Abstract:
A single stage AC/DC converter includes a rectifier to rectify an input AC voltage and output the input AC voltage from first and second input nodes to first and second output nodes, an input capacitor connected between the first and second output nodes to store a rectified voltage and output a constant voltage, a transformer unit to transform the voltage received from the input capacitor, and transmit the voltage to a secondary side, and a power factor correction circuit to correct a power factor of a circuit. The power factor correction circuit includes a first auxiliary diode having one terminal connected with the first input node, a second auxiliary diode having one terminal connected with the second input node, and an auxiliary winding inductor connected among opposite terminals of the first and second auxiliary diodes and the first output node or the second output node.

Description:
BACKGROUND 
       [0001]    The embodiment relates to a power converter. More particularly, the embodiment relates to a single stage AC/DC converter representing high efficiency. 
         [0002]    Generally, in an AC/DC power converter, a simple rectifying unit including an LC filter  10 , a diode rectifier  20 , and an input capacitor C in  is used as an input power source unit in a typical power supply as shown in  FIG. 1 . In this case, although the structure of the rectifying unit may be simplified, since a harmonic current is included in an AC input power supply current as shown in  FIG. 2 , an input power factor characteristic may be degraded. Accordingly, IEC61000-3-2 and IEEE 519 standards have been suggested to suppress the harmonic current that may be generated from the power supply. 
         [0003]    Recently, in order to solve a problem related to the input power factor characteristic, a power supply employing an input power factor correction circuit to suppress the harmonic current has been used as a lower-power power supply for a laptop adaptor, an LED lighting device, or a display device according to the restriction of the IEC61000-3-2 and IEEE 519 standards as shown in  FIG. 3 . 
         [0004]    A two-stage power supply including a power factor correction (PFC) AC/DC converter  40 , which is an input power factor correction circuit to correct the input power factor and a low total harmonic distortion, and a DC/DC converter  50 , which is insulated to control an output voltage, is applied to the circuit shown in  FIG. 3  to correct the input power factor. However, as the power supply is configured in two stages, components are increased, and limitations exist in efficiency improvement and high-integration. 
         [0005]    Therefore, instead of manufacturing the two-stage power supply by using the PFC AC/DC converter  40  to correct the input power factor and the DC/DC converter  50  for insulation, a recent trend is to apply a power supply including a single stage AC/DC converter for the high-power factor in order to reduce cost and accomplish high integration and high efficiency. 
         [0006]    Meanwhile, U.S. Pat. No. 6,751,104 B2, which is a related art, discloses a single stage AC/DC converter as shown in  FIG. 4 . According to the related art, since a rectified current flows through diodes D b1  and D b2  at the rear end of a rectifier as well as a diode of the rectifier for the operation, a conduction loss may be increased, so that efficiency may be degraded. 
         [0007]    Accordingly, a single stage AC/DC power converter representing high efficiency, high integration, and a high power factor is necessary. 
       SUMMARY 
       [0008]    The embodiment provides a power converter representing improved efficiency. More particularly, the embodiment provides a single stage AC/DC power converter representing high integration, high efficiency, and a high power factor. 
         [0009]    According to the embodiment, there is provided a single stage AC/DC converter. The single stage AC/DC converter includes a rectifier to rectify an input AC voltage and output the input AC voltage from a first input node and a second input node to a first output node and a second output node, an input capacitor connected between the first and second output nodes to store a rectified voltage and output a constant voltage, a transformer unit to transform the voltage, which is received from the input capacitor, and transmit the voltage to a secondary side, and a power factor correction circuit to correct a power factor of a circuit. The power factor correction circuit includes a first auxiliary diode having one terminal connected with the first input node, a second auxiliary diode having one terminal connected with the second input node, and an auxiliary winding inductor connected among opposite terminals of the first and second auxiliary diodes and the first output node or the second output node. 
         [0010]    As described above, according to the embodiment, a single stage power factor correction circuit can be realized. 
         [0011]    According to the embodiment, the input power factor and the harmonic distortion resulting from the reduction of the harmonic current can be improved by using the auxiliary unit. 
         [0012]    According to the embodiment, a novel main circuit scheme representing an improved path is suggested so that a conduction loss can be reduced. 
         [0013]    According to the embodiment, high integration is possible and the production cost can be reduced by realizing the single stage AC/DC converter. 
