Abstract:
An energy effective switching power supply apparatus and an energy effective method thereof. The energy effective switching power supply apparatus includes a power transforming part having first and second coils to induce a voltage to the second coil using interactions between the first and the second coils with respect to the input voltage, a power outputting part to output a sensing signal when it is determined that a first DC voltage output by rectifying and smoothing the voltage induced to the second coil is greater than or equal to a reference voltage level, and a switching controlling part to adjust a switching frequency of a switching device to interrupt a current flowing in the first coil of the power transforming part when the sensing signal is received. Accordingly, a switching loss is controlled and an energy loss is reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 2005-89890, filed Sep. 27, 2005, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to an energy effective switching power supply apparatus and an energy effective method thereof. More particularly, the present general inventive concept relates to an energy effective switching power supply apparatus and an energy effective method thereof that saves energy by improving power efficiencies of an SMPS (Switching Mode Power Supply) used as a switching power apparatus in electronics appliances. 
     2. Description of the Related Art 
     Generally, an SMPS (Switching Mode Power Supply) is used as a switching power supply apparatus in an image forming apparatus, such as a printer. The SMPS refers to an apparatus that rectifies an AC (alternating current) voltage externally input and supplies the rectified voltage to each part of an electronics appliance. 
     The SMPS reduces power loss by having a switching device operating in a switching mode to reduce power loss, and is compact-sized by use of a high frequency power transformer. The SMPS is designed to simultaneously output DC voltages (Direct current) having different amplitudes. For example, it is possible to simultaneously output DC voltages of 3.3V or 5V supplied to a main power supply in a printer, and a DC voltage of 24V supplied to a HVPS (High Voltage Power Supply) and a printing engine part. 
       FIG. 1  illustrates a conventional switching power supply apparatus. 
     Referring to  FIG. 1 , the switching power supply apparatus includes an external power inputting part  10 , a rectifying part  20 , a switching controlling part  30 , a power transforming part  40 , a first power outputting part  50 , a second power outputting part  60 , and a feedback circuit part  70 . 
     The external power inputting part  10  receives an AC power from an external power supply (not shown) as an input. The rectifying part  20  rectifies the input AC power using a bridge diode (not shown) and a capacitor (not shown), and outputs a DC power. The DC power output from the rectifying part  20  is supplied to a first coil of a power transformer of the power transforming part  40 , and the power transforming part  40  induces a voltage to a second coil by interactions between the first coil and the second coil. 
     The switching controlling part  30  interrupts electric current flowing in the first coil of the power transforming part  40  and controls the voltage induced to the second coil of the power transforming part  40 . The voltage induced to the second coil of the power transforming part  40  is rectified and smoothed by a first power outputting part  50  and a second power outputting part  60 , respectively. The first power outputting part  50  outputs a first DC voltage Va as a first output voltage, and the second power outputting part  60  outputs a second DC voltage Vb as a second output voltage. 
     The switching controlling part  30  has a PWM-IC (Pulse Width Modulation-integrated Circuit)  35 , and the PWM-IC  35  is connected to the first coil of the power transforming part  40  through a transistor TR 1 . An OUT terminal of the PWM-IC  35  turns on/off the transistor TR 1 , interrupts the current flowing in the first coil and controls the voltage induced to the second coil of the power transforming part  40 . 
     A diode D 1 , a resistance R 1 , and a first capacitor C 1  rectify and smooth a current flowing in an auxiliary coil of the power transforming part  40  and supply an operating power to a Vcc terminal of the PWM-IC  35 . A switching frequency is determined with respect to the transistor TR 1  output to the OUT terminal by a capacitance of a second capacitor C 2  connected to a CT terminal of the PWM-IC  35 . 
     The feedback circuit part  70  senses the second output voltage of the second power outputting part  60  and transmits a feedback signal to an FB terminal of the PWM-IC  35 . An operation of the PWM-IC  35  is determined according to the transmitted feedback signal. That is, when the second output voltage of the second power outputting part  60  is higher than a reference voltage, the feedback circuit part  70  transmits a feedback signal instructing the PWM-IC  35  to stop operating. 
