Patent Publication Number: US-2023135362-A1

Title: Power source device and image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a power source device and an image forming apparatus which is provided with a power source. 
     A switching power source which is used for a general electronic device often use a capacitor input type method, in which a smoothing capacitor for smoothing DC voltage is arranged at a rear stage of a diode bridge which fully rectifies an AC voltage which is input from an AC power source. A capacitor input type switching power source is characterized by a low power factor since an input current flows into a transformer when an output voltage of a diode bridge exceeds a smoothing capacitor voltage. Therefore, as a technique to increase the power factor, a switching power source is invented in which a current waveform of an input current is a shape whose peak portion is suppressed rather than a shape of a sine wave. For example, in Japanese Patent 03288367, a technique is proposed to improve a power factor by connecting an electronic device in which the switching power source is mounted and an electronic device in which a switching power source of a capacitor input type is mounted to a same AC power source to make a composed waveform of an input current approximated to a sinusoidal wave shape. 
     However, the circuit configuration of the switching power source which is described above is based on a power factor correction circuit of a general step-up type, and is a circuit configuration which applies a transformer which outputs a relatively high voltage in which a primary side and a secondary side are not insulated. Thus, the circuit configuration is not suitable for a switching power source which uses a transformer in which the primary side and the secondary side are insulated and which outputs low voltage from several volts to several tens of volts. 
     SUMMARY OF THE INVENTION 
     In response to such situation, an object of the present invention is to improve power factor of a switching power source in which a primary side and a secondary side are insulated from each other. 
     In order to solve the problems which are described above, the present invention is provided with following configurations. 
     According to an aspect of the present invention, there is provided a power source device comprising, a transformer including a first primary winding and a second primary winding, and a secondary winding, and of which a primary side and a secondary side are insulated from each other, a rectifying circuit including a first output terminal and a second output terminal, and configured to fully rectify an AC voltage, a first series circuit in which an inductor and a first rectifying element are connected in series, the first series circuit being connected between the first output terminal and a first connecting point where one end of the first primary winding and one end of the second primary terminal are connected, a switching element connected between the other end of the second primary winding and the second output terminal, and configured to be switched between an on state and an off state and a first capacitor connected between the other end of the first primary winding and the second output terminal, wherein an inductance of the inductor is set so that a voltage of the first capacitor is higher than an output voltage of the rectifying circuit, and a number of turns of the first primary winding is larger than the number of turns of the second primary winding. 
     According to another aspect of the present invention, there is provided an image forming apparatus comprising, an image forming portion configured to form an image on a recording material and a power source device configured to supply power to the image forming portion, wherein the power source device including a transformer including a first primary winding and a second primary winding, and a secondary winding, and of which a primary side and a secondary side are insulated from each other, a rectifying circuit including a first output terminal and a second output terminal, and configured to fully rectify an AC voltage, a first series circuit in which an inductor and a first rectifying element are connected in series, the first series circuit being connected between the first output terminal and a first connecting point where one end of the first primary winding and one end of the second primary terminal are connected, a switching element connected between the other end of the second primary winding and the second output terminal, and configured to be switched between an on state and an off state and a first capacitor connected between the other end of the first primary winding and the second output terminal, wherein an inductance of the inductor is set so that a voltage of the first capacitor is higher than an output voltage of the rectifying circuit, and a number of turns of the first primary winding is larger than the number of turns of the second primary winding. 
     According to a further aspect of the present invention, there is provided an image forming system comprising, an image forming apparatus configured to form an image on a recording material, and a processing apparatus connected to the image forming apparatus and configured to supply the recoding material to the image forming apparatus or to perform post processing to the recording material on which the image is formed by the image forming apparatus, wherein the image forming apparatus is provided with a first power source and the processing apparatus is provided with a second power source, wherein the first power source includes a first transformer of which a primary side and a secondary side are insulated from each other, a first rectifying circuit including a first output terminal and a second output terminal, and configured to fully rectify an AC voltage, a first switching element connected between one end of a primary winding of the first transformer and the second output terminal, and configured to be switched between an on state and an off state, and a first capacitor connected between the first output terminal and the second output terminal, wherein the second power source includes a second transformer including a first primary winding and a second primary winding and a secondary winding, and of which a primary side and a secondary side are insulated from each other, a second rectifying circuit including a third output terminal and a fourth output terminal, and configured to fully rectify an AC voltage, a first series circuit in which an inductor and a first rectifying element are connected in series, the first series circuit being connected between the third output terminal and a first connecting point where one end of the first primary winding and one end of the second primary terminal are connected, a second switching element connected between one end of the second primary winding and the fourth output terminal, and configured to be switched between an on state and an off state, and a second capacitor connected between the first primary winding and the second output terminal, wherein an inductance of the inductor is set so that a voltage of the second capacitor is higher than an output voltage of the second rectifying circuit. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic sectional view illustrating a configuration of an image forming apparatus according to a first embodiment and a second embodiment. 