         [0014]    According to the embodiment, power conversion representing high efficiency is possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a circuit diagram showing an AC/DC power converter according to the related art. 
           [0016]      FIG. 2  is a waveform diagram showing an input voltage and an input current in the circuit of  FIG. 1 . 
           [0017]      FIG. 3  is a circuit diagram showing a two-stage AC/DC power converter including a PFC circuit according to the related art. 
           [0018]      FIG. 4  is a circuit diagram showing a single stage AC/DC power converter according to the related art. 
           [0019]      FIG. 5  is a block diagram showing an AC/DC converter according to one embodiment. 
           [0020]      FIG. 6  is a circuit diagram showing an AC/DC converter according to one embodiment. 
           [0021]      FIG. 7  is a waveform diagram showing an input voltage and an input current in the circuit of  FIG. 6 . 
           [0022]      FIGS. 8A to 8D  are circuit diagrams showing a positive input voltage operating mode in the circuit of  FIG. 6 . 
           [0023]      FIG. 9  is a waveform diagram showing the operation of each unit in the circuit of  FIGS. 8A to 8D . 
           [0024]      FIG. 10  is a circuit diagram showing an AC/DC converter according to another embodiment. 
           [0025]      FIGS. 11A to 11D  are circuit diagrams showing a positive input voltage operating mode in the circuit of  FIG. 10 . 
           [0026]      FIGS. 12 to 18  are circuit diagrams showing various applications of the AC/DC converter. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    Hereinafter, embodiments will be described in detail with reference to accompanying drawings so that those skilled in the art can easily work with the embodiments. However, the embodiments may not be limited to those described below, but have various modifications. In addition, only components related to the embodiment are shown in drawings for the clarity of explanation. Hereinafter, the similar reference numerals will be assigned to the similar elements. 
         [0028]    In the following description, when a part is connected to the other part, the parts are not only directly connected to each other, but also electrically connected to each other while interposing another part therebetween. 
         [0029]    In the following description, when a predetermined part “includes” a predetermined component, the predetermined part does not exclude other components, but may further include other components unless otherwise indicated. In addition, the term “˜part”, “˜device”, or “˜module” refer to a unit to process at least one function or at least operation, and may be implemented in hardware, software, or the combination of the hardware and the software. 
         [0030]    Hereinafter, a single stage AC/DC converter according to one embodiment will be described with reference to  FIGS. 5 to 9 . 
         [0031]      FIG. 5  is a block diagram showing an AC/DC converter according to one embodiment.  FIG. 6  is a circuit diagram showing an AC/DC converter according to one embodiment.  FIG. 7  is a waveform diagram showing an input voltage and an input current in the circuit of  FIG. 6 .  FIGS. 8A to 8D  are circuit diagrams showing a positive input voltage operating mode in the circuit of  FIG. 6 .  FIG. 9  is a waveform diagram showing the operation of each unit in the circuit of  FIGS. 8A to 8D . 
         [0032]    Referring to  FIGS. 5 and 6 , the single stage AC/DC converter according to the present invention includes a filter unit  100 , an input inductor unit  200 , a rectifying unit  300 , an auxiliary unit  400 , and a transformer unit  500 . 
         [0033]    The filter unit  100  removes noise, which is input together with an input AC signal, from the input AC signal and outputs the input AC signal to the input inductor unit  200 . 
         [0034]    The rectifying unit  300  converts an output AC signal from the filter unit  100  into a DC signal to be output to the transformer unit  500 . 
         [0035]    The auxiliary unit  400  improves an input power factor and harmonic distortion according to the reduction of a harmonic current from an output AC signal of the rectifying unit  300 . 
         [0036]    The transformer unit  500  transforms the converted DC signal subject to the power factor correction into a signal having a predetermined magnitude and supplies the signal having the predetermined magnitude to a load. 
         [0037]    Hereinafter, a power converter according to one embodiment will be described in more detail with reference to  FIG. 6 . The filter unit  100  may be realized by connecting inductors and capacitors with each other in series/parallel. According to one embodiment, the filter unit  100  may include filter capacitors C 100  and C 110 , and filter inductors L 110  and L 120 . The filter unit  100  includes the filter capacitor C 100 , to which an input signal is applied, the filter inductor L 110  connected with one terminal of the filter capacitor C 100 , the filter inductor L 120  connected with an opposite terminal of the filter capacitor C  100 , and the filter capacitor C 110  having both terminals connected with opposite terminals of the filter inductors L 110  and L 120 . 
