Abstract:
A ballast circuit is provided. The ballast circuit comprises a first lamp set, a second lamp set, a detection circuit, and a latch circuit. The first lamp set comprises a first inductor and a plurality of containing areas. The second lamp set comprises a second inductor and at least one containing area. The detection circuit is configured to receive a direct current (DC) voltage and coupled to the containing areas of the first and second lamp sets so that the detection circuit, the first inductor, the second inductor, and a plurality of lamps contained in the containing areas are in a series connection and generate a first signal. The latch circuit is coupled to the detection circuit and configured to selectively start in response to the first signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority based on Taiwan Patent Application No. 097110792 filed on 26 Mar. 2008, the contents of which are incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a ballast circuit. More specifically, the present invention relates to a ballast circuit capable of detecting and automatically restarting all lamps. 
         [0004]    2. Descriptions of the Related Art 
         [0005]    Lamps have found more and more widespread applications since the advent thereof. One of the most widespread and well-known applications is lighting. As increasingly heightened requirements are being imposed on the lighting effect, ballasts with a plurality of lamps have been used wider than that with one lamp. 
         [0006]    Please refer to  FIG. 1 , where a conventional ballast circuit  1  is illustrated. The ballast circuit  1  comprises a first lamp set  11 , a second lamp set  12 , a drive circuit  13 , capacitors  150 ,  151 , switches  152 ,  153 , a detection circuit, a latch circuit  140 , and preheat circuits  160 ,  161 . The lamp set  11  comprises a resonant module  110 , preheat circuits  111 ,  112  and two containing areas (not shown) for receiving the lamps  113 ,  114  respectively. The second lamp set  12  comprises a resonant module  120 , preheat circuits  121 ,  122  and two containing areas (not shown) for receiving the lamps  123 ,  124  respectively. The drive circuit  13  is configured to start the switches  152 ,  153  of the ballast circuit  1 . Various elements of the ballast circuit  1  are well known to those of ordinary skill in the art, and thus only those relevant to this invention will be described. 
         [0007]    As the number of lamps contained in the ballast circuit  1  increases, the lighting effect gets significantly improved. However, there are some shortcomings arisen in the ballast circuit containing a plurality of lamps. One of the shortcomings is that not all lamps can be detected whether they have been connected into the circuit. More specifically, the detection circuit of the ballast circuit  1  comprises a capacitor  141  and resistors  142 ,  143 ,  144 . The resistor  142  is connected to a direct current (DC) voltage input terminal  163  and a filament of the lamp  114 . The resistor  143  is connected to a filament of the lamp  124  and the latch circuit  140 . The resistor  144  is connected to the resistor  143  and the latch circuit  140 . 
         [0008]    As the detection circuit is connected to the lamps  114 ,  124  and the latch circuit  140 , the latch circuit  140  may determine whether the lamps  114 ,  124  have been connected into the circuit according to a voltage at a juncture  17 . More particularly, in case either or both of the lamps  114 ,  124  fail to be connected into the circuit, the juncture  17  will experience a voltage drop so that the ballast circuit  1  can determine that the lamp(s) has not been connected into the circuit. Once all the lamps have been connected into the circuit, the voltage at the juncture  17  will be restored to a normal value, and the drive circuit  13  can restart the lamps. 
         [0009]    It follows from the above descriptions that the detection circuit equipped in the ballast circuit  1  is only able to detect whether a portion of the lamps (i.e., lamps  114 ,  124 ) has been connected to the circuit or not, but fails to detect whether all of the lamps (i.e., fails to detect the lamps  111 ,  121 ) have been connected to the circuit or not. Consequently, the aforementioned ballast circuit is inconvenient for users. 
         [0010]    In summary, efforts still have to be made in the art to provide a ballast circuit capable of detecting if all lamps have been connected into the circuit. 
       SUMMARY OF THE INVENTION 
       [0011]    One objective of this invention is to provide a ballast circuit capable of detecting if lamps mounted therein have all been connected into the circuit. 
         [0012]    To this end, the ballast circuit of the present invention comprises a first lamp set, a second lamp set, a detection circuit and a latch circuit. The first lamp set comprises a first inductor and a plurality of containing areas. Each of the containing areas is adapted to contain a lamp so that the lamps are connected in series. The containing areas are connected in series with the first inductor. The second lamp set, which is connected in parallel with the first lamp set, comprises a second inductor and at least one containing area. The second inductor is connected to the first inductor, and the at least one containing area is connected in series with the second inductor. Each of the at least one containing area is adapted to contain a lamp so that the at least one lamp is connected in series with the second inductor. The detection circuit is connected to each of the containing areas of the first lamp set and each of the containing areas of the second lamp set, so that the detection circuit, the first inductor, the second inductor, and the lamps contained in the containing areas form a series connection. The detection circuit is configured to receive a DC voltage signal and generate a first signal. The latch circuit, which is coupled to the detection circuit, is configured to selectively start the ballast circuit in response to the first signal. 