         FIG.  2    is a circuit diagram of a switching power source according to the first embodiment. 
       Part (a) and part (b) of  FIG.  3 A  are graphs showing a current waveform and a voltage waveform according to the first embodiment. 
       Part (a) and part (b) of  FIG.  3 B  are graphs showing a current waveform and a voltage waveform according to the first embodiment. 
       Part (a) and part (b) of  FIG.  4    are a circuit diagram of a switching power source of a capacitor input type and a diagram illustrating a current waveform according to from the first through the third embodiments. 
       Part (a) and part (b) of  FIG.  5    are drawings comparing input current waveforms according to the first embodiment. 
         FIG.  6    is a drawing illustrating a usage pattern of an electronic device according to the first embodiment. 
         FIG.  7    is a circuit diagram of the switching power source according to the second embodiment. 
         FIG.  8    is a schematic diagram of a configuration of an image forming apparatus according to the third embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, embodiments of the present invention will be specifically described with reference to Figures. 
     First Embodiment 
     [Configuration of Image Forming Apparatus] 
     In the first embodiment, a case that a power source device according to the present invention is applied to an image forming apparatus will be described with reference to  FIGS.  1  through  6   .  FIG.  1    is a sectional view showing a schematic configure of a laser beam printer as an example of an image forming apparatus. A laser beam printer  100  (hereinafter referred to as a “printer  100 ”) is provided with a photosensitive drum  101  on which an electrostatic latent image is formed, a charging portion  102  which uniformly charges the photosensitive drum  101 , and a developing portion  103  which develops the electrostatic latent image which is formed on the photosensitive drum  101  and form a toner image. Further, the printer  100  is provided with an exposure device  110  which emits a laser light onto the photosensitive drum  101  and form the electrostatic latent image on a surface of the photosensitive drum  101 . In the printer  100 , the toner image which is formed on the photosensitive drum  101  is transferred to a sheet P as a recording material which is fed from a cassette  104  by a roller  111 , etc. with a transfer portion  105 . The sheet P onto which the toner image is transferred is conveyed to a fixing device  106 , the toner image is fixed on the sheet Pin the fixing device  106 , the sheet P on which the toner image is fixed is discharged to a tray  107 . The photosensitive drum  101 , the charging portion  102 , the developing portion  103 , and the transfer portion  105  are an image forming portion. Further, the printer  100  is provided with a low voltage power source device  108  which is a power source device, and the low voltage power source device  108  supplies power to a driving portion such as a motor and a control portion (not shown) which controls an image forming operation by the image forming portion and conveying operation of the sheet P. 
     [Configuration of Switching Power Source] 
       FIG.  2    is a circuit diagram showing a circuit configuration of a switching power source  200  in the embodiment, in which the printer  100  in  FIG.  1    is provided as the low voltage power source device  108 . In  FIG.  2   , when an AC plug  201  is connected to an outlet, AC voltage is input from a commercial AC power source (not shown) to the switching power source  200 . The input AC voltage is input to a diode bridge  203  via a filter circuit  202 . The diode bridge  203 , which is a rectifier circuit, includes terminals  203   a  and  203   b  on an input side and terminals  203   c  (a first output terminal) and  203   d  (a second output terminal) on an output side. The diode bridge  203  fully rectifies the AC voltage which is input from the terminals  203   a  and  203   b  on the input side, and outputs to the terminals  203   c  and  203   d  on the output side. On the other hand, in a case that an external load, to which power of the switching power source  200  is supplied, is substantially constant and an output voltage Vout is almost stable, a charging voltage Vc, which is charged to an electrolytic capacitor  207  which is a smoothing means, is almost constant, although the charging voltage Vc includes some ripple voltage depending on a capacity of the electrolytic capacitor. Incidentally, since the switching power source  200  includes a power factor correction circuit, the electrolytic capacitor  207  is configured on a downstream side of a primary winding of a transformer  206 . 
     In  FIG.  2   , the terminal  203   c  on the output side of the diode bridge  203  is connected to one end of an inductor  204 . The other end of the inductor  204  is connected to an anode terminal of a diode  205  (a first rectifier element), and a cathode terminal of the diode  205  is connected to a primary winding  206   a  (a first primary winding) and a primary winding  206   b  (a second primary winding) of the transformer  206 . In this way, the inductor  204  and the diode  205  are connected in series and configures a series circuit. 
