Abstract:
There is provided a bridgeless power factor correction circuit that corrects a power factor by complementarily switching two switches according to phase of input power without using rectifier bridge diodes. A bridgeless power factor correction circuit according to an aspect of the invention may include: a switching unit having a plurality of switches and alternately switching input AC power; a stabilizing unit rectifying and smoothing the power switched by the switching unit; and a control unit controlling an alternate switching operation between the plurality of switches according to phases of the input power.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 2007-0140713 filed on Dec. 28, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a bridgeless power factor correction circuit, and more particularly, to a bridgeless power factor correction circuit that corrects a power factor by complementarily switching two switches on and off according to phases of input power without using a rectifier bridge diode. 
     2. Description of the Related Art 
     In recent years, as harmonics regulations have been tightened worldwide, the use of power factor correction circuits in electronic products has become common and required. 
     In general, the power factor correction circuit is divided into a passive power factor correction circuit and an active power factor circuit. The passive power factor correction circuit is configured by appropriately designing a passive line filter composed of an inductor and a capacitor at a power input side so as to attenuate harmonic components of power current. The passive power factor correction circuit has a simple configuration and is manufactured at low cost. However, it is difficult to stabilize a voltage since the size of an output voltage varies according to the size of an input power voltage. Further, since the passive power factor correction circuit needs to be designed according to commercial power frequency, it increases in size and volume significantly. 
     The active power factor correction circuit is configured by applying a generally known boost converter. The active power factor correction circuit has a power factor almost close to 1 and can output stable direct current power regardless of a variation in input voltage. However, since the active power factor correction circuit uses a switching method, a configuration circuit becomes complex to increase the unit cost, and it becomes difficult to control the circuit. 
     Therefore, in order to satisfy the harmonic regulations that have been tightened worldwide, most of the high power products are using active power factor correction circuits. 
       FIG. 1  is a circuit diagram illustrating a general active power factor correction circuit. 
     As shown in  FIG. 1 , an active power factor correction circuit using a general boost converter uses bridge diodes BD at an input terminal. The bridge diodes BD cause high conduction loss of approximately 2 to 3% of all power capacity. Therefore, studies on various types of bridgeless power factor correction circuits have been conducted these days. 
       FIG. 2A  is a circuit diagram illustrating a general active power factor correction circuit.  FIG. 2B  is a waveform diagram illustrating a main part of the general active power factor correction circuit. 
     Referring to  FIG. 2A , as described above, a general bridgeless power factor correction circuit, which is an improvement on the general active power factor correction circuit, is shown. 
     The above-described general bridgeless power factor correction circuit detects a current flowing through boost inductors L 1  and L 2  through a detection resistor Rsense. That is, the detection resistor Rsense is connected between diodes D 1  and D 3  and a ground terminal of the circuit to detect the current flowing through the inductors. 
     Then, a sine wave having the same phase as the input voltage is obtained from the detected current flowing through the inductors by using a correction circuit. At the same time, an output voltage is detected by using resistors R 1  and R 2 , and the sine wave obtained by detecting the current flowing through the inductors is multiplied by appropriate gain according to a value of the detected output voltage. 
     The signal, formed as described above, is compared with a triangle wave to generate a gate signal for driving a switch. That is, the gate signal of the switch is generated by detecting the current flowing through the inductors and the output voltage. At this time, the gate signal of the above-described switch is used to turn on or off the first and second switches M 1  and M 2  at the same time. 
       FIG. 2B  is a waveform diagram illustrating a main part of the general bridgeless power factor correction circuit. 
     Referring to  FIGS. 2A and 2B , the difference between forward voltage drop across the diodes D 1  and D 2  and voltage drop the sensing resistor Rsense and on-resistance of the switches M 1  and M 2  and backward voltage drop across the diodes D 3  and D 4  is applied to the first and second inductors L 1  and L 2 . 
     That is, when the switches M 1  and M 2  are turned on at the same time, one of the first and second inductors L 1  and L 2  operates as a boost inductor according to phases of the input voltage. When the switches M 1  and M 2  are turned on, voltage drop across the switches M 1  and M 2  becomes smaller than voltage drop across the diodes D 1  to D 4 , so that the drop voltage across the diodes D 1  to D 4  is applied to the other inductor. Even though a very small voltage obtained by subtracting the voltage drop across the switches M 1  and M 2  from the voltage drop across the diodes D 1  to D 4  is applied to the other inductor, since the voltage is applied for a long period of time, that is, a half cycle of the input voltage of approximately 8.3 msec, a considerable amount of current continues to flow through the inductors, which is supposed to operate at very fast switching frequency, during the half cycle of the input voltage. 
