Abstract:
A power supply control apparatus and method are provided. The apparatus includes a controller outputting a first pulse width modulation (PWM) signal for supplying an electric power and a second PWM signal to be compared to the first PWM signal, a first PWM signal input unit converting the second PWM signal to a direct current (DC) signal, a second PWM signal input unit receiving the converted second PWM signal, a comparator comparing the first PWM signal and the converted second PWM signal, a switching unit generating a waveform having a voltage according to the comparison result of the comparator, a transformer transforming the voltage of the generated pulse waveform according to the switching result of the switching unit and a rectifier and voltage divider for rectifying and voltage-dividing the transforming result of the transformer, wherein the controller adjusts the second PWM signal by receiving the rectifying and voltage-dividing result of the rectifier &amp; voltage divider.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2006-0020389, filed on Mar. 3, 2006, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high voltage output device applied to laser printers and laser multi function peripherals (MFPs). More particularly, the present invention relates to a power control apparatus and method for addressing a problem in image quality by constantly controlling an alternating current (AC) power used for developing. 
     2. Description of the Related Art 
     AC power is very important in image forming devices, such as laser beam printers (LBPs), which are a contactless developing method. 
       FIG. 1  is a circuit diagram of an apparatus known in the prior art for controlling electric power supplied to a developing unit. 
     As illustrated in  FIG. 1 , the prior art power control apparatus includes a pulse width modulation (PWM) input unit  10  receiving a PWM signal from an engine controller (CPU: Central Processing Unit) (not shown), a comparator  20  comparing the PWM signal to a reference signal, a switching unit  30  forming a reference comparison output signal using a voltage Vcc, and a transformer  400  transforming a switching result into a high voltage, in order to output an AC power of a high voltage. The AC power output from the transformer  400  is applied to the developing unit. 
     The prior art apparatus is configured to output a constant voltage in response to an input PWM signal. However, since a feedback control is not performed, deviation of an output voltage occurs according to an environment. The variation of the output voltage is caused by an environmental characteristic (temperature/humidity) of each of the components constructing the prior art circuit and the variation of a load (the developing unit) connected to a high voltage output terminal. 
     Thus, if the AC power supplied to the developing unit cannot output a voltage as required by a process, a problem in image quality occurs. That is, if a voltage higher or lower than the required voltage is applied to the developing unit, a problem in image quality occurs. 
     Accordingly, there is a need for an improved power supply apparatus and method of its use. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention address at least the above problems and/or disadvantages and provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a power supply control apparatus and method for supplying an optimal voltage by compensating for an output voltage when a voltage variation occurs according to an environment, a load or other factors. 
     According to an exemplary aspect of the present invention, there is provided a power supply control apparatus comprising a controller outputting a first pulse width modulation (PWM) signal for supplying an electric power and a second PWM signal to be compared to the first PWM signal, a first PWM signal input unit converting the second PWM signal to a direct current (DC) signal, a second PWM signal input unit receiving the converted second PWM signal, a comparator comparing the first PWM signal and the converted second PWM signal, a switching unit generating a pulse waveform having a voltage according to the comparison result of the comparator, a transformer transforming the voltage of the generated pulse waveform according to the switching result of the switching unit and a rectifier and voltage divider for rectifying and voltage-dividing the transforming result of the transformer, wherein the controller adjusts the second PWM signal by receiving the rectifying and voltage-dividing result of the rectifier and voltage divider. 
     According to another exemplary aspect of the present invention, there is provided a power supply control method comprising outputting a first pulse width modulation (PWM) signal for supplying an electric power and a second PWM signal to be compared to the first PWM signal, converting the second PWM signal to a direct current (DC) signal, comparing the first PWM signal to the converted second PWM signal, generating a pulse waveform having a voltage according to the comparison result, transforming the voltage of the generated pulse waveform, rectifying and voltage-dividing the transforming result and adjusting the second PWM signal according to the rectifying and voltage-dividing result. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a circuit diagram of an apparatus known in the prior art for controlling an electric power supplied to a developing unit; 
         FIG. 2  is a block diagram of a power supply control apparatus according to an exemplary embodiment of the present invention; and 
         FIG. 3  is a flowchart illustrating a power supply control method according to an exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention and are merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. Exemplary embodiments of the present invention will now be described more fully with reference to the accompanying drawings. 
