Power supply apparatus

A power supply apparatus for supplying a direct current to a load includes a circuit breaker, and an AC/DC converter for converting an alternating current passed through the circuit breaker into a direct current. The direct current is supplied to the load. A battery supplies a direct current to the load when the AC/DC converter is in an abnormal state, and a switch is connected between the output of the AC/DC converter and the battery and between the load and the battery. Switch drive units control the switch in such a way that, when the circuit breaker is in an on state, the switch is turned on to connect the battery to the AC/DC converter and to the load. When the circuit breaker is in an off state, the switch is turned off to disconnect the battery from the load, whereby an unnecessary battery back up operation is prevented.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a power supply apparatus having a back-up 
battery for supplying a power to a load, which power supply apparatus is 
used in, for example, computers. 
Computers are now required to continue operation even when a power failure 
or an instantaneous power cut occurs, and to this end, various back-up 
method are conventionally provided. 
(2) Description of the Related Art 
In the conventional power supply apparatus for supplying a power to a load, 
a back-up battery is directly connected to the output of an AC/DC 
converter. During a period when the AC/DC converter generates a DC 
current, the battery is charged up, and when the AC/DC converter does not 
generate a DC current, the charged-up battery supplies power to the 
device. 
When a work in the load is finished, and when an operator manually turns 
off a circuit breaker for turning the power supply apparatus on or off, 
the output from the AC/DC converter becomes zero volts and the situation 
becomes the same as that when a power failure occurs, with the result that 
the battery automatically executes a back up operation. 
Therefore, even when a power failure or a fault in the AC/DC converter does 
not occur, the back-up operation is executed every time the circuit 
breaker is manually turned off, and this causes a problem in that the 
shortening the life of the battery is accelerated. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a power supply apparatus 
in which the shortening of the life of a back-up battery is suppressed as 
much as possible. 
To attain the above object, according to the present invention, there is 
provided a power supply apparatus for supplying a direct current to a 
load, comprising: a circuit breaker for closing and opening a circuit 
between separable contacts under both normal and abnormal operating 
conditions; an AC/DC converter, connected to the circuit breaker and to 
the load, for converting an alternating current passed through the circuit 
breaker into a direct current, the direct current being supplied to the 
load; and a battery for supplying a direct current to the load when the 
AC/DC converter is in an abnormal state. Further, in the power supply 
apparatus, there is provided a switch connected between the output of the 
AC/DC converter and the battery and between the load and the battery; and 
a switch drive unit, operatively connected to the circuit breaker, for 
driving the switch in such a way that, when the circuit breaker is in an 
on state, the switch is turned on to connect the battery to the AC/DC 
converter, and when the circuit breaker is in an off state, the switch is 
turned off to disconnect the battery and the load. 
The battery and the switch are connected in series between one polarity 
output and another polarity output of the AC/DC converter. 
The switch driving unit comprises an auxiliary contact and a relay 
connected in series between one polarity output and another polarity 
output of the AC/DC converter. The auxiliary contact is closed when the 
circuit breaker is in an on state, and the auxiliary contact is open when 
the circuit breaker is in an off state. The relay turns on the switch when 
the auxiliary contact is closed, and turns off the switch when the 
auxiliary contact is opened. 
According to another aspect of the present invention, the power supply 
apparatus further comprises an over current detecting unit, operatively 
connected to the circuit breaker and to the switch driving unit, for 
detecting an over current flowing through the circuit breaker (1). In 
response to the detection of an over current by the over current detecting 
unit, the switch drive unit turns on the switch to connect the battery to 
the load. 
The over current detecting unit comprises a short detecting contact and a 
relay connected in series between one polarity and another polarity of the 
outputs of the AC/DC converter. The short detecting contact is closed so 
that the relay turns on the switch when the circuit breaker is turned off 
due to an over current flowing through the circuit breaker.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
For a better understanding of the present invention, a conventional power 
supply apparatus is first described with reference to FIGS. 1 and 2. 
FIG. 1 shows a conventional power supply apparatus for supplying a voltage 
to a central processing unit and a disk unit. In general, a computer 
system is constructed by a central processing unit (CPU), disk apparatus 
(DISK), and so forth, but the power supply voltages for the CPU, disk 
apparatus, and so forth are usually different; for example, a -5.3 V power 
supply is used for the CPU, and a 5 V power supply is used for the disk 
apparatus. Therefore, as shown in FIG. 1, DC/DC converters 3-1 and 3-2 are 
provided separately for a CPU 14-1 and the disk apparatus 14-2, 
respectively, to generate the necessary voltages to be applied thereto. 
