Abstract:
An AC to DC converter circuit includes a main circuit including a first circuit and a second circuit connected to an AC power supply in parallel to each other, the first circuit including diodes and a switching device, the second circuit including diodes and a switching device. The switching devices are controlled to be ON and OFF corresponding to the input voltage polarity discriminated with an input voltage polarity discriminator such that two DC outputs are obtained from one AC power supply. The AC to DC converter circuit reduces the semiconductor devices, through which a current flows, facilitates reducing the losses caused therein, improving the conversion efficiency thereof, and reducing the size, weight and manufacturing costs of the cooling means thereof.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to an AC to DC converter circuit that obtains DC electric power from an AC power supply while controlling an input current efficiently. 
       FIG. 9  is a block circuit diagram describing a conventional AC to DC converter circuit including a power factor improving circuit as described in Japanese Patent Publication No. 2005-110434 and a DC to DC converter circuit.  FIG. 10  is a wave chart describing the operations of the conventional AC to DC converter circuit. 
     In  FIG. 9 , an AC power supply  1 ; coils  2 ,  26 ; diodes  4 ,  7  through  10 ,  15  through  18 ; switching devices  20 ,  22 ,  23 ; capacitors  30 ,  32 ; and a transformer  40  are shown. The power factor improving circuit is formed of a rectifying circuit, including diodes  15  through  18 , and switching device  20 . The DC to DC converter circuit is formed of a converter circuit including diodes  7 ,  8  and switching devices  22 ,  23  and a rectifying and smoothing circuit including diodes  9 ,  10  and capacitor  32 . 
     As switching device  20  turns ON when the voltage V in  of AC power supply  1  is positive, a current flows from AC power supply  1  to AC power supply  1  via diode  15 , coil  2 , switching device  20 , and diode  18 , increasing the current i 2  of coil  2 . As switching device  20  turns OFF, a current flows from coil  2  to coil  2  via diode  4 , capacitor  30 , diode  18 , AC power supply  1 , and diode  15 , decreasing the current i 2 . When the voltage V in  is negative, diodes  15  and  17  are electrically conductive, resulting in the same operations as described above. Therefore, by driving the switching device  20  with an appropriate gate signal, the input current is controlled to be sinusoidal at a high power factor and a DC voltage is obtained between both ends of capacitor  30 . 
     The DC voltage obtained as described above is higher than the input voltage amplitude. Therefore, it is necessary to dispose the DC to DC converter circuit considering the occasion, in which it is necessary to obtain a voltage lower than the input voltage amplitude or the occasion, in which a small high-frequency transformer is used for the insulation from the AC input side. As switching devices  22  and  23  turn ON, the voltage of capacitor  30  is applied to transformer  40  via switching devices  22  and  23 . Since a similar voltage proportional to the transformation ratio of the transformer is generated on the secondary side of transformer  40 , the current i 26  of coil  26  increases. As switching devices  22  and  23  turn OFF, the excitation energy stored in transformer  40  is regenerated to capacitor  30  via diodes  7  and  8 , generating a reverse voltage in the transformer. The current i 26  decreases while circulating from coil  26  to coil  26  via capacitor  32  and diode  10 . Therefore, a desired DC voltage insulated is obtained by appropriately selecting the control signal pulse width for controlling switching devices  22  and  23  and the transformer turn ratio. 
     In the power factor improving circuit in  FIG. 9 , a current flows always through three semiconductor devices and conduction losses are caused in the semiconductor devices, resulting in large losses. In order to suppress the temperature rise caused by the generated losses, cooling means is required, and volume and costs for cooling means increases. 
     Therefore, it would be desirable to provide an AC to DC converter circuit that facilitates decreasing the number of semiconductor devices, through which a current flows, reducing the losses caused, improving the conversion efficiency, reducing the cooling means size, and reducing the manufacturing costs of the cooling means. 