       FIG. 2  is a block diagram of a power supply control apparatus according to an exemplary embodiment of the present invention. Referring to  FIG. 2 , the power supply control apparatus includes a controller  100 , a first PWM signal input unit  200 , a second PWM signal input unit  300 , a comparator  400 , a switching unit  500 , a transformer  600 , and a rectifier and voltage divider  700 . 
     The controller  100  outputs a first PWM signal for supplying an electric power and a second PWM signal to be compared to the first PWM signal. 
     The first PWM signal is a signal for supplying an AC power having a high voltage. The second PWM signal is a signal to be compared to the first PWM signal by the comparator  400 . A duty ratio of the second PWM signal is adjusted by the controller  100 . 
     The first PWM signal input unit  200  converts the second PWM signal output from the controller  100  into a DC signal and outputs the conversion result to the second PWM signal input unit  300 . The first PWM signal input unit  200  includes a resistor R 1  and a capacitor C 1  to convert the second PWM signal into the DC signal. 
     The second PWM signal input unit  300  receives the DC-converted second PWM signal from the first PWM signal input unit  200 . The second PWM signal input unit  300  voltage-divides the second PWM signal. To do this, the second PWM signal input unit  300  includes at least two resistors R 2  and R 3 . The second PWM signal input unit  300  outputs the voltage-divided second PWM signal to the comparator  400 . 
     The comparator  400  compares the first PWM signal and the voltage-divided second PWM signal which are input from the second PWM signal input unit  300 , and outputs the comparison result to the switching unit  500 . 
     The switching unit  500  generates a waveform having a voltage VCC 1  according to the comparison result of the comparator  400  and outputs the generated waveform to the transformer  600 . In an exemplary embodiment, the waveform may be a pulse waveform. 
     The switching unit  500  generates the waveform having the voltage VCC 1  according to on/off operations of transistors and includes at least two transistors T r1  and T r2  and at least two resistors R 4  and R 5 . 
     The transformer  600  transforms the voltage of the generated waveform to an AC high voltage according to the switching result of the switching unit  500  and outputs the transformed AC high voltage to a developing unit (not shown) and the rectifier and voltage divider  700 . 
     The rectifier and voltage divider  700  rectifies and voltage-divides the AC high voltage transformed by the transformer  600  and the rectifying and voltage-dividing result to the controller  100 . 
     The rectifier and voltage divider  700  includes at least one diode D 1 , a capacitor C 2 , and resistors R 6  and R 7  to rectify and voltage-divide a positive (+) voltage of the AC high voltage of the transformer  600 . 
     The rectifier and voltage divider  700  also includes at least one diode D 2 , a capacitor C 3 , and resistors R 8  and R 9  to rectify and voltage-divide a negative (−) voltage of the AC high voltage of the transformer  600 . The directions of the diode D 2  and the diode D 1  are opposite to each other. 
     The rectified and voltage-divided negative (−) voltage must be a positive (+) voltage in order to be input to the controller  100 . To do this, a voltage applying unit  800  applies a voltage VCC 2  to the rectifier and voltage divider  700 . The voltage VCC 2  may have a value at least greater than the absolute value of the rectified and voltage-divided negative (−) voltage. The negative voltage becomes a positive voltage by the voltage applying unit  800  supplying the voltage VCC 2 , and the positive voltage is input to the controller  100 . 
     The controller  100  adjusts the second PWM signal by receiving the rectifying and voltage-dividing result from the rectifier and voltage divider  700 . The controller  100  includes an analog-to-digital converter (ADC)  110  for receiving the rectifying and voltage-dividing result of the rectifier and voltage divider  700 . 
