DETAILED DESCRIPTION

[0017] What is desired is an apparatus and associated operating technique for power supply load balancing in a modular system. What is further desired is a system that can exploit the power capacity of a modular system to meet power needs of components and devices in the system even when loaded near or to capacity, and in conditions of power supply failure.

[0018] Embodiments of a power supply load balancer enable output load sharing in a multiple output power supply configuration. A power supply load balancer can be implemented in the input power supply line of individual modules in a system or enclosure that can accept multiple modules. A power supply load balancer enables a module to draw power from any of multiple output power supply lines.

[0019] Referring to FIG. 1 , a schematic circuit diagram illustrates an embodiment of circuit 100 capable of power supply load balancing. The power supply load balancer 100 performs output load sharing in a multiple output power supply configuration. In the illustrative example, a system has two supply voltages V _i1 and V _i2 on a backplane and generates an output voltage V ₀ that is operational for powering an individual module in a modular system that can combine multiple modules. In other embodiments, additional power supply voltages may be available and a circuit may balance loads for the additional voltages.

[0020] The power supply load balancer 100 comprises a voltage converter, for example a DC/DC converter 108 , that can accept either voltage V _i1 or V _i2 , and generate from the input voltage an output voltage of V ₀ . The DC/DC converter 108 is connected to pathways connected to the backplane supply lines V _i1 and V _i2 . The pathways include Schottky diodes that function as an isolator to isolate the input voltages V _i1 and V _i2 , and field effect transistors (FETs) that manage switching of the power sources V _i1 and V _i2 . For example, the V _i1 pathway includes FET 110 and Schottky diode 112 . An R/C circuit including capacitor C ₁ and resistor R ₁ adjusts FET 110 . V _i2 pathway includes FET 120 and Schottky diode 122 and passes a shared voltage V _i2 -SH that can be shared with other devices and components. An RIC circuit including capacitor C ₂ and resistor R ₂ adjusts FET 120 . In other embodiments, other types of isolating devices, such as other types of diodes, may be used.

[0021] The power supply load balancer 100 can be the power interface for a module for installation in a system that accepts multiple modules to enable output load sharing for the multiple output (V _i1 and V _i2 ) power supply configuration. The power supply load balancer 100 is useful when multiple modules with a voltage requirement of V ₀ in combination exceed the power supply capabilities of the V _i1 and V _i2 power supplies alone. The power supply load balancer 100 enables the module to draw power from either supply V _i1 or V _i2 . The DC/DC converter 108 can accept either V _i1 or V _i2 . The V _i1 and V _i2 power supplies are connected to the DC/DC converter 108 through Schottky diode 112 and Schottky diode 122 , respectively, to mutually isolate the V _i1 supply from the V _i1 supply. Schottky diodes efficiently isolate the different supplies although other types of isolation may be used.

[0022] The FET 110 and associated R ₁ C ₁ circuit, and FET 120 and associated R ₂ C ₂ circuit, operate in conjunction to form a soft switch 106 that generates a soft start behavior and controls application of the V _i1 and V _i2 to the DC/DC converter 108 with different time constants. A backplane pin SLOT_PO passed through a gate such as inverter 114 selects the power supply voltage V _i1 or V _i2 passed by DC/DC converter 108 . The backplane pin connection SLOT_PO through gate inverter 114 enables switching on and off of the V _i1 supply. In the illustrative embodiment, the voltage V _i1 is larger that voltage V _i2 . Also in the illustrative embodiment, the V _i2 supply line does not use a switch function since the V _i1 supply overrides the V _i2 supply when V _i1 is enabled. In the illustrative embodiment, the enabler for the V _i1 supply is the backplane pin SLOT_PO that alternates high and low for adjacent slots in a card cage. Accordingly, the modules in adjacent slots alternate between the V _i1 and V _i2 supplies as the card cage is filled sequentially. In other embodiments, other selection criteria may be used.

[0023] The soft start behavior is useful to enable one supply, for example V _i1 , to begin operating more quickly than the second supply, here V _i2 , to unambiguously select the voltage supply, eliminating the possibility that all modules could simultaneously attempt to draw from the same supply, here V _i2 , causing overloading.

[0024] In a specific implementation, the power supply load balancer 100 can be used in a storage device such as a tape or disk library. The power supply load balancer 100 can be implemented on individual fibre bridge modules in a system that can accept multiple bridges. The power supply in the storage device can supply 5V at 25 A and 12V at 8 A. The primary voltage requirement of the individual modules is 3.3V at 5 A so that capacity usage of the system exceeds the power capability of either the 5V or the 12V supply alone.

