Abstract:
A power control apparatus and an image forming apparatus including the same are disclosed. The power control apparatus can directly enable or disable a DC/DC converter for converting reference DC power to a secondary DC power without an additional microcomputer based power circuit by connecting an enable or disable operation of the DC/DC converter with an operation of a power button by a user. Accordingly, the number of components of a power control circuit can be reduced to decrease material cost and simplify the power control circuit. Furthermore, the power control apparatus and the image forming apparatus including the same can reduce unnecessary power consumption in a system off state.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit of Korean Patent Application No. 2011-107088, filed on Oct. 19, 2011 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments relate to a power control apparatus and an image forming apparatus including the same and, more particularly, to a power control apparatus capable of minimizing unnecessary power consumption during power off of an image forming apparatus, and an image forming apparatus including the same. 
         [0004]    2. Description of the Related Art 
         [0005]    An image forming apparatus includes a printer, a copier, a facsimile machine, and a multi-purpose peripheral apparatus having a combination of the functions of the printer, copier and facsimile. 
         [0006]    The image forming apparatus provides power to a controller and principal components thereof using a power supply, a DC/DC converter, etc. Specifically, the power supply converts alternating current (AC) power provided by an external power source into primary direct current (DC) power. The DC/DC converter generates secondary DC power used for the controller that controls the image forming apparatus and internal components of the image forming apparatus using the DC power. 
         [0007]    While other power converters such as a regulator can replace the DC/DC converter, a DC/DC converter having high power conversion efficiency is increasingly used in order to minimize power consumption of the image forming apparatus and save energy. 
         [0008]    A recent image forming apparatus adopts a scheme of converting AC power to a DC voltage and then converting the DC voltage into secondary DC voltages having different levels using the DC/DC converter. 
         [0009]    In general, the DC/DC converter includes an enable pin through which the DC/DC converter can be enabled or disabled by an external signal. The DC/DC converter is activated (or enabled) or inactivated (shut down or disabled) according to the level of a signal input to the enable pin. 
         [0010]    A microcomputer-based power control circuit is additionally provided to control activation or inactivation of the DC/DC converter in such a manner that a signal having an appropriate voltage level is applied to the enable pin of the DC/DC converter. Accordingly, when the image forming apparatus is powered off, unnecessary power consumption is minimized by disabling the DC/DC converter using the microcomputer-based power control circuit. 
         [0011]    However, a conventional power control apparatus additionally includes the microcomputer-based power control circuit for controlling activation or inactivation of the DC/DC converter, and thus the number of components of the power control apparatus increases, raising manufacturing costs and complicating the configuration of the power control circuit. 
         [0012]    Furthermore, since the microcomputer-based power control circuit needs to be continuously provided with power even when the image forming apparatus is powered off, unnecessary power consumption still occurs. 
       SUMMARY 
       [0013]    In accordance with an aspect of one or more embodiments, there is provided a power control apparatus capable of controlling activation/inactivation of a DC/DC converter without using an additional microcomputer-based power control circuit and an image forming apparatus including the same. 
         [0014]    In accordance with an aspect of one or more embodiments, there is provided a power control apparatus including a DC/DC converter including an enable pin and being enabled or disabled according to a level of a signal input to the enable pin, a switch connected to the enable pin and switched to change the level of the signal input to the enable pin, and an input unit connected to one terminal of the switch and including a power button to control a switching state of the switch. 
         [0015]    The power control apparatus may further include a trigger unit to divide a DC power into a reference voltage and output a trigger signal for turning on the switch such that a signal for disabling the DC/DC converter is input to the enable pin in case of power off. 
         [0016]    The power control apparatus may further include a CPU to recognize an operation of the power button and a power controller to control the switching state of the switch according to a control signal of the CPU. 
         [0017]    The power controller may include a logic OR gate to receive a signal for powering off a system and a reset signal from the CPU as inputs and a transistor switched according to the output signal of the logic OR gate. 
         [0018]    The transistor may include a collector connected to an output terminal of the trigger unit and an emitter grounded. 
         [0019]    One terminal of the power button may be connected to the collector of the transistor and the other terminal thereof may be ground. 
