Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a fluorescent lamp driving circuit; in particular, to a multi-lamp driving circuit with built-in MOSFET (Metal Oxide Semiconductor Field Effect Transistor). 
     2. Description of Related Art 
     A backlight module of a liquid crystal display uses high-frequency sinusoidal-wave power supply to supply power as the energy required for lighting the Cold Cathode Fluorescent Lamp (CCFL), therefore it is demanded to employ DC/AC inverters to achieve the purpose of energy conversion. An ordinary CCFL driving circuit uses a resonant module to convert a DC voltage into an AC voltage to drive a CCFL to light up. The driving voltage and the driving current of the CCFL are detected by the voltage and current detection circuits. A Pulse-Width-Modulation (PWM) controller receives the generated voltage detection signal and current detection signal for the purposes of stabilizing the illumination of the CCFL and circuit protection. 
     Due to the trend of large-scaled liquid crystal panel, the number of CCFLs in the backlight module needed to be driven increases accordingly, conventional driving circuit applying single PWM controller and single resonant module for driving single lamp may result in complexity in circuit design as well as increasing of production cost. In order to reduce cost of multi-lamp driving, it is common to apply one PWM controller to control the multi-lamp driving circuit, so as to reduce the number of components and simplify circuit design. 
       FIG. 1  shows a circuit diagram of a conventional multi-lamp driving circuit. The multi-lamp driving circuit comprises a PWM controller  100 , a switch module SW, a resonant module, a multi-lamp module, a plurality of current detection modules  110 ,  130 , and a plurality of voltage detection modules  120 ,  140 , wherein the multi-lamp module consists of a plurality of lamps L 1 , L 2 , and the resonant module consists of a transformer T as well as resonant capacitors C 1 , C 2 . The switch module SW is connected to an input voltage Vin, and is utilized to control the energy transferred to the resonant module according to the control signals from the PWM controller  100 . The secondary side windings of the transformer T are connected to the lamps L 1 , L 2 , respectively. The current detection modules  110 ,  130  are connected in series with the lamps L 1 , L 2  respectively so as to generate current detection signals A 1 , A 4  representing the magnitude of current passing through the lamps L 1 , L 2  respectively, and also to generate lamp status signals A 3 , A 6  representing the status of the lamps L 1 , L 2 , respectively. The voltage detection modules  120 ,  140  are connected in parallel with the lamp L 1 , L 2  respectively so as to generate voltage detection signals A 2 , A 5  representing the magnitude of voltage drop on the lamps L 1 , L 2  respectively. The PWM controller  100  receives the aforementioned signals A 1 ˜A 6  to performs soft start and feedback control in order to control the power transferred by the switch module SW for stabilizing the illumination of the lamp and also for providing circuit protection upon the occurrence of abnormality in the circuit. 
     By using the above-described circuit, it is possible to use one PWM controller to control two lamps simultaneously, thus reducing the number of PWM controllers. But, the number of pins of the PWM controller and the required electronic components are still too many, as a result, how to effectively reduce the number of pins needed in the PWM controller and lessen the required electronic components so as to simplify the circuit design, is still a critical topic for present research and development of CCFL driving circuit. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to effectively reduce the number of pins in a PWM controller and lessen the required electronic components, in order to reduce circuit cost as well as simplify circuit layout. 
     To achieve the above-stated object the present invention provides a fluorescent lamp driving circuit, which comprises a resonant module, a lamp module, a detection device, and a controller. The resonant module has a primary side and a secondary side and is used to convert an input voltage received on the primary side into an AC signal outputted on the secondary side. The resonant module has a transformer. The primary side of the transformer has two connection ends and a central tap end. The lamp module has a plurality of lamps and is coupled to the secondary side of the resonant module to receive the AC signal. The detection device and the lamp module are connected in series to the secondary side of the resonant module and one end of the detection device is connected to a reference potential end (e.g. ground). The detection device generates a current detection signal and a protection feedback signal based on the current flowing through the lamps. The controller has two semiconductor switches, wherein one end of each of the two semiconductor switches is mutually connected, while the other end of each of the two semiconductor switches is coupled to the two connection ends of the primary side of the transformer, respectively. The controller controls the switching of the two semiconductor switches in accordance with the current detection signal so as to stably transfer power of the input voltage to the resonant module. When the protection feedback signal is higher than a first preset value or lower than a second preset value, the controller stops the switching of the two semiconductor switches, wherein the first preset value is greater than the second preset value. 
