Prior Art
For driving various apparatuses, a plurality of power sources such as card type are connected in parallel. Such a case is usually divided into the following two cases. One is the case of using a plurality of card type power sources to gain simply necessary power for driving the apparatus, and in this case it is desirable to switch all power sources on and off simultaneously. Another is the case of providing not only the necessary number of card type power sources to gain necessary power but also a preparatory power source. This is the so-called (N+1) redundancy configuration which enables a rapid back up even in case that either of the working powers has a trouble. In this case it is desirable to make only a part of sources off.
FIG. 2 illustrates a conventional switching power source circuit composed by using card type switching power sources in parallel. Two card type switching power source circuits 11 and 12 are provided in this circuit.
The switching power source comprises separate switching power source units 12 and 22 which have respective first input terminals A.sub.1 and A.sub.2 connected in parallel to the positive side of an input power source 31, and respective second input terminals B.sub.1 and B.sub.2 connected in parallel to the negative side of the input power source 31. The negative side of the input power source 31 is branched into two terminals through a common start-up switch 32 provided outside, and the terminals are respectively connected to the start-up signal input terminals I.sub.1 and I.sub.2 of the first and the second switching power source units 12 and 22. The common start-up switch 32 has a so-called make contact which is closed when the actuator is turned on.
Further, the negative side of the input power source 31 is connected to the drive stop signal input terminals R.sub.1 and R.sub.2 of the switching power source units 12 and 22 through individual power source switches 13 and 23 provided in the switching power source 12 and 22 respectively the power source switch 13 and 23 have so-called break contacts which becomes open when its actuator is turned on.
Furthermore, the output sides of the switching power source units 12 and 22 are connected in parallel to a common load 33.
Both of the start-up signal input terminal I.sub.1 and the drive stop signal input terminal R.sub.1 of the first switching power source unit 12 become active when they are connected to the negative side of the input terminal 31. And only if the start-up signal input terminal I.sub.1 is active and the drive stop signal input terminal R.sub.1 is non-active, the switching power source unit 12 starts. In other words, the switching power source 12 starts and operates when the the negative side of the input power source 31 is connected to the start-up signal input terminal I.sub.1 and the drive stop signal input terminal R.sub.1 is open. Except for this combination, it does not start or it stops output. The second switching power source 22 is of course configured likewise.
Next, the operation of the above-mentioned configuration of the conventional switching power source circuit is explained.
As both of the individual power source switches 13 and 23 are off before the power source starts, these contacts are closed as FIG. 2 shows. Both of the drive stop signal input terminals R.sub.1 and R.sub.2 are active. As the common start-up switch 32 is also off before the power source starts, its contact is open. Both of the start-up signal input terminals I.sub.1 and I.sub.2 are then non-active.
For example, when the individual power source switch 13 of the first switching power source is turned on in this condition, its contact becomes open. Therefore, the drive stop signal input terminal R.sub.1 becomes non-active. Similarly, when the individual power switch 23 in the second switching power source 21 is turned on, its contact also becomes open. Therefore the drive stop signal input terminal R.sub.2 becomes non-active. Then, when the common switch 32 is turned on, its contact becomes closed, and the start-up signal input terminal I.sub.1 and I.sub.2 become active. By this operation, these two switching power sources are brought into a start-up condition and start simultaneously.
However suppose, for example, a case where the common start-up switch 32 is turned on after the individual power source switch 13 in the first switching power source 11 was turned on, while the individual power switch 23 in the second switching power source switch 21 is kept off. In this case the first switching power source 11 meets the start-up condition while the second switching power source 21 does not meet this condition. Only the first switching power source starts.
As described above, a part of the switching power sources of the conventional parallel configuration may not be energized for the reason of some mistakes on the procedure of the start-up operation. In this case, the system's fault may occur, because the necessary power is not delivered to the load. Further, in the case that the power lack detecting mechanism is added to the power source, some problems such as an alarm's output occur. Anyhow, in this case, it must be determined whether it comes from some essential malfunctions of the system or a simple mistake. When it is determined that the fault comes from a mistake, it is necessary to repeat the start operation.
Thus, the conventional switching power source has defects in that it needs a common start-up switch as well as individual power source switches for the switching power sources and in that it lacks operability and reliability.
There is the Japanese Published Unexamined Utility Model Application H3-3018 as prior art relating to this invention. In this prior art wherein an AND signal of individual start-up signals of a plurality of power sources is generated in each power source, all the power sources are turned on simultaneously when all the individual start-up signals are arranged. However, the number of terminals increases in this configuration, because it is needed to supply the individual start-up signals of each power source to all the other power sources. Also, when the number of the power sources connected in parallel increases, large scale circuits are needed because the number of the inputs of the AND circuits increases.