Abstract:
A power factor correction apparatus with an embedded direct-current to direct-current (DC-DC) converter is provided. The apparatus includes a power factor controller, a high-voltage adapter and a low-voltage adapter. The power factor controller, which receives an AC power source, includes a transformer. The secondary side of the transformer includes a first sub-coil and a second sub-coil for outputting a first power source and a second power source respectively. The high-voltage adapter converts the first power source into a high DC power source. The low-voltage adapter converts the second power source into a first DC power source. The power factor controller corrects the power factor of the power factor correction apparatus according to the first DC power source.

Description:
[0001]     This application claims the benefit of Taiwan application Serial No. 92135288, filed Dec. 12, 2003, the subject matter of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates in general to a power correction factor (PFC) apparatus, and more particularly to a PFC apparatus with an embedded DC-DC converter.  
         [0004]     2. Description of the Related Art  
         [0005]     Ordinary display apparatus, such as cathode-ray tube (CRT) display or liquid crystal display (LCD), can only provide an image up to 30-40 inches wide and is not convenient to carry with due to huge size. The projector, which is capable of outputting an image up to tens or hundreds inches wide and is much smaller than that of a CRT display or an LCD, outdoes the CRT display and the LCD in terms of entertainment purpose or business briefing.  
         [0006]      FIG. 1  is a block diagram of a projector of prior art. A projector  100  comprises a power factor controller  110 , a direct-current to direct-current (DC-DC) conversion circuit  120 , a lamp-ignition circuit  130 , a control circuit  140 , and a lamp  150 . The power factor controller  110  and the DC-DC conversion circuit  120  are power suppliers of the projector  100 . The power factor controller  110  supplies a high-voltage DC power source of about 380V to the lamp-ignition circuit  130  and a high-voltage DC power source of about 380V of to the DC-DC conversion circuit  120 . The lamp-ignition circuit  130 , an electronic ballast for instance, is for igniting and providing power to the lamp  150 . The DC-DC conversion circuit  120 , such as an isolated fly-back circuit, provides a DC power source of 12V, 5V or 3.3V for the control circuit  140  to use. The control circuit  140  is for controlling the operation of the projector  100 .  
         [0007]     Along with the advance in technology, the projector is also becoming smaller, lighter, slimmer and shorter to give the user a better portability. Therefore, miniaturization has always been an important object for the manufacturer to achieve.  
       SUMMARY OF THE INVENTION  
       [0008]     It is therefore an object of the invention to provide a power factor correction (PFC) apparatus with an embedded DC-DC converter for reducing the size of a projector.  
         [0009]     According to the object of the invention, a PFC apparatus comprising a power factor controller, a high-voltage rectifier, and a low-voltage rectifier is provided. The power factor control apparatus, which is receives an alternating-current (AC) power source, comprises a rectifier. The secondary side of the transformer has a first coil for outputting a first power source according to an AC power source and a second coil for outputting a second power source according to the AC power source. The high-voltage rectifier receives and converts the first power source into a high-voltage direct-current (DC) power source. The low-voltage rectifier receives and converts the second power source into a first DC power source. The power factor controller corrects the power factor of the PFC apparatus according to the first DC power source.  
         [0010]     Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a block diagram of a projector of prior art;  
         [0012]      FIG. 2  is a block diagram of a projector according to a preferred embodiment of the invention;  
         [0013]      FIG. 3  is a block diagram of a PFC apparatus with an embedded DC-DC converter;  
         [0014]      FIG. 4  is a circuit diagram of a PFC apparatus with an embedded DC-DC converter;  
         [0015]      FIG. 5A  is a circuit diagram of low-voltage rectifier  350  in another preferred embodiment; and  
         [0016]      FIG. 5B  is a circuit diagram of DC-DC converter  360  in another preferred embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     The power supply circuit of a conventional projector comprises a power factor correction (PFC) apparatus and a DC-DC conversion circuit. The invention has the DC-DC conversion circuit embedded in the PFC apparatus to reduce the size of the power supply circuit of the projector so that the projector volume can be reduced.  