     The present invention also provides another fluorescent lamp driving circuit, which comprises a resonant module, a lamp module, a detection device, and a controller. The resonant module has a primary side and a secondary side and is used to convert an input voltage received on the primary side into an AC signal outputted on the secondary side. The lamp module has a plurality of lamps and is coupled to the secondary side of the resonant module to receive the AC signal. The detection device and the lamp module are connected in series to the secondary side of the resonant module and one end of the detection device is connected to a reference potential end (e.g. ground). The detection device generates a current detection signal and a protection feedback signal based on the current flowing through the lamps. The controller has two semiconductor switches, wherein one end of each of the two semiconductor switches is mutually connected, while the other end of each of the two semiconductor switches is respectively coupled to an input voltage source and the reference potential end. The controller controls the switching of the two semiconductor switches in accordance with the current detection signal, so as to stably transfer power of the input voltage to the resonant module. When the protection feedback signal is higher than a first preset value or lower than a second preset value, the controller stops the switching of the two semiconductor switches. 
     The present invention further provides a fluorescent lamp driving circuit, which comprises a resonant module, a lamp module, a detection device, and a controller. The resonant module has a primary side and a secondary side and is used to convert an input voltage received on the primary side into an AC signal outputted on the secondary side. The lamp module has a plurality of lamps and is coupled to the secondary side of the resonant module to receive the AC signal. The detection device and the lamp module are connected in series to the secondary side of the resonant module and one side of the detection device is connected to a reference potential end (e.g. ground). The detection device generates a current detection signal and a protection feedback signal based on the current flowing through these lamps. The controller has two semiconductor switches, wherein one end of each of the two semiconductor switches is mutually connected and coupled to the primary side of the resonant module. The controller controls the switching of the two semiconductor switches in accordance with the current detection signal, so as to stably transfer power of the input voltage to the resonant module. When the protection feedback signal is lower than a preset value, the controller stops the switching of the two semiconductor switches. 
     In summary, the present invention provides a fluorescent lamp driving circuit, in the case of simultaneously driving multiple lamps, whose controller needs one pin for receiving the current detection signal to achieve the feature of feedback control, and another pin for receiving the protection feedback signal to offer protection control, as a result, the number of pins in the controller and the corresponding electronic components required for the purposes of feedback and protection are reduced, and circuit design is simplified as well. 