     The transformer  206  is an isolation transformer for converting energy of a primary side to a secondary side and includes the primary windings  206   a  and  206   b , and a secondary winding  206   c . In the transformer  206 , a polarity of the primary windings  206   a  and  206   b  is different from that of the secondary winding  206   c . The primary winding  206   a  of the transformer  206  and the primary winding  206   b  are connected in series. One end of the primary winding  206   a  is connected to a positive side of the electrolytic capacitor  207  (a first capacitor), and the other end of the primary winding  206   a  is connected to one end of the primary winding  206   b  and a cathode terminal of the diode  205 . The other end of the primary winding  206   b  is connected to a drain terminal of a field effect transistor (hereinafter referred to as FET) which is a switching element. On the other hand, a source terminal of the FET  208  is connected to a negative side of the electrolytic capacitor  207  and the terminal  203   d  on an output side of the diode bridge  203 . That is, the FET  208  is connected to the primary winding  206   b  of the transformer  206  in series. Further, a gate terminal of the FET  208  is connected to a control IC (not shown), and the FET  208  is set to ON state or OFF state according to a signal which is input to the gate terminal from the control IC. With the connection configuration which is described above, the electrolytic capacitor  207  is connected in parallel to the primary winding  206   a  and primary winding  206   b  of the transformer  206  which are connected in series. 
     Further, one end of the secondary winding  206   c  of the transformer  206  is connected to an anode terminal of a diode  209 , and the cathode terminal of the diode  209  is connected to a positive side of an electrolytic capacitor  210 . The positive side of the electrolytic capacitor  210  is connected to the cathode terminal of the diode  209  and the negative side of the electrolytic capacitor  210  is connected to the other end of the secondary winding  206   c . A charge voltage of the electrolytic capacitor  210  is output to the external load which is connected to the switching power source  200  as the output voltage Vout of the switching power source  200 . 
     When the FET  208  becomes a conductive state by an application of a gate voltage from the control IC (not shown) to a gate terminal of the FET  208 , a charge voltage of the electrolytic capacitor  207  is divided by the primary winding  206   a  and the primary winding  206   b  of the transformer  206 . When an output voltage of the diode bridge  203  is higher than the divided voltage, an input current to the transformer  206  flows to the inductor  204  and the diode  205 . 
     Here, by increasing the number of turns of the primary winding  206   a  over the number of turns of the primary winding  206   b , a voltage value which is divided by the primary winding  206   a  and the primary winding  206   b  is decreased, and an input current flows from an output voltage of the diode bridge  203  which is a lower voltage. Further, while the voltage value which is divided by the primary windings  206   a  and  206   b  is almost constant voltage, since the output voltage of the diode bridge  203  varies sinusoidally in terms of time, the waveform of the input current also varies substantially sinusoidally. Thus, the switching power source  200  is possible to obtain a power source characteristic with a high power factor. 
     On the other hand, during a period when the gate voltage is not supplied from the control IC (not shown) to the gate terminal of the FET  208 , power (energy) which is stored in the primary side of the transformer  206  is transmitted to the secondary side. An operation of the switching power source  200  is similar to an operation of a flyback power source, as power is supplied to the secondary side of the transformer  206  when the FET  208  is turned off. And it is possible to set the output voltage Vout arbitrarily according to a turn ratio of the primary winding and the secondary winding of the transformer  206 , and output from a few volts. 
     [A Relationship Between an Output Voltage of a Diode Bridge and an Input Current from a Transformer] 
       FIG.  3 A  is a diagram illustrating waveforms of an input current Iin and output voltage Vin in a state that a power factor is high, in a case that an input current to the primary windings  206   a  and  206   b  of the transformer  206  is defined as Iin and an output voltage of the terminal  203   c  of the diode bridge  203 . A waveform diagram shown in part (a) of  FIG.  3 A  shows a current waveform of the input current Iin in which a vertical axis indicates a current value and a horizontal axis indicates a time t, while a waveform diagram shown in part (b) of  FIG.  3 A  shows a voltage waveform of the output voltage Vin in which a vertical axis indicates a voltage value and a horizontal axis indicates a time t. Incidentally, t 1  through t 6  indicate timings. In part (b) of  FIG.  3 A , a voltage Vc is a voltage waveform which indicates a voltage of the electrolytic capacitor  207 , and a dashed line indicates a voltage in which the voltage Vc of the electrolytic capacitor  207  is divided by a turn ratio of the primary winding  206   a  and the primary winding  206   b . Incidentally, the voltage which is shown by the dashed line is also a voltage at a connection point (a primary connection point) between the primary winding  206   a  and the primary winding  206   b.    
     As shown in  FIG.  3 A , at a time (time t 1  (t 3 , t 5 , . . . )) when the voltage of the electrolytic capacitor  207  is divided by the primary winding  206   a  and the primary winding  206   b  and the output voltage Vin of the diode bridge  203  exceeds the divided voltage (a divided voltage value), the input current Iin flows. The input current Iin flows until a time (time t 2  (t 4 , t 6 , . . . )) when the output voltage Vin becomes less than the divided voltage value. Paradoxically, until the output voltage Vin reaches the divided voltage value (for example, from time t 2  to time t 3 ), the input current Iin is configured not to flow (Iin=0). In this way, at the time when the output voltage Vin of the diode bridge  203  exceeds the voltage of the charging voltage of the electrolytic capacitor  207  which is divided by the primary winding  206   a  and the primary winding  206   b , the input current Iin starts to flow, however, the input current Iin does not flow for a predetermined period of time. 