         [0020]    The power control apparatus may further include a barrier diode connected in a forward direction to a circuit line that connects the collector of the transistor and one terminal of the power button. 
         [0021]    The power control apparatus may further include a diode connected in a forward direction to a circuit line that connects the trigger unit and the switch to prevent the DC/DC converter from being disabled when the switch is turned on according to an ON operation of the power button when the system is changed from a power off state to a power on state. 
         [0022]    In accordance with an aspect of one or more embodiments, there is provided a power management (control) apparatus including a DC/DC converter including an enable pin and being enabled or disabled according to a level of a signal input to the enable pin, a switch to apply a first voltage level signal for disabling the DC/DC converter to the enable pin when turned on and to apply a second voltage level signal to the enable pin when turned off, a trigger unit connected to one terminal of the switch to divide a DC power into a reference voltage and to tune on the switch such that the first voltage level signal is input to the enable pin in a power off state of a system, an input unit connected to one terminal of the switch and including a power button to control a switching state of the switch, a CPU to recognize an operation state of the power button of the input unit, and a power controller to control the switching state of the switch according to a control signal of the CPU. 
         [0023]    The trigger unit may turn on the switch to disable the DC/DC converter in the power off state of the system, the CPU may turn off the switch through the power controller to enable the DC/DC converter when the power button is pressed in the power off state of the system, and the CPU may control the trigger unit to turn on the switch through the power controller to disable the DC/DC converter when the power button is pressed in a power on state of the system. 
         [0024]    In an aspect of one or more embodiments, there is provided an image forming apparatus including a photosensitive member, an optical scanning unit to form an electrostatic latent image on the photosensitive member, a developing unit to develop the electrostatic latent image formed on the photosensitive member into a developer image, a transfer unit to transfer the developer image formed on the photosensitive member to a printing medium, a fusing unit to fusing the developer image transferred by the transfer unit onto the printing medium, a control board to control an operation of at least one of the photosensitive member, optical scanning unit, developing unit, transfer unit and fusing unit, and a power control apparatus to supply power to at least one of the components, wherein the power control apparatus includes a DC/DC converter including an enable pin and being enabled or disabled according to a level of a signal input to the enable pin, a switch connected to the enable pin and switched to change the level of the signal input to the enable pin, and an input unit connected to one terminal of the switch and including a power button to control a switching state of the switch. 
         [0025]    The image forming apparatus may further include a trigger unit to divide a DC power into a reference voltage and output a trigger signal for turning on the switch such that a signal for disabling the DC/DC converter is input to the enable pin in case of power off. 
         [0026]    The image forming apparatus may further include a CPU to recognize an operation of the power button and a power controller to control the switching state of the switch according to a control signal of the CPU. 
         [0027]    The power controller may include a logic OR gate to receive a signal for powering off a system and a reset signal from the CPU as inputs and a transistor switched according to the output signal of the logic OR gate. 
         [0028]    The transistor may include a collector connected to an output terminal of the trigger unit and an emitter grounded. 
         [0029]    One terminal of the power button may be connected to the collector of the transistor and the other terminal thereof may be ground. 
         [0030]    The image forming apparatus may further include a barrier diode connected in a forward direction to a circuit line that connects the collector of the transistor and one terminal of the power button. 
         [0031]    The image forming apparatus may further include a diode connected in a forward direction to a circuit line that connects the trigger unit and the switch to prevent the DC/DC converter from being disabled when the switch is turned on according to an ON operation of the power button when the system is changed from a power off state to a power on state. 
         [0032]    According to an aspect of one or more embodiments, the DC/DC converter can be disabled without an additional microcomputer based power control circuit in a power off state of the image forming apparatus by connecting activation/inactivation of the DC/DC converter with operation of the power button. When the power off state is changed to a power on state, the DC/DC converter can be enabled according to an operation of the user of pressing the power button. When the power on state is changed to the power off state, the DC/DC converter can be disabled according to an operation of the user of releasing the power button. Accordingly, the number of components of the power control circuit can be reduced to decrease material cost and simplify the configuration of the power control circuit. Furthermore, unnecessary power consumption can be reduced in case of system power off. 
