Backup power supply

1. A backup power supply built in a device constituted by a power supply circuit for converting an alternating current (AC) received from a commercial AC power supply to a direct current (DC), and a load operated by said direct current (DC) generated by said power supply circuit, the backup power supply comprising:

at least one AC-DC converter connectable to said commercial alternating current (AC);

a load connected to a DC output side of said AC-DC converter;

at least one two-way DC—DC converter in which one side of said two-way DC—DC converter is connected to said DC output side;

a Ni-MH secondary battery or a Li ion secondary battery connected to another side of said two-way DC—DC converter;

detecting means for detecting a service interruption of the AC power supply or a failure of said AC-DC converter;

means operable during occurrence of a detected service interruption or failure, for discharging electric power from said secondary battery, to supply said load;

charge state determining means for determining a state of charge of said secondary battery;

battery current detecting means for detecting battery current of said secondary battery; and

control means for altering and controlling a charging current which flows to said secondary battery, according to the state of charge determined by the charge state determining means, based on the battery current detected by said battery current detecting means.

2. The backup power supply according to claim 1 , wherein said control means comprises:

means for changing between a charging mode for charging said Ni-MH secondary battery or said Li ion secondary battery, and a discharging mode for discharging said Ni-MH secondary battery or said Li ion secondary battery;

separate charging and discharging controlling circuits; and

means for switching among driving signals output by the charging controlling circuit and the discharging controlling circuits.

3. In a backup power supply having a peak cut function and built in a device constituted by a power supply circuit for converting an alternating current (AC) received from a commercial AC power supply to a direct current (DC) and a load operated by said direct current (DC) generated by said power supply circuit, the backup power supply having the peak cut function and comprising:

at least one AC-DC converter connectable to said commercial AC power supply;

a load connected to a DC output side of said AC-DC converter;

at least one two-way DC—DC converter in which one side of said two-way DC—DC converter thereof is connected to said DC output side; and

a secondary battery connected to another side of said two-way DC—DC converter;

wherein when a load current is a predetermined peak cut current value or larger, said backup power supply supplies a difference current between said load current and said predetermined peak cut current value to said load via said two-way DC—DC converter, and said backup power supply carries out a peak cut operation;

wherein when said load current is smaller than said predetermined peak cut current value, said backup power supply supplies said load current from said AC-DC converter and charges said secondary battery via said two-way DC—DC converter; and

wherein the peak cut current value is varied according to residual capacity of the secondary battery.

4. A backup power supply according to claim 3 , wherein from a residual capacity of said secondary battery and said load current, said backup power supply has a function for calculating and displaying a service interruption time at said point of time.

5. In a device for supplying a DC current to operate a load, a backup power supply system comprising:

at least one AC-DC converter connectable to a commercial AC power supply, for converting AC current received from said commercial AC power supply to DC current at a DC output side of said at least one AC-DC converter;

a load connected to said DC output side of said AC-DC converter;

at least one two-way DC—DC converter having first and second input/output sides, one of which input/output sides is connected to said DC output side of the AC-DC converter;

a Ni-MH secondary battery or a Li ion secondary battery connected to the other of said first and second input/output sides of said two-way DC—DC converter;

detecting means for detecting a service interruption of the AC power supply or a failure of said AC-DC converter;

means operable during occurrence of a detected service interruption or failure, for discharging electric power from said secondary battery, to supply said load;

charge state determining means for determining a state of charge of said secondary battery;

battery current detecting means for detecting battery current of said secondary battery; and

control means for altering and controlling a charging current which flows to said secondary battery, according to the state of charge determined by the charge state determining means, based on the battery current detected by said battery current detecting means.

6. The backup power supply according to claim 5 , wherein said control means comprises:

means for changing between a charging mode for charging said Ni-MH secondary battery or said Li ion secondary battery, and a discharging mode for discharging said Ni-MH secondary battery or said Li ion secondary battery,

separate charging and discharging controlling circuits; and

means for switching among driving signals output by the charging controlling circuit and the discharging controlling circuits.