     The above-mentioned Summary and the following Detailed Descriptions are exemplary, all for further illustrating the claimed scope of the present invention. Other purposes and advantages of the present invention will be explained in the subsequent descriptions and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a circuit diagram of a conventional multi-lamp driving circuit; 
         FIG. 2  shows a circuit diagram of the multi-lamp driving circuit in accordance with a first embodiment of the present invention; 
         FIG. 3  shows a circuit diagram of the multi-lamp driving circuit in accordance with a second embodiment of the present invention; 
         FIG. 4  shows a circuit diagram of the multi-lamp driving circuit in accordance with a third embodiment of the present invention; 
         FIG. 5  shows a circuit diagram of the multi-lamp driving circuit in accordance with a fourth embodiment of the present invention; 
         FIG. 6  shows a circuit diagram of the controller applicable to the embodiments in  FIGS. 3 and 4 ; 
         FIG. 7  shows a circuit diagram of the controller applicable to the embodiments in  FIGS. 2 and 5 ; and 
         FIG. 8  is a schematic view showing a package structure of the controller according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Refer now to  FIG. 2 , which shows a circuit diagram of the multi-lamp driving circuit in accordance with a first embodiment of the present invention, the multi-lamp driving circuit has a controller  210 , a resonant module  220 , a lamp module, and a detection device. The lamp module has lamps L 1 , L 2 . The detection device has a detection part  232 , a current detection feedback part  234 , a voltage detection feedback part  235 , and a protection detection feedback part  236 . The resonant module  220  has a primary side and a secondary side. The primary has a transformer T and resonant capacitors C 1 ˜C 3 . The primary side of the transformer T has two connection ends and a central tap end, wherein the central tap end is connected to an input voltage source VCC, and the two connection ends are respectively connected to the pins D 1 , D 2  of the controller  210 . In this way, the resonant module  220  may convert the power of the input voltage from the input voltage source VCC received on the primary side into an AC signal outputted on the secondary side for operating the lamp module. The lamp module has a plurality of lamps. Every two lamps in the lamp module are connected in series to the secondary side of the resonant module  220  to receive the AC signal, respectively. In the present embodiment, the lamps L 1 , L 2  are connected in series to the secondary side of the resonant module  220 . The detection part  232  of the detection device and the lamp module are connected in series to the secondary side of the resonant module  220 , and one end of the detection part  232  is connected to a reference potential end (e.g. ground). The detection part  232  detects the current flowing through the lamp module by using the resistors R 1 , R 2  to generate a detection signal and transfers the detection signal to the current detection feedback part  234  and the protection detection feedback part  236 , respectively. In the present embodiment, the protection detection feedback part  236  has two diodes and a capacitor. The protection detection feedback part  236  receives the detection signal, rectifies the detection signal by using the diode, converts the detection signal into a protection feedback signal PS, and outputs the protection feedback signal PS to a protection pin PROT in the controller  210 . The current detection feedback part  234  rectifies and converts the detection signal into a current detection signal FS and outputs the current detection signal FS to a feedback pin FB of the controller  210 . In addition, the output voltage of the resonant module  220  is divided by the resonant capacitors C 1 ˜C 3  to generate a voltage division signal VS applied to the voltage detection feedback part  235  in order to provide over-voltage protection. 
     Under normal operation, a stable current is generated flowing through the resonant module  220 . The stable current passes through the resistors R 1 , R 2  and generates stable detection signal. At this moment, the level of the detection signal is located within a safe range. Upon the occurrence of short-circuit in the multi-lamp driving circuit, a larger current is generated flowing through the resonant module  220 . Upon the occurrence of open-circuit in the multi-lamp driving circuit, a smaller current is generated flowing through the resonant module  220 . Both of the aforementioned situations cause the level of the detection signal to deviate beyond a safe range (i.e. greater than an upper limit or smaller than a lower limit). Therefore, the controller  210  determines whether it is required to enter into a protection status based on the protection feedback signal PS. Also, when the voltage on the secondary side of the resonant module  220  shows abnormally surges, the level of the voltage division signal VS will be higher than the level of the detection signal, thus pulls up the level of the current detection signal FS, such that the controller  210  reduces the power inputted to the resonant module  220  so as to decrease the voltage on the secondary side. The controller  210  has two built-in semiconductor switches (not shown in  FIG. 2 , but will be described in more detail later in  FIG. 7 ), wherein one end of each of the two semiconductor switches is mutually connected and also connected to the reference potential end, and the other end of each of the two semiconductor switches is respectively coupled to the two connection ends on the primary side of the transformer T. The controller  210  receives a high level enable signal at the enable pin EN thereof and then starts to operate. The switching of the two semiconductor switches is controlled based on the current detection signal FS so as to control the magnitude of the power inputted by the input voltage source VCC to the resonant module  220 , thus provides the function of output stabilization. While the protection feedback signal PS is higher than a first preset value or lower than a second preset value (the first preset value is greater than the second preset value), the controller  210  stops switching of the two semiconductor switches and enters into the protection status in order to protect the circuit from being damaged. 
