Abstract:
A multiple power supply unit includes two DC stabilized power supplies that provide electrical power in parallel to a load, each power supply providing its own operation indication to the other power supply. Each power supply changes a reference voltage used to detect excess current of its own output to the load according to whether the operation indication is received from the other power supply.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention generally relates to a multiple power supply unit comprising a plurality of DC stabilized power supplies that provides a constant voltage in parallel to a single common load. 
     More particularly, the present invention relates to a multiple power supply unit comprising a plurality of DC stabilized power supplies, each power supply having improved sensitivity to an overcurrent state of output current to the single common load during operation. 
     II. Background and Material Information 
     FIG. 3 is a block diagram depicting the configuration of a conventional DC stabilized power supply unit, namely, a DC/DC converter  300 . 
     DC/DC converter  300  comprises a DC voltage supply  1 , a switching element  2 , a transformer  3 , diodes  4 ,  5 , and  6 , an inductor  7 , an electrolytic capacitor  8 , a sense resistor  9 , and a load  10 . Sense resistor  9  is connected between a negative electrode of transformer  3  and load  10 . An overcurrent detection circuit  11  is connected to both ends of sense resistor  9 . Overcurrent detection circuit  11  comprises an amplification circuit  12 , a resistor  13 , a comparator  14 , and a Zener diode  15 , and detects excess current based on a voltage across sense resistor  9 . Amplification circuit  12  comprises an amplifier  16 , and resistors  17  and  18 . An output from overcurrent detection circuit  11  (hereinafter referred to as an “overcurrent signal”) is inputted to an alarm latch circuit  19 . When receiving an output from alarm latch circuit  19  (hereinafter referred to as an “alarm signal”), a voltage control circuit  20  controls switching element  2  to stop generating pulses. 
     Next, the operation of overcurrent detection circuit  11  will be described. An amplified voltage across sense resistor  9 , which corresponds to an output current to load  10 , is compared with a reference voltage V Z , by comparator  14 . The reference voltage V Z  is a value used to determine whether the output current is in a state of overcurrent. That is, when the voltage across sense resistor  9  exceeds the reference voltage V Z , the output current is determined to be in a state of overcurrent. 
     When detecting the state of overcurrent, overcurrent detection circuit  11  outputs the overcurrent signal to alarm latch circuit  19 . Alarm latch circuit  19  holds the overcurrent state and releases the state when it receives a release signal from another circuit (not shown in FIG.  3 ). While alarm latch circuit  19  holds the overcurrent state, voltage control circuit  20  outputs the alarm signal which causes switching element  2  to switch off. When the input is cut off in this way, DC/DC converter  300  shifts to a state in which it provides no output. 
     Recently, an electronic device in which two DC/DC converters are connected in parallel to a single common load to achieve improved reliability, has been provided. In this device, even when one of the DC/DC converters fails, the other continues to provide a load with a constant voltage. Therefore, this device can be used in a computer system which requires continuous operation, such as a non-stop server computer. 
     FIG. 4 is an exemplary graph depicting the volt-ampere characteristic of two DC/DC converters. In this device, while both DC/DC converters provide power to the load (hereinafter referred to as “two converter operation”) in parallel, the output current from each DC/DC converter is one-half of the value output when a single DC/DC converter provides power to the load (hereinafter referred as to “single converter operation”). However, in this case of both converters being provided as DC/DC converter  300 , even if the output current is one-half during two converter operation, the reference voltage V Z  is the same as during single converter operation. As a result, the sensitivity of each of the two DC/DC converters to an overcurrent state of output is deteriorated during double operation. 
     Therefore, there is a need for a high-reliability multiple power supply unit, which maintains its sensitivity to an overcurrent state of output even when two DC stabilized power supply units are connected in parallel to a single common load. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention solves the problem in the art related to the sensitivity to an overcurrent by providing a multiple power supply unit. The multiple power supply unit comprises a plurality of individual power supplies, including first and second power supplies, which provide electrical power in parallel to a load. Each individual power supply includes: an overcurrent detection circuit for detecting excess output current to the load relative to a reference value, means for providing an operation indication of the individual power supply, each of the first and second power supplies coupled to receive the operation indication of the second and first power supplies, respectively, and a reference value circuit for changing the reference value when the operation indication is received. 
     Also in accordance with the present invention, there is provided a multiple power supply unit. The multiple power supply unit comprises a plurality of individual power supplies, including first and second power supplies, which provide electrical power in parallel to a load. Each individual power supply includes: means for detecting excess output current to the load relative to a reference value, means for providing an operation indication of the individual power supply, each of the first and second power supplies coupled to receive the operation indication of the second and first power supplies, respectively, and means for changing the reference value when the operation indication is received. 