[0025] The illustrative DC/DC converter 108 accepts either 5V or 12V and generates 3.3V. Schottky diodes 112 and 122 mutually isolate the 5V and 12V supplies. The FET and RC circuits generate the soft start behavior and the capability to switch the 12V supply. The soft start capability enables the 12V supply to activate faster than the 5V supply, so that all modules do not attempt to simultaneously draw from and overload the 5V supply.

[0026] Referring to FIG. 2 , a schematic circuit diagram shows an alternative embodiment of a circuit capable of power supply load balancing 200 . The circuit 200 can select from among an additional power supply V _i3 and includes a power line filter, soft switch 206 , and isolation for the additional supply line. FET 130 , resistance R ₃ , and capacitance C ₃ supply filtering and switching for the additional line. Schottky diode 132 supplies isolation to the supply V _i3 . A select signal SELECT that can be any suitable signal for activating a particular supply is passed through gate inverter 124 and enables switching on and off of the V _i2 supply. In the illustrative embodiment, the voltage V _i1 is larger that voltage V _i2 , which, in turn is larger that voltage V _i3 .

[0027] Referring to FIG. 3 , a pictorial block diagram shows an embodiment of a modular system 300 that comprises an enclosure 302 with a plurality of slots 310 capable of accepting a plurality of functional modules 314 . The functional modules 314 can include a power supply load balancer such as the balancers described in FIGS. 1 and 2 . The power supply load balancers are capable of selecting a supply voltage from among a plurality of supply voltages and converting the selected supply voltage to an operational voltage. The modular system 300 further comprises a power supply 308 capable of supplying two or more supply voltages.

[0028] The modular system 300 can also have a card cage 304 coupled to the enclosure 302 that forms the structure for holding the plurality of slots 310 , and a backplane 306 that supplies power and signal lines. The signal lines can include a signal for controlling activation or deactivation of one or more of the voltage supply sources.

[0029] In some embodiments, only one supply is switched and the other supplies are intrinsically enabled or disabled accordingly. In other embodiments, switches can control some or all supply lines. 100301 In some embodiments, the modular system 300 can be a storage system such as a storage library. In one example, the card cage 304 can supply slots for a plurality of similar or identical functional modules that perform the same function. In a specific example, the card cage 304 supplies storage for a plurality of fibre bridges that convert fibre channel to Small Systems Computer Interface (SCSI) protocol. The fibre bridges connect one server or host to a plurality of storage drives 312 such as tape or disk drives.

[0030] In the particular example, the power supply 308 can supply two voltages, such as 5V and 12V. In some systems, the 5V supply can power electronic functional modules, and the 12V supply is generally furnished to power electromechanical components such as robotic systems for moving media to the drives. The illustrative power supply load balancer can exploit availability of the 12V supply to ensure sufficient power capabilities for supporting capacity or near-capacity functional module configurations.

[0031] Referring to FIG. 4 , a schematic block diagram shows an example of a suitable storage device 400 that can implement embodiments of power supply load balancing. The storage device 400 can be any type of storage device such as a drive or library. Some storage devices 400 can be tape drives or tape libraries, others can be disk drives or other storage drives, for example optical storage drives.

[0032] The storage device 400 incorporates a bus backplane such as a Peripheral Component Interconnect (PCI) bus backplane to interface with multiple various types of devices, systems, or components. For example, the storage device 400 includes a bus 402 with connections to a plurality of slots that can accommodate multiple types of functional modules. The functional modules can include a load balancer such as the circuits shown in FIGS. 1 and 2 . In an illustrative example, the functional modules with a power supply load balancer 100 may include a host interface 412 , a network interface 414 , a server 416 , and a Redundant Array of Inexpensive Tapes (RAIT) interface 420 . The host interface 412 can support connectivity to various links including SCSI, Ultra-SCSI, Ultra-2 SCSI, Gigabit Ethernet, Fibre Channel, and others, enabling connection directly to Fibre Channel backup servers and networks with additional fibre channel adapter cards. The network interface 414 can directly connect to networks with the addition of PC-Ethernet, Peripheral Component Interconnect-Fiber Distributed Data Interface (PCI-FDDI) and Peripheral Component Interconnect-Asynchronous Transfer Mode (PCI-ATM) cards. The server 416 interface can accommodate single card processors or CPUs or be used as a network-attached storage device. The RAIT interface 420 enables support of fault tolerance through auto tape copy, mirroring, and tape stripping with parity by adding tape RAIT cards.