         [0013]    The ballast circuit has the detection circuit coupled to all the containing areas of the ballast circuit. Consequently, when lamps are contained in the ballast circuit, the detection circuit will also be coupled to all the lamps. As all the lamps are coupled to the detection circuit, the ballast circuit is capable of determining status of the lamps according to a voltage on the detection circuit, so that the latch circuit thereof will open or close the ballast circuit in response to the voltage on the detection circuit. 
         [0014]    The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]      FIG. 1  is a schematic view of a conventional ballast circuit; 
           [0016]      FIG. 2  is a schematic view of a first preferred embodiment of the present invention; 
           [0017]      FIG. 3  is a schematic view of a second preferred embodiment of the present invention; 
           [0018]      FIG. 4  is a schematic view of a third preferred embodiment of the present invention; 
           [0019]      FIG. 5  is a schematic view of a fourth preferred embodiment of the present invention; and 
           [0020]      FIG. 6  is a schematic view of a fifth preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    In the following descriptions, the present invention will be explained with reference to embodiments thereof. However, these embodiments are not intended to limit that this invention can only be embodied in any specific context, applications, or with particular methods described in these embodiments. Therefore, description of these embodiments is only intended to illustrate rather than to limit this invention. It should be noted that in the following embodiments and the attached drawings, elements unrelated to this invention are omitted and not drawn, and relationships among individual elements are only illustrated to facilitate understanding rather than to limit the actual scales. 
         [0022]      FIG. 2  illustrates a first preferred embodiment of the present invention, which is a ballast circuit  2 . The ballast circuit  2  comprises a first lamp set  21 , a second lamp set  22 , a detection circuit, a latch circuit  24 , capacitors  251 ,  253 , and switches  255 ,  257 . 
         [0023]    Each of the switches  255 ,  257  has a control terminal, a first terminal, and a second terminal. Each of the capacitors  251 ,  253  has a first terminal and a second terminal. The control terminals of the switches  255 ,  257  are connected to a drive circuit  260 . The first terminal of the switch  255  is coupled to the first terminal of the capacitor  251 . The second terminal of the switch  255  is coupled to the first terminal of the switch  257 . The second terminal of the switch  257  is grounded and coupled to the second terminal of the capacitor  253 . The second terminal of the capacitor  251  is coupled to the first terminal of the capacitor  253 . The first lamp set  21  is coupled to the second terminal of the switch  255 , the first terminal of the switch  257 , the second terminal of the capacitor  251 , and the first terminal of the capacitor  253 . The second lamp set  22  is also coupled to the second terminal of the switch  255 , the first terminal of the switch  257 , the second terminal of the capacitor  251 , and the first terminal of the capacitor  253 . 
         [0024]    The first lamp set  21  comprises a first inductor  211 , a first capacitor  216 , a first containing area (not shown) for containing a first lamp  212 , a second containing area (not shown) for containing a second lamp  213 , and a plurality of preheat circuits  214 ,  215 ,  270 . These containing areas are connected in series with the first inductor  211 . Specifically, the first containing area is coupled in series to the first inductor  211  and the second containing area is coupled to the first containing area, so that the first lamp  212  and the second lamp  213  contained therein are connected in series. The first capacitor  216  is coupled/connected to the last containing area of the first lamp set  21  (i.e., the second containing area), and thus also coupled/connected to the lamp contained therein (i.e. the second lamp  213 ). Meanwhile, the first capacitor  216  is also coupled to the first inductor  211 . The first inductor  211  and the first capacitor  216  are adapted to form a resonant circuit in the first lamp set  21 ; functions and effects of the resonant circuit will be readily appreciated by those of ordinary skill in the art and thus will not be described in details. The preheat circuit  214  is coupled to the first inductor  211  and the first containing area, and thus is also coupled to the first lamp  212  contained therein. The preheat circuit  215  is coupled to the first containing area and the second containing area, and thus is also coupled to the first lamp  212  and the second lamp  213  contained therein. The preheat circuit  270  is coupled to the second containing area, and thus is also coupled to the second lamp  213  contained therein. The preheat circuits  214 ,  215 ,  270  are configured to preheat the first lamp  212  and the second lamp  213  when the ballast circuit  2  is just started. 