Each of the DC/DC converters 3-1 and 3-2 is duplicated. 
A single AC/DC converter 2 is commonly connected to the plurality of DC/DC 
converters, and converts a commercial voltage of 100 V or 200 V to a low 
voltage which is harmless to the human body. The converted voltage is then 
applied to the respective DC/DC converters. 
Note that a circuit breaker 12 is turned off when an over current of the 
commercial power source flows through the circuit breaker, to protect the 
devices such as the CPU or the disk apparatus. To this end, the circuit 
breaker 12 includes, for example, a fuse (not shown in the figure) which 
will blow when an over current flows therethrough. Further, the circuit 
breaker 12 includes a switch (not shown in the figure) which is turned on 
or off manually at the beginning or the end of work in the CPU. 
Computers are now required to be operated without stopping, and to this 
end, various conventional back-up methods have been provided. 
In a power supply apparatus, when a fault occurs in the AC/DC converter 2 
or the DC/DC converters 3-1 and 3-2, so that the output voltage of the 
AC/DC converter 2 or the output voltage of the DC/DC converter 3-1 or 3-2 
becomes zero volts, the loads such as the CPU 14-1 and the disk apparatus 
14-2 must be supplied with back-up voltages by some means, in order to 
continue the operation of the computers. 
The DC/DC converters have a small size and are duplicated as back ups for 
each other. The AC/DC converter, however, has a large size because it uses 
a commercial power supply, and thus it is not preferable to duplicate over 
AC/DC converter as a back up for another. 
FIG. 2 shows a conventional power supply apparatus provided with a back-up 
battery 7. As shown in FIG. 2, when a fault occurs in the AC/DC converter 
2, the back-up battery 7 supplies a voltage to the DC/DC converters 3-1 
and 3-2. In the apparatus shown in FIG. 2, also, the DC/DC converters are 
duplicated. 
In operation, when the circuit breaker 12 is turned on, an alternating 
current power supply of 100 or 200 V is applied to the AC/DC converter 2 
and is converted therein to a direct current having a low voltage. The 
converted direct current charges up the battery 7, and is also converted 
by the DC/DC converter 3 into the necessary voltages to be applied to a 
CPU 14-1 and a magnetic disk 14-2. 
In this construction, when a power failure of the alternating power source 
occurs or when a fault occurs in the AC/DC converter 2, so that an output 
cannot be obtained therefrom, the AC/DC converter 2 is backed up by the 
battery 7. 
When the work is finished, and when an operator manually turns off the 
circuit breaker 12, the output from the AC/DC converter 2 cannot be 
obtained, and therefore, the situation becomes the same as that when a 
power failure occurs or when a fault occurs in the AC/DC converter 2, with 
the result that the battery 7 automatically executes the back up 
operation. 
Therefore, a problem arises in that, even when a power failure or a fault 
in the AC/DC converter does not occur, the back-up operation is executed 
every time the circuit breaker 12 is turned off, and thus the shortening 
of the life of the battery 7 is accelerated. 
Now, embodiments of the present invention will be described. 
FIG. 3 is a block diagram showing a power supply apparatus according to a 
first embodiment of the present invention. In the figure, 3-1 and 3-2 are 
DC/DC converters, 4-1 and 4-2 are loads such as a CPU or a magnetic disk 
apparatus, 5 is an auxiliary contact which is closed when the circuit 
breaker 1 is in on, and which is in an open when the circuit breaker 1 is 
off, 6a is a relay, 6b is a relay contact, and 8 is a smoothing capacitor. 
Each of the DC/DC converters 3-1 and 3-2 is duplicated. 
The auxiliary contact 5 and the relay 6a are connected in series between 
the positive output and the negative output of the AC/DC converter 2. 
When an alternating current is normally supplied to the circuit breaker 1, 
and when the circuit breaker 1 is turned on to start work, then the 
auxiliary contact 5 is automatically closed. The relay 6a causes the 
switch 6b to be closed when the auxiliary contact 5 is closed, and when 
the switch 6b is closed, the battery 7 is charged up by the output voltage 
of the AC/DC converter 2 during a normal condition, and the battery 7 
supplies a DC current to the DC/DC converters 3-1 and 3-2 when the output 
of the AC/DC converter 2 is lost due to a power failure or a fault in the 
AC/DC converter 2. 