     Therefore, in a case that a frequency of a pulse signal which is input to the gate terminal of the FET  208  and switches the FET  208  to an ON state or an OFF state is set to a fixed frequency, a following pulse signal control is performed in order to keep the output voltage Vout of the switching power source  200  constant. That is, when the output voltage Vin from the diode bridge  203  is low, a width of the pulse signal which is input to the gate terminal (a time during the ON state) is widened (lengthened) and the time during the ON state of the FET  208  is extended. On the other hand, when the output voltage Vin from the diode bridge  203  is high, a width of the pulse signal which is input to the gate terminal (a time during the ON state) is narrowed (shortened) and the time during the ON state of the FET  208  is shortened. Therefore, the shape of the current waveform of the input current Iin is a waveform shape such that a height of a peak portion of a sinusoidal wave which includes a period when no current flows at all (a period when the input current Iin=0) is suppressed, as shown in part (a) of  FIG.  3 A . Incidentally, during the period when no input current Iin does not flow at all, a power supply to a load is performed by flowing a current from the electrolytic capacitor  207  to the primary windings of the transformer  206 . Further, an important condition for the current shape of the input current Iin to become a waveform shape which is shown in part (a) of  FIG.  3 A  is that the voltage Vc of the electrolytic capacitor  207  is always higher than the output voltage Vin of the diode bridge  203  as shown in part (b) of  FIG.  3 A . 
     On the other hand,  FIG.  3 B  is a diagram illustrating the current waveform of the input current Iin and the voltage waveform of the output voltage Vin in a case that the charging voltage Vc of the electrolytic capacitor  207  is instantaneously lower than the output voltage Vin of the diode bridge  203 . A waveform diagram which is shown in part (a) of  FIG.  3 B  shows a current waveform of the input current Iin in which a vertical axis indicates a current value and a horizontal axis indicates a time t, while a waveform diagram which is shown in part (b) of  FIG.  3 B  shows a voltage waveform of an output voltage Vin in which a vertical axis indicates a voltage value and a horizontal axis indicates a time t. Incidentally, t 11  through t 22  indicate timings. 
     The waveform diagram which is shown in  FIG.  3 B  differs from the waveform diagram shown in  FIG.  3 A , in that the voltage around the peak of the output voltage Vin of the diode bridge  203  is higher than the charging voltage Vc of the electrolytic capacitor  207  in  FIG.  3 B . When the output voltage Vin is higher than the charging voltage Vc of the electrolytic capacitor  207  (during periods from t 12  through t 13 , t 16  through t 17  and t 20  through t 21 ), the input current Iin instantaneously becomes a large current. As a result, as shown in part (a) of  FIG.  3 B , a waveform shape of the input current Iin is such that a protrusion portion is formed around a peak value, in contrast to the current waveform which is shown in part (a) of  FIG.  3 A . In the embodiment, to prevent from forming protrusion portions in an input current waveform, the charging voltage Vc of the electrolytic capacitor  207  is set to be always higher than the output voltage Vin of the diode bridge  203 . Thus, it is possible for the current waveform of the input current Iin to be the waveform shape such that the peak portion of the sinusoidal wave shape which includes the period when no current flows at all is suppressed. 
     [Switching Power Source of Capacitor Input Type] 
     Part (a) of  FIG.  4    is a circuit diagram showing a circuit configure of an example of a switching power source of a capacitor input type in which a smoothing capacitor for smoothing an input DC voltage at a rear stage of the diode bridge which rectifies the full wave AC voltage which is input from the AC power source. A switching power source  400  which is shown in part (a) of  FIG.  4    is a flyback converter in which winding directions of a primary winding  405   a  and a secondary winding  405   b  of a transformer  405  are opposite directions. 
     In part (a) of  FIG.  4   , when an AC plug  401  is connected to an outlet, an AC voltage is input to the switching power source  400  from an AC power source (not shown). The AC voltage which is input is input to a diode bridge  403  through a filter circuit  402 . The diode bridge  403  which is a rectifier circuit rectifies a full wave AC voltage which is input from input terminals  403   a  and  403   b  on an input side and outputs to terminals  403   c  and  403   d  on an output side. ADC voltage is output from the diode bridge  403  in which the full wave AC voltage is rectified, and is smoothed to a substantially constant voltage by an electrolytic capacitor  404  and charged. 