         [0038]    The configuration of the filter unit  100  is not limited thereto, but may have various configurations to filter an input AC signal. 
         [0039]    An input inductor L 200  may be connected between an upper terminal of an output port of the filter unit  100  and a first input node nin 1 , or connected between a lower terminal of the output port of the filter unit  100  and a second input node nin 2 . 
         [0040]    Accordingly, one terminal of the input inductor L 200  is connected with the output port of the filter unit  100 , and an opposite terminal of the input terminal L 200  is connected with the first input node nin 1  of the rectifying unit  300 . In more detail, the one terminal of the input inductor L 200  is connected with an output terminal of the filter inductor L 110 , and the opposite terminal of the input inductor L 200  is connected with a first diode D 310  in a forward direction at the first input node. 
         [0041]    Alternately, according to another embodiment, the one terminal of the input inductor L 200  may be connected with the output terminal of the filter unit  100 , and the opposite terminal of the input inductor L 200  may be connected with the second input node nin 2  of the rectifying unit  300 . 
         [0042]    The rectifying unit  300  includes a bridge rectifier and a capacitor. The bridge rectifier may be realized by connecting a plurality of diodes in series/parallel. For example, the rectifying unit  300  includes four diodes that are bridge-connected with each other, and an AC input signal, which has passed through the bridge rectifier, is converted into an AC signal inverted in the same direction. The inverted AC signal is charged in the input capacitor C 300  so that a DC voltage having a predetermined size is output to the transformer unit  500 . 
         [0043]    In more detail, the bridge rectifier includes the first diode D 310 , a second diode D 320 , a third diode D 330 , and a fourth diode D 340 . 
         [0044]    The first diode D 310  is connected between a first input node and a first output node in a forward direction, the second diode D 320  is connected between the first input node and a second output node in a reverse direction, the third diode D 330  is connected between a second input node and the first output node in the forward direction, and the fourth diode D 340  is connected between the second input node and the second output node in the reverse direction. 
         [0045]    The auxiliary unit  400  includes an auxiliary winding inductor L 400  coupled with the transformer unit  500  and two auxiliary diodes D 410  and D 420  connected with the auxiliary winding inductor L 400 . The first auxiliary diode D 410  is connected with the first input node nin 1  in the forward direction, and the second auxiliary diode D 420  is connected with the second input node nin 2  in the reverse direction. 
         [0046]    Cathodes of the first and second auxiliary diodes D 410  and D 420 , which are connected with each other, are connected with one terminal of the auxiliary winding inductor L 400  coupled with the transformer unit  500 . 
         [0047]    An opposite terminal of the auxiliary winding inductor L 400 , which is coupled with the transformer unit  500 , is connected with one terminal of the input capacitor C 300  and the transformer unit  500 , that is, the first output node nout 1 . 
         [0048]    The transformer unit  500  transforms an input voltage into a voltage having a predetermined size and transmits the voltage having the predetermined size to the load. The transformer unit  500  may include a flyback converter according to one embodiment. 
         [0049]    The flyback converter includes a transformer unit-primary winding L 510  and a switching device Q 500  connected with one terminal of the transformer unit-primary winding L 510 . The switching device Q 500  may include a power MOSFET, or may have a configuration in which a plurality of power MOSFETs are connected with in series/parallel. A secondary configuration of the transformer unit  500  includes a transformer unit-secondary winding L 520  magnetic-coupled with the transformer unit-primary winding L 510 , a diode D 500  connected with one terminal of the transformer unit-secondary winding L 520  in the forward direction, and an output capacitor C 500  having one terminal connected with an opposite terminal of the diode D 500  in the reverse direction and an opposite terminal connected with an opposite terminal of the transformer unit-secondary winding L 520 . 
         [0050]    Hereinafter, the variation of the input current according to the variation of the input voltage in the circuit of  FIG. 6  will be described with reference to  FIG. 7 . 
         [0051]    V AC  is an AC input voltage, V ac-1  is a voltage applied to the cathodes of the auxiliary diodes D 410  and D 420 , V in  is a voltage applied to the input capacitor C 300 , V LA  is a voltage applied across the auxiliary winding inductor L 400  coupled with the transformer unit  500 , I AC  is an input current, and I L1  is a current of the input inductor L 200 . 
