps according to the preset periods.  
         [0033]     Correspondingly, in the Nth (N=1, 2, 3 . . . ) preset period, the multi-phase PWM controller  14 ′ receives a feedback current from a corresponding lamp module  13 ,  23 , . . . , or N 3 , and outputs control signals to the corresponding AC/DC converter  11 ,  21 , . . . , or N 1 . The AC/DC converter  11 ,  21 , . . . , or N 1  regulates the outputted DC voltage thereof, in order to change the brightnesses of the lamps in the lamp module  13 ,  23 , . . . , or N 3 . In the third embodiment, the DC voltages outputted from the AC/DC converters  11 ,  21 , . . . , N 1  are variable.  
         [0034]      FIG. 4  is a block diagram of a fourth embodiment of a system for driving plural lamps in accordance with the present invention. The circuit structure of  FIG. 4  is substantially the same as that of the third embodiment shown in  FIG. 3 , except that the circuit has a plurality of DC/DC converters  11 ′,  21 ′, . . . , N 1 ′ instead of AC/DC converters  11 ,  21 , . . . , N 1 . The DC/DC converters  11 ′,  21 ′, . . . , N 1 ′ receive DC voltages from a power source (not shown), in order to light up the lamps at different preset times.  
         [0035]     While particular embodiments have been described above, it should be understood that they have been presented by way of example only and not by way of limitation. Thus the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.