     The transformer  405  is a transformer whose primary and secondary sides are insulated, and includes the primary winding  405   a  and the secondary winding  405   b  which is wound in an opposite direction of the primary winding. Further, the primary winding  405   a  is connected to a positive side of the electrolytic capacitor  404  and the terminal  403   c  of the diode bridge  403  on an output side on one end, and is connected to a drain terminal of a field effect transistor (hereinafter referred to as a FET)  406  on the other end. Further, a source terminal of the FET  406  is connected to a negative side of the electrolytic capacitor  404  and the terminal  403   d  on the output side of the diode bridge  403 . Further, a gate terminal of the FET  406  is connected to a control IC (not shown), and the FET  406  is set to ON state or OFF state according to a signal which is input to the gate terminal from the control IC. Further, the secondary winding  405   b  includes a diode  407  and an electrolytic capacitor  408  which are rectifying and smoothing means for rectifying and smoothing a voltage which is induced by the secondary winding  405   b . One end of the secondary winding  405   b  is connected to an anode terminal of the diode  407 , and the other end of the secondary winding  405   b  is connected to a negative side of the electrolytic capacitor  408 . Further, a cathode terminal of the diode  407  is connected to a positive side of the electrolytic capacitor  408 , and the negative side of the electrolytic capacitor  408  is connected to the other end of the secondary winding  405   b  and is also grounded. 
     When the FET  406  is in a conduction state (an ON state) by applying a gate voltage from a control IC (not shown) to a gate terminal of the FET  406 , a current is supplied from the electrolytic capacitor  404  and an electric power (energy) is accumulated in the primary winding  405   a . And when the gate voltage supply from the control IC to the gate terminal of the FET  406  is blocked and the FET 406  is in a non-conduction state (an OFF state), the electric power (energy) which is accumulated in the primary winding  405   a  is induced in the secondary winding  405   b . The induced voltage is rectified and smoothed by the diode  407  and the electrolytic capacitor  408 , and the output voltage Vout is output. Incidentally, a same function is realized by being configured of a field effect transistor (FET) instead of the diode  407 , and it is possible to further suppress an electric power loss. 
     Further, part (b) of  FIG.  4    shows a current waveform of an input current of the switching power source  400  which is a flyback converter in part (a) of  FIG.  4   . In a circuit diagram of part (a) of  FIG.  4   , the input current from the diode bridge  403  flows only when the charging voltage of the electrolytic capacitor  404  is lower than the output voltage of the diode bridge  403 . Therefore, as shown in part (b) of  FIG.  4   , a waveform of an input current from the diode bridge  403  become a very narrow shape of a conduction angle which is a phase angle in which the input current flows, a power factor in a state that the conduction angle is very narrow is very low, and an amount of a reactive current is large. Incidentally, here, the flyback converter is used as an example of a switching power source of a capacitor input type and is described. For example, even though other type of a power source such as a forward converter and a LLC power source in which winding directions of the primary winding and the secondary winding are same, an input current waveform is similar to an input current waveform which is shown in part (b) of  FIG.  4   . 
     [A Composite Current Waveform of Two Switching Power Sources] 
     Part (a) and part (b) of  FIG.  5    show current waveforms of composite currents in which current waveforms of the switching power source  200  in  FIG.  2    which are shown in part (a) of  FIG.  3 A  and part (b) of  FIG.  3 B  and current waveform of the switching power source  400  of the capacitor input type in part (a) of  FIG.  4    which is shown in part (b) of  FIG.  4    are composed. Part (a) of  FIG.  5    is the current waveforms of the composite current in which an input current waveform in part (a) of  FIG.  3 A  and an input current waveform of the switching power source  400  of the capacitor input type in part (b) of  FIG.  4    are composed. A current waveform which is shown in part (a) of  FIG.  5    is added by (composed of) the input current waveform of the switching power source  400  of the capacitor input type which is shown in part (a) of  FIG.  4    in such a way that suppressed amount of waveform in which peak portions of a waveform of a sinusoidal wave shape which is shown in part (a) of  FIG.  3 A  are suppressed is supplemented. Thus, a shape of the waveform is similar to waveform shape of a sinusoidal waveform, and it is possible to achieve a high power factor. 
     On the other hand, part (b) of  FIG.  5    is the current waveform of the composite current in which an input current waveform in part (a) of  FIG.  3 B  and an input current waveform of the switching power source  400  of the capacitor input type in part (b) of  FIG.  4    are composed. In the current waveform which is shown in part (b) of  FIG.  5   , a protrusion portion is formed in a waveform of a sinusoidal waveform shape which is shown in part (a) of  FIG.  3 B , and, furthermore, the input current waveform of the switching power source  400  of the capacitor input type which is shown in part (b) of  FIG.  4    is added. Therefore, the current waveform becomes nearly triangular in shape, as shown in part (b) of  FIG.  5   . So it is difficult to achieve a high power factor. 
