Power factor correction apparatus with embedded DC—DC converter

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.

1. Field of the Invention

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.

2. Description of the Related Art

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.

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 .

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.

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.

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.

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.

FIG. 1 is a block diagram of a projector of prior art;

FIG. 2 is a block diagram of a projector according to a preferred embodiment of the invention;

FIG. 3 is a block diagram of a PFC apparatus with an embedded DC-DC converter;

FIG. 4 is a circuit diagram of a PFC apparatus with an embedded DC-DC converter;

FIG. 5A is a circuit diagram of low-voltage rectifier 350 in another preferred embodiment; and

FIG. 5B is a circuit diagram of DC-DC converter 360 in another preferred embodiment.

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.

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 .

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.

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.

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.

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.

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.

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.

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 .

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 .

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 .

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.

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.