Conversely, when the circuit breaker 1 is turned off manually at the end of 
the work, the auxiliary contact 5 is also automatically turned off, and 
thus the relay 6a opens the switch 6b. When the switch 6b is opened, the 
battery 7 is not charged-up and does not supply a DC current to the DC/DC 
converters 3-1 and 3-2, and therefore, the back-up operation is not 
effected by the battery 7. Before manually turning off the circuit breaker 
1, data processed in the load 14-1 or 14-2 is saved into an non-volatile 
storage, and therefore, even when the back up operation is not effected by 
the battery 7, the data is not destroyed. 
Note that, even when a power failure of the alternating current power 
source or an instantaneous cut of the alternating current power source 
occurs, the circuit breaker 1 is kept on so that the auxiliary contact 5a 
is also kept closed. Accordingly, the battery 7 remains connected to the 
DC/DC converters 3-1 and 3-2 and the back up is thus executed. 
Accordingly, the acceleration of the shortening of the life of the battery 
can be prevented. 
In the above construction shown in FIG. 1 however, when an over current 
flows through the circuit breaker 1, whereby the circuit breaker 1 is 
turned off, the auxiliary contact 5 is also automatically opened and the 
switch 6b is turned off by the relay 6a, and therefore, the back-up 
operation by the battery 7 cannot be effected. As a result, a problem 
arises in this case in that the data being processed by the load such as a 
CPU is destroyed. 
To prevent this data destruction, a second embodiment of the present 
invention is provided as shown in FIG. 4. 
In FIG. 4, a short detecting contact 9 is added to the embodiment shown in 
FIG. 3. Note that the auxiliary contact 5 and the short detecting contact 
9 are included in the circuit breaker. Such a circuit breaker itself is 
known in the field of the market; for example, a circuit breaker is marked 
under the trade name, IEG series, by Sanken Air Packs K.K. Each of the 
DC/DC converters 3-1 and 3-2 is duplicated. 
The short detecting contact 9 and the relay 6a are connected in series 
between the positive output and the negative output of the AC/DC converter 
2. 
The short detecting contact 9 is open while an over current does not flow 
through the circuit breaker 1, and is closed when an over current flows 
through the circuit breaker 1. 
In operation, when an over current flows through the circuit breaker 1, the 
circuit breaker 1 is turned off and the auxiliary contact 5 is opened. 
But, in response to the over current, the short detecting contact 9 is 
closed and thus the relay 6a driving the switch 6b remains closed, and 
accordingly, the battery 7 backs up the AC/DC converter 2 by supplying a 
DC current to the DC/DC converters 3-1 and 3-2. 
The relationships among the states of the circuit breaker 1, the auxiliary 
contact 5, the short detecting contact 9, and the relay contact 6b are 
shown in FIG. 5. 
In FIG. 5, a state (1) is that when the circuit breaker 1 is in an on state 
in an normal condition; a state (2) is that when the circuit breaker is 
turned off manually, and a state (3) is that case when an over current 
flows through the circuit breaker 1 so that the circuit breaker 1 is 
turned off. 
The addition of the short detecting contact 9 is effective in the state 
(3). 
The respective states are explained as follows. 
In the state (1), since the circuit breaker 1 is in an on state, the 
auxiliary contact 5 is closed. Also, since an over current is not flowing 
through the circuit breaker 1, the short detecting contact 9 is opened, 
and thus the switch 6b is in an on state. In this state, the battery 7 can 
back up the AC/DC converter 2. 
In the state (2), since the circuit breaker 1 is turned off, the auxiliary 
contact 5 is opened. Also, since there an over current is not flowing 
through the circuit breaker 1, the short detecting contact 9 is opened, 
and thus the switch 6b is in an off state. Therefore, the charge in the 
battery 7 is not consumed. 
In the state (3), since an over current is flowing therethrough, the 
circuit breaker 1 is turned off and the auxiliary contact 5 is opened. 
According to the first embodiment shown in FIG. 3, the switch 6b is turned 
off in response to an opening of the auxiliary contact 5, so that the back 
up operation is not effected and the apparatus will be stopped. In the 
second embodiment shown in FIG. 4, however, the short detecting contact 9 
is closed in response to an over current, and thus, the relay 6a continues 
to be energized and the switch 6b remains in an on state. Accordingly, the 
back up operation is effected by the battery 7 and the data is not 
destroyed. 
As described above, according to the present invention, by utilizing an 
auxiliary contact which is automatically turned on or off in response to 
an on or off state of the circuit breaker, an unnecessary back up can be 
prevented and a shortening of the life of the battery is suppressed. Also, 
by adding the short detecting contact, which is turned on in response to 
an over current flowing through the circuit breaker, a back up by the 
battery is possible even when the circuit breaker is turned off due to the 
over current.