         [0033]    In accordance with one or more embodiments, there is provided an image forming apparatus including a photosensitive member; an optical scanning unit to form an electrostatic latent image on the photosensitive member; a developing to develop the electrostatic latent image formed on the photosensitive member into a developer image; a transfer unit to transfer the developer image formed on the photosensitive member to a printing medium; a fusing unit to fuse the developer image transferred by the transfer unit onto the printing medium; a control board to control an operation of at least one of the photosensitive member, optical scanning unit, developing unit, transfer unit and fusing unit; and a power control apparatus to supply power to at least one of the components, wherein the power control apparatus includes a DC/DC converter including an enable pin and being enabled or disabled according to a level of a signal input to the enable pin; a switch to apply a first voltage level signal for disabling the DC/DC converter to the enable pin when turned on and to apply a second voltage level signal to the enable pin when turned off; a trigger unit connected to one terminal of the switch to divide a DC power into a reference voltage and to tune on the switch such that the first voltage level signal is input to the enable pin in a power off state of a system; an input unit connected to one terminal of the switch and including a power button to control a switching state of the switch; a central processing unit (CPU) to recognize an operation state of the power button of the input unit; and a power controller to control the switching state of the switch according to a control signal of the CPU. 
         [0034]    The trigger unit may turn on the switch to disable the DC/DC converter in the power off state of the system, the CPU may turn off the switch through the power controller to enable the DC/DC converter when the power button is pressed in the power off state of the system, and the CPU may control the trigger unit to turn on the switch through the power controller to disable the DC/DC converter when the power button is pressed in a power on state of the system. 
         [0035]    In accordance with one or more embodiments, there is provided an image forming apparatus including a photosensitive member; an optical scanning unit to form an electrostatic latent image on the photosensitive member; a developing unit to develop the electrostatic latent image formed on the photosensitive member into a developer image; a transfer unit to transfer the developer image formed on the photosensitive member to a printing medium; a fusing unit to fuse the developer image transferred by the transfer unit onto the printing medium; a control board to control an operation of at least one of the photosensitive member, optical scanning unit, developing unit, transfer unit and fusing unit; and a power control apparatus to supply power to at least one of the components, wherein the power control apparatus includes a DC/DC converter including an enable pin and being enabled or disabled according to a level of a signal input to the enable pin; a switch connected to the enable pin and switched to change the level of the signal input to the enable pin; an input unit connected to one terminal of the switch; and a kick start unit connected to the input unit to automatically enable the image forming apparatus when alternating current (AC) power is supplied to the image forming apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    These and/or other aspects will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings of which: 
           [0037]      FIG. 1  illustrates the configuration of an image forming apparatus to which a power control apparatus according to an embodiment; 
           [0038]      FIG. 2  is a block diagram of the power control apparatus according to an embodiment; 
           [0039]      FIG. 3  is a circuit diagram of the power control apparatus according to an embodiment; 
           [0040]      FIG. 4  illustrates a DC/DC converter enable pin in the power control apparatus according to an embodiment; 
           [0041]      FIG. 5  illustrates a power-off state operation of the power control apparatus according to an embodiment; 
           [0042]      FIG. 6  illustrates a power-on operation in a power off state in the power control apparatus according to an embodiment; 
           [0043]      FIG. 7  illustrates a power-off operation in a power-on state in the power control apparatus according to an embodiment; 
           [0044]      FIG. 8  is a table for explaining output of a control signal for controlling operations of a DC/DC converter by a CPU of the power control apparatus according to input signal; and  FIG. 9  is a circuit diagram of a power control apparatus according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0045]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0046]    An image forming apparatus may be a color image forming apparatus for convenience of description. 
         [0047]      FIG. 1  illustrates the configuration of an image forming apparatus  1  according to an embodiment. 
         [0048]    Referring to  FIG. 1 , the image forming apparatus  1  may include a main body  10 , a printing medium feeding unit (printing medium feeder)  20 , an image forming unit  30 ,  40 ,  50  and  60 , a fusing unit  70 , and a printing medium discharging unit  80 . 
         [0049]    The main body  10  forms the appearance of the image forming apparatus  1  and supports components provided therein. A main body cover  11  is rotatably attached to one side of the main body  10  and opens/closes part of the main body  10 . 