         [0052]    In the state that the switching device Q 500  is turned on, if the magnitude of V AC  is greater than the magnitude of V ac-1 , a current may flow through the input inductor L 200 , and a current may be supplied to the transformer unit  500  for the power transformation. 
         [0053]    According to the embodiment, since the magnitude of V ac-1  is reduced by the voltage applied across the auxiliary winding inductor L 400  coupled with the transformer unit  500 , the duration, in which the magnitude of V AC  is greater than the magnitude of V ac-1 , is increased, so that the durations, in which I L1  and L AC  are generated, are increased. Accordingly, the phase difference between the input voltage and the input current is reduced, so that the power factor is corrected. 
         [0054]    When comparing with the related art shown in  FIG. 2 , since the magnitude of V in  has a greater value in  FIG. 2 , the duration in which the magnitude of V AC  is greater than the magnitude of V in  is shorter. Therefore, the duration in which I AC  is generated is shorter, so that the phase difference between the input voltage and the input current is increased, and the superior power factor is not represented. According to the embodiment, since a current can flow through the input inductor L 100  even at a low input voltage by the auxiliary winding inductor L 400  coupled with the transformer unit  500 , so that the power factor can be corrected. 
         [0055]    Hereinafter, the operation of a circuit according to a switching operation if a positive AC voltage is input will be described with reference to  FIGS. 8 and 9 . 
         [0056]    Regarding each duration, a duration of t 0  to t 1  is a duration in which the switching device Q 500  is turned on, and a duration of t 1  to t 4  is a duration in which the switching device Q 500  is turned off. 
         [0057]    The turn-off duration may be divided as follows. The duration of t 1  to t 2  is a duration in which energy stored in the input inductor L 100  at the duration of t 0  to t 1  is reset, a duration of t 1  to t 3  is a duration in which the energy stored in the magnetic inductor M 500  of the transformer unit  500  is transmitted to the transformer unit-secondary winding L 520 , and a duration of t 3  to t 4  is a duration in which energy is not delivered to the secondary side from the primary side, but the energy stored in the output capacitor C 500  at the secondary side is reset. 
         [0058]    First, the duration of t 0  and t 1  will be described below. 
         [0059]    A first operating mode (duration of t 0  to t 1 ) will be described with reference to  FIG. 8A  below. If the switching device Q 500  is turned on, the auxiliary winding inductor L 400  coupled with the transformer unit  500  is connected to the input capacitor C 300  together with the input power source through the input inductor L 200 , the auxiliary diode D 410 , and the fourth diode D 340  of the bridge rectifier. In addition, energy is stored in the magnetic inductor M 500  of the transformer unit  500 . 
         [0060]    In more detail, if the switching device Q 500  is turned on, an input inductor-current I L1  flowing through the input inductor L 200  is constantly raised. In addition, an auxiliary winding inductor-current I L2  flowing through the auxiliary winding inductor L 400  coupled with the transformer unit  500  is constantly raised together with the inductor-current I L1 . 
         [0061]    In other words, the first diode D 310  of the bridge rectifier is reverse-biased, so that a current does not flow through the first diode D 310  of the bridge rectifier, but the first auxiliary diode D 410  of the auxiliary unit  400  is forward-biased, so that the input inductor-current I L1  is identical to the auxiliary winding inductor-current I L2 . 
         [0062]    The input capacitor-voltage V in  is constantly maintained, and the switching device Q 500  is turned on, so that voltage having the same magnitude as that of the input capacitor voltage V in  is applied across both terminals of the magnetic inductor M 500  of the transformer unit  500 . The current flowing through the switching device Q 500  is the sum of the current I Lm  flowing through the magnetic inductor M 500  of the transformer unit  500  and the current flowing through the auxiliary winding inductor L 400  coupled with the transformer unit  500 , which is induced to the primary side of the transformer unit  500 , and constantly raised. 
         [0063]    The secondary side of the transformer unit  500  is in an open state because the diode D 500  at the secondary side is reverse-biased. Accordingly, an induced current does not flow through the secondary side of the transformer unit  500 . 