     The capacitance on the output side of the DC to DC converter circuit (capacitor  32 ) is determined such that current ripples and voltage ripples are allowable. Therefore, the current ripples and the voltage ripples not only increase the volume and costs of the electrolytic capacitor connected to the output side but also shorten the life of the AC to DC converter circuit. The ripple component in the output voltage causes adverse effects such as malfunction or breakdown of the apparatus connected to the load. 
     Therefore, it would be also desirable to provide an AC to DC converter circuit that facilitates reducing the ripple current and the ripple voltage caused in the electrolytic capacitor, using a small and inexpensive electrolytic capacitor, elongating the life thereof, and providing the output voltage with an excellent quality. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided an AC to DC converter circuit that obtains a plurality 2N of DC outputs from an AC power supply, the N being a nonnegative integer. The AC to DC converter circuit comprises a pair of AC input terminals; 2N pairs of DC output terminals corresponding to the 2N DC outputs; 2N series circuits connected between the AC input terminals, each of the series circuits including a first diode and a switching device; the connection point of the first diode and one end of the switching device in each of the series circuits being connected to one of the pairing DC output terminals for the series circuit via a second diode; and the other end of the switching device being connected to the other one of the pairing DC output terminals for the series circuit. 
     According to a second aspect of the invention, there is provided an AC to DC converter circuit that obtains a plurality 2N of DC outputs from an AC power supply, the N being a nonnegative integer. The AC to DC converter circuit comprises a pair of AC input terminals; 2N pairs of DC output terminals corresponding to the 2N DC outputs; 2N series circuits connected between the AC input terminals, each of the series circuits including a first diode and a switching device, one end thereof being connected to the first diode; one end of each of the series circuits being connected to one of the pairing DC output terminals for the series circuit via a second diode; and the other end of the switching device being connected to the other one of the pairing DC output terminals for the series circuit. 
     In the AC to DC converter circuit described in the second aspect, the switching device is provided with a capability of blocking the current flow in the reverse direction (hereinafter referred to as a “reverse current blocking capability”) so that the first diode connected in series to the switching device may be omitted without problem (third aspect). 
     In the AC to DC converter circuit described in any of the first to third aspects, the respective switching devices in the 2N series circuits are controlled with a same signal (fourth aspect). 
     In the AC to DC converter circuit described in any of the first to fourth aspects, the AC to DC converter circuit further includes DC to DC converter circuits connected to the respective 2N pairs of DC output terminals; the output terminal pairs of the respective DC to DC converter circuits being connected in parallel to each other; and the phases of the control signals controlling the respective DC to DC converter circuits being made to be different from each other (fifth aspect). 
     In the AC to DC converter circuit described in any of the first to fourth aspects, the AC to DC converter circuit further includes DC to DC converter circuits connected to the respective 2N pairs of DC output terminals; the output terminal pairs of the respective DC to DC converter circuits being connected in series to each other; and the phases of the control signals controlling the respective DC to DC converter circuits being made to be different from each other (sixth aspect). 
     Since the semiconductor devices, through which a current flows, are decreased according to the invention, the conversion efficiency of the AC to DC converter circuit according to the invention is improved. By combining the DC to DC converter circuits with the AC to DC converter circuit, ripple currents and ripple voltages are reduced. Therefore, the AC to DC converter circuit according to the invention facilitates reducing the size and manufacturing costs, improving the performances and elongating the life thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an AC to DC converter circuit according to a first embodiment of the invention. 
         FIG. 2  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 1 . 
         FIG. 3  is a block diagram of an AC to DC converter circuit according to a second embodiment of the invention. 
         FIG. 4  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 3 . 
         FIG. 5  is a block diagram of an AC to DC converter circuit according to a third embodiment of the invention. 
         FIG. 6  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 5 . 
         FIG. 7  is a block diagram of an AC to DC converter circuit according to a fourth embodiment of the invention. 