         [0025]    On the other hand, the second lamp set  22  is connected in parallel with the first lamp set  21 , and comprises a second inductor  221 , a second capacitor  226 , a third containing area (not shown) for containing a third lamp  223 , and a plurality of preheat circuits  225 ,  271 . The second inductor  221  is coupled to the first inductor  211 , and the third containing area is connected in series with the second inductor  221 , so that the third lamp  223  contained in the third containing area is also connected in series with the second inductor  221 . The second capacitor  226  is coupled/connected to the last containing area of the second lamp set  22  (i.e. the containing area for the third lamp  223 ), and is thus also coupled to the third lamp  223  contained therein. Meanwhile, the second capacitor  226  is also coupled to the second inductor  221 . The second inductor  221  and the capacitor  226  are adapted to form a resonant circuit in the second lamp set  22 . The preheat circuit  225  is coupled to the second inductor  221  and the third containing area, and thus is also coupled to the third lamp  223  contained therein. The preheat circuit  271  is coupled to the third containing area, and thus is also coupled to the third lamp  223  contained therein. The preheat circuit  271  is further coupled to the preheat circuit  270 . The preheat circuits  225 ,  271  are configured to preheat the third lamp  223  when the ballast circuit is just started. 
         [0026]    The detection circuit is coupled to each of the containing areas (i.e., the first and the second containing areas) of the first lamp set  21  and each of the containing areas (i.e., the third containing area) of the second lamp set  22 . Furthermore, the detection circuit, the first inductor  211 , the second inductor  221 , the first lamp  212  contained in the first containing area, the second lamp  213  contained in the second containing area and the third lamp  223  contained in the third containing area form a series connection, details of which will be set forth later. Additionally, the detection circuit is connected to a juncture  200 , which is the DC voltage input terminal  263  of the ballast circuit  2  in this embodiment, to receive a DC voltage signal for use to detect the status of the lamps—whether all the lamps have been connected into the circuit or not. In other embodiments, the DC voltage input terminal  263  may also be replaced by other DC voltage input terminals while still achieving the same objective as this preferred embodiment; this will be readily appreciated by those of ordinary skill in the art with reference to this preferred embodiment, and thus will not be described again. 
         [0027]    Particularly, the first lamp  212  of the first lamp set  21  is coupled to the first inductor  211 . The second lamp  213  is coupled to the first lamp  212 . The third lamp  223  of the second lamp set  22  is coupled to the second inductor  221  and the second lamp  213 . The detection circuit comprises three detection sub-circuits, namely, the first detection sub-circuit, the second detection sub-circuit and the third detection sub-circuit. 
         [0028]    Specifically, the first detection sub-circuit is coupled to the second containing area and a DC voltage input terminal (e.g., the juncture  200 ) to receive a DC voltage. Further, when the second lamp  213  is contained in the second containing area, the first detection sub-circuit is also coupled to the second lamp  213 . It can be seen from  FIG. 2  that the first detection sub-circuit comprises the juncture  200 , the first resistor  231 , and the second resistor  232  in a series connection, where the second resistor  232  is connected in series with the first resistor  231 . Hence, the first detection sub-circuit is coupled to the DC input terminal and the second containing area via the first resistor  231  and the second resistor  232  respectively. 
         [0029]    The second detection sub-circuit is coupled to the first containing area and the third containing area. Further, when the first containing area and the third containing area have the first lamp  212  and the third lamp  223  contained therein respectively, the second detection sub-circuit is also coupled to the first lamp  212  and the third lamp  223 . It can be seen from  FIG. 2  that the second detection sub-circuit comprises a third resistor  233 , via which the second detection sub-circuit is coupled to the first and the third containing areas. Additionally, the first detection sub-circuit and the second detection sub-circuit are connected in series via a filament  280  of the second lamp  213  and a filament  281  of the third lamp  223 . 