     Further in accordance with the present invention, there is provided a multiple power supply unit. The multiple power supply unit comprises first and second power supplies which provide electrical power in parallel to a load. Each power supply includes: a transformer including a primary circuit and a secondary circuit, the primary circuit connecting to a power source, and the secondary circuit connecting to the load, means for extracting a voltage generated across a resistor in the secondary circuit, means for detecting excess output current to the load by comparing the generated voltage to a reference voltage, means for controlling an input to the primary circuit from the power source, based on whether the excess current is detected, means for providing an operation indication of the power supply, each of the first and second power supplies coupled to receive the operation indication of the second and first power supplies, respectively, and means for changing the reference voltage when the operation indication is received. 
     Additionally in accordance with the present invention, there is provided a power supply. The power supply for use in a multiple power supply unit that includes a plurality of the power supplies which provide electrical power in parallel to a load. The power supply comprises: an overcurrent detection circuit for detecting excess output current to the load relative to a reference value, means for providing an operation indication of the power supply to another one of the power supplies, means for receiving the operation indication from another one of the power supplies, and a reference value circuit for changing the reference value when the operation indication is received. 
     Also in accordance with the present invention, there is provided a power supply. The power supply for use in a multiple power supply unit that includes a plurality of the power supplies which provide electrical power in parallel to a load. The power supply comprises: means for detecting excess output current to the load relative to a reference value, means for providing an operation indication of the power supply to another one of the power supplies, means for receiving the operation indication from another one of the power supplies, and means for changing the reference value when the operation indication is received. 
     Further in accordance with the present invention, there is provided a power supply for use in a multiple power supply unit that includes first and second power supplies which provide electrical power in parallel to a load. The power supply comprises: a transformer including a primary circuit and a secondary circuit, the primary circuit connecting to a power source, and the secondary circuit connecting to the load, means for extracting a voltage generated across a resistor in the secondary circuit, means for detecting excess output current to the load by comparing the generated voltage to a reference voltage, means for controlling an input to the primary circuit from the power source, based on whether the excess current is detected, means for providing an operation indication of the power supply, each of the first and second power supplies to receive the operation indication of the second and first power supplies, respectively, and means for changing the reference voltage when the operation indication is received. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments and/or features of the invention and together with the description, serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is an exemplary block diagram depicting the configuration of a multiple power supply unit according to the principles of the present invention; 
     FIG. 2 is another exemplary block diagram depicting the configuration of a multiple power supply unit according to the principles of the present invention; 
     FIG. 3 is a block diagram depicting the configuration of a conventional DC stabilized power supply unit; and 
     FIG. 4 is an exemplary graph depicting the volt-ampere characteristic of two DC/DC converters. 
    
    
     DETAILED DESCRIPTION 
     The various aspects and features of the present invention will be hereinafter described with reference to the accompanying drawings. 
     FIG. 1 is an exemplary block diagram depicting the configuration of a multiple power supply unit  100 , according to the principles of the present invention. 
     Multiple power supply unit  100  comprises two individual DC/DC converters  110  that are substantially the same and connected in parallel with a single common load  120 . DC/DC converter  110  comprises a DC voltage supply  122 , a switching element  124 , a transformer  126 , diodes  128 ,  130 , and  132 , an inductor  134 , a smoothing electrolytic capacitor  136 , and a sense resistor  138 . Sense resistor  138  is connected between a negative electrode of transformer  126  and load  120 . An indication providing circuit  140  comprises a transistor  142 , and resistors  144  and  146 . Resistors  144  and  146  are connected in series, and a base of transistor  142  is connected to a connection point between resistors  144  and  146 . Indication providing circuit  140  is connected between an input side of diode  132  and a ground terminal [GND]. 
     Indication providing circuit  140  provides an indication (hereinafter referred to as an “operation indication”) of the operation of DC/DC converter  110  with which it is associated to the other DC/DC converter  110  of unit  100 . Thus, the operation indication is transmitted from one of DC/DC converters  110  to the other DC/DC converter  110 . Each DC/DC converter  110  includes an output terminal [INS], connected to transistor  142 , and an input terminal [OCC]. The [INS] and [OCC] of one DC/DC converter  110  are respectively connected with the [OCC] and [INS] of the other, so that each DC/DC converter  110  can transmit the operation indiation to the other. 