         [0064]    Next, if the switching device Q 500  is turned off, the voltage polarity of the auxiliary winding inductor L 400  coupled with the transformer unit  500  is changed. Accordingly, the auxiliary diodes D 410  and D 420  are reverse-biased, so that a current does not flow through the auxiliary diodes D 410  and D 420 . 
         [0065]    In addition, if the switching device Q 500  is turned off, a reverse voltage is applied to the magnetic inductor M 500  of the transformer unit  500 , so that the secondary side of the transformer unit  500  is forward-biased. Accordingly, the induced current flows through the transformer unit-secondary winding L 520 . 
         [0066]    Hereinafter, a second operating mode (duration of t 1  to t 2 ) will be described with reference to  FIG. 8B . The auxiliary diodes D 410  and D 420  are reverse-biased, so that a current does not flow through the auxiliary diodes D 410  and D 420 , but the energy stored in the input inductor L 200  at the turn-on duration of the switching device flows through the first diode D 310  of the bridge rectifier and the input capacitor C 300  is reset. At the moment when the switching device Q 500  is turned off, a constant reverse voltage is applied to the magnetic inductor M 500  of the transformer unit  500 . Accordingly, the energy stored in the magnetic inductor M 500  of the transformer unit  500  during the turn-on duration of the switching device is transmitted to the output capacitor C 500  through the diode D 500  at the secondary side of the transformer unit  500 . The magnitude of a secondary-side diode current ID is reduced. 
         [0067]    Hereinafter, a third operating mode (duration of t 2  to t 3 ) will be described with reference to  FIG. 8C . The energy stored in the input inductor L 200  is completely consumed at a previous step, so that currents do not flow through the input inductor L 200  and the first diode D 310  of the bridge rectifier. Meanwhile, since energy remains in the magnetic inductor M 500  of the transformer unit  500 , the energy stored in the magnetic inductor M 500  of the transformer unit  500  is transmitted to the output capacitor C 500  through the diode D 500  at the secondary side of the transformer unit  500  similarly to the duration of t 1  to t 3 , and the magnitude of the secondary-side diode current ID is steadily reduced. 
         [0068]    Finally, a fourth operating mode (duration of t 3  to t 4 ) will be described with reference to  FIG. 8D . If all energy stored in the magnetic inductor M 500  of the transformer unit  500  is transmitted to the transformer unit-secondary winding L 520 , the voltage V Lm  of the magnetic inductor M 500  of the transformer unit  500  becomes 0, and a voltage V Q  having a magnitude, which is reduced by the magnitude of the voltage applied to the magnetic inductor M 500  of the transformer unit  500  at a previous step, is applied to the switching device. In addition, the energy is not transmitted from the primary side to the secondary side of the transformer unit  500 , and the diode D 500  at the secondary side is reverse-biased, so that a current does not flow, and the energy stored in the output capacitor C 500  is transmitted to the load and reset. 
         [0069]    Hereinafter, another embodiment will be described with reference to  FIGS. 10 to 11D . 
         [0070]      FIG. 10  is a circuit diagram showing an AC/DC converter according to another embodiment, and  FIGS. 11A to 11D  are circuit diagrams showing a positive input voltage operating mode in the circuit of  FIG. 10 . 
         [0071]    Referring to  FIG. 10 , a single stage AC/DC converter of  FIG. 10  makes a difference from the AC/DC converter of  FIG. 6  in the connection relationship of the auxiliary unit  400 . In other words, the single stage AC/DC converter of  FIG. 10  makes a difference from the AC/DC converter of  FIG. 6  in the connection directions of the auxiliary diodes D 410  and D 420 , the connection of the auxiliary winding inductor L 400  coupled with the transformer unit  500 , and the connection relationship between the auxiliary winding inductor L 400  coupled with the transformer unit  500  and the input capacitor C 300 . 
         [0072]    In more detail, one terminal of the first and second auxiliary diodes D 410  and D 420  are connected with the filter unit  100  in a reverse direction, and opposite terminals of the first and second auxiliary diodes D 410  and D 420  are connected with one terminal of the auxiliary winding inductor L 400  coupled with the transformer unit  500 . In addition, an opposite terminal of the auxiliary winding inductor L 400  is connected with one terminal of the input capacitor C 300  and the switching device Q 500 . 
         [0073]    Hereinafter, description will be made regarding a circuit operation according to a switching operation if a positive AC voltage is input. 
         [0074]    Operation durations according to the switching operation are divided in the same manner as the operation durations described with reference to  FIGS. 8 and 9  are divided. 