7. In a device for supplying DC current to operate a load, a backup power supply system having a peak cut function, said backup power supply system comprising:

at least one AC-DC converters connectable to a commercial AC power supply, for converting AC current received from said commercial AC power supply to DC current at a DC output side of said at least one AC-DC converter;

a load connected to said DC output side of said AC-DC converter;

at least one two-way DC—DC converter having first and second input/output sides, one of which input/output sides is connected to said DC output side of the AC-DC converter; and

a secondary battery connected to the other of said first and second input sides of said two-way DC—DC converter;

wherein when a load current equals or exceeds a predetermined peak cut current value, said backup power supply system supplies a current having a magnitude equal to a difference between said load current and said predetermined peak cut current value to said load via said two-way DC—DC converter, and said backup power supply system carries out a peak cut operation;

wherein when said load current is smaller than said predetermined peak cut current value, said backup power supply supplies said load current from said AC-DC converter and charges said secondary battery via said two-way DC—DC converter; and

wherein the peak cut current value is varied according to residual capacity of the secondary battery.

8. A backup power supply according to claim 7 , wherein from a residual capacity of said secondary battery and said load current, said back up power supply has a function for calculating and displaying a service interruption time at said point of time.

9. A backup power supply built in a device constituted by a power supply circuit for converting an alternating current (AC) received from a commercial AC power supply to a direct current (DC), and a load operated by said direct current (DC) generated by said power supply circuit,

the backup power supply comprising:

at least one AC-DC converter connectable to said commercial alternating current (AC);

a load connected to a DC output side of said AC-DC converter;

at least one two-way DC—DC converter in which one side of said two-way DC—DC converter is connected to said DC output side;

a Ni-MH secondary battery or a Li ion secondary battery connected to another side of said two-way DC—DC converter; and

detecting means for detecting a service interruption of the AC power supply or a failure of said AC-DC converter;

means operable during occurrence of a detected service interruption or failure, for discharging electric power from said secondary battery, to supply said load;

charge state determining means for determining a state of charge of said secondary battery;

battery current detecting means for detecting battery current of said secondary battery; and

control means for altering and controlling a charging current which flows to said secondary battery, according to the state of charge determined by the charge state determining means, based on the battery current detected by said battery current detecting means; and

from a residual capacity of said secondary battery and said load current, said back up power supply has a function for calculating and displaying a service interruption time at said point of time.

10. In a device for supplying a DC current to operate a load, a backup power supply system comprising:

at least one AC-DC converter, connectable to a commercial AC power supply, for converting AC current received from said commercial AC power supply to DC current at a DC output side of said at least one AC-DC converter;

a load connected to said DC output side of said AC-DC converter;

at least one two-way DC—DC converter having first and second input/output sides, one of which input/output sides is connected to said DC output side of the AC-DC converter;

a Ni-MH secondary battery or a Li ion secondary battery connected to the other of said first and second input/output sides of said two-way DC—DC converter;

detecting means for detecting a service interruption of the AC power supply or a failure of said AC-DC converter;

means operable during occurrence of a detected service interruption or failure, for discharging electric power from said secondary battery, to supply said load;

charge state determining means for determining a state of charge of said secondary battery;

battery current detecting means for detecting battery current of said secondary battery; and

control means for altering and controlling a charging current which flows to said secondary battery, according to the state of charge determined by the charge state determining means, based on the battery current detected by said battery current detecting means;

wherein from a residual capacity of said secondary battery and said load current, said back up power supply has a function for calculating and displaying a service interruption time at said point of time.

11. A backup power supply comprising:

a two-way DC/DC converter in which one end thereof is connected to a DC output power of an AC/DC converter and another end thereof is connected to a secondary battery, the DC output power of the AC/DC converter being carried out with a down-convert during charging of the secondary battery and output power of the secondary battery being carried out with an up-convert while the secondary battery is discharging and supplied to a load;

means for detecting AC service interruption and for detecting a fault of the AC/DC converter; and

means for transmitting a signal having a state which changes according to occurrence of the service interruption to the load.