         [0030]    The third detection sub-circuit is coupled to the third containing area and the latch circuit  24 . It can be seen from  FIG. 2  that the third detection sub-circuit comprises a fifth resistor  291 , a sixth resistor  292 , and a detection capacitor  293 . The fifth resistor  291  is connected to the latch circuit  24  and the third containing area. The sixth resistor  292  is connected to the latch circuit  24  and the fifth resistor  291 . The detection capacitor  293  is connected to the latch circuit  24  and the fifth resistor  291  and connected in parallel with the sixth resistor  292 . Consequently, the third detection sub-circuit is coupled to the third containing area and the latch circuit  24  via the fifth resistor  291 , the sixth resistor  292 , and the detection capacitor  293 . When the third containing area has the third lamp  223  contained therein, the fifth resistor  291  of the third detection sub-circuit is also coupled to the third lamp  223 . The second detection sub-circuit is connected in series with the third detection sub-circuit via the filament  282  of the first lamp  212 , the first inductor  211 , the second inductor  221 , and a filament  283  of the third lamp  223 . 
         [0031]    In other words, the juncture  200 , the first resistor  231 , the second resistor  232 , the second lamp  213 , the third lamp  223 , the third resistor  233 , the first lamp  212 , the first inductor  211 , the second inductor  221 , and the other side of the third lamp  223  are connected to the latch circuit  24  in series to form the aforementioned series circuit. 
         [0032]    In the following descriptions, how the detection circuit detects whether all of the lamps (i.e., the first lamp  212 , the second lamp  213 , and the third lamp  223 ) are connected into the circuit and how the ballast circuit  2  is restarted will be explained. The latch circuit  24  comprises resistors  246 ,  247 , a capacitor  243 , and switches  245 ,  248 , and the connections among which are illustrated in  FIG. 2 . In this preferred embodiment, the switch  245  is a PNP-type transistor, and the switch  248  is an NPN-type transistor. In other embodiments, the switches  245  and  248  may be replaced by other switches having the same properties. 
         [0033]    The detection circuit is connected to a DC voltage input terminal (e.g., the juncture  200 ) to receive a DC voltage and generate a first signal at a juncture  240  between the fifth resistor  291  and the sixth resistor  292 . The switches  245  and  248  of the latch circuit  24  are turned on or off in response to the first signal, so that the drive circuit  260  is able to turn off or restart all the lamps in the ballast circuit  2 . For example, in the event that a lamp of the ballast circuit  2  is not connected into the circuit, the first signal at the juncture  240  will have a voltage value lower than a first predetermined voltage value, in which case the switch  245  will be turned on. Once the switch  245  is turned on, a voltage value at the juncture of the resistor  246  and the resistor  247  is higher than a second predetermined voltage value to turn on the switch  248  and further latch the drive circuit  260 . Upon replacement of the lamp(s), a voltage higher than or equal to a third predetermined voltage value will occur at the juncture  240  so that the switch  245  is turned off. As a consequence, the switch  248  is also turned off. Then the ballast circuit resumes normal operation. Herein, the third predetermined voltage value may be equal to the first predetermined voltage value. 
         [0034]    It follows from the above descriptions that in the detection circuit of the first preferred embodiment, the first, second, and third detection sub-circuits connect the first lamp  212  contained in the first containing area, the second lamp  213  contained in the second containing area, the third lamp  223  contained in the third containing area, the first inductor  211  and the second inductor  212  into a series circuit. Since all the lamps (i.e., the first lamp  212 , the second lamp  213  and the third lamp  223 ) are disposed in the series circuit, failure of any of the lamps will change the operation status of the latch circuit  24 . With the arrangement of the first preferred embodiment, the problem that the status of only a portion of the lamps can be detected is solved. 
         [0035]      FIG. 3  illustrates a second preferred embodiment of the present invention, which is a ballast circuit  3 . The ballast circuit  3  also comprises a first lamp set  21 , a second lamp set  22 , a detection circuit, a latch circuit  24 , capacitors  251 ,  253 , and switches  255 ,  257 . The first lamp set  21 , the second lamp set  22 , the latch circuit  24 , the capacitors  251 ,  253 , the switches  255 ,  257 , and connections between them are just the same as those of the ballast circuit  2  of the first embodiment, and thus will be omitted from description herein. The following descriptions will focus on differences between the second embodiment and the first embodiment, i.e., connections of the detection circuit. 
         [0036]    Likewise, the detection circuit of the ballast circuit  3  comprises three detection sub-circuits, namely, the first detection sub-circuit, the second detection sub-circuit, and the third detection sub-circuit. The first detection sub-circuit is coupled to the first containing area and a DC voltage input terminal (e.g., the juncture  200 , which is connected to the DC voltage input terminal  263 ) to receive a DC voltage. Further, when the first containing area has the first lamp  212  contained therein, the first detection sub-circuit is also coupled to the first lamp  212 . It can be seen from  FIG. 3  that the first detection sub-circuit comprises the juncture  200 , the first resistor  231 , and the second resistor  232  in a series connection, wherein the second resistor  232  is connected in series with the first resistor  231 . Hence, the first detection sub-circuit is coupled to the DC input terminal and the first containing area via the first resistor  231  and the second resistor  232  respectively. 