         [0075]    First, the first operating mode (duration of t 0  to t 1 ) will be described with reference to  FIG. 11A  below. If the switching device Q 500  is turned on, the auxiliary winding inductor L 400  coupled with the transformer unit  500  is connected to the input capacitor C 300  together with the input power source through the input inductor L 200 , the auxiliary diode D 420 , and the first diode D 340  of the bridge rectifier. In addition, energy is stored in the magnetic inductor M 500  of the transformer unit  500 . 
         [0076]    Next, if the switching device Q 500  is turned off, the voltage polarity of the auxiliary winding inductor L 400  coupled with the transformer unit  500  is changed. Accordingly, the auxiliary diodes D 410  and D 420  are reverse-biased, so that a current does not flow through the auxiliary diodes D 410  and D 420 . In addition, if the switching device Q 500  is turned off, a reverse voltage is applied to the magnetic inductor M 500  of the transformer unit  500 , so that the secondary side of the transformer unit  500  is forward-biased. Accordingly, the induced current flows through the transformer unit-secondary winding L 520 . 
         [0077]    The operations at the second operating mode (duration of t 1  and t 2 ), the third operating mode (t 2  and t 3 ), and the fourth operating mode (duration of t 3  and t 4 ) have the same as operations when the switching device Q 500  is turned, off in  FIGS. 8 and 9  (see  FIGS. 11B ,  11 C, and  11 D). 
         [0078]    Therefore, the operation waveform of each unit according to the present embodiment is the same as the operation waveform of each unit of  FIG. 9 . 
         [0079]    The insulating effect between the auxiliary winding inductor L 400  and the transformer unit  500  can be improved by connecting an opposite terminal of the auxiliary winding inductor L 400  to one terminal of the input capacitor C 300  and one terminal of the switching device Q 500  differently from  FIG. 7  showing the direct connection of the auxiliary winding inductor L 400 , which is coupled with the transformer unit  500 , to the transformer unit  500 . 
         [0080]    In other words, the magnetic noise phenomenon between the auxiliary winding inductor L 400  and the transformer unit  500  can be reduced through the insulating effect of the input capacitor C 300  and the insulating effect depending on the threshold voltage of the switching device Q 500 . 
         [0081]    Hereinafter, various applications will be described with reference to  FIGS. 12  to  18 . 
         [0082]      FIGS. 12 to 15  are circuit diagrams showing various applications of the embodiment. The applications are different from each other in the positions and the configuration of the input inductor  200 . 
         [0083]    The circuit of  FIG. 12  makes a difference from the circuit of  FIG. 6  in the position of the input inductor L 200 , and the circuit of  FIG. 13  makes a difference from the circuit of  FIG. 10  in the position of the input inductor L 200 . The position of the input inductor L 200  interposed between a rear end of the filter unit  100  and a front end of the diode rectifier (D 310 , D 320 , D 330 , and D 340 ) shown in  FIGS. 6 and 10  is changed to a position between a rear end of the diode rectifier (D 310 , D 320 , D 330 , and D 340 ) and the input capacitor C 300  shown in  FIGS. 12 and 13 . 
         [0084]    When the position of the input inductor L 200  is differently changed as shown in  FIGS. 12 and 13 , energy stored in the input inductor L 200  can be rapidly reduced. 
         [0085]    In order to prevent the discharge delay of energy stored in the input inductor L 200  occurring according to the threshold voltage of the first diode D 310 , the input inductor L 200  is directly connected to the input capacitor C 300 . 
         [0086]    In other words, as described with reference to  FIG. 8B , at the second operating mode (duration of t 1  to t 2 ), the energy stored in the input inductor L 200  directly flows through the input capacitor C 300  without passing through the first diode D 310  of the bridge rectifier, so that reset can be rapidly performed. 
         [0087]      FIGS. 14 and 15  are circuit diagrams according to still another embodiment realized by constructing the input inductor L 200  with coupling inductors L 210  and L 220 . 
         [0088]    In other words, according to the previous embodiment, the input inductor L 200  is connected between the rear end of the filter unit  100  and the front end of the diode rectifier (D 310 , D 320 , D 330 , and D 340 ) or connected between the rear end of the diode rectifier (D 310 , D 320 , D 330 , and D 340 ) and the input capacitor C 300 . 