     In a circuit configuration of the switching power source  200  which is shown in  FIG.  2   , the inductor  204  includes a function to adjust the charging voltage Vc of the electrolytic capacitor  207 . For example, when an inductance value of the inductor  204  is reduced, an input current from the diode bridge  203  is increased. As a result, a charging amount of the electrolytic capacitor  207  is increased and the charging voltage Vc is easily increased, then it is possible to be approximated to the input current waveform which is shown in part (a) of  FIG.  3 A . On the other hand, when the inductance value of the inductor  204  is increased, the input current from the diode bridge  203  is decreased. As a result, a discharging amount of the electrolytic capacitor  207  is increased and the charging voltage Vc is easily decreased, then it is easily to become the input current waveform which is shown in part (a) of  FIG.  3 B . In this way, the inductance value of the inductor  204  is greatly affected by the input voltage range conditions of the switching power source  200 , and also greatly affects a withstand voltage of the electrolytic capacitor  207 . Therefore, it is necessary to consider and adjust power source specifications of the switching power source  200  and ratings of components which are used. 
     [Example of Product Use Pattern] 
       FIG.  6    is a diagram illustrating a use pattern of a product which is provided with the switching power source which is described above. In  FIG.  6   , the printer  100  is provided with the low voltage power source device  108  which includes the switching power source  200  in the embodiment which is shown in  FIG.  2   , as described in  FIG.  1   . On the other hand, an electronic device  600  is an electronic device which is different from the printer  100  and is provided with the switching power source  400  of the capacitor input type which is shown in  FIG.  4    as a switching power source. And the AC plug  201  of the switching power source  200  which is mounted on the printer  100  and the AC plug  401  of the switching power source  400  which is mounted on the electronic device  600  are connected to an outlet  601  which is provided with a wall. As shown in  FIG.  6   , the switching power source  200  and the switching power source  200  are in a state that they are connected in parallel to a same AC power source (a same AC power source outlet  601 ). At this time, as described above, the current waveform, which is composed of the input current to the switching power source  200  of the printer  100  and the input current to the switching power source  400  of the electronic device  600 , is approximated to a shape of a sinusoidal waveform which is shown in part (a) of  FIG.  5   , and it is possible to improve the power factor. 
     As described above, the switching power source  200  in the embodiment includes the circuit configuration which is shown in  FIG.  2    and the voltage of the electrolytic capacitor  207  is set higher than the output voltage Vin of the diode bridge  203 . As a result, the current waveform of the input current Iin becomes a waveform of the sinusoidal waveform shape such that a height of the peak portion of the sinusoidal waveform is suppressed. As a result, in a case that the printer  100  on which the switching power source  200  is mounted and the electronic device  600  on which the switching power source  400  of the capacitor input type is mounted are connected to a common wall outlet  601 , it is possible to increase a power factor of a composed current waveform of both of the devices. Incidentally, in the embodiment, it is described by using an example that the printer  100  and the electronic device  600  are connected the common wall outlet  601 , however, a same effect is also achieved in a case that same cable taps are used for example. 
     Further, the switching power source  200  which is described in  FIG.  2    may be designed to support a wide range of input voltages (for example, from 85V to 264V) as a universal power source. At this time, in a case that it is difficult to make entire input voltage range and load current range input current waveforms without any protrusion portions as shown in part (a) of  FIG.  3 A , a following manner may be done. That is, only an input current near a maximum load at a low input voltage may be a current waveform which includes a protrusion shape as shown in part (b) of  FIG.  5   . In this case, since the input current near the maximum load is a current which flows instantaneously, when the power factor during this period is dropped, it is considered that it has no trouble. That is, in a case that a voltage which is input to the diode bridge  203  is a first voltage, the inductance value of the inductor  204  is set so that the voltage of the electrolytic capacitor  207  is always higher than the output voltage Vin of the diode bridge  203 . At this time, in a case that the input voltage is a second voltage which is lower than the first voltage, the voltage of the electrolytic capacitor  207  may not always higher than the output voltage Vin of the diode bridge  203 . In a case the input voltage is the second voltage, according to the external load which is connected to the switching power source  200 , it may be configured that periods when the electrolytic capacitor  207  voltage is higher and lower than the output voltage Vin of the diode bridge  203  are occurred. 
     As described above, according to the embodiment, it is possible to improve the power factor of the switching power source in which the primary side and the secondary side are insulated. 
     Second Embodiment 
     In the first embodiment, the switching power source, which includes the circuit configuration which is capable of low voltage output with the high power factor and which sets the charging voltage of the electrolytic capacitor so that it is always higher than the output voltage of the diode bridge and the input current waveform is made to be the shape in which the peak value of the sinusoidal waveform is suppressed, is described. Since the switching power source in the first embodiment is configured of only a basic circuit, there is concern that a surge voltage which is occurred during switching of the switching element may become large depending on the power which is supplied to the load and the switching power source may become noisy. In a second embodiment, a switching power source, in which a circuit which suppresses a noise is added, will be described. Incidentally, the image forming apparatus in which the switching power source in the embodiment is mounted is same as the printer  100  in the first embodiment, and same devices and same members are described by using the same reference numerals and descriptions here are omitted. 