     Next refer to  FIG. 3 , wherein a circuit diagram of the multi-lamp driving circuit in accordance with a second embodiment of the present invention is shown. Similarly, the multi-lamp driving circuit of the present embodiment comprises a controller  310 , a resonant module  320 , a lamp module, and a detection device. The lamp module has lamps L 1 , L 2 . The detection device includes a detection part  332 , a current detection feedback part  334 , and a protection detection feedback part  336 . Compared with the first embodiment of  FIG. 2 , the major difference lies in that, failure of any lamp L 1 , L 2  in the lamp module of the second embodiment to result in open-circuit will break the current loop of the secondary side of the resonant module  320 , which causes the lamp current becomes zero. In this case, the level at the protection pin PROT of the controller  310  is pulled down by the detection signals FB 1 , FB 2  through the protection detection feedback part  336  to have the controller  310  enter the protection status. Also, in the second embodiment, the controller  310  may receive a dimming signal of DC level dimming or pulse dimming via a dimming pin DIM, so as to control the switching of the two semiconductor switches according to the dimming signal in order to show the feature of dimming the lamps. 
     In the aforementioned two embodiments, the resonant module and the semiconductor switches in the controller form a push-pull converter. The following embodiment takes a half-bridge converter as an example for illustration. However, the circuits described in these embodiments can be mutually exchanged is well known to those skilled in the art, and the scope of the present invention is by no means limited thereto. 
     Refer now to  FIG. 4 , a circuit diagram of the multi-lamp driving circuit in accordance with a third embodiment of the present invention is shown. The multi-lamp driving circuit of the present embodiment comprises a controller  410 , a resonant module  420 , a lamp module, and a detection device. The lamp module has lamps L 1 ˜L 4 . The detection device includes two detection parts  432   a ,  432   b , a current detection feedback part  434 , and a protection detection feedback part  436 . The resonant module  420  has a primary side and a secondary side and primarily has a transformer T and resonant capacitors C 1 ˜C 3  for converting the power received on the primary side into an AC signal outputted on the secondary side. The secondary side of the transformer T has two windings. The lamp module has a plurality of lamps L 1 ˜L 4 , wherein lamps L 1 , L 2  are coupled in series to a winding on the secondary side of the transformer T, and lamps L 3 , L 4  are coupled in series to the other winding on the secondary side of the transformer T. The detection part  432   a  of the detection device and the lamps L 1 , L 2  are coupled in series to the secondary side of the resonant module  420 , and one end of the detection part  432   a  of the detection device is connected to a reference potential end (i.e. ground) to generate the detection signals FB 1 , FB 2 . Meanwhile, the detection part  432   b  and the lamps L 3 , L 4  are coupled in series to the secondary side of the resonant module  420 , and one end of the detection part  432   b  is connected to the reference potential end (i.e. ground) to generate the detection signals FB 3 , FB 4 . When the AC signal outputted by the resonant module  420  is at the positive half-wave, current sequentially flows through the lamp L 1 , the resistor R 1 , the diode connected in parallel to the resistor R 2 , and the lamp L 2 , and thus the detection signal FB 1  is outputted. When the AC signal is at the negative half-wave, current sequentially flows through the lamp L 2 , the resistor R 2 , the diode connected in parallel to the resistor R 1 , and the lamp L 1 , and thus the detection signal FB 2  is outputted. Therefore, the detection device according to the present invention has the function of time-sharing outputting the detection signals of the different lamps to the protection pin PROT. The detection signal is rectified before outputted to the current detection feedback part  434 , and then filtered by the current detection feedback part  434  and transferred to the feedback pin FB of the controller  410 , as a result, the feedback control of the controller  410  would not be affected by the time-sharing outputted detection signals. The controller  410  has two built-in semiconductor switches (not shown), wherein one end of the each of the two semiconductor switches is mutually connected and also connected to the primary side of the resonant module  420 , while the other end of each of the two semiconductor switches is coupled to an input voltage source VCC and the reference potential end, respectively. The controller  420  starts to operate upon the reception of the high level enable signal at the enable pin EN, and controls the switching of the two semiconductor switches based on the current detection signal FS to control the magnitude of power inputted by the input voltage VCC to the resonant module  420  so as to achieve the effect of output stabilization. As the protection feedback signal PS becomes higher than the first preset value or lower than the second preset value (the first preset value is greater than the second preset value), the controller  410  stops the switching of the two semiconductor switches and enters into the protection status to avoid circuit destruction. 
