# Patent

## Title
Multi-output power supply device

## Abstract

A multi-output power supply device includes a first power switch, a first switch controller that controls the first power switch, a transformer that transforms a 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 that switches the power output from one of the first through Nth output circuits, a second switch controller that controls the second power switch, a feedback circuit that feeds back output voltages of the first through Nth output circuits, and a feedback compensation circuit that performs a switching operation complementarily with the second power switch to compensate for a resistance of the feedback circuit. Accordingly, when power output to one of the output circuits is blocked, the multi-output power supply device can stably control the power output to the other output circuits.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2007-59126, filed Jun. 15, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 OF THE INVENTION
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 obvious 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 100A is connected in parallel with a resistor R01 used to observe (or detect) an output voltage V01 of the first output circuit 16. The resistor R01 is included in the feedback circuit 28.
The feedback compensation circuit 100A includes a compensation resistor Rcomp 102 and a compensation switch 104 such that the compensation resistor Rcomp 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 100A 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 R01 and the compensation resistor Rcomp are connected in parallel to each other, and thus, an impedance (or resistance) for observing an output voltage V01 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 V01 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 R01 for observing the output voltage V01 of the first output circuit 16, a resistor R02 for observing the output voltage V02 of the second output circuit 18, and a reference resistor Rref for a reference voltage Vref for the feedback circuit 28, have values represented by Equation 1, the value of the compensation resistor Rcomp is determined by Equation 2.




  
    
      
        
          
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Here, X denotes a feedback weight factor, and Iref is a value of a reference current of the feedback circuit 28.




  
    
      
        
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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 100B is connected in parallel with a reference resistor Rref of the feedback circuit 28 that includes a compensation resistor Rcomp 112 and a compensation switch 114. The compensation resistor Rcomp 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 Rref and the compensation resistor Rcomp are connected in parallel with each other, and thus, a reference impedance (or resistance) for an output voltage V01 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 R01, 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 Rcomp is determined by Equation 3.




  
    
      
        
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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 Rref is connected between the observation resistors R01, R02, and a ground. Accordingly, in FIG. 3, the feedback compensation circuit 100A is connected in parallel with the observation resistors R01 of the feedback circuit 28. On the other hand, in FIG. 4, the feedback compensation circuit 100B is connected in parallel with the reference resistor Rref 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.

## Claims

1. A multi-output power supply device comprising:
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; 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.

2. The multi-output power supply device of claim 1, wherein the feedback compensation circuit is connected in parallel to one or more of a plurality of resistors or a reference resistor.

3. The multi-output power supply device of claim 2, wherein the feedback compensation circuit to perform a switching operation complementarily with the second power switch comprises:
a compensation switch to perform an off switching operation if the second power switch is on and to perform an on switching operation if the second power switch is off; and
a compensation resistor serially connected to the compensation switch.

4. The multi-output power supply device of claim 3, wherein the compensation switch performs the off switching operation if a system employing the multi-output power supply device is in a normal operation mode, and performs the on switching operation if the system is in a standby mode.

5. The multi-output power supply device of claim 1, wherein the feedback circuit includes a reference resistor and the feedback compensation circuit is connected in parallel with the reference resistor.

6. The multi-output power supply device of claim 5, wherein the feedback compensation circuit to perform a switching operation complementarily with the second power switch comprises:
a compensation switch to perform an off switching operation if the second power switch is on and to perform an on switching operation if the second power switch is off; and
a compensation resistor serially connected to the compensation switch.

7. The multi-output power supply device of claim 6, wherein the compensation switch performs the off switching operation if a system employing the multi-output power supply device is in a normal operation mode and performs the on switching operation if the system is in a standby mode.

8. The multi-output power supply device of claim 1, wherein the multi-output power supply device is used for an image forming apparatus.

9. The multi-output power supply device of claim 3, wherein a value of the compensation resistor Rcomp is determined by;




  
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where, R01 is a value of the one resistor that is connected in parallel with the feedback compensation circuit, V01 is the output voltage of the output circuit corresponding to the one resistor, Rref, Vref, and Iref are values of the reference resistor, a corresponding reference voltage, and a reference current, respectively, of the feedback circuit.

10. The multi-output power supply device of claim 6, wherein a value of the compensation resistor Rcomp is determined by;




  
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where, R01 is a value of a resistor for observing the output voltages of one of the first through Nth output circuits, V01 is the output voltage corresponding to the resistor having value of R01, Rref and Vref are values of the reference resistor and a corresponding reference voltage, respectively, of the feedback circuit.

11. The multi-output power supply device of claim 1, wherein the feedback circuit further comprises a reference resistor and a plurality of resistors corresponding to the first through Nth output circuits.

12. The multi-output power supply device of claim 11, wherein the feedback compensation circuit is connected in parallel to one or more of the plurality of resistors or the reference resistor.

13. The multi-output power supply device of claim 11, wherein the feedback compensation circuit comprises:
a compensation switch; and
a compensation resistor serially connected to the compensation switch.

14. The multi-output power supply device of claim 13, wherein the compensation resistor is connected in parallel to one or more of the plurality of resistors or the reference resistor.

15. The multi-output power supply device of claim 13, wherein, when the compensation switch is off, the second power switch is on, and vice versa.

16. A multi-output power supply device comprising:
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.

17. The multi-output power supply device of claim 16, wherein the feedback circuit comprises a reference resistor and a resistor that corresponds to the first output circuit.

18. The multi-output power supply device of claim 17, wherein the feedback compensation circuit is connected in parallel to the resistor that corresponds to the first output circuit or the reference resistor.

19. The multi-output power supply device of claim 18, wherein the feedback compensation circuit comprises:
a compensation switch; and
a compensation resistor serially connected to the compensation switch, and the compensation resistor is connected in parallel to the resistor that corresponds to the first output circuit or the reference resistor.

20. The multi-output power supply device of claim 16, wherein the feedback compensation circuit comprises:
a compensation switch; and
a compensation resistor serially connected to the compensation switch.