         [0037]    The second detection sub-circuit is coupled to the second containing area and the third containing area. Further, when the second containing area and the third containing area have the second lamp  213  and the third lamp  223  contained therein respectively, the second detection sub-circuit is also coupled to the second lamp  213  and the third lamp  223 . It can be seen from  FIG. 3  that the second detection sub-circuit comprises a third resistor  233 , via which the second detection sub-circuit is coupled to the second and third containing areas. Additionally, the second detection sub-circuit is connected in series with the first detection sub-circuit via the filament  283  of the third lamp  223 , the first inductor  211 , the second inductor  221 , and the filament  282  of the first lamp  212 . 
         [0038]    The third detection sub-circuit is coupled to the third containing area and the latch circuit  24 . It can be seen from  FIG. 3  that the third detection sub-circuit comprises a fifth resistor  291 , a sixth resistor  292 , and a detection capacitor  294 . The fifth resistor  291  is connected to the latch circuit  24  and the third containing area. The sixth resistor  292  is connected to the latch circuit  24  and the fifth resistor  291 . The detection capacitor  294  is connected to the latch circuit  24  and the fifth resistor  291  and connected in parallel with the sixth resistor  292 . Consequently, the third detection sub-circuit is coupled to the third containing area and the latch circuit  24  via the fifth resistor  291 , the sixth resistor  292 , and the detection capacitor  294 . 
         [0039]    In other words, when the third containing area has the third lamp  223  contained therein, the third detection sub-circuit is also coupled to the third lamp  223 . The third detection sub-circuit is connected in series with the second detection sub-circuit via the filament  281  of the third lamp  223  and the filament  280  of the second lamp  213 . As a result, the juncture  200 , the first resistor  231 , the second resistor  232 , the filament  282  of the first lamp  212  contained in the first containing area, the first inductor  211 , the second inductor  221 , the filament  283  of the third lamp  223  contained in the third containing area, the third resistor  233 , the filament  280  of the second lamp  213  contained in the second containing area, and the filament  281  of the third lamp  223  are connected in series with the latch circuit  24  to form the aforementioned series circuit. 
         [0040]    According to aforementioned descriptions, in a different way from that of the first embodiment, the detection circuit of the second preferred embodiment cascades the first lamp  212 , the second lamp  213 , the third lamp  223 , the first inductor  211  and the second inductor  212  into a series circuit. Since all the lamps (i.e., the first lamp  212 , the second lamp  213  and the third lamp  223 ) are disposed in the series circuit, the status that if any of the lamps is not connected to the circuit will change the operation status of the latch circuit  24 . 
         [0041]      FIG. 4  illustrates a third preferred embodiment of the present invention, which is a ballast circuit  4 . The ballast circuit  4  comprises a first lamp set  21 , a second lamp set  32 , a detection circuit, a latch circuit  24 , capacitors  251 ,  253 , and switches  255 ,  257 . The first lamp set  21 , the latch circuit  24 , the capacitors  251 ,  253 , the switches  255 ,  257  and their connections are just the same as those described in the ballast circuit  2  of the first preferred embodiment, and thus will be omitted from description herein. The following description will focus on differences between this embodiment and the first embodiment. 
         [0042]    The first difference between the ballast circuit  4  and the ballast circuit  2  of the previous preferred embodiment is in that the second lamp set  32  further comprises a preheat circuit  224  and a fourth containing area for containing a fourth lamp  222 . The containing areas (i.e., the third and fourth containing areas) included in the second lamp set  32  are connected in series with the second inductor  221 , so that the third lamp  223  and the fourth lamp  222  contained in the containing areas (i.e., the third and the fourth containing areas) of the second lamp set  32  are connected in series with the second inductor  221 . 
         [0043]    Specifically, the fourth containing area is coupled to the second inductor  221 , and when the fourth containing area has the fourth lamp  222  contained therein, the fourth lamp  222  will also be coupled to the second inductor  221 . The third lamp  223  is coupled to the fourth lamp  222  and the second lamp  213 . Both the preheat circuits  224 ,  225  are coupled to the fourth containing area, i.e., coupled to the fourth lamp  222  contained in the fourth containing area simultaneously. The preheat circuits  224 ,  225  are configured to preheat the fourth lamp  222  when the ballast circuit  4  is just started. 