     In the present embodiment, although the number of lamps is greater than the aforementioned embodiments, because the detection device has time-sharing function to output detection signal of each lamps and the protection detection feedback part  436  receiving these detection signals is capable of selectively outputting the abnormal detection signals to the protection pin PROT of the controller  410 , the function of circuit protection can be achieved. 
     Subsequently, refer to  FIG. 5 , wherein a circuit diagram of the multi-lamp driving circuit in accordance with a fourth embodiment of the present invention is shown. The multi-lamp driving circuit of the present embodiment comprises a controller  510 , a resonant module  520 , a lamp module, and a detection device. The lamp module has lamps L 1 ˜L 4 . The detection device has a detection part  532  and a protection detection feedback part  536 . Compared with the third embodiment in  FIG. 4 , the major difference lies in the design of the detection device. In detail, in the present embodiment, the polarities of the two windings on the secondary side of the transformer T are opposite, the current flowing through the resistor R 1  in the detection part  532  and the current flowing through the resistor R 2  are substantially opposite in phase. As a result, under normal operations, the level of the protection feedback signal outputted from the protection detection feedback part  536  is located around zero. However, in case an abnormality occurs in the circuit, the difference of magnitude between the detection signals generated by the resistor R 1  and in the resistor R 2  would be increased and/or the phase difference between the detection signals would be deviated away from 180 degrees. In both cases, the level of the protection feedback signal PS would be increased. After the level of the protection feedback signal PS exceeds a preset value, the controller  510  stops providing the power from the input voltage source VCC to the resonant module  520 , in order to provide the function of circuit protection. It is obvious that the external electronic components employed in the embodiment of  FIG. 5  are more concise in contrast with that of  FIG. 4  and thus the circuit cost can be further reduced. 
     Next, refer to  FIG. 6 , wherein a circuit diagram of the controller applicable to the embodiments in  FIGS. 3 and 4  is shown. As shown, the controller substantially comprises a processing unit  610 , an error amplification unit  620 , a protection unit  630 , a frequency generator  640 , a PWM unit  650 , a first semiconductor switch  680 , and a second semiconductor switch  685 . The first semiconductor switch  680  and the second semiconductor switch  685  may be MOS transistors, BJT transistors, silicon controlled rectifier (SCR), silicon bidirectional thyristor (TRAIC), and so forth. The processing unit  610  receives the high level enable signal from the enable/dimming pin EN/DIM and starts to operate. At the moment, the processing unit  610  generates voltage reference signals REF, REF_PRO and a soft start signal SST. The two input ends of the error amplification unit  620  respectively receives the voltage reference signal REF and the current detection signal inputted from the feedback pin FB to generate an error amplification signal. The protection unit  630  includes a protection comparator COMP and a protection circuit. The protection comparator COMP receives the voltage reference signal REF_PRO and the protection feedback signal inputted from the protection pin PROT. When the level of the protection feedback signal is lower than the level of voltage reference signal REF_PRO, the protection comparator COMP generates a protection comparison signal. After receiving the protection comparison signal, the protection circuit will generate a frequency-conversion control signal in a predetermined period of time. Whereas, as the protection comparison signal lasts over the predetermined period of time, the protection circuit may generate a protection control signal. The frequency generator  640  generates a slope signal at a normal operation frequency. Upon the reception of the frequency-conversion control signal, the frequency generator  640  increases the operation frequency to strike the lamps. In addition, after a period of time since the reception of the protection control signal, the frequency generator  640  stops its operations. The PWM unit  650  receives the soft start signal SST, the error amplification signal, and the slope signal, and accordingly generates two driving signals to control the switching of first semiconductor switch  680  and the second semiconductor switch  685  respectively. 