         [0089]    The embodiment of  FIGS. 14 and 15  shows a configuration with the first and second input inductors L 210  and L 220 . The first input inductor L 210  is connected between the rear end of the filter unit  100  and the front end of the diode rectifier (D 310 , D 320 , D 330 , and D 340 ), and the second input inductor L 220  is connected between the rear end of the diode rectifier (D 310 , D 320 , D 330 , and D 340 ) and the input capacitor C 300 . The first input inductor L 210  and the second input inductor L 220  are variously coupled depending on a turn ratio. 
         [0090]    Energy can be transmitted between the first and second input inductors L 210  and L 220  through the coupling between the first and second input inductors L 210  and L 220 , and the magnetic coupling between the first input inductor L 210  and the second input inductor L 220 . As described above, the energy stored in the first input inductor L 210  may be dissipated through two paths formed of a path to the first diode D 310  and a path formed through the magnetic coupling with the second input inductor L 220 . Accordingly, the energy stored in the input first inductor L 210  can be rapidly increased. 
         [0091]      FIG. 16  is a circuit diagram according to still yet another embodiment in which the transformer unit  500  in the circuit of  FIG. 6  is realized by using a flyback converter employing two switching devices. 
         [0092]    The configuration of the circuit shown in  FIG. 16  is the same as that of the circuit shown in  FIG. 6  except for the configuration of the transformer unit  500 . Regarding one embodiment of the flyback converter employing two switching devices, which makes a difference from that of the circuit shown in  FIG. 6 , the flyback converter employing two switching devices includes a first switching device Q 510 , a second switching device Q 520 , a first diode D f1  at the primary side of the transformer unit  500 , a second diode D f2  at the primary side of the transformer unit  500 , the diode D 500  at the secondary side of the transformer unit  500 , the transformer unit-primary winding L 510 , the transformer unit-secondary winding L 520 , and the output capacitor C 500 . 
         [0093]    One terminal of the first switching device Q 510  is connected to one terminal of the input capacitor C 300  and the first diode D f1  at the primary side of the transformer unit  500  in the reverse direction. An opposite terminal of the first switching device Q 510  is connected to one terminal of the transformer unit-primary winding L 510  and the second diode D f2  at the primary of the transformer unit  500 . An opposite terminal of the transformer unit-primary winding L 510  is connected to one terminal of the second switching device Q 520  and the first diode D f1  at the primary side in the forward direction. An opposite terminal of the second switching device Q 520  is connected to the opposite terminal of the input capacitor C 300  and the second diode D f2  at the primary side of the transformer unit  500 . 
         [0094]    The secondary side of the transformer unit  500  includes a transformer unit-secondary winding L 520  electrically connected with the transformer unit-primary winding L 510 , the diode D 500  connected with one terminal of the transformer unit-secondary winding L 520  in the forward direction, and the capacitor C 500  having one terminal connected with the opposite terminal of the diode D 500  in the reverse direction and an opposite terminal connected with the opposite terminal of the transformer unit-secondary winding L 520 . 
         [0095]    In addition, although the configuration of the transformer unit  500  shown in  FIGS. 10 , and  12  to  15  is differently changed to the configuration of the transformer unit  500  having the flyback converter employing two switching devices, the overall operation of the circuit of  FIG. 16  have the same operating characteristic as those of the circuits of  FIGS. 10 , and  12  to  15 . 
         [0096]    As shown in  FIG. 16 , when the transformer unit  500  is configured with the two switches, the transformer unit  500  may be more advantageous in a large-capacity topology. 
         [0097]    According to stilly yet another embodiment,  FIGS. 17 and 18  are circuit diagrams showing a converter including a forward converter. 
         [0098]      FIG. 17  shows an AC/DC converter including a forward converter employing one switching device, and  FIG. 18  shows an AC/DC converter including a forward converter employing two switching devices. 
         [0099]      FIG. 17  shows an AC/DC converter in which a forward converter employing one switching device is applied to the configuration of the transformer unit  500  provided in the circuit of  FIG. 6 , and  FIG. 18  shows a single stage AC/DC converter in which a forward converter employing two switching devices is applied to the configuration of the transformer unit  500  provided in the circuit of  FIG. 16 . 