[0033] The storage device 400 has multiple controllers that control and manage various electrical or electromechanical components. In some systems, electro-mechanical components may be configured to utilize a power source, for example a 12V supply, that differs from the power supply to other electronics modules in general, for example a 5V supply. The illustrative system utilizes load balancing that exploits availability of the 12V supply to facilitate scalability, availability, and reliability of a modular storage system.

[0034] The controllers can include a main library controller 404 , a load port controller 406 , a robotics controller 408 , and a drive controller 410 . The main library controller 404 is a system controller that performs multiple various control, management, and monitoring operations including multiple-host and library partitioning, serial communications control, diagnostics, and data pass-through. For example, the main library controller 404 supports system administration via connection to a control panel 428 such as a graphical user interface (GUI) touch screen for facilitating operational functionality, configuration, fault determination, and diagnostic testing.

[0035] The drive controller 410 communicates with multiple storage drives 422 and controls multiple operations including data routing, drive utilization, and drive failover. In one example, the storage device 400 can be a tape library that includes a dozen or more tape drives and slots for hundreds of tape cartridges.

[0036] The load port controller 406 communicates with a load port 426 and manages entry and exit of data cartridges into the storage device 400 . In one example, the load port 426 can include one or more multiple cartridge removable magazines to facilitate cartridge import and export and off-site data storage.

[0037] The robotics controller 408 communicates with robotics such as a cartridge handling mechanism 424 that carries data cartridges between storage slots, the storage drives 422 , and the load port 426 .

[0038] Commands received from the various interfaces, the host interface 404 , network interface 406 , server 408 , and RAIT interface 410 can control operations of at least the storage drives 422 and the robotics 424 .

[0039] Referring to FIG. 5 , a schematic pictorial diagram shows an example of a media storage module 500 that includes one or more fibre bridges 510 , one or more power supplies 508 , and can include a plurality of storage drives 524 . The fibre bridges 510 can be modules that implement a power supply load balancer 100 using a circuit such as those shown in FIGS. 1 and 2 . The storage drives 524 can be any suitable storage read/write devices such as tape drives, disk drives, or drives for other storage types. The media storage module 500 can include one or more of which can be used in a media storage library system to store and retrieve data cartridges 514 and to read and write data onto to data cartridges 514 .

[0040] The illustrative media storage module 500 comprises a cartridge engaging assembly 516 that is sometimes termed a robotic carrier that is moveably mounted to a guide frame 518 contained within the media storage module 500 . The media storage module 500 also comprises one or more storage drives 524 that can perform read and write access of a data cartridge 514 . The data cartridges 514 may be contained within one or more different types of cartridge receiving devices such as one or more cartridge magazines 522 and one or more storage drives 524 . The transport assembly 550 engages cartridge changing assembly 516 to move data cartridges 514 within media storage module 500 .

[0041] In some systems, cartridge engaging assembly 516 , transport assembly 550 , and other electromechanical components may be configured to utilize a power source, for example a 12V supply, that differs from the power supply to other electronics modules in general, for example a 5V supply. The illustrative system utilizes load balancing that exploits availability of the 12V supply to facilitate scalability, availability, and reliability of a modular storage system.

[0042] Referring to FIG. 6 , a schematic pictorial diagram depicts an embodiment of a suitable storage system 600 that can utilize power supply load balancing. The illustrative embodiment shows a modular system that can include multiple modular levels with each level having a plurality of slots for accepting functional modules. In the illustrative storage system 600 , each level has a power supply 610 and has capacity for two drives 612 such as tape drives or disk drives. Each power supply 610 generates a plurality of supply voltages. Each level has a plurality of slots that can accept functional modules including fibre bridges 614 , controllers 616 , remote management cards 618 , server controllers 622 , and the like. The scalable system may have vacant slots 620 . In some embodiments, the fibre bridges 614 include load balancing capabilities.

[0043] Many variations, modifications, additions and improvements of the embodiments described are possible. For example, although Schottky diodes are disclosed for usage in isolating the power sources, other isolating devices and circuits may be used. Although the controlled rate switch are described as FETs with associated RC circuits, other transistors or other types of filtering elements may be used. Although the illustrative embodiment shows a control signal applied to only one supply line, other embodiments may apply control signals to multiple lines. In some embodiments, the various types of functional modules can include a power supply load balancing circuit to balance loads among a plurality of functional modules of different types.