         [0050]    The printing medium feeding unit  20  feeds printing media to the image forming unit  30 ,  40 ,  50  and  60 . The printing medium feeding unit  20  includes a cassette  21  storing the print media S, a pick-up roller  22  for picking up the print media S stored in the cassette  21  one by one, and a transfer roller  23  for transferring the picked up print media to a transfer unit  60 . 
         [0051]    The image forming unit  30 ,  40 ,  50  and  60  forms an image to be printed on a printing medium and includes an optical scanning unit  30 , a photosensitive member  40 , a developing unit  50 , and the transfer unit  60 . 
         [0052]    The optical scanning unit  30  is located under the developing unit  50  and scans the photosensitive member  40  with light corresponding to image information to form an electrostatic latent image on the surface of the photosensitive member  40 . 
         [0053]    The photosensitive member  40  is constructed in such a manner that an optical conductive layer is formed on the surface of a cylindrical metal drum. The photosensitive member  40  forms an electrostatic latent image according to the optical scanning unit  30  and forms a developer image according to the developing unit  50 . A charging roller  41  is set in the main body  10 . The charging roller  41  charges the photosensitive member  40  to a predetermined potential before the optical scanning unit  30  scans the photosensitive member  40  with light. The charging roller  41  is an exemplary charger that charges the photosensitive member  40  to a uniform potential. The charging roller  41  supplies charges to the photosensitive member  40  while rotating in contact or without contact with the outer surface of the photosensitive member  40  to charge the outer surface of the photosensitive member  40  to a uniform potential. 
         [0054]    The developing unit  50  supplies a developer to the photosensitive member  40  on which the electrostatic latent image is formed so as to form a developer image. The developing unit  50  may include four developer cartridges  50 Y,  50 M,  50 C and  50 K respectively containing developers in different colors, for example, yellow (Y), magenta (M), cyan (C) and black (K). The developer cartridges  50 Y,  50 M,  50 C and  50 K respectively include developer containers  51 Y,  51 M,  51 C and  51 K, feeding rollers  52 Y,  52 M,  52 C and  52 K, and developing rollers  53 Y,  53 M,  53 C and  53 K. The developer containers  51 Y,  51 M,  51 C and  51 K contain developers to be supplied to the photosensitive member  40 . The feeding rollers  52 Y,  52 M,  52 C and  52 K supply the developers contained in the developer containers  51 Y,  51 M,  51 C and  51 K to the developing rollers  53 Y,  53 M,  53 C and  53 K. The developing rollers  53 Y,  53 M,  53 C and  53 K attach the developers onto the surface of the photosensitive member  40  to form a developer image. 
         [0055]    The transfer unit  60  includes a transfer belt  61 , a first transfer roller  62  and a second transfer roller  63 . The developer image formed on the surface of the photosensitive member  40  is transferred to the transfer roller  61 . The transfer roller  61  is supported by supporting rollers  64  and  65  and runs at the same velocity as the linear velocity of the photosensitive member  40 . The first transfer roller  62  faces the photosensitive member  40  with the transfer belt  61  located therebetween to transfer the developer image formed on the surface of the photosensitive member  40  to the transfer belt  61 . The second transfer roller  63  faces the supporting roller  65  with the transfer belt  61  located therebetween. The second transfer roller  63  is separated from the transfer belt  61  while the developer image is transferred from the photosensitive member  40  to the transfer belt  61  and comes into contact with the transfer belt  61  at a predetermined pressure upon completion of transfer of the developer image from the photosensitive member  40  to the transfer belt  61 . When the second transfer roller  63  comes into contact with the transfer belt  61 , the image of the transfer belt  61  is transferred to a printing medium. 
         [0056]    The fusing unit  70  fuses the developer image onto the printing medium and then delivers the printing medium onto which the developer image is fused to the printing medium discharging unit  80 . The fusing unit  70  includes a heating roller  71  having a heat source and a pressure roller  72  located opposite to the heating roller  71 . When the printing medium passes between the heating roller  71  and the pressure roller  72 , the developer image is fixed onto the printing medium by heat from the heating roller  71  and pressure acting between the heating roller  71  and the pressure roller  72 . 