     An overcurrent detection circuit  150  is connected to both ends of sense resistor  138 . Overcurrent detection circuit  150  comprises amplifier  152 , and resistors  154 ,  156 ,  158 ,  160 , and  162 , a comparator  164 , and a Zener diode  166 , and detects excess current based on the voltage across sense resistor  138 . A supply voltage V CC  is connected to resistor  154  and input terminal [OCC] is connected to resistor  162 . Overcurrent detection circuit  150  outputs an overcurrent signal to an alarm latch circuit  168  which, in turn, provides an output signal to a voltage control circuit  170 . In response to the overcurrent signal held in latch circuit  168 , voltage control circuit  170  controls switching element  124  to stop generating pulses. Voltage control circuit  170  also controls the output voltage to load  120  based on a voltage at an input side of diode  132 . 
     Next, an operation of this embodiment will be described. 
     When each DC/DC converter  110  normally operates, the voltage at the input side of diode  132  is applied to transistor  142  via resistor  144  and transistor  142  in turned on, i.e., becomes conductive. While both DC/DC converters  110  operate, current flows from supply voltage V CC  to the [OCC] through resistors  154 ,  160 , and  162 . Subsequently, the current flows from the [OCC] of DC/DC converter  110  to the [GND] of the other DC/DC converter  110  via the [INS] of the other DC/DC converter  110  and transistor  142  of the other DC/DC converter  110 . 
     In other words, each DC/DC converter  110  transmits a low level signal, such as 0.0V-0.6V, as an operation indication via its own output terminal [INS] to the input terminal [OCC] of the other DC/DC converter  110 . Meanwhile, each DC/DC converter  110  receives the low level signal via its own [OCC] from the [INS] of the other DC/DC converter  110 . 
     A voltage generated at a connection point between resistors  160  and  162  is inputted to comparator  164  as a reference voltage V Z ′. 
     In overcurrent detection circuit  150 , the voltage across sense resistor  138  amplified by amplifier  152  is compared with the reference voltage V Z ′ by comparator  164 . When the voltage across sense resistor  138  exceeds the reference voltage V Z ′, it is determined that DC/DC converter  110  is providing load  120  with excess current. 
     When detecting the state of overcurrent, overcurrent detection circuit  150  outputs the overcurrent signal to alarm latch circuit  168 . Alarm latch circuit  168  holds the overcurrent signal and is in an overcurrent state. Alarm latch circuit  168  releases the state when it receives a release signal from another circuit (not shown in FIG.  1 ). While alarm latch circuit  168  is in the overcurrent state, voltage control circuit  170  outputs a signal controlling switching element  124  to switch off. As a result of the input to transformer  126  being cut off in this way, DC/DC converter  110  shifts to a state in which it provides no output. 
     If resistance values of resistors  160  and  162  are set equal to each other, the reference voltage V Z ′ is one-half of a reference voltage V Z , which is the reference value during single converter operation. When only one DC/DC converter  110  provides power supply during single converter operation, its own [OCC] is open. Therefore, current flows from the supply voltage V CC  to its own [GND] through resistor  154  and Zener diode  166 , and does not flow to its own [OCC] through resistors  154 ,  160 , and  162 . As a result, the reference voltage of DC/DC converter  110  during single converter operation is twice the voltage which is determined by dividing the supply voltage V CC  based on a ratio of resistor  154  to Zener diode  166 , namely, V Z ′, which is the reference voltage during two converter operation. 
     As shown in FIG. 4, the output current from conventional DC/DC converter  300  during two converter operation is one-half the output during single converter operation. However, the reference voltage V Z  of overcurrent detection circuit  150  is the same. On the other hand, in DC/DC converter  110 , the reference voltage V Z ′ of overcurrent detection circuit  150  during two converter operation is one-half the voltage V Z  during single converter operation. Therefore, even during two converter operation, overcurrent detection circuit  150  has the same sensitivity to an overcurrent state of output during single converter operation. 
     FIG. 2 is another exemplary block diagram depicting the configuration of a multiple power supply unit  200 , according to the principles of the present invention. 
     Multiple power supply unit  200  comprises two individual DC/DC converters  210  that are substantially the same and connected in parallel to single common load  120 . 
