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In the case where there coexist general loads requiring backup only for a short duration and a specific load requiring backup for a longer duration, uninterruptible power with higher reliability is supplied to the specific load with the adoption of a simple configuration. A DC backup power supply s

In the case where there coexist general loads requiring backup only for a short duration and a specific load requiring backup for a longer duration, uninterruptible power with higher reliability is supplied to the specific load with the adoption of a simple configuration. A DC backup power supply system comprises an AC/DC converter for normally supplying DC power to loads in while (the general loads and the specific load, included), and a control circuit for supplying DC output backing up the loads in whole for relatively short time only from a battery at the time of a power outage, while supplying DC output backing up the specific load, such as a cache memory and so forth, for relatively long time. Thus, it is possible to implement an uninterruptible power supply system small in size and low in cost, provided with a function for proper use depending on a prevailing situation.

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What is claimed is: 1. A DC backup power supply system having a plurality of loads to which AC from a commercial power source is supplied, and DC power storage means for supplying DC power to the plurality of the loads at the time of a power outage of the commercial power source, said DC backup pow

What is claimed is: 1. A DC backup power supply system having a plurality of loads to which AC from a commercial power source is supplied, and DC power storage means for supplying DC power to the plurality of the loads at the time of a power outage of the commercial power source, said DC backup power supply system comprising: a control circuit having a first DC backup output for supplying a power from the DC power storage means to the plurality of the loads, including a specific load, only during the power outage of the commercial power source, and a second DC backup output for continuously supplying a power from the DC power storage means to the specific load regardless of the power outage of the commercial power source or sound operation thereof, the control circuit supplying the respective powers from the same DC power storage means to the first and second DC backup outputs. 2. A DC backup power supply system according to claim 1, wherein a line for the first DC backup output toward the plurality of the loads is a two-way output line through which recharging or discharging of the DC power storage means can be carried out. 3. A DC backup power supply system according to claim 1, wherein the control circuit supplies the first DC backup output from the DC power storage means to the plurality of the loads in response to the power outage of the commercial power source, and stops the first DC backup output upon passage of a predetermined time. 4. A DC backup power supply system according to claim 1, wherein a power capacity of the first DC backup output to the plurality of the loads, is not less than ten times as large as the power capacity of the second DC backup output to the specific load. 5. A DC backup power supply system according to claim 1, wherein a duration of the first DC backup output is not more than one tenth of a duration of the second DC backup output. 6. A DC backup power supply system according to claim 1, wherein the control circuit supplies the first DC backup output from the DC power storage means to the plurality of the loads in response to the power outage of the commercial power source, and stops the first DC backup output in response to a signal from the loads. 7. A DC backup power supply system according to claim 1, wherein the specific load comprises a cache memory or a non-volatile memory, and/or a DC/DC converter for supplying DC power to the memory. 8. A DC backup power supply system having an AC/DC converter for receiving AC from a commercial power source, and supplying DC power to a plurality of loads, and DC power storage means for supplying DC power to the plurality of the loads at the time of a power outage of the commercial power source, said DC backup power supply system comprising: a control circuit having a first DC backup output for supplying a power from the DC power storage means to the plurality of the loads, including a specific load, only during the power outage of the commercial power source, and for stopping thereafter the first DC backup output upon passage of a predetermined time, and/or in response to a predetermined signal, and having a second DC backup output for continuously supplying a power from the DC power storage means to the specific load regardless of the power outage of the commercial power source or sound operation thereof, the control circuit supplying the respective powers from the same DC power storage means to the first and second DC backup outputs. 9. A DC backup power supply system according to claim 8, wherein a line for the first DC backup output toward the plurality of the loads is a two-way output line through which recharging or discharging of the DC power storage means can be carried out. 10. A DC backup power supply system according to claim 8, wherein a power capacity of the first DC backup output to the plurality of the loads, is not less than ten times as large as a power capacity of the second DC backup output to the specific load. 11. A DC backup power supply system according to claim 8, wherein a duration of the first DC backup output is not more than one tenth of a duration of the second DC backup output. 12. A DC backup power supply system according to claim 8, wherein the control circuit supplies the first DC backup output from the DC power storage means to the plurality of the loads in response to the power outage of the commercial power source, and stops the first DC backup output in response to a signal from the loads. 13. A DC backup power supply system according to claim 8, wherein the specific load comprises a cache memory or a non-volatile memory, and/or a DC/DC converter for supplying DC power to the memory. 14. A DC backup power supply system according to claim 8, wherein the specific load receives the first DC backup output via a diode, and receives the second DC backup output via a plurality of diodes. 15. A DC backup power supply system according to claim 8, wherein the DC power storage means comprise a plurality of secondary battery groups connected in parallel, each composed of a plurality of secondary batteries connected in series, including a secondary battery group different in kind from other secondary battery groups. 16. A DC backup power supply system according to claim 15, comprising the secondary battery group having a different discharge rate from the other secondary battery groups. 17. A DC backup power supply system according to claim 8, wherein the control circuit comprises a charger for supplying power to the DC power storage means, first and second output circuits for passing the first and second DC backup outputs from the DC power storage means, respectively, a latch circuit for controlling the second output circuit, an auxiliary power source as the power source of the latch circuit, and a CPU for controlling the charger, the output circuits, the latch circuit, and the auxiliary power source. 18. A DC backup power supply system according to claim 17, wherein power is supplied from the auxiliary power source to the latch circuit during supply of the second DC backup output to the specific load at the time of the power outage of the commercial power source, and while power supply to other circuits within the control circuit is stopped, the latch circuit is configured so as to interrupt the second output circuit in response to a predetermined instruction. 19. A disk array having an AC/DC converter for receiving AC from a commercial power source to be converted into DC, a CPU to which DC output from the AC/DC converter is supplied, a plurality of loads including a cache memory, and a plurality of hard disk drives, and DC power storage means for supplying DC power to the plurality of the loads at the time of a power outage of the commercial power source, said disk array comprising: a control circuit having a first DC backup output for supplying a power from the DC power storage means to the plurality of the loads, including the cache memory until a predetermined time or a predetermined signal is received, only during the power outage of the commercial power source, and a second DC backup output for continuously supplying a power from the DC power storage means to the cache memory regardless of the power outage of the commercial power source or sound operation thereof, the control circuit supplying the respective powers from the same DC power storage means to the first and second DC backup outputs. 20. A disk array according to claim 19, comprising a plurality of DC/DC converters for stepping down the first and second DC backup outputs to be thereby supplied to the CPU, the hard disk drives, and/or the cache memory, respectively. 21. A DC backup power supply system having DC power storage means comprising: a unit battery composed of a single cell or a plurality of battery cells connected in series; and a plurality of parallel-connected unit battery groups composed of a plurality of the unit batteries connected in series, said DC backup power supply system further comprising a control circuit incorporating: connection switchover means capable of optionally changing the number of parallel-connections of the unit battery groups so as to correspond to a backup capacity of loads and implementing series-connection of the unit batteries inside the respective unit battery groups; a charger for recharging the respective unit battery group with DC power; and an output circuit through which DC power is discharged from the respective unit battery group to the loads. 22. A DC backup power supply system according to claim 21, wherein the charger and the output circuit comprise a DC/DC converter. 23. A DC backup power supply system according to claim 21, wherein the connection switchover means comprise a relay circuit, and series-connection of the unit batteries is controlled by the relay circuit.