Abstract:
A method of controlling a plurality of output voltages in a multi-output power supply device for generating a plurality of output powers by using a transformer. The method includes, if a system to which power is supplied from the multi-output power supply device is in a standby mode, blocking any one of at least two output powers of a secondary side of the transformer, wherein the blocked power is supplied to the system; and compensating for a resistance of a feedback circuit connected to a switching controller of a power switch of a primary side of the transformer in relation to one or more unblocked output powers of the transformer and maintaining the output of the unblocked output power to be constant.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. application Ser. No. 12/805,678 filed Aug. 12, 2010, which issued as U.S. Pat. No. 8,097,977 which is a continuation of U.S. application Ser. No. 12/023,226 filed Jan. 31, 2008, which issued as U.S. Pat. No. 7,791,222, which claims the benefit of Korean Application No. 2007-59126, filed Jun. 15, 2007, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of the present invention relate to a multi-output power supply device, and more particularly, to a multi-output power supply device which, when power supplied to one output circuit of multiple output circuits is blocked, stably controls power output to other output circuits of the multiple output circuits. 
     2. Description of the Related Art 
     To obtain multiple output voltages from a low-capacity power supply device, a single converter using a single transformer is widely used to generate the multiple output voltages. Since the single converter only uses a single controller, the single converter employs a multi-output sensing (or feedback) circuit that observes and controls output of the multiple output voltages. However, when the feedback circuit is used for a power supply device that is able to switch off some of the multiple output voltages in order to reduce use of standby power during a standby mode, voltages of non-switched off output voltages cannot be controlled within a desired range. 
       FIG. 1  is a block diagram of a typical multi-output power supply device. Referring to  FIG. 1 , power is provided to a transformer  14  according to a switching operation of a first power switch  10  that is controlled by a first switch controller  12 . The transformer  14  transforms the provided power according to its turn ratio and outputs a transformed power to a first output circuit  16  and a second output circuit  18 . If required, the typical multi-output power supply device can have additional output circuits similar to the first output circuit  16  and a second output circuit  18  shown. 
     The first output circuit  16  outputs the transformed power supplied from the transformer  14  to a subsidiary load  24  and the second output circuit  18  outputs the transformed power to a second power switch  20  that switches the transformed power to a main load  26  according to a control of the second power switch  20 . The respective transformed powers output from the first and second output circuits  16  and  18  pass through a feedback circuit  28  and are fed back as signals for controlling the first switch controller  12 . 
     Power switching-off at a secondary side of the transformer  14  is used to restrain unnecessary load power consumption in or during the standby mode. In the standby mode, a standby mode controller of the subsidiary load  24  turns off the second power switch  20  to restrain power supply to the main load  26 . Furthermore, in the standby mode, a value of the subsidiary load  24  is also minimized by a system power sequence, and the typical multi-output power supply device operates with the standby mode controller as a central element that senses an external interrupt to detect when the standby mode is converted into a normal mode. 
     When the typical multi-output power supply device is controlled using a single controller, however, an output voltage of a switched off output circuit from among the multiple output circuits of the power supply device cannot be observed (or determined) so that an error in controlling of the other output voltages is increased. This causes output voltages error to deteriorate control characteristics of the typical multi-output power supply device and to excessively increase the output voltages of the power supply devices so as to destroy a load. 
     SUMMARY 
     Aspects of the present invention provide a multi-output power supply device which, when power applied to one output circuit of the multiple output circuits is blocked, stably controls power output to remaining output circuits of the multiple output circuits. 
     According to an aspect of the present invention, a multi-output power supply device includes: a first power switch to perform a switching operation of a power supply; a first switch controller to control the first power switch; a transformer to transform the power supplied from the first power switch; first through Nth output circuits connected to a secondary side of the transformer, where N is a positive integer greater than 1; a second power switch to switch the power output from one of the first through Nth output circuits; a second switch controller to control the second power switch; a feedback circuit to feed back output voltages of the first through Nth output circuits; and a feedback compensation circuit to perform a switching operation complementarily with the second power switch to compensate for a resistance of the feedback circuit. 
     According to an aspect of the present invention, the feedback circuit includes a plurality of resistors to observe the output voltages of the first through Nth output circuits, and the feedback compensation circuit may be connected in parallel with one of the plurality of resistors. 
     According to an aspect of the present invention, the feedback circuit includes a reference resistor, and the feedback compensation circuit may be connected in parallel with the reference resistor. 
     According to an aspect of the present invention, the feedback compensation circuit may comprise a compensation switch to perform an off switching operation if the second power switch is on and carry out an on switching operation if the second power switch is off, and a compensation resistor serially connected to the compensation switch. 