     [Configuration of Switching Power Source] 
       FIG.  7    is a circuit diagram showing a circuit configuration of the switching power source  200  in the embodiment. In the circuit diagram which is shown in  FIG.  7   , compared to the circuit diagram which is shown in  FIG.  2    of the first embodiment, it differs in that diodes  701  and  704 , a capacitor  702 , and an auxiliary winding  703  in the transformer  206  are added. Incidentally, in the switching power source  200  in the embodiment, descriptions here are omitted by using same reference numerals to describe parts with same configurations as the switching power source  200  of the first embodiment which is shown in  FIG.  2   . Further, in the switching power source  200  in the embodiment, descriptions are omitted with regard to same circuit operations as in the switching power source  200  in the first embodiment. 
     In  FIG.  7   , one end of the capacitor  702  (a second capacitor) is connected to the other end of the primary winding  206   b  of the transformer  206  and the drain terminal of the FET  208 , and the other end of the capacitor  702  is connected to an anode terminal of the diode  701 . Further, a cathode terminal of the diode  701  (a second rectifier element) is connected to a positive side of the electrolytic capacitor  207  and the other end of the primary winding  206   a  of the transformer  206 . The diode  701  and the capacitor  702  are connected in series and are connected in parallel to the primary windings  206   a  and  206   b  of the transformer  206  which are connected in series. 
     The anode terminal of the diode  704  (a third rectifier element) is connected to the source terminal of the FET  208 , the negative side of the electrolytic capacitor  207 , and the output terminal of  203   d  of the diode bridge  203 . The cathode terminal of the diode  704  is connected to one end of the auxiliary winding  703  of the transformer  206 . The other end of the auxiliary winding  703  of the transformer  206  is connected to a connection point (a second connection point) to which the other end of the capacitor  702  and the anode terminal of the diode  701  are connected. Incidentally, the diode  704  is provided for backflow prevention in order to prevent a charge of the capacitor  702  from discharging through auxiliary winding  703 . 
     In  FIG.  7   , when the FET  208  is turned off, through the primary winding  206   b  of transformer  206 , a current which flows between the drain terminal and the source terminal of the FET  208  switches to a charging current which charges a capacitance between the drain terminal and the source terminal. As a result, a voltage between the drain terminal and the source terminal of the FET  208  gradually increases due to the charging current. And when the voltage between the drain terminal and the source terminal of the FET  208  exceeds a charging voltage of the electrolytic capacitor  207 , a current from the primary winding  206   b  flows to the electrolytic capacitor  207  through the capacitor  702  and the diode  701 . At this time, the voltage between the drain terminal and the source terminal of the FET  208  is suppressed to a predetermined voltage value. 
     On the other hand, when the FET  208  is turned on, a discharging current which flows from the capacitor  702  is divided into a current which flows through the FET  208  and a current which flows backward through the primary windings  206   a  and  206   b . The current which flows backward through the primary windings  206   a  and  206   b  becomes a regenerative current to the electrolytic capacitor  207 , and part of energy (a charging voltage of the capacitor  702 ) which is generated by a surge voltage when the FET  208  turns off is regenerated in electrolytic capacitor  207  and reused. And by flowing the discharging current, the capacitor  702 , in which the voltage which is charged by the surge voltage is discharged, becomes a state just before the charge current flows when the FET  208  turns off, and is reset to a state in which it is possible to accumulate the surge voltage (surge energy) again. 
     On the other hand, the current which flows from the capacitor  702  to the FET  208  flows to the auxiliary winding  703  through the diode  704 , and a current energy of the discharging current is accumulated in the auxiliary winding  703 . And the energy which is accumulated in the auxiliary winding  703  is converted as the secondary side current when the FET  208  is turned off next time, and is added to the secondary side current in which the energy which is accumulated by the current which flows in the primary windings  206   a  and  206   b  is converted. As described above, in the switching power source  200  which is shown in  FIG.  7   , when the FET  208  turns on and turns off, it is configured that energy is regenerated in the electrolytic capacitor  207 . Thus, the switching power source  200  is a highly efficient switching power source by regenerating the energy of the surge voltage while the surge voltage of the FET  208  is suppressed, since the diodes  701  and  704 , the capacitor  702 , and the auxiliary winding  703  are added. 
     Further, in the switching power source  200  which includes a circuit configuration which is shown in  FIG.  7   , it is possible to make an input current waveform a current waveform as shown in part (a) of  FIG.  3 A  by setting the voltage of the electrolytic capacitor  207  to be always larger than the output voltage of the diode bridge  203 . In a case that a product on which the switching power source  200  is mounted and an electronic device on which the switching power source of the capacitor input type are connected to a common outlet  601  ( FIG.  6   ), it is possible to approximate a composite current waveform of both devices to a sinusoidal waveform shape and to make the power factor higher. 