         [0044]    The second difference between the ballast circuit  4  and the ballast circuit  2  of the previous preferred embodiment lies in connections of the detection circuit. The detection circuit of the ballast circuit  4  comprises three detection sub-circuits, namely, the first detection sub-circuit, the second detection sub-circuit, and the third detection sub-circuit. The first detection sub-circuit is coupled to the second containing area and a DC voltage input terminal (e.g., the juncture  200 , which is coupled to the DC voltage input terminal  263 ) to receive a DC voltage. Further, when the second containing area has the second lamp  213  contained therein, the first detection sub-circuit is also coupled to the second lamp  213 . It can be seen from  FIG. 4  that the first detection sub-circuit comprises the first resistor  231  and the second resistor  232  connected in series. Hence, the first detection sub-circuit is coupled to the DC input terminal and the second containing area via the first resistor  231  and the second resistor  232  respectively. 
         [0045]    The second detection sub-circuit is coupled to the first containing area and the third containing area. Further, when the first containing area and the third containing area have the first lamp  212  and the third lamp  223  contained therein respectively, the second detection sub-circuit is also coupled to the first lamp  212  and the third lamp  223 . It can be seen from  FIG. 4  that the second detection sub-circuit comprises a third resistor  233 , via which the second resistor  232  is coupled to the first and third containing areas. Additionally, the second detection sub-circuit is connected in series with the first detection sub-circuit via the filament  281  of the third lamp  223  and the filament  280  of the second lamp  213 . 
         [0046]    The third detection sub-circuit is coupled to the fourth containing area and the latch circuit  24 . It can be seen from  FIG. 4  that the third detection sub-circuit comprises a fifth resistor  291 , a sixth resistor  292 , and a detection capacitor  294 . The fifth resistor  291  is connected to the latch circuit  24  and the fourth containing area. The sixth resistor  292  is connected to the latch circuit  24  and the fifth resistor  291 . The detection capacitor  294  is connected to the latch circuit  24  and the fifth resistor  291  and connected in parallel with the sixth resistor  292 . Consequently, the third detection sub-circuit is coupled to the fourth containing area and the latch circuit  24  via the fifth resistor  291 , the sixth resistor  292 , and the detection capacitor  294 . 
         [0047]    In other words, when the fourth containing area has the fourth lamp  222  contained therein, the third detection sub-circuit is also coupled to the fourth lamp  222 . The second detection sub-circuit is connected in series with the third detection sub-circuit via the first inductor  211  and the second inductor  221 . In other words, the juncture  200 , the first resistor  231 , the second resistor  232 , the filament  280  of the second lamp  213  contained in the second containing area, the filament  281  of the third lamp  223  contained in the third containing area, the third resistor  233 , the filament  282  of the first lamp  212  contained in the first containing area, the first inductor  211 , the second inductor  221 , the filament  284  of the fourth lamp  222  contained in the fourth containing area, and the latch circuit  24  are connected together to form the aforementioned series circuit. 
         [0048]    According to the aforementioned descriptions, by use of the first inductor  211  and the second inductor  212 , the detection circuit cascades all lamps contained in the containing areas into a series circuit no matter how many containing areas are included in the first and second lamp sets. Consequently, failure of any of the lamps will change the operation status of the latch circuit  24 . 
         [0049]      FIG. 5  illustrates a fourth preferred embodiment of the present invention, which is a ballast circuit  5 . The ballast circuit  5  also comprises a first lamp set  21 , a second lamp set  32 , a detection circuit, a latch circuit  24 , capacitors  251 ,  253 , and switches  255 ,  257 . The first lamp set  21 , the second lamp set  32 , the latch circuit  24 , the capacitors  251 ,  253 , the switches  255 ,  257 , and their connections are just the same as those of the ballast circuit  4 , and thus will be omitted and not described again. The following descriptions will focus on differences between the ballast circuit  5  and the ballast circuit  4 . The difference between the ballast circuit  5  and the ballast circuit  4  lies in connections of the detection circuit. Likewise, the detection circuit of the ballast circuit  5  comprises three detection sub-circuits, namely, the first detection sub-circuit, the second detection sub-circuit, and the third detection sub-circuit. 