         [0057]    The printing medium discharging unit  80  includes a discharging roller  81  and a discharge backup roller  82  and discharges the printing medium that has passed through the fusing unit  70  to the outside of the main body  10 . 
         [0058]    Operations of the image forming apparatus having the above-mentioned configuration are briefly described. 
         [0059]    The optical scanning unit  30  scans the photosensitive member  40  charged to a uniform potential by the charging roller  41  with light corresponding to yellow image information, for example, to form an electrostatic latent image corresponding to the yellow image information on the photosensitive member  40 . 
         [0060]    A developing bias is applied to the developing roller  53 Y of the yellow developer cartridge  50 Y such that the yellow developer is attached to the electrostatic latent image to form a yellow developer image on the photosensitive member  40 . This developer image is transferred to the transfer belt  61  by the first transfer roller  62 . 
         [0061]    Upon completion of transfer of a yellow developer image corresponding to one page, the optical scanning unit  30  scans the photosensitive member  40  with light corresponding to magenta image information, for example, to form an electrostatic latent image corresponding to the magenta image information on the photosensitive member  40 . 
         [0062]    The magenta developer cartridge  50 M feeds the magenta developer to the electrostatic latent image to develop the electrostatic latent image such that a magenta developer image is formed on the photosensitive member  40 . The magenta developer image formed on the photosensitive member  40  is transferred to the transfer belt  61  such that the magenta developer image is superimposed on the previously transferred yellow developer image. 
         [0063]    The above-mentioned process is performed on cyan and black image information to form a color developer image including yellow, magenta, cyan and black developer images formed in a superimposed manner on the transfer belt  61 . The color developer image is transferred to a printing medium passing between the transfer belt  61  and the second transfer roller, and the image transferred to the printing medium is fused onto the printing medium while passing through the fusing unit  70 . The printing medium that has passed through the fusing unit  70  is discharged by the printing medium discharging unit  80 . 
         [0064]    A power control apparatus according to an embodiment supplies power to at least one of the feeding unit  20 , the image forming unit  30 ,  40 ,  50  and  60 , the fusing unit  70  and the discharging unit  80 , which are components of the image forming apparatus, and a control board on which various circuit elements are mounted to control the image forming apparatus. 
         [0065]      FIG. 2  is a block diagram of the power control apparatus according to an embodiment. 
         [0066]    As shown in  FIG. 2 , the power control apparatus includes a DC/DC converter unit  100 , a trigger unit (trigger)  110 , a switch  120 , an input unit  130 , a power controller  140  and a central processing unit (CPU)  150 . 
         [0067]    The DC/DC converter unit  100  is enabled or disabled according to a switching operation of the switch  120 . 
         [0068]    The switch  20  is turned on or turned off according to a trigger signal of the trigger unit  110 . 
         [0069]    The input unit  130  includes a power button operated by a user. When the power button is pressed in order to change a system off state to a system on state, the level of the trigger signal input to the switch  120  from the trigger unit  110  is decreased, for example, to 0V from 3.3V, to turn off the switch  120 , thereby enabling the DC/DC converter unit  100 . Furthermore, the input unit  130  outputs an input signal corresponding to the operation state of the power button operated by the user to the CPU  150 . 
         [0070]    The power controller  140  turns the switch  120  on or off by changing the level of the trigger signal input to the switch  120  from the trigger unit  110  according to a control signal of the CPU  150 . In addition, the power controller  140  may maintain the enable state of the DC/DC converter unit  100  even when the power button of the input unit  130  is released. 
         [0071]    The CPU  150  recognizes whether the user turns the power button on or off according to the input signal from the input unit  130 . The CPU  150  outputs the control signal for controlling the operation of the power controller  140  according to the recognition result. 
         [0072]      FIG. 3  is a circuit diagram of the power control apparatus according to an embodiment. 
         [0073]    As shown in  FIG. 3 , the DC/DC converter unit  100  includes a DC/DC converter  101  for converting a primary DC power (e.g. 24V) changed from AC power supplied to a system such as an image forming apparatus to a secondary DC power (e.g. 5V). The DC/DC converter  101  includes an enable pin EN though which the DC/DC converter  101  is enabled or disabled according to an external signal input to the enable pin EN. 