       FIG. 3  is a current waveform diagram illustrating a general bridgeless power factor circuit. 
     Referring to  FIG. 3 , it can be seen that the shape of the input current is distorted due to a reverse current of the inductor. This causes a reduction in power factor and generation of high harmonic components. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a bridgeless power factor correction circuit that corrects a power factor by complementarily switching two switches on and off according to phases of input power without using a rectifier bridge diode. 
     An aspect of the present invention also provides a bridgeless power factor correction circuit including: a switching unit having a plurality of switches and alternately switching input AC power; a stabilizing unit rectifying and smoothing the power switched by the switching unit; and a control unit controlling an alternate switching operation between the plurality of switches according to phases of the input power. 
     The switching unit may include: first and second inductors receiving different phases of the input power; and first and second switches connected in series with the first and second inductors, respectively, and alternately turned on and off under the control of the control unit. 
     The switching unit may further include first and second diodes removing common mode noise of the input power. 
     The control unit may include: a detector detecting phases of the input power; a comparator comparing the phases detected by the detector with a reference phase; and a signal generator multiplying results of the comparison from the comparator by predetermined gate signals and generating first and second switching signals for alternately turning the two switches on and off. 
     The detector may include: third and fourth diodes detecting phases of the input power; and a plurality of division resistors dividing a voltage of the input power from the third and fourth diodes. 
     The comparator may include: first and second comparison units comparing the phases detected by the detector with the reference phase based on the ground; and first and second inversion units inverting the comparison results of the first and second comparison units, respectively. 
     The signal generator may include: a gate signal generator supplying the predetermined gate signals; a first logic device multiplying the gate signal from the gate signal generator by the comparison result from the first inversion unit to generate the first switching signal; and a second logic device multiplying the gate signal from the gate signal generator by the comparison result from the second inversion unit to generate the second switching signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a circuit diagram illustrating a general active power factor correction circuit; 
         FIG. 2A  is a circuit diagram illustrating a general bridgeless power factor correction circuit; 
         FIG. 2B  is a waveform diagram illustrating a main part of the general bridgeless power factor correction circuit; 
         FIG. 3  is a current waveform diagram of the general bridgeless power factor correction circuit; 
         FIG. 4  is a circuit diagram illustrating a bridgeless power factor correction circuit according to an exemplary embodiment of the present invention; 
         FIG. 5  is a detailed diagram illustrating a configuration of a control unit used in the bridgeless power factor correction circuit according to the exemplary embodiment of the present invention; 
         FIG. 6  is a simulation waveform diagram illustrating a main part of the control unit of  FIG. 5 ; 
         FIG. 7  is a waveform diagram illustrating the bridgeless power factor correction circuit according to the exemplary embodiment of the present invention; 
         FIG. 8A  is a graph illustrating a comparison in efficiency between the related art and the present invention; and 
         FIG. 8B  is a graph illustrating a comparison in power loss between the related art and the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
       FIG. 4  is a circuit diagram illustrating a bridgeless power factor circuit according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , a bridgeless power factor correction circuit  100  according to an exemplary embodiment of the invention includes a switching unit  110 , a stabilizing unit  120 , and a control unit  130 . 
     The switching unit  110  includes first and second inductors L 1  and L 2  that are individually connected in series with an input AC power Vac terminal, and first and second switches M 1  and M 2  that are connected to the first and second inductors L 1  and L 2 , respectively. 
     The first and second inductors L 1  and L 2  are used as boost inductors according to a switching operation between the first and second switches M 1  and M 2 . The first and second switches M 1  and M 2  are alternately turned on and off according to switching control signals. 
     First and second diodes may be individually connected in series with the input AC power Vac terminal to remove common mode noise of input AC power. 
     The stabilizing unit  120  rectifies and smoothes the power switched by the switching unit  110  to stabilize the power. The stabilizing unit  120  may include third and fourth diodes D 3  and D 4  and a capacitor Co. 
     The control unit  130  supplies first and second switching signals according to phases of the input AC power Vac to control the switching unit  110  so that the first and second switches M 1  and M 2  of the switching unit  110  are alternately turned on and off. 
       FIG. 5  is a detailed view illustrating a control unit used in the bridgeless power factor correction circuit according to the embodiment of the present invention. 