     Likewise, the conventional switching power supply apparatus switches the transistor TR 1  ON or OFF at a uniform frequency all the time, regardless of changes of the first and second output voltages Va and Vb, respectively, and accordingly, a switching loss is incurred and unnecessary power consumption occurs. If an output current of the first power outputting part  50  rises, the second output voltage of the second power outputting part  60  rises by cross regulation, and an apparatus that is supplied with the second output voltage by the second power outputting part  60  may be damaged by the increase in the second output voltage. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides an energy effective switching power supply apparatus and an energy effective method thereof to adjust a switching frequency of a PWM-IC (Pulse Width Modulation-integrated Circuit) in order to prevent unnecessary power consumption and damages caused by overvoltage. 
     Additional aspects of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     The foregoing and/or other aspects of the present general inventive concept may be achieved by providing a switching power supply apparatus including a power transforming part having first and second coils to induce voltage to the second coil using interactions between the first and the second coils with respect to an input voltage received on the first coil, a power outputting part to output a sensing signal when it is determined that a first DC voltage output by rectifying and smoothing the voltage induced to the second coil is greater than or equal to a reference voltage level, and a switching controlling part to adjust a switching frequency of a switching device to interrupt a current flowing in the first coil of the power transforming part when the sensing signal is received. 
     The power outputting part may output the sensing signal by operating an LED (Light Emitting Diode) when the first DC voltage output is greater than or equal to the reference voltage level. 
     A capacitance may be changed by a photo transistor operated by the LED to serve as a photo coupler, and the switching controlling part may adjust the switching frequency of the switching device based on the changed capacitance. 
     When the first DC voltage is greater than or equal to the reference voltage level, the LED of the power outputting part is operated by a photo programmable shunt diode. 
     The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a power supply apparatus, including a transformer to receive an input voltage at a first coil and to output at least one output voltage on at least one second coil, a controller to switch the transformer ON and OFF at two or more operating frequencies to regulate the at least one output voltage according to a feedback signal, and at least one power output part to receive the at least one output voltage from the transformer, to output at least one output DC voltage, and to provide a first feedback signal to the controller to decrease the frequency with which the transformer is switched when the at least one output DC voltage is greater than a reference voltage level. 
     The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing an energy effective method of a switching power supply apparatus, the method including receiving an input voltage on a first coil of a power transforming part including the first coil and a second coil, inducing a voltage to the second coil using interactions between the first and the second coils with respect to the input voltage, outputting a sensing signal when a DC voltage output by rectifying and smoothing the voltage induced to the second coil is determined to be greater than or equal to a reference voltage level, and adjusting a switching frequency of a switching device to interrupt a current flowing in the first coil when the sensing signal is received. 
     The outputting of the sensing signal may include outputting the sensing signal by operating an LED when the DC voltage is greater than or equal to the reference voltage level. 
     The adjusting of the switching frequency of the switching device may include changing a capacitance by operating a photo transistor with the LED to serve as a photo coupler. 
     The outputting of the sensing signal may include operating the LED with a photo programmable shunt diode when the DC voltage is greater than or equal to the reference voltage level. 
     The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a method of switching power, the method including transforming an input voltage received on a first coil of a transformer to induce at least one output voltage on a second coil, interrupting current flowing through the first coil of the transformer and inducement of the at least one output voltage on the second coil according to a switching control signal, rectifying the at least one output voltage induced on the second coil to at least one DC output voltage, determining whether the at least one DC output voltage is greater than a reference voltage, and operating a photocoupler to adjust a frequency of the switching control signal when it is determined that the at least one DC output voltage is greater than the reference voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above aspects of the present general inventive concept will be more apparent by describing certain embodiments of the present general inventive concept with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a conventional switching power supply apparatus; 
         FIG. 2  illustrates a switching power supply apparatus according to an embodiment of the present general inventive concept; 
         FIG. 3  illustrates a second power outputting part according to an exemplary embodiment of the present general inventive concept; and 
         FIG. 4  is a flowchart illustrating an operation of the switching power supply apparatus according to an embodiment of the present general inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
       FIG. 2  illustrates a switching power supply apparatus according to an embodiment of the present general inventive concept. 
     Referring to  FIG. 2 , the switching power supply apparatus includes an external power inputting part  100 , a rectifying part  110 , a switching controlling part  130 , a power transforming part  150 , a first power outputting part  160 , a second power outputting part  170 , and a feedback circuit part  190 . 
     The external power inputting part  100  receives an AC (Alternating Current) power from an external power supply (not shown) as an input. 