         [0074]    The DC/DC converter  101  is disabled when the enable pin EN is grounded. Conversely, the DC/DC converter  101  is enabled when the enable pin EN is open or the primary DC power (e.g. 24V) is applied to the enable pin EN as pull-up (refer to  FIG. 4 ). 
         [0075]    When the DC/DC converter  101  is enabled, the DC/DC converter  101  generates the secondary DC power (e.g. 5V) necessary to operate components of the image forming apparatus, such as a control board, from the primary DC power (e.g. 24V) and provides the secondary DC power. Particularly, when power is supplied to the CPU  150  that is a microprocessor for controlling the image forming apparatus, the CPU  150  is enabled to supply a control signal necessary for a peripheral circuit. 
         [0076]    The trigger unit  110  divides the primary DC power, 24V, supplied from a power supply, and outputs a trigger signal with respect to the divided voltage. For example, the trigger unit  110  divides the primary DC power, 24V, into 3.3V and outputs a trigger signal for 3.3V. The switch  120  is turned on or turned off according to the level of the trigger signal. 
         [0077]    The switch  120  is connected to the enable pin EN of the DC/DC converter  101  and grounds or opens the enable pin EN, or connects the primary DC power to the enable pin EN as pull-up power according to a switching operation thereof so as to enable or disable the DC/DC converter  101 . 
         [0078]    To achieve this, the switch  120  includes a transistor Q 1  as a switching element. The transistor Q 1  may be an NPN transistor. The NPN transistor is constructed in such a manner that a P type single-crystalline semiconductor is interposed between N type semiconductors and includes an emitter formed of an N type semiconductor material, a base made of a P type semiconductor material and a collector formed of an N type semiconductor material. 
         [0079]    The transistor Q 1  is turned on when 3.3V is applied to the base thereof, and thus the collector and the emitter thereof are short-circuited. Conversely, when 0V is applied to the base, the transistor Q 1  is turned off and thus the collector and emitter thereof are open. 
         [0080]    As shown in  FIG. 5 , in a power off state of the image forming apparatus, the transistor Q 1  of the switch  120  is turned on according to the trigger signal of the trigger unit  110  for 3.3V. Upon turning on the transistor Q 1 , the enable pin EN of the DC/DC converter  101  is grounded, and thus a low signal is input to the DC/DC converter  101  through the enable pin EN to disable the DC/DC converter  101 . 
         [0081]    Referring back to  FIG. 3 , the input unit  130  includes a power button PB used to power the image forming apparatus on or off. The power button PB is a push button and is open in a power off state. When the power button PB is not pressed, a voltage level of an nKEY_POWER signal input to the CPU  150  is 3.3V. When the power button PB is pressed, the voltage level of the nKEY_POWER signal input to the CPU  150  changes to 0V from 3.3V. The CPU  150  determines whether the user presses the power button PB on the basis of this variation in the nKEY_POWER signal. 
         [0082]    In case of power off, 3.3V is supplied from the trigger unit  110  to the switch  120  since the power button PB is open. Accordingly, the transistor Q 1  of the switch  120  is turned on, and thus the enable pin EN of the DC/DC converter  101  is grounded to disable the DC/DC converter  101 . That is, the operation of the DC/DC converter  101  is stopped in case of power off. 
         [0083]    Referring to  FIG. 6 , if the user presses the power button PB of the input unit  130  when the image forming apparatus is powered off, the power button PB is grounded to allow trigger current of the trigger unit  110  to flow to the ground through the power button PB, and thus the trigger voltage input to the switch  120  from the trigger unit  110  decreases to 0V from 3.3V. Accordingly, the transistor Q 1  of the switch  120  is turned off. In this case, 24V pull-up is applied to the enable pin EN of the DC/DC converter  101  and thus a high signal is input to the DC/DC converter  101  so as to change the disable state of the DC/DC converter  101  to the enable state. That is, the DC/DC converter  101  operates to generate the secondary DC voltage, 5V, from the primary DC voltage, 24V, applied to an input pin IN thereof and outputs 5V through an output pin OUT thereof. Upon activation of the DC/DC converter  101 , power is supplied to the CPU  150  and thus an nPOWER_OFF signal input to the power controller  140  from the CPU  150  becomes a high signal. Accordingly, a transistor Q 3  of the power controller  140  is turned on to maintain the turn off state of the transistor Q 1  of the switch  120 , and thus the DC/DC converter  101  maintains the enable state thereof. 