         [0050]    The first detection sub-circuit is coupled to the first containing area and a DC voltage input terminal (e.g., the juncture  200 , which is coupled to the DC voltage input terminal  263 ) to receive a DC voltage. Further, when the first containing area has the first lamp  212  contained therein, the first detection sub-circuit is also coupled to the first lamp  212 . It can be seen from  FIG. 5  that the first detection sub-circuit comprises the first resistor  231  and the second resistor  232  connected in series. The first detection sub-circuit is coupled to the DC input terminal and the first containing area via the first resistor  231  and the second resistor  232  respectively. 
         [0051]    The second detection sub-circuit is coupled to the second and fourth containing areas. Further, when the second containing area and the fourth containing area have the second lamp  213  and the fourth lamp  222  contained therein respectively, the second detection sub-circuit is also coupled to the second lamp  213  and the fourth lamp  222 . It can be seen from  FIG. 5  that the second detection sub-circuit comprises a third resistor  233 , via which the second detection sub-circuit is coupled to the second and fourth containing areas. The first detection sub-circuit is connected in series with the second detection sub-circuit via the first inductor  211  and the second inductor  221 . 
         [0052]    In addition, the third detection sub-circuit is coupled to the third containing area and the latch circuit  24 . It can be seen from  FIG. 5  that the third detection sub-circuit comprises a fifth resistor  291 , a sixth resistor  292 , and a detection capacitor  294 . The fifth resistor  291  is connected to the latch circuit  24  and the third containing area. The sixth resistor  292  is connected to the latch circuit  24  and the fifth resistor  291 . The detection capacitor  294  is connected to the latch circuit  24  and the fifth resistor  291  and connected in parallel with the sixth resistor  292 . Consequently, the third detection sub-circuit is coupled to the third containing area and the latch circuit  24  via the fifth resistor  291 , the sixth resistor  292  and the detection capacitor  294 . 
         [0053]    In other words, when the third containing area has the third lamp  223  contained therein, the third detection sub-circuit is also coupled to the third lamp  223 . The third detection sub-circuit is connected in series with the second detection sub-circuit via the filament  281  of the third lamp  223  and the lamp  280  of the second lamp  213 . 
         [0054]    With the above arrangement, the juncture  200 , the first resistor  231 , the second resistor  232 , the filament  282  of the first lamp  212  contained in the first containing area, the first inductor  211 , the second inductor  221 , the filament  284  of the fourth lamp  222  contained in the fourth containing area, the third resistor  233 , the filament  280  of the second lamp  213  contained in the second containing area, the filament  281  of the third lamp  223  contained in the third containing area, and the latch circuit  24  are connected together to form the aforementioned series circuit. 
         [0055]    In a different way from that of the third embodiment, the detection circuit of the fourth preferred embodiment cascades the lamps contained in the containing areas of the first lamp set  21  and the second lamp set  22 , the first inductor  211  and the second inductor  212  into a series circuit. Since all the lamps are disposed in the series circuit, failure of any of the lamps will change the operation status of the latch circuit  24 . 
         [0056]      FIG. 6  illustrates a fifth preferred embodiment of the present invention, which is a ballast circuit  6 . The ballast circuit  6  comprises a first lamp set  21 , a second lamp set  52 , a detection circuit, a latch circuit  24 , capacitors  251 ,  253 , and switches  255 ,  257 . The first lamp set  21 , the latch circuit  24 , the capacitors  251 ,  253 , the switches  255 ,  257 , and their connections are just the same as those of the ballast circuit  5  of the fourth preferred embodiment, and thus will be omitted and not described again. The following descriptions will focus on differences between this embodiment and the fourth embodiment. 
         [0057]    The first difference of the ballast circuit  6  and the ballast circuit  5  of the fourth preferred embodiment is in that the second lamp set  52  further comprises a preheat circuit  228  and a fifth containing area (not shown) for containing a fifth lamp  227 . The containing areas (i.e., the third, the fourth and the fifth containing areas) included in the second lamp set  52  are connected in series with the second inductor  221 , so that the third lamp  223 , the fourth lamp  222 , and the fifth lamp  227  contained therein are connected in series with the second inductor  221 . 
         [0058]    Specifically, the fifth containing area is coupled to the second inductor  221 , and when the fifth containing area has the fifth lamp  227  contained therein, the fifth lamp  227  will also be coupled to the second inductor  221 . The fourth lamp  222  is coupled to the fifth lamp  227 , and the third lamp  223  is coupled to the fourth lamp  222  and the second lamp  213 . Both the preheat circuits  224 ,  228  are coupled to the fifth lamp  227 , and configured to preheat the fifth lamp  227  when the ballast circuit  6  is just started. 