     At the beginning of the initializing the multi-lamp driving circuit, the lamp has not yet been struck and the level of the protection feedback signal is extremely low, therefore the protection circuit generates the frequency-conversion control signal first. At this moment, the frequency generator  640  operates at the start-up frequency as the protection feedback signal is lower than a preset value (i.e. the level of the voltage reference signal REF_PRO). As the level of soft start signal SST gradually rises, duty cycle of the driving signal generated by the PWM unit  650  increases gradually, and the output voltage on the secondary side of the resonant module increase gradually to strike the lamp. When the lamp is started successfully, the level of the protection feedback signal exceeds the preset value. At this moment the frequency generator  640  operates at the normal operation frequency, wherein the start-up frequency is higher than the normal operation frequency. Additionally, in case the lamp fails to be started or some abnormal conditions occur in the circuit, the protection feedback signal remains continuously lower than the preset value over a preset period of time. At this moment, the frequency generator  640  stops operating, causing the PWM unit  650  to stop generating the driving signal and having the controller enter into the protection status. 
     When the signal from the enable/dimming pin EN/DIM turns to be a dimming signal, the processing unit  610  determines the dimming signal based on the frequency or level of the signal received from the enable/dimming pin EN/DIM and generates a dimming control signal DIMMING based on the dimming signal. The dimming control signal DIMMING is transferred to the frequency generator  640 , making the frequency generator  640  stop operating to achieve the objective of dimming lamps. 
     Next, refer to  FIG. 7 , in which a circuit diagram of the controller applicable to the embodiments in  FIGS. 2 and 5  is shown. The controller of the present embodiment comprises a processing unit  710 , an error amplification unit  720 , a protection unit  730 , a frequency generator  740 , a PWM unit  750 , a dimming unit  760 , a frequency-conversion hysteresis comparator  770 , a first semiconductor switch  780 , and a second semiconductor switch  785 . The first semiconductor switch  780  and the second semiconductor switch  785  may be MOS transistors, BJT transistors, SCR, TRAIC, and so forth. The processing unit  710  receives the high-level enable signal from the enable/dimming pin EN/DIM and starts to operate. At the moment, the processing unit  710  generates voltage reference signals REF 1 , REF 2 / 3 , REF_H, REF_L, a dimming control signal DIMMING, and a soft start signal SST. The three input ends of the error amplification unit  720  receives the voltage reference signal REF 1 , current detection signal inputted from the feedback pin FB, and the dimming signal transferred by the dimming unit  760 , respectively, and the error amplification unit  720  accordingly generates an error amplification signal. The protection unit  730  has a first protection comparator COMP 1 , a second protection comparator COMP 2 , a protection circuit, and a current source. The non-inverted input end of the first protection comparator COMP 1  receives the voltage reference signal REF_H and the inverted input end of the first protection comparator COMP 1  receives the protection feedback signal inputted from the protection pin PROT. When the level of the protection feedback signal is higher than the level of the voltage reference signal REF_H, the first protection comparator COMP 1  generates a first protection comparison signal. The non-inverted input end of the second protection comparator COMP 2  receives the voltage reference signal REF_L and the inverted input end of the second protection comparator COMP 2  receives the protection feedback signal. When the level of the protection feedback signal is lower than the level of the voltage reference signal REF_L, the second protection comparator COMP 2  generates a second protection comparison signal. The level of the voltage reference signal REF_H is higher than that of the voltage reference signal REF_L. The protection circuit is coupled to the input ends of the first comparator COMP 1  and the second comparator COMP 2  to receive the protection comparison signals and generates a protection control signal. As a preferred embodiment, when any of these protection comparison signals continuously lasts over a predetermined period of time, the protection control signal is generated to stop the switching of the first semiconductor switch  780  and the second semiconductor switch  785  via the PWM unit  750 . 