         [0018]      FIG. 2  is a block diagram of a projector according to a preferred embodiment of the invention. A projector  200  comprises a PFC apparatus  210  with an embedded DC-DC converter, a lamp-ignition circuit  230 , a control circuit  240 , and a lamp  250 . The PFC apparatus  210 , which is the power supplier of the projector  200 , supplies a high-voltage direct-current (DC) power source of about 380V to the lamp-ignition circuit  230 , and supplies a DC power source, a DC power source of 12V, 5V or 3.3V for instance, for the control circuit  240  to operate the control circuit  240  with. The lamp-ignition circuit  230 , an electronic ballast for instance, is for switching on the lamp  250 . The control circuit  240  is for controlling the operation of the projector  200 .  
         [0019]      FIG. 3  is a block diagram of a PFC apparatus with an embedded DC-DC converter. The PFC apparatus  210  with an embedded DC-DC converter comprises a power factor controller, a high-voltage rectifier  345 , a low-voltage rectifier  350 , a DC-DC converter  360 , and a DC-DC converter  370 . The power factor controller comprises a rectifying circuit  310 , a power supply circuit  320 , a transformer T, a power factor control chip  330 , a power factor switch  335 , a sensing resistor R 5 , and a feedback circuit  340 . The rectifying circuit  310  is for receiving and converting an alternating-current (AC) power source AC into a DC power source, and then outputs the DC power source. The power supply circuit  320 , after receiving the DC power source outputted by the rectifying circuit  310 , converts the DC power source into a DC power source Vcc, which supplies power for the power factor control chip  330  and the feedback circuit  340 . The transformer T comprises a primary side coil and a secondary side coil, wherein the secondary side coil comprises sub-coils SL 1  and SL 2 . The power factor control chip  330  receives the primary side voltage of the transformer T through a sensing resistor R 5 , and receives a feedback signal FB 1  of the feedback circuit  340  as well as a feedback signal FB 2  of the power factor switch  335  for controlling the power factor switch  335  accordingly so as to improve the power factor.  
         [0020]     The high-voltage rectifier  345  receives the output of the sub-coil SL 1  disposed on the secondary side of the transformer T and accordingly outputs a high-voltage DC power source Vh to the lamp-ignition circuit  230 . The value of the high-voltage DC power source Vh can be a DC power source of 380V for instance.  
         [0021]     The low-voltage rectifier  350  receives the output of the sub-coil SL 2  disposed on the secondary side of the transformer T and accordingly outputs a DC power source V 1 . The value of DC power source V 1  can be 12V for instance. Moreover, the DC power source V 1  is fed back to the feedback circuit  340  for the power factor control chip  330  to control the power factor value accordingly.  
         [0022]     The DC-DC converter  360  receives and reduces a DC power source V 1  to a DC power source V 2 , then outputs the DC power source V 2 . The value of the DC power source V 2  can be 5V for instance. The DC-DC converter  370  receives and reduces a DC power source V 1  to a DC power source V 3 , then outputs the DC power source V 3 . The value of the DC power source V 3  can be 3.3V for instance. The DC power sources V 1 , V 2  and V 3  supply power for the control circuit  240  to operate.  