     According to an aspect of the present invention, a multi-output power supply device includes a first power switch to perform a switching operation of a power supply, a first switch controller to control the first power switch; a transformer to transform the power supplied from the first power switch; first through Nth output circuits connected to a secondary side of the transformer, wherein N is a positive integer greater than 1; a second power switch to switch the power output from one of the first through Nth output circuits; a second switch controller to control the second power switch; a feedback circuit to feed back output voltages of the first through Nth output circuits, the feedback circuit containing a reference resistor and a plurality of resistors corresponding to the first through Nth output circuits; and a feedback compensation circuit to perform an opposite switching operation relative to the second power switch to compensate for a resistance of the feedback circuit. 
     According to an aspect of the present invention, a multi-output power supply device includes a first output circuit to output a first output voltage using an input voltage; a second output circuit to output a second output voltage using the input voltage; a power switch to control supply of the second output voltage to a load; a feedback circuit to output a signal used to control supply of the input voltage using the first output voltage received from the first output circuit and the second output voltage selectively received from the power switch; and a feedback compensation circuit to compensate for a resistance of the feedback circuit when the second output voltage is not received from the power switch. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the aspects, taken in conjunction with the accompanying drawings of which 
         FIG. 1  is a block diagram of a typical multi-output power supply device; 
         FIG. 2  is a block diagram of a multi-output power supply device according to an aspect of the present invention; 
         FIG. 3  is a circuit diagram of a multi-output power supply device according to an aspect of the present invention that includes an aspect of a feedback compensation circuit illustrated in  FIG. 2 ; and 
         FIG. 4  is a circuit diagram of a multi-output power supply device according to another aspect of the present invention that includes an aspect of the feedback compensation circuit illustrated in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to aspects of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The aspects are described below in order to explain the present invention by referring to the figures. 
       FIG. 2  is a block diagram of a multi-output power supply device according to an aspect of the present invention. Referring to  FIG. 2 , the multi-output power supply device includes a first power switch  10  that switches a supply of power, a first switch controller  12  that controls the first power switch  10 , a transformer  14  that transforms the power supplied from the first power switch  10 , a first output circuit  16  and a second output circuit  18  that are connected to a secondary side of the transformer  14 , a second power switch  20  that switches a supply of power output from the second output circuit  18 , a second switch controller  22  that controls the second power switch  20 , and a feedback circuit  28  that feeds back output voltages of the first and second output circuits  16  and  18 . In aspects of the present embodiment, though the multi-output power supply device is shown having the first and second output circuits  16  and  18 , aspects of the present invention are not limited thereto. That is, the multi-output power supply device can include a plurality of output circuits (i.e., N output circuits, where N is a natural number greater than 1). The aforementioned components of the multi-output power supply device are identical to those of the typical multi-output power supply device illustrated in  FIG. 1  so that detailed explanations thereof are omitted. 
     Unlike the typical multi-output power supply device illustrated in  FIG. 1 , the multi-output power supply device according to an aspect of the present invention further includes a feedback compensation circuit  100  to compensate for a resistance of the feedback circuit  28 . Thus, the feedback compensation circuit  100  and the second power switch  20  complementarily perform switching operations, as further described below. 
       FIG. 3  is a circuit diagram of a multi-output power supply device according to an aspect of the present invention that includes an aspect of the feedback compensation circuit  100  illustrated in  FIG. 2 . Referring to  FIG. 3 , a feedback compensation circuit  100 A is connected in parallel with a resistor R 01  used to observe (or detect) an output voltage V 01  of the first output circuit  16 . The resistor R 01  is included in the feedback circuit  28 . 
     The feedback compensation circuit  100 A includes a compensation resistor R comp    102  and a compensation switch  104  such that the compensation resistor R comp  is serially connected to the compensation switch  104 . The compensation switch  104  performs an off switching operation if the second power switch  20  is on, and carries out an on switching operation if the second power switch  20  is off. 
     When a system employing the multi-output power supply device of  FIG. 3  is in a normal operation mode, the second power switch  20  maintains an on state and the compensation switch  104  performs the off switching operation. Accordingly, the feedback compensation circuit  100 A does not operate. If the system is in a standby mode, the second power switch  20  is converted into an off state and the compensation switch  104  performs the on switching operation. Accordingly, the observation resistor R 01  and the compensation resistor R comp  are connected in parallel to each other, and thus, an impedance (or resistance) for observing an output voltage V 01  of the first output circuit  16  is compensated, and then, an output voltage of the multi-output power supply device is uniformly maintained. Consequently, a voltage error observed by the feedback circuit  28  due to erroneous feed back of the output voltage V 01  from the first output circuit  16 , which is caused by the switching-off of the second output circuit  18 , can be compensated. That is, a voltage error, observed by a feedback circuit due to an erroneous feed back of an output voltage from a non switched off output circuit that is caused by a switched off output circuit, can be compensated. In various aspects, one or more of the output circuits may be switched off in the standby mode. 
     In the aspect shown in  FIG. 3 , if values of the resistor R 01  for observing the output voltage V 01  of the first output circuit  16 , a resistor R 02  for observing the output voltage V 02  of the second output circuit  18 , and a reference resistor R ref  for a reference voltage V ref  for the feedback circuit  28 , have values represented by Equation 1, the value of the compensation resistor R comp  is determined by Equation 2. 
     