         FIG. 8  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 7 . 
         FIG. 9  is a block circuit diagram of a conventional AC to DC converter circuit. 
         FIG. 10  is a wave chart describing the operations of the conventional AC to DC converter circuit. 
         FIGS. 11 and 12  are block diagrams of the AC to DC converter circuit according to further embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Now, the invention will be described in detail hereinafter with reference to the accompanied drawings which illustrate the preferred embodiments of the invention. 
       FIG. 1  is a block diagram of an AC to DC converter circuit according to the first embodiment of the invention. The AC to DC converter circuit shown in  FIG. 1  obtains two DC outputs. Generally, the AC to DC converter circuit according to the invention facilitates obtaining 2N DC outputs, wherein N is a nonnegative integer.  FIG. 2  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 1 . 
     Referring now to  FIG. 1 , a main circuit includes a first circuit having diodes  3 ,  4  and a switching device  20 , and a second circuit including diodes  5 ,  6  and a switching device  21 . The first and second circuits are connected to an AC power supply  1  in parallel to each other. In the first circuit, a series circuit of diode  3  and switching device  20  is connected between a pair of AC input terminals, and diode  4  is connected between the connection point of diode  3  and switching device  20  and a DC output terminal. In the second circuit, diodes  5 ,  6  and switching device  21  are connected in the same manner as in the first circuit. Desired voltages are generated across capacitors  30  and  31 , respectively, by driving the first and second circuits under the control described later so that two DC outputs may be obtained from one AC power supply. 
     The control section for controlling the main circuit described above includes an input voltage detector  101 , an input voltage polarity discriminator  102 , an output voltage error amplifier  103 , a multiplier circuit  104 , an input current error amplifier  105 , a pulse width modulator  106 , a pulse distributor  107 , and an output voltage detector  108 . 
     In addition, V G20  and V G21  are gate signals of switching devices  20  and  21  in  FIG. 2 . 
     An input voltage is detected by input voltage detector  101  and the polarity thereof is discriminated by input voltage polarity discriminator  102 . Two output voltages from the first and second circuits are detected by output voltage detector  108  and controlled in output voltage error amplifier  103  so that the detected output voltages may be equal to the reference value thereof. The input voltage detected by input voltage detector  101  is multiplied in multiplier circuit  104  by the output from output voltage error amplifier  103  and adjusted to have a predetermined amplitude. The output from multiplier circuit  104  and the input current detected via a current transformer are fed to input current error amplifier  105  to generate a reference signal for controlling the input current to be sinusoidal. A PWM signal having a pulse width corresponding to the output signal from input current error amplifier  105  is generated in pulse width modulator  106 . The PWM signal is forwarded to switching device  20  or  21  for the gate signal thereof depending on the polarity of the input voltage. 
     In the circuit configuration described above, the control section drives switching device  20  while the voltage of AC power supply  1  is positive, and switching device  21  while the voltage of AC power supply  1  is negative. As switching device  20  turns ON while the voltage of AC power supply  1  is positive, a current flows from AC power supply  1  to AC power supply  1  via coil  2 , diode  3 , and switching device  20 , increasing the current i 3  of diode  3  and the current i 2  of coil  2  (cf.  FIG. 2 ). As switching device  20  turns OFF while the voltage of AC power supply  1  is positive, a current flows from coil  2  to coil  2  via diode  3 , diode  4 , capacitor  30 , and AC power supply  1 , decreasing the current i 3  of diode  3  and the current i 2  of coil  2 . 
     By driving switching device  21  while the voltage of AC power supply  1  is negative, operations similar to those described above are conducted. Thus, the AC to DC converter circuit shown in  FIG. 1  converts the AC voltage to two DC voltages while controlling the input current to be sinusoidal. Since the number of the semiconductor devices, through which the current flows, is always 2, the loses caused in the converter circuit are reduced. 