         [0084]    Referring to  FIG. 7 , if the power button PB is pressed when the image forming apparatus is powered on, the nKEY_POWER signal input to the CPU  150  changes from 3.3V to 0V to inform the CPU  150  that the power button PB is pressed. When the power button PB is continuously pressed for a predetermined time, the CPU  150  recognizes it as a command for turning off the image forming apparatus according to a predetermined program. When the user releases the pressed power button PB of the input unit  130 , the CPU  150  changes the nPOWER_OFF signal to a low signal (0V) and supplies the low signal to the power controller  140 . 
         [0085]    In this case, the transistor Q 1  of the switch  120  is turned off to disable the DC/DC converter  101 . That is, power supply to the DC/DC converter  101  is cut off to interrupt the operation of the DC/DC converter  101 . 
         [0086]    Referring to  FIG. 8 , when nKEY_POWER signal is 3.3V, the CPU  150  determines that the power button PB is pressed and outputs the nPOWER_OFF signal at a low level to the power controller  140  to turn off the image forming apparatus. Conversely, when nKEY_POWER signal is 0V, the CPU  150  determines that the power button PB is released and outputs the nPOWER_OFF signal at a high level to the power controller  140  to turn on the image forming apparatus. 
         [0087]    The power controller  140  turns on or turns off the DC/DC converter  101  according to the nPOWER_OFF signal output from the CPU  150 . The power controller  140  is connected to the trigger unit  110  and turns the transistor Q 1  of the switch  120  off or on by adjusting the voltage supplied to the switch  120  from the trigger unit  110  so as to turn the DC/DC converter  101  on or off. 
         [0088]    Referring back to  FIG. 3 , the power controller  140  includes a logic OR gate U 4  and the transistor Q 3 . The logic OR gate U 4  receives the nPOWER_OFF signal and an nRESET signal output from the CPU  150 , as input signals. The logic OR gate U 4  outputs 3.3V when both the nPOWER_OFF signal and nRESET signal output from the CPU  150  are high (5V) and outputs 0V if one of the two signals is low (0V). The transistor Q 3  is turned on or turned off according to the voltage level of the output signal of the logic OR gate U 4 . That is, the transistor Q 3  is turned on when the voltage level of the output signal of the logic OR gate U 4  is 3.3V and turned off when 0V. 
         [0089]    When the user presses the power button PB of the input unit  130  in a power off state of the image forming apparatus, the CPU  150  is enabled to output the nPOWER_OFF signal at a high level. In this case, the transistor Q 3  of the power controller  140  is turned on to turn off the transistor Q 1  of the switch  120 , and the enable pin EN of the DC/DC converter  120  is provided with 24V to enable the DC/DC converter  101 . In this case, even when the user releases the power button PB, the DC/DC converter  101  keeps the enable state thereof because the nPOWER_OFF signal supplied to the power controller  140  from the enabled CPU  150  is a high signal. 
         [0090]    When the user continues pressing the power button PB of the input unit  130  in the power on state of the image forming apparatus, the nPOWER_OFF signal changes to a lower signal in order to turn off the image forming apparatus and is supplied to the power controller  140 . In this case, the transistor Q 3  of the power controller  140  is turned off so as to turn on the transistor Q 1  of the switch  120 . Accordingly, the DC/DC converter  101  changes to a disable state from the enable state. 
         [0091]    The nRESET signal supplied to the power controller  140  is used to solve a problem that the image forming apparatus is rebooted due to voltage drop using the fact that the nRESET signal is maintained at a low level during a power on reset period when the CPU changes the nPOWER_OFF signal to a low signal in the power on state to turn off the image forming apparatus. 
         [0092]    A barrier diode D 1  is provided between the trigger unit  110  and the input unit  130 . 