     DC/DC converter  210  comprises components that are the same as those of DC/DC converter  110  including DC voltage supply  122 , switching element  124 , transformer  126 , diodes  128 ,  130 , and  132 , inductor  134 , smoothing electrolytic capacitor  136 , sense resistor  138 . Sense resistor  138  is connected between a negative electrode of transformer  126  and load  120 . An operation indication is transmitted from one of DC/DC converters  210  to the other DC/DC converter  210 . Each DC/DC converter  210  includes output terminal [INS], connected to the common connection between capacitor  136  and resistor  138 , and input terminal [OCC]. The [INS] and [OCC] of one DC/DC converter  210  are respectively connected with the [OCC] and [INS] of the other, so that each DC/DC converter  210  can transmit a multiple operation recognition signal to the other. 
     Overcurrent detection circuit  150  is connected to both ends of sense resistor  138 . Overcurrent detection circuit  150  comprises amplifier  152 , and resistors  154 ,  156 ,  158 ,  160 , and  162 , comparator  164 , and Zener diode  166 , and detects excess current based on the voltage across sense resistor  138 . Supplying voltage V CC  is connected to resistor  154  and input terminal [OCC] is connected to resistor  162 , overcurrent detection circuit  150  outputs an overcurrent signal to alarm latch circuit  168 , which, in turn, provides an output signal to voltage control circuit  170 . In response to the overcurrent signal held in alarm latch circuit  168 , voltage control circuit  170  controls switching element  124  to stop generating pulses. 
     Next, an operation of this embodiment will be described. 
     When each DC/DC converter  210  normally operates, a voltage at its own input terminal [GND] is outputted as the operation indication via its own output terminal [INS] to the input terminal [OCC] of other DC/DC converter  210 . Meanwhile, each DC/DC converter  210  receives the voltage at terminal [GND] of the other DC/DC converter  210  via its own input terminal [OCC]. 
     In this case, current flows from supply voltage V CC  to the [OCC] through resistors  154 ,  160 , and  162 . A voltage generated at a connection point between resistors  160  and  162  is inputted to comparator  164  as reference voltage V Z ′. 
     In overcurrent detection circuit  150 , the voltage across sense resistor  138  amplified by amplifier  152  is compared with the reference voltage V Z ′ by comparator  164 . When the voltage across sense resistor  138  exceeds the reference voltage V Z ′, it is determined that DC/DC converter  210  is providing load  10  with excess current. 
     When detecting the state of overcurrent, overcurrent detection circuit  150  outputs the overcurrent signal to alarm latch circuit  168 . Alarm latch circuit  168  holds the overcurrent signal and is in an overcurrent state. Alarm latch circuit  168  releases the state when it receives a release signal from another circuit (not shown in FIG.  2 ). While alarm latch circuit  168  is in the overcurrent state, voltage control circuit  170  outputs a signal controlling switching element  124  switch off. As a result of the input to transformer  126  being cut off in this way, DC/DC converter  210  shifts to a state in which it provides no output. 
     If resistance values of resistors  160  and  162  are set equal to each other, the reference voltage V Z ′ is one-half of a reference voltage V Z , which is the reference value during single converter operation. When only one DC/DC converter  210  provides power supply during single converter operation, its own input terminal [OCC] is open. Therefore, current flows from the supply voltage V CC  to its own terminal [GND] through resistor  154  and Zener diode  166 , and does not flow to its own input terminal [OCC] through resistor  154 ,  160 , and  162 . As a result, the reference voltage of DC/DC converter  210  during single converter operation is twice the voltage which is calculated by dividing the supply voltage V CC  based on a ratio of resistor  154  to Zener diode  166 , namely, V Z ′, which is the reference voltage during two converter operation. 
     As shown in FIG. 4, the output current from DC/DC converter  300  during two converter operation is one-half the output during single converter operation. However, the reference voltage V Z  of overcurrent detection circuit  150  is same. On the other hand, in DC/DC converter  210 , the reference voltage V Z ′ of overcurrent detection circuit  150  during two converter operation is one-half the reference voltage V Z  during single converter operation. Therefore, even during two converter operation, overcurrent detection circuit  150  has the same sensitivity to an overcurrent state of output during single converter operation. 
     As described above, consistent with the principles of the present invention, each DC stabilized power supply unit recognizes a state of two converter operation when receiving an operation indication from the other DC stabilized power supply unit. In response, the DC stabilized power supply unit corrects its reference voltage for detecting excess current to a value suitable for two converter operation. Therefore, the sensitivity to an overcurrent state of output to a load during two converter operation is the same as during single converter operation. 
     While embodiments of the present invention have been disclosed including two DC/DC converters, the invention is not so limited. The principle of the invention can be practiced in multiple power supply unit comprising three or more DC/DC converters. 
     Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present invention being indicated by the following claims.