     The rectifying part  110  rectifies the input AC power and outputs a DC (Direct Current) voltage (power) using, for example, a bridge diode (not shown) and a capacitor (not shown). The DC voltage output from the rectifying part  110  is supplied to a first (or primary) coil of the power transforming part  150 . 
     The power transforming part  150  induces a voltage to a second (or secondary) coil and an auxiliary coil by interactions between the first coil and the second coil. The auxiliary coil is connected to the switching controlling part  130 . 
     The switching controlling part  130  interrupts a current flowing through the first coil of the power transforming part  150 , thereby controlling the voltage induced to the second coil and the auxiliary coil of the power transforming part  150 . The switching controlling part  130  includes a PWM-IC (Pulse Width Modulation-integrated Circuit)  135 , transistors TR 1  and TR 2 , capacitors C 1 , C 2 , and C 3 , diodes D 1  and D 2 , and a resistance R 1 . 
     The PWM-IC  135  is connected to one end of the first coil of the power transforming part  150  through the transistor TR 1 . The transistor TR 1  may be a MOSFET (Metal oxide Semiconductor Field Effect). An OUT terminal of the PWM-IC  135  controls the voltage induced to the second coil and the auxiliary coil of the power transforming part  150  by turning the transistor TR 1  ON and OFF, thereby interrupting the current of the first coil. 
     The diode D 1 , the resistance R 1 , and the capacitor C 1  rectify and smooth a current flowing in the auxiliary coil of the power transforming part  150  and supply a Vcc terminal of the PWM-IC  135  with operating power to operate the PWM-IC  135 . 
     A CT terminal of the PWM-IC  135  determines a switching frequency output to the OUT terminal of the PWM-IC  135 , and the switching frequency is determined by a capacitance of the capacitor C 2  connected to the CT terminal. The transistor TR 2  may be a phototransistor. When the phototransistor TR 2  turns OFF in  FIG. 2 , the switching frequency is determined by the capacitance C 2 . When the phototransistor TR 2  turns ON, the switching frequency is determined by the capacitances C 2  and C 3 . Since the capacitance at the CT terminal of the PWM-IC  135  increases by parallel connections between the capacitors C 2  and the C 3 , the switching frequency decreases. 
     The voltage induced to the second coil of the power transforming part  150  is rectified and smoothed at the first and second power outputting parts  160  and  170 , respectively. The first power outputting part  160  outputs a first DC voltage Va as a first output voltage, and the second power outputting part  170  outputs a second DC voltage Vb as a second output voltage. The switching power supply apparatus may alternatively include a greater number of power outputting parts. 
     The second power outputting part  170  includes coils L 1  and L 2  (i.e., inductances), diodes D 2  through D 5 , capacitors C 4  and C 5 , resistances R 2  through R 6 , and a transistor TR 3 . 
     The coil L 2  is used for a forward converter, and is charged with a current when a high voltage is supplied to the first coil of the power transforming part  150 . When a low voltage is supplied to the first coil of the power transforming part  150 , the current charged at the coil L 2  flows through the capacitor C 5  and the diode D 4 , and the current charged at the coil L 2  supplements current shortages and outputs the second DC voltage Vb. 
     The coil L 1  may be a MAG-AMP coil used for a magnetic amplifier. The magnetic amplifier controls load current by changes in an input current, using the fact that reactance of a coil changes depending on a current level thereof. That is, the magnetic amplifier prevents the first outputting part  160  from causing cross regulation to occur at the second power outputting part  170 . 
     For example, if the current of the first power outputting part  160  rises and the second output voltage of the second power outputting part  170  increases, current “i” which represents the current charged at the coil L 1  flows through the diode D 3  and the transistor TR 3 , and the diode D 2  is turned ON. The transistor TR 3  is turned ON by the diode D 5  (e.g., Programmable Shunt Diode or Zener diode) operating when the second output voltage Vb is greater than or equal to a first reference voltage. 
     When the second output voltage Vb is greater than or equal to the first reference voltage, the diode D 2  is turned ON, and the diode D 2  of the second power outputting part  170  and the transistor TR 2  of the switching controlling part  130  are operated by a photo coupler. Accordingly, the capacitor C 2  and the capacitor C 3  are connected in parallel to the CT terminal of the PWM-IC  135  and the switching frequency output to the OUT terminal decreases, to reduce a switching loss. 