         [0100]    Regarding the circuit of  FIG. 17 , the circuit of  FIG. 17  is the same as the circuit of  FIG. 6  in configuration except for the transformer unit  500 . In the configuration of the transformer unit  500  provided in the circuit of  FIG. 17 , a primary side further includes a reset winding L 530  and a reset diode D rf , and a secondary side further includes a secondary-side first diode D 510 , a secondary-side second diode D 520 , and an output inductor L 540 . 
         [0101]    In more detail, the reset winding L 530  of the transformer unit  500  has one terminal connected with a first output node n out1  and an opposite terminal connected with the reset diode D rf  in the reverse direction. An opposite terminal of the reset diode D rf  is connected with a second output node n out2 . 
         [0102]    The transformer unit-secondary winding L 520  is magnetic-coupled with the transformer unit-primary winding L 510 . One terminal of the secondary side-first diode D 510  is connected with the transformer unit-secondary winding L 520  in the forward direction, and an opposite terminal of the secondary side-first diode D 510  is connected with one terminal of the secondary side-second diode D 520  and one terminal of an output inductor L 540  in the reverse direction. An opposite terminal of the output inductor L 540  is connected with one terminal of the output capacitor C 500 . In addition, opposite terminals of the transformer unit-secondary winding L 520 , the secondary side-second diode D 520 , and the output capacitor C 500  are connected with one node. 
         [0103]    Although the forward converter is applied to the configuration of the transformer unit  500  as described above, the circuit of  FIG. 17  has the same power factor correction characteristic as that of the circuit of  FIG. 6 . 
         [0104]    In addition, although the modification in the connection relationships of the input inductor L 200  and the auxiliary unit  400  is applied to the circuit of  FIG. 17  similarly to the circuits of  FIGS. 10 , and  12  to  15 , the above circuits can obtain the same result. 
         [0105]    Regarding the circuit of  FIG. 18 , the circuit of  FIG. 18  includes a single stage AC/DC forward converter employing two switching devices. 
         [0106]    Regarding the configuration of  FIG. 18 , the circuit of  FIG. 18  makes a difference from the circuit of  FIG. 16  in the configuration of the secondary side of the transformer unit  500 . 
         [0107]    Hereinafter, the configuration of the secondary side of the transformer unit  500  will be described. The transformer unit-secondary winding L 520  is magnetic-connected with the transformer unit-primary winding L 510 . One terminal of the secondary-side first diode D 510  is connected with the transformer unit-secondary winding L 520  in the forward direction, and an opposite terminal of the secondary-side secondary diode D 520  is connected with one terminal of the secondary-side second diode D 520  and one terminal of the output inductor L 540  in the reverse direction. An opposite terminal of the output inductor L 540  is connected with one terminal of the output capacitor C 500 . In addition, opposite terminals of the transformer unit-secondary winding L 520 , the secondary-side second diode D 520 , and the output capacitor C 500  are connected with one node. 
         [0108]    Although the forward converter is applied to the configuration of the transformer unit  500  as described above, the circuit of  FIG. 18  has the same power factor correction characteristics as those of the circuit of  FIGS. 6 ,  16 , and  17 . 
         [0109]    In addition, although the modification in the connection relationships of the input inductor L 200  and the auxiliary unit  400  is applied to the circuit of  FIG. 18  similarly to the circuits of  FIGS. 10 , and  12  to  15 , the above circuits can obtain the same result. 
         [0110]    In other words, even if the configuration of the transformer unit  500  is changed to a forward converter type, the configuration of the auxiliary unit  400  and the connection relationship between the auxiliary unit  400  and the input capacitor  0300  are not changed. Accordingly, as shown in  FIGS. 6 and 16 , since a current may flow through the input inductor L 200  depending on a voltage applied to the auxiliary winding inductor L 400  coupled with the transformer unit  500  even if a low voltage is applied to the input inductor L 200 , power factor correction can be achieved. 
         [0111]    Meanwhile, the configuration of the transformer unit  500  is not limited to the flyback converter type or the forward converter type, but may be realized by using a DC-DC converter connected with the input capacitor C 300 . 
         [0112]    The above described embodiment is not only implemented only through an apparatus and a method, but also implemented through a program to execute functions corresponding to the components of the embodiment and recording media in which the program is recorded. The above implementation can be easily performed based on the above-described embodiment by one ordinary skilled in the art. 
         [0113]    Although the exemplary embodiments have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.