     A third circuit and a fourth circuit (both not shown), both having the configuration same with that of the first and second circuits, may be connected to the AC input terminal pair. The first and third circuits may be driven in the same phase. And, the second and fourth circuits may be driven in the same phase. If the circuits connected in parallel to each other are increased, the circuits may be driven in the same manner as described above without problem. 
       FIG. 3  is a block diagram of an AC to DC converter circuit according to the second embodiment of the invention.  FIG. 4  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 4 . 
     The AC to DC converter circuit according to the second embodiment is a modification of the AC to DC converter circuit according to the first embodiment. 
     The main circuit configuration in the AC to DC converter circuit in  FIG. 3  is the same as the main circuit configuration in the AC to DC converter circuit in  FIG. 1 . According to the second embodiment, the control circuit is simplified. In detail, a same signal is used for the drive signals (gate signals) v G20  and v G21 , described in  FIG. 4  for driving switching devices  20  and  21 , respectively. And, input voltage polarity discriminator  102  and pulse distributor  107  are omitted from the control section described in  FIG. 1 . Since it is possible to block the current with diode  5  when the voltage of power supply  1  is positive and with diode  3  when the voltage of power supply  1  is negative, it is not necessary to change over the control signals depending on the power supply voltage polarity. Therefore, it is possible to simplify the control circuit as described above. 
     Based on the above description, diodes  3  and  5  for current blocking may be inserted in series to switching devices  20  and  21 , respectively, without problem ( FIG. 11 ). In detail, a series circuit of diode  3  and switching device  20  is connected between the AC input terminals, and diode  4  is connected between the series circuit of diode  3  and switching device  20  and capacitor  30 . The positions of the diode  3  and the switching device  20  may be exchanged. Diodes  5 ,  6  and switching devices  21  are connected in the similar manner as described above. Moreover, diodes  3  and  5  may be omitted without problem by providing switching devices  20  and  21  with a reverse current blocking capability ( FIG. 12 ). 
       FIG. 5  is a block diagram of an AC to DC converter circuit according to the third embodiment of the invention.  FIG. 6  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 5 . 
     The AC to DC converter circuit according to the third embodiment includes DC to DC converter circuits connected to the respective DC output terminal pairs of the AC to DC converter circuit shown in  FIG. 1 , and the output terminal pairs of the DC to DC converter circuits are connected in parallel to each other. The DC to DC converter circuits operate in the same manner as the conventional DC to DC converter circuit. However, the phase of the control signal fed to switching devices  22  and  23  is made to be different from the phase of the control signal fed to switching devices  24  and  25 . If the phase difference is, for example, 180° as described in  FIG. 6 , the current i 26  of coil  26  will increase and the current i 27  of coil  27  will decrease, when switching devices  22 ,  23  are ON and switching devices  24 ,  25  are OFF. Since the ripple current flowing through electrolytic capacitor  32  is the sum of the AC components in i 26  and i 27 , the ripple current decreases and the ripples on the output voltage v 32  also decrease. 
       FIG. 7  is a block diagram of an AC to DC converter circuit according to the fourth embodiment of the invention.  FIG. 8  is a wave chart describing the operations of the AC to DC converter circuit shown in  FIG. 7 . 
     The AC to DC converter circuit according to the fourth embodiment includes DC to DC converter circuits connected to the respective DC output terminal pairs of the AC to DC converter circuit shown in  FIG. 1 , and the output terminal pairs of the DC to DC converter circuits are connected in series to each other. The phase of the control signal fed to switching devices  22  and  23  is made to be different from the phase of the control signal fed to switching devices  24  and  25 . Although ripples are caused on the voltages v 32  and v 33  of electrolytic capacitors  32  and  33 , the ripples on the output voltage v 32 +v 33  are decreased as described in  FIG. 8 . 
     The disclosure of Japanese Patent Application No. 2005-283755 filed on Sep. 29, 2005 is incorporated herein as a reference. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.