         [0093]    The barrier diode D 1  is serially connected between the trigger unit  110  and the input unit  130 . Specifically, the barrier diode D 1  is connected in a forward direction between the output terminal of the trigger unit  110  and the power button PB of the input unit  130 . One terminal of the barrier diode D 1  is connected to one terminal of the power button PB and the other terminal thereof is connected to the collector of the transistor Q 3  of the power controller  140 . That is, the barrier diode D 1  is connected in a forward direction between the transistor Q 3  and the power button PB. 
         [0094]    When the user presses the power button PB to turn on the image forming apparatus and then releases the power button PB, the nKEY_POWER signal corresponding to 0V may be continuously input to the CPU  150 , that is, the power button PB may be recognized as being continuously pressed. In this case, when the barrier diode D 1  is used, the nKEY_POWER signal is immediately changed to 3.3V when the user releases the power button PB. Accordingly, the barrier diode D 1  can prevent the CPU  150  from incorrectly recognizing the operation state of the power button PB. 
         [0095]    That is, when the barrier diode D 1  is not provided, the CPU  150  may recognize the power button PB as being continuously pressed even in a ready state of the image forming apparatus. Even when the DC/DC converter  101  is enabled by pressing the power button PB and then the power button PB is released, the nKEY_POWER signal corresponding to 0V is still input to the CPU  150 . Accordingly, the CPU  150  may perform a control operation for turning off the image forming apparatus upon misrecognizing the power button PB as being pressed again by the user to turn off the image forming apparatus. If the barrier diode D 1  is provided, however, the barrier diode D 1  prevents the power controller  140  and the trigger unit  110  from being affected by an operation of releasing the power button PB after power on of the image forming apparatus. More specifically, since the transistor Q 3  of the power controller  140  is turned on in the power on state, the nKEY_POWER signal maintains 0V even if the user releases the pressed power button PB, and thus the CPU  150  may misrecognize the press operation of the power button PB. However, when the barrier diode D 1  is used, the voltage level of the nKEY_POWER signal is changed according to the press operation of the power button PB so that the CPU  150  can correctly recognize the press operation of the power button PB. 
         [0096]    A diode D 3  is provided between the trigger unit  110  and the switch  120 . 
         [0097]    The diode D 3  is serially connected between the trigger unit  110  and the switch  120 . Specifically, the diode D 3  is connected in a forward direction between the output terminal of the trigger unit  110  and the base of the transistor Q 1  of the switch  120 . 
         [0098]    The diode D 3  prevents the collector and the emitter of the transistor Q 1  of the switch  120  from being electrically connected due to excess voltage applied to the base of the transistor Q 1  even when the power button PB is pressed due to a resistant component that exists on a circuit line connected to the power button PB of the input unit  130 . That is, the diode D 3  provides a threshold voltage to prevent the transistor Q 1  of the switch  120  from being turned on by a voltage generated when the power button PB is operated. 
         [0099]      FIG. 9  is a circuit diagram of a power control apparatus according to an embodiment. 
         [0100]    Referring to  FIG. 9 , the power control apparatus may include a kick start unit  160 . 
         [0101]    The kick start unit  160  is provided between the power controller  140  and the input unit  130 . More specifically, the kick start unit  160  is arranged between the power controller  140  and the barrier diode D 1 . 
         [0102]    The kick start unit  160  is an automatic power on circuit that automatically enables the image forming apparatus when AC power is supplied to the image forming apparatus without pressing the power button PB. When the primary DC power, 24V, supplied from the power supply is divided into 5V by resistors R 99  and R 100  and supplied to a capacitor C 167 , a transistor Q 4  is turned on while the capacitor C 167  is charged. Accordingly, the transistor Q 1  of the switch  120  is turned off so as to enable the DC/DC converter  101  to generate the power (secondary DC power, 5V) necessary for the image forming apparatus from the primary DC power, 24V. Upon completion of charging the capacitor C 167 , the output terminal of the capacitor C 167  is opened to turn off the transistor Q 4 . 
         [0103]    While the color image forming apparatus is exemplified as an image forming apparatus to which the power control apparatus according to an embodiment is applied, embodiments are not limited thereto and can be applied to a black-and-white image forming apparatus. 
         [0104]    Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.