         [0059]    The second difference between the ballast circuit  6  and the ballast circuit  5  of the fourth preferred embodiment lies in connections of the detection circuit. The first detection sub-circuit is coupled to the first containing area and a DC voltage input terminal (e.g., the juncture  200 , which is coupled to the DC voltage input terminal  263 ) to receive a DC voltage. Further, when the first containing area has the first lamp  212  contained therein, the first detection sub-circuit is also coupled to the first lamp  212 . It can be seen from  FIG. 6  that the first detection sub-circuit comprises the first resistor  231  and the second resistor  232  connected in series. Hence, the first detection sub-circuit is coupled to the DC input terminal and the first containing area via the first resistor  231  and the second resistor  232  respectively. 
         [0060]    The second detection sub-circuit is coupled to the fifth containing area and the fourth containing area. Further, when the fifth containing area and the fourth containing area have the fifth lamp  227  and the fourth lamp  222  contained therein respectively, the second detection sub-circuit is also coupled to the fifth lamp  227  and the fourth lamp  222 . It can be seen from  FIG. 6  that the second detection sub-circuit comprises a fourth resistor  234 , via which the second detection sub-circuit is coupled to the fifth and the fourth containing areas. It should be noted that the first detection sub-circuit is connected in series with the second detection sub-circuit via the filament  282  of the first lamp  212 , the first inductor  211 , the second inductor  221 , and the filament  285  of the fifth lamp  227 . 
         [0061]    The third detection sub-circuit is coupled to the fourth containing area and the second containing area. Further, when the fourth containing area and the second containing area have the fourth lamp  222  and the second lamp  213  contained therein respectively, the third detection sub-circuit is also coupled to the fourth lamp  222  and the second lamp  213 . It can be seen from  FIG. 6  that the third detection sub-circuit comprises a third resistor  233 , via which the third detection sub-circuit is coupled to the fourth and the second containing areas. It should be noted that the third detection sub-circuit is connected in series with the second detection sub-circuit via the filament  284  of the fourth lamp  222 . 
         [0062]    Additionally, the fourth detection sub-circuit is coupled to the third containing area and the latch circuit  24 . It can be seen from  FIG. 6  that the fourth detection sub-circuit comprises a fifth resistor  291 , a sixth resistor  292 , and a detection capacitor  294 . The fifth resistor  291  is connected to the latch circuit  24  and the third containing area. The sixth resistor  292  is connected to the latch circuit  24  and the fifth resistor  291 . The detection capacitor  294  is connected to the latch circuit  24  and the fifth resistor  291  and connected in parallel with the sixth resistor  292 . Consequently, the fourth detection sub-circuit is coupled to the third containing area and the latch circuit  24  via the fifth resistor  291 , the sixth resistor  292 , and the detection capacitor  294 . 
         [0063]    In other words, when the third containing area has the third lamp  223  contained therein, the fourth detection sub-circuit is also coupled to the third lamp  223 . The fourth detection sub-circuit is connected in series with the third detection sub-circuit via the filament  281  of the third lamp  223  and the filament  280  of the second lamp  213 . 
         [0064]    With the above arrangement, the juncture  200 , the first resistor  231 , the second resistor  232 , the filament  282  of the first lamp  212  contained in the first containing area, the first inductor  211 , the second inductor  221 , the filament  285  of the fifth lamp  227  contained in the fifth containing area, the fourth resistor  234 , the filament  284  of the fourth lamp  222  contained in the fourth containing area, the third resistor  233 , the filament  280  of the second lamp  213  contained in the second containing area, the filament  281  of the third lamp  223  contained in the third containing area, the fifth resistor  291 , the sixth resistor  292  and the latch circuit  24  are connected together to form the aforementioned series circuit. 
         [0065]    According to the aforementioned descriptions, by use of the first inductor  211  and the second inductor  221 , the detection circuit cascades all lamps contained in the containing areas into a series circuit no matter how many lamps are included in the first and the second lamp sets. Consequently, failure of any of the lamps will change the operation status of the latch circuit  24 . 
         [0066]    This invention relates to a ballast circuit which, by use of a detection circuit coupled to each lamp contained in the containing areas of the ballast circuit, is able to detect if all the lamps are connected into the circuit. Once all the lamps are connected into the circuit, the ballast circuit may restart all the lamps of the ballast circuit by turning on a latch circuit. As a result, the problem that conventional ballast circuits fail to detect if all the lamps are connected into the circuit can be effectively solved by this invention. 
         [0067]    The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.