       
         
           
             
               
                 
                   
                     
                       R 
                       01 
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               V 
                               01 
                             
                             - 
                             
                               V 
                               ref 
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           R 
                           ref 
                         
                       
                       
                         XV 
                         ref 
                       
                     
                   
                   , 
                   
                     
                       R 
                       02 
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               V 
                               02 
                             
                             - 
                             
                               V 
                               ref 
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           R 
                           ref 
                         
                       
                       
                         
                           ( 
                           
                             1 
                             - 
                             X 
                           
                           ) 
                         
                         ⁢ 
                         
                           V 
                           ref 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, X denotes a feedback weight factor, and I ref  is a value a value of a reference current of the feedback circuit  28 . 
     
       
         
           
             
               
                 
                   
                     R 
                     comp 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           
                             V 
                             01 
                           
                           - 
                           
                             V 
                             ref 
                           
                         
                         ) 
                       
                       ⁢ 
                       
                         R 
                         01 
                       
                     
                     
                       
                         
                           R 
                           01 
                         
                         ⁢ 
                         
                           I 
                           ref 
                         
                       
                       - 
                       
                         V 
                         01 
                       
                       + 
                       
                         V 
                         ref 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
       FIG. 4  is a circuit diagram of a multi-output power supply device according to an aspect of the present invention that includes an aspect of the feedback compensation circuit  100  illustrated in  FIG. 2 . Referring to  FIG. 4 , a feedback compensation circuit  100 B is connected in parallel with a reference resistor R ref  of the feedback circuit  28  that includes a compensation resistor R comp    112  and a compensation switch  114 . The compensation resistor R comp    112  is serially connected to the compensation switch  114  that performs an off switching operation when the second power switch  20  is on, and carries out an on switching operation when the second power switch  20  is off. 
     If a system employing the multi-output power supply device is in a normal operation mode, the second power switch  20  is in on state and the compensation switch  114  performs the off switching operation, and thus, the compensation circuit  114  does not operate. If the system is in a standby mode, the second power switch  20  is converted into an off state and the compensation switch  114  performs the on switching operation. Accordingly, the reference resistor R ref  and the compensation resistor R comp  are connected in parallel with each other, and thus, a reference impedance (or resistance) for an output voltage V 01  from the first output circuit  16  is compensated, and thereby the output voltage of the multi-output power supply device is uniformly maintained. 
     If a resistor R 01 , for observing the output voltage of the first output circuit  16 , has the value represented by Equation 1, then a value of the compensation resistor R comp  is determined by Equation 3. 
     
       
         
           
             
               
                 
                   
                     R 
                     comp 
                   
                   = 
                   
                     
                       
                         R 
                         01 
                       
                       ⁢ 
                       
                         R 
                         ref 
                       
                     
                     
                       
                         
                            
                           
                             
                               
                                 V 
                                 01 
                               
                               
                                 V 
                                 ref 
                               
                             
                             - 
                             1 
                           
                            
                         
                         ⁢ 
                         
                           R 
                           ref 
                         
                       
                       - 
                       
                         R 
                         01 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     The aforementioned multi-output power supply device is used for image forming apparatuses including printers, scanners and multi-function peripherals. In other aspects, other devices that use different voltages among its subcomponents may use the aforementioned multi-output power supply device. 
     The multi-output power supply device according to an aspect of the present invention can compensate for a voltage error observed by a feedback circuit when power output to one output circuit of multiple output circuits is blocked, and thus, stably control power output to other output circuits of the multiple output circuits. 
     In  FIGS. 3 and 4 , the reference resistor R ref  is connected between the observation resistors R 01 , R 02 , and a ground. Accordingly, in  FIG. 3 , the feedback compensation circuit  100 A is connected in parallel with the observation resistors R 01  of the feedback circuit  28 . On the other hand, in  FIG. 4 , the feedback compensation circuit  100 B is connected in parallel with the reference resistor R ref  of the feedback circuit  28 . 
     Although a few aspects of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in the aspects without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.