     Referring to  FIG. 5 , the control unit  130  may include a detector  131 , a comparator  132 , and a signal generator  133 . 
     The detector  131  may include fifth and sixth diodes D 5  and D 6  and a plurality of division resistors R 1  to R 4 . The fifth and sixth diodes D 5  and D 6  are individually connected in series with the input AC power Vac terminal and detect the phase of the input AC power. Each of the plurality of division resistors R 1  to R 4  divides a voltage level of the power detected by each of the fifth and sixth diodes D 5  and D 6 . 
     The comparator  132  compares the phases of the input AC power detected by the detector  131  with a predetermined reference phase and transmits results of the comparison to the signal generator  133 . Then, the comparator  132  may include first and second comparison units U 1  and U 2  and first and second inversion units U 3  and U 4 . The first and second comparison units U 1  and U 2  compare the detected phases of the input AC power with the reference phase. The first and second inversion units U 3  and U 4  invert the comparison results from the first and second comparison units U 1  and U 2 , respectively. 
     The first and second comparison units U 1  and U 2  compare the detected phases of the input AC power with the reference phase based on the ground. 
     The signal generator  133  generates the first and second switching signals according to the comparison results from the comparator  132 . The signal generator  133  may include first and second logic devices U 5  and U 6  that multiply predetermined gate signals from a gate signal generator So by the comparison results from the comparator  132  to generate the first and second switching signals, respectively. 
       FIG. 6  is a simulation waveform diagram illustrating a main part of the control unit of  FIG. 5 . 
     Referring to  FIGS. 5 and 6 , each of the fifth and sixth diodes D 5  and D 6  detects the phase of the input AC power. The detected phase is divided by the plurality of division resistors R 1  to R 4  and input to the first and second comparison units U 1  and U 2 . When the input voltage has a positive (+) phase, the first comparison unit U 1  has an output of 1 (V+ in  FIG. 6 ). When the input voltage has a negative (−) phase, the second comparison unit U 2  has an output of 1 (V− in  FIG. 6 ). The comparison results are inverted by the first and second inversion units U 3  and U 4 , respectively, and are transmitted to the first and second logic devices U 5  and U 6 , respectively. In order to control the switches formed of MOS-FETs, the first and second logic devices U 5  and U 6  multiply the predetermined gate signals from the gate signal generator So by the inverted comparison results to supply the first and second switching signals, respectively. 
     That is, for example, an alternate switching operation is performed during a half cycle of the phase of the input AC power. That is, when the first switching signal is output at a high level, and the second switching signal is output at a low level, the first switch M 1  is turned on and the second switch M 2  is turned off. Then, an alternating switching operation is performed during a next half cycle of the phase of the input AC power. That is, when the second switching signal is output at a high level, and the first switching signal is output at a low level, the second switch M 2  is turned on and the first switch M 2  is turned off. 
       FIG. 7  is a waveform diagram illustrating a bridgeless power factor correction circuit according to an exemplary embodiment of the present invention. 
     Waveforms, shown in  FIG. 7 , are generated when an input voltage is 115 Vac, and output power is 280 W. In  FIG. 7 , the waveforms of the first and second switching signals and the input current that are generated according to the above-described conditions are shown. In the waveforms of the bridgeless power factor correction circuit according to the embodiment of the invention, as shown in  FIG. 7 , since reverse current does not flow through the inductors, it is possible to obtain sine-wave input current without distortion. 
       FIG. 8A  is a graph illustrating a comparison in efficiency between the related art and the present invention.  FIG. 8B  is a graph illustrating a comparison in power loss between the related art and the present invention. 
     According to the conditions of the graphs shown in  FIGS. 8A and 8B , input voltages are 90V, 115V, and 220V, and output power is in the range of 0 to 1300W. The graphs in  FIGS. 8A  and  8 B illustrate the comparison between the bridgeless power factor correction circuit according to the related art and the bridgeless power factor correction circuit according to the embodiment of the invention according to the above-described conditions. As shown in  FIGS. 8A and 8B , the bridgeless power factor circuit according to the embodiment of the invention can obtain a higher efficiency that that in the related art by 0.1 to 0.2%. This increase in efficiency is obtained by controlling the switches so that the switches are alternately turned on and off according to the phase of the input AC power to thereby prevent distortion in input current. 
     As set forth above, according to the exemplary embodiments of the invention, the bridgeless power factor correction circuit can correct a power factor and reduce harmonics by complementarily switching two switches on and off according to phases of input power to prevent distortion in input current. 
     While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.