     If the controller  100  determines that the output voltage of the transformer  600  is lower than a reference value by referring to the rectifying and voltage-dividing result of the rectifier and voltage divider  700 , the controller  100  adjusts the duty ratio of the second PWM signal to high, and if the controller  100  determines that the output voltage of the transformer  600  is higher than the reference value by referring to the rectifying and voltage-dividing result of the rectifier and voltage divider  700 , the controller  100  adjusts the duty ratio of the second PWM signal to low. For example, if the reference value of the output voltage is set to 1500V, and if it is determined that the output voltage of the transformer  600  is 1200V from the rectifying and voltage-dividing result of the rectifier and voltage divider  700 , the controller  100  increases the amplitude of a DC component of the second PWM signal rectified by the first PWM signal input unit  200  by adjusting the duty ratio of the second PWM signal to high. An increase of the amplitude of a DC component of the second PWM signal compared to the first PWM signal results in an increase of the amplitude of the output voltage to be output from the transformer  600  thereafter. On the contrary, if the reference value of the output voltage is set to 1500V, and if it is determined that the output voltage of the transformer  600  is 1700V from the rectifying and voltage-dividing result of the rectifier and voltage divider  700 , the controller  100  decreases the amplitude of the DC component of the second PWM signal rectified by the first PWM signal input unit  200  by adjusting the duty ratio of the second PWM signal to low. A decrease of the amplitude of a DC component of the second PWM signal compared to the first PWM signal results in a decrease of the amplitude of the output voltage to be output from the transformer  600  thereafter. 
     A power supply control method according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawing. 
       FIG. 3  is a flowchart illustrating a power supply control method according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , in operation  900 , a first PWM signal for supplying an electric power and a second PWM signal to be compared to the first PWM signal are output. 
     The first PWM signal is a signal for supplying an AC power having a high voltage. The second PWM signal is a signal compared to the first PWM signal by the comparator  400  and is used to adjust a duty ratio of the second PWM signal. 
     In operation  902 , the second PWM signal is converted into a DC signal. 
     In operation  904 , the first PWM signal is compared to the converted second PWM signal. 
     In operation  906 , a waveform having a certain voltage is generated according to the comparison result. In an exemplary embodiment, the waveform may be a pulse waveform. 
     In operation  908 , the voltage of the generated waveform is transformed. 
     In operation  910 , the transforming result is rectified and voltage-divided. 
     In the rectifying and voltage-dividing of the transforming result, a positive (+) voltage or a negative (−) voltage of an AC high voltage corresponding to the transforming result is rectified and voltage-divided. 
     The rectified and voltage-divided negative (−) voltage must be a positive (+) voltage in order to be input to the controller  100  of  FIG. 2 . To do this, a voltage VCC 2  is applied to the rectified and voltage-divided negative (−) voltage. The voltage VCC 2  may have a value at least greater than the absolute value of the rectified and voltage-divided negative (−) voltage. The negative voltage becomes a positive voltage by supplying the voltage VCC 2 , and the positive voltage is input to the controller  100  of  FIG. 2 . 
     In operation  912 , the second PWM signal is adjusted according to the rectifying and voltage-dividing result. 
     If it is determined that the transformed voltage is lower than a reference value by referring to the rectifying and voltage-dividing result, the duty ratio of the second PWM signal is adjusted to high, and if it is determined that the transformed voltage is higher than the reference value by referring to the rectifying and voltage-dividing result, the duty ratio of the second PWM signal is adjusted to low. 
     Exemplary embodiments of the present invention can be written as codes/instructions/programs and can be implemented in general-use digital computers that execute the codes/instructions/programs using a computer readable recording medium. Examples of the computer readable recording medium include magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.), optical recording media (e.g., CD-ROMs, or DVDs). It is also envisioned that carrier waves (e.g., transmission through the Internet) can be utilized as an equivalent to a computer readable medium. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains. 
     As described above, by a power supply control apparatus and method according to exemplary embodiments of the present invention, an optimal voltage is supplied by compensating for an output voltage when a voltage variation occurs according to an environment, a load or other factors, an image of good quality can be printed. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.