     A current source is coupled to the protection pin PROT, and the level of the protection pin PROT can be pulled upward by using a resistor. Thereby, during normal circuit operations, the level on the protection pin PROT is kept to fall within the range between the levels of the voltage reference signal REF_H and the voltage reference signal REF_L to prevent the protection unit  730  from wrongly operating. 
     The frequency-conversion hysteresis comparator  770  receives the voltage reference signal REF 2 / 3  and the current detection signal inputted from the feedback pin FB. When the lamp has not been started, the current detection signal is lower than the voltage reference signal REF 2 / 3 , and the frequency-conversion hysteresis comparator  770  generates a frequency-conversion control signal. The dimming unit  760  has a dimmer and a hysteresis comparator. The hysteresis comparator receives the voltage reference signal REF 2 / 3  and the current detection signal inputted from the feedback pin FB. The dimmer receives the dimming control signal DIMMING. When the lamp has not been started yet, the current detection signal is lower than the voltage reference signal REF 2 / 3 . At this time, the dimmer blocks the output of the dimming control signal DIMMING to isolate the striking of the lamp from dimming function of the controller. When the lamp has been started, the level of the current detection signal is higher than the voltage reference signal REF 2 / 3 . At this time, the dimmer outputs the dimming signal, such that the controller starts to perform dimming function. The frequency generator  740  operates at a normal operation frequency to generate a slope signal. When the frequency-conversion control signal generated by the frequency-conversion hysteresis comparator  770  is received, the frequency generator  740  turns to operate at a higher start-up frequency to strike the lamp. The PWM unit  750  receives the soft start signal SST, the error amplification signal, the protection control signal, and the slope signal, and accordingly generates two driving signals to respectively control the switching of the first semiconductor switch  780  and the second semiconductor switch  785 . 
     In the embodiment of  FIG. 7 , it is also possible, as the embodiment shown in  FIG. 6 , to replace the frequency conversion hysteresis comparator  770  with the protection unit  730  in order to control the operating frequency of the frequency generator  740 . When the level of the protection feedback signal falls within the range between the levels of the voltage reference signal REF_H and the voltage reference signal REF_L, the frequency generator  740  operates at the normal operation frequency, whereas, when the level of the protection feedback signal is higher than the level of the voltage reference signal REF_H or lower than the level of the voltage reference signal REF_L, the frequency generator  740  operates at a start-up frequency so as to achieve the function of frequency-conversion for striking lamp. 
       FIG. 8  is a schematic view showing a package structure of the controller according to the present invention, wherein the feedback pin FB and the protection pin PROT are separated from the pins D 1 , S 1 , D 2 , S 2  of the two semiconductor switches by more than one pin so as to avoid the levels of the signals received at the feedback pin FB and the protection pin PROT from being influenced by the pins of the two semiconductor switches due to the coupling effect. Since the semiconductor switches and the PWM are encapsulated in the same package and the controller needs only one single pin to receive the current detection signal to achieve feedback control and another pin to receive the protection feedback signal to provide protection control, the number of pins of the controller can thus be significantly reduced and the packaging cost can be effectively reduced. Meanwhile, the external electronic components demanded for feedback control and protection control are reduced and the circuit layout is simplified. 
     The aforementioned discussions simply present the preferred embodiment of the present invention, but the scope of the present invention is by no means limited thereto. All changes or modifications in the field of the present invention that any skilled ones in the art can conveniently consider are deemed to be embraced by the scope of the present invention delineated in the following claims.

Technology Category: h