         [0023]      FIG. 4  is a circuit diagram of a PFC apparatus with an embedded DC-DC converter. The rectifying circuit  310 , such as a full-wave rectifying circuit illustrated in the diagram, comprises a capacitor C 1  and four diodes namely BD 1 , BD 2 , BD 3 , and BD 4 . The power supply circuit  320 , which provides a DC power source Vcc to the power factor control chip, comprises resistors R 1 , R 2 , and R 4 , a diode D 1 , capacitors C 2 , C 3 , a zener diode ZD 1 . The feedback circuit  340 , which comprises resistors R 3 , R 6 , and R 7  and a photo-coupler IC 2 , is for outputting the feedback signal FB 1  to the power factor control chip  330  according to the DC power source V 1  outputted by the low-voltage rectifier  350 . The power factor switch  335  comprises a transistor Q 1  and resistors R 8  and R 9 . The voltage value of the drain electrode of the transistor Q 1  is the feedback signal FB 2 . The power factor control chip  330  controls the conductivity of the transistor Q 1  through the resistor R 8  according to the feedback signals FB 1  and FB 2 . When the transistor Q 1  is conducted, power is saved in the transformer T; when the transistor Q 1  is disconnected, the transformer T releases power energy to the high-voltage rectifier  345  and the low-voltage rectifier  350 . The high-voltage rectifier  345 , a half-wave rectifying circuit for instance, comprising a diode D 2  and a capacitor C 7 , is for converting the output of the sub-coil SL 1  of the transformer T into a high-voltage DC power source Vh.  
         [0024]     The low-voltage rectifier  350  comprises a rectifying unit  352 , a filtering unit  354  and a feedback unit  356 . The low-voltage rectifier  350  receives the output of the sub-coil SL 2  disposed on the secondary side of the transformer T, and then outputs the DC power source V 1  through the rectifying unit  352  and the filtering unit  354 . The rectifying unit  352 , a full-wave rectifying circuit for instance, comprises a capacitor C 4  and diodes BD 5 , BD 6 , BD 7 , and BD 8 . The filtering circuit  354  comprises an inductor L 1  and a capacitor C 5 . The DC power source V 1  is fed back to the power factor control chip  330  as a reference for power factor correction through the feedback unit  356  and the feedback circuit  340 . The feedback unit  356  comprises resistors R 10 , R 11 , R 12 , R 13  and R 14 , a capacitor C 6 , a voltage-stabilizing chip IC 3  and a photo-coupler IC 2 . The feedback unit  356  feedbacks the value of the DC power source V 1  through the photo-coupler IC 2  lest the stability of the DC power source V 1  might be affected.  
         [0025]     The DC-DC converter  360 , a buck converter for instance, comprises a step-down stabilizing circuit such as an exchange-type voltage-stabilizing chip IC 4 , a diode D 4 , an inductor L 2 , a capacitor C 8 , and resistors R 15  and R 16  for reducing the DC power source V 1  to the DC power source V 2 . The DC-DC converter  370 , a buck converter for instance, comprises a step-down stabilizing circuit such as an exchange-type voltage-stabilizing chip IC 5 , a diode D 5 , an inductor L 3 , a capacitor C 9 , and resistors R 17  and R 18  for reducing the DC power source V 1  to a DC power source V 3 .  
         [0026]      FIG. 5A  is a circuit diagram of low-voltage rectifier  350  in another preferred embodiment. The low-voltage rectifier  350  comprises a rectifying unit  353  and a feedback unit  356 . The rectifying unit  353 , which is a half-wave rectifying circuit, comprises a diode D 6  and a capacitor C 10 . The circuit of the low-voltage rectifier illustrated in  FIG. 5A  is simpler and costs less than that illustrated in  FIG. 4 .  
         [0027]      FIG. 5B  is a circuit diagram of DC-DC converter  360  in another preferred embodiment. The DC-DC converter  360  comprises a serial-type linear voltage-stabilizing chip IC 6  and a capacitor C 10  for reducing the DC power source V 1  to the DC power source V 2 .  
         [0028]     The low-voltage rectifying circuit and the DC-DC converter of the PFC apparatus disclosed in the above preferred embodiment of the invention can adopt various circuits disclosed above according to the consideration of cost. The PFC apparatus adopts an embedded DC-DC converter, so that the power supply circuit of the projector is reduced and that the projector volume is reduced accordingly.  
         [0029]     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.