     As described above, according to the embodiment, it is possible to improve the power factor of the switching power source in which the primary side and the secondary side are insulated. 
     Third Embodiment 
     In the first embodiment and the second embodiment, the switching power source, which includes the circuit configuration which is capable of low voltage output with the high power factor and which sets the charging voltage of the electrolytic capacitor so that it is always higher than the output voltage of the diode bridge and the input current waveform is made to be the shape in which the peak value of the sinusoidal waveform is suppressed, is described. And, by shaping the waveform of the input current in such a way that the peak value of the sinusoidal waveform is suppressed, it is possible to improve the power factor in the composite waveform of the input current with another electronic device  600  on which the switching power source of the capacitor input type is mounted. In a third embodiment, an image forming system with a configuration, in which a switching power source of a capacitor input type is mounted as a main power source and a switching power source of a high power factor which is described in the first embodiment and the second embodiment is mounted as a sub-power source, will be described. 
     [Configuration of Image Forming System] 
       FIG.  8    is a diagram showing a configuration of an image forming system while all optional devices are mounted. In  FIG.  8   , an image forming apparatus  800  shows the smallest configuration to perform an image forming operation, and the image forming apparatus  800  by itself is able to print a sheet P based on an image data which is received according to a print request which is sent from a computer (not shown), etc. Incidentally, the image forming apparatus  800  is same as the printer  100  which is shown in  FIG.  1    of the first embodiment, and a description of the image forming operation will be omitted. 
     An image scanner  802 , an input option device  803 , and an output option device  804  are mounted on the image forming apparatus  800  which is shown in  FIG.  8   . The image scanner  802  is an image reading device which reads a document which is placed on a glass table and a copy function is realized by printing the read image on a sheet P The input option device  803  is possible to accommodate a large number of sheets P, and is possible to accommodate a large number of sheets P of various sizes so as to correspond to a designation of the sheet P at a time of printing. The output option device  804  includes a plurality of sorter bins  804   a ,  804   b  and  804   c  and is an optional device which includes a sorting function which sorts and outputs the sheets P which are printed. Incidentally, it is not limited to an output option device which includes a sorting function, however, it may also be an optional processing device which processes the sheets P such as an output option device which includes a stapling function for the plurality of sheets Pin which images are formed. 
     Further, in the image forming system which is shown in  FIG.  8   , a switching power source  801  (corresponding to the low voltage power source device  108  in  FIG.  1   ) which is a low voltage power source device is mounted on the image forming apparatus  800 , and a switching power source  805  which is a low voltage power source device is mounted on the output option device  804 . And in the image forming system of  FIG.  8   , the switching power source  801  (a first power source device) is configured as a main power source and the switching power source  805  (a second power source device) is configured as a sub-power source. For example, when a single switching power source  801  is configured to be able to supply power to all optional devices, in a case of the image forming apparatus  800  alone in which no optional devices are mounted at all, power supply capability from the switching power source  801  become in an excessive state. As a result, costs of the switching power source  801  become no longer optimal. Therefore, in a case that a plurality of optional devices are mounted as shown in  FIG.  8   , it is more likely to reduce overall costs when it is configured with two switching power sources  801  and  805 . In the embodiment, the switching power source  801  is a switching power source of a capacitor input type, and the switching power source  805  is configured to be the switching power source of the high power factor type which is described in the first embodiment and the second embodiment and is configured so that AC voltage is supplied from a common AC power source. Thus, a current waveform which is composed of current waveforms of each input current of the switching power sources  801  and  805  become a shape of a substantially sinusoidal waveform as shown in  FIG.  3 A  which is described in the first embodiment, and it is possible to achieve a high power factor. 
     As described above, the image forming system in the embodiment mounts all optional devices and is configured that two switching power sources of the main power source and the sub-power source are mounted as power sources. One of the two switching power sources is a conventional switching power source of a capacitor input type, and the other is a switching power source of a high power factor type which is described in the first embodiment and the second embodiment. By a configuration of the power source device, it is possible to approximate the composite waveform of the input current of each switching power source to a sinusoidal wave and to improve the power factor. Incidentally, in the embodiment, the switching power source  805  which is mounted on the output option device  804  is a switching power source of a high power factor type and performs power supply to the output option device  804 . On the other hand, it is configured that the switching power source  801  of the capacitor input type which is mounted on the image forming apparatus  800  performs the power supply of the image scanner  802  and the input option device  803  in addition to the image forming apparatus. Incidentally, it is possible to achieve a similar effect even when it is configured that, for example, the switching power source of the high power factor type which supplies power to the input option device  803  is mounted on the input option device  803 , and the switching power source  801  and two switching power sources of the high power factor type perform power supply. 
     As described above, according to the embodiment, it is possible to improve the power factor of the switching power source in which the primary side and the secondary side are insulated. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-179726, filed on Nov. 2, 2021, which is hereby incorporated by reference herein in its entirety.