     The feedback circuit part  190  senses the second output voltage Vb of the second power outputting part  170  and transmits a feedback signal to an FB terminal of the PWM-IC  135 . When the second output voltage of the second power outputting part  170  is greater than or equal to a second reference voltage, the feedback circuit part  190  transmits a stop feedback signal to stop an operation of the PWM-IC  135 . Voltages of different levels may be used as the second reference voltage of the feedback circuit part  190  and the first reference voltage determined by the diode D 5 , respectively. In particular, the second reference voltage may be greater than the first reference voltage. Since general feedback circuits should be known to those of ordinary skill in the art, a detailed description of the feedback circuit part  190  will not be provided here. 
       FIG. 3  illustrates another example of a second power outputting part  170 ′. 
     Referring to  FIGS. 2 and 3 , in the second power outputting part  170 ′ of the switching power supply apparatus, a diode D 6  is operated with the transistor TR 2  as the photo coupler. 
     More particularly, when the second output voltage Vb of the second power outputting part  170  is greater than or equal to the first reference voltage, the diode D 5  operates, the current “i” flows and the diode D 6  turns ON. Accordingly, the capacitors C 2  and C 3  (see  FIG. 2 ) are connected in parallel to the CT terminal of the PWM-IC  135 . The switching frequency output to the OUT terminal decreases and the switching loss decreases. 
       FIG. 4  is a flowchart illustrating an operation of the switching power supply apparatus according to an embodiment of the present general inventive concept. The operation of the switching power supply apparatus is described below with reference to  FIGS. 2 and 3 . 
     Referring to  FIGS. 2 and 4 , when the external power is input (operation S 200 ), the input external power is rectified and converted into the DC voltage. That is, the rectifying part  110  rectifies the external power input through the external power inputting part  100  using, for example, the bridge diode (not shown) and the condenser (not shown), and outputs the DC voltage (operation S 210 ). 
     The PWM-IC  135  controls interruption of the current flowing in the first coil of the power transforming part  150  and the inducement of the voltage to the second coil. In other words, the DC voltage output from the rectifying part  110  is supplied to the first coil of the power transforming part  150  and the switching controlling part  130  interrupts the current flowing in the first coil of the power transforming part  150 , thereby controlling the voltage induced to the second coil (operation S 220 ). 
     The first and the second power outputting parts  160  and  170  (or  170 ′) rectify and smooth the voltage induced to the second coil, and output the first and second output voltages Va and Vb, respectively (operation S 230 ). 
     When the second output voltage output by the second power outputting part  170  (or  170 ′) is greater than or equal to the first reference voltage at operation S 240 , the photo coupler is operated by the current “i.” That is, if the second output voltage Vb is greater than or equal to the reference voltage, the current “i” charged to the coil L 1  turns ON the diode D 2  (see  FIG. 2 ) or the diode D 6  (see  FIG. 3 ). When the diode D 2  or the diode D 6  are turned on, the transistor TR 2  is operated by the diode D 2  or the diode D 6 , and the photo coupler is turned ON. 
     Accordingly, the capacitor C 2  and the capacitor C 3  are connected in parallel to the CT terminal of the PWM-IC  135  such that the switching frequency output to the OUT terminal decreases, and the switching loss decreases. 
     The cross regulation is finished, and when the second output voltage Vb is maintained less than or equal to the first reference voltage, the current “i” does not flow, and the diode D 2  (see  FIG. 2 ) or the diode D 6  (see  FIG. 2 ) stop emitting the light. Finally, the capacitance connected to the CT terminal of the PWM-IC  135  gets normalized (i.e., back to C 2 ) and the switching frequency gets back to an original state. The method may further include a feedback operation performed by the feedback circuit part  190 . For example, the feedback operation may be performed continuously, periodically, or as part of the operation S 240 . As described above, the feedback operation can be used to cut off operation of the PWM-IC  135  when the second output voltage Vb is greater than or equal to the second reference voltage. 
     As described above, the coil L 1  is actively operated when a sensed output voltage (i.e., the second output voltage Vb) is greater than or equal to a certain voltage level (i.e., the first reference voltage). As the second output voltage Vb increases, a switching frequency of the PWM-IC  135  decreases, so that switching loss decreases such that unnecessary power consumption and overvoltage-causing damage can be prevented. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will 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 general inventive concept, the scope of which is defined in the appended claims and their equivalents.