Rack PS Designed for Reliability

Currently publicity about the Patton rack chassis stresses the convenience and flexibility of its mid-plane architecture. While these are important benefits, another key advantage of Patton's design is its reliability. This is of particular importance with respect to the power supply system.

The Typical Redundant Power Supply
A typical redundant power supply used on a rack chassis might look something like this: One power supply unit, with a common AC power input, feeds duplicate transformers and duplicate power supply circuits. The primary transformer/power supply is normally on-line, feeding the load (i.e. all the cards in the rack). If the primary transformer/power supply fails, the secondary supply automatically switches over and feeds the load. An LED shows that the secondary supply has kicked in, and the user replaces the unit as soon as possible. This is quite important, since failure of the secondary supply will bring the entire rack down.

Not as Good as it Looks
The problem with the typical redundant power supply is that is still leaves the rack quite vulnerable to overall failure and subsequent down time. The presence of redundant transformers is of little consequence, since the transformer failrures are statistically rare. What normally fails is the power supply circuit, which incorporates less hearty components. In the case of a typical redundant power supply, one circuit is feeding up to 16 cards. This means that a relatively high amomut of current flows constantly through a single, substantially stressed circuit. In this scenario, a second power supply circuit is highly desireable, since the primary circuit is quite vulnerable to failure.

If primary power supply failure does occur, and the secondary supply take over as intended, user intervention is then critical. This is because failure of the secondary power supply will take down all 16 cards in the rack. In either case (another failure or replacement of the power supply unit) the entire rack must eventually come down, taking up to 16 connections off line. Such down time, even if done as routine maintenaces, is costly with respect to productivity.

Patton's Distributed Alternative
Patton's distributed power supply system addresses the critical shortcomings in the typical redundant power supply set-up. As mentioned above, the transformer is part of the power supply that rarely fails. And this is the only major portion of the power supply system that resides in Patton's power supply card (one card per rack). The MTBF of the transformer used in Patton's power supply card is 14 million hours! The card itself (1000RPSM and 1000 RPEM modules) has an impressive MTBF of 2.24 million hours. So the chance of failure in the card itself is slim.

When it comes to the power supply circuit, the Patton distributed power system is a distincet improvement over the traditional redundant power supply. Rather than using one power supply circuit (plus a back-up) for all sixteen cards, Patton's distributed system gives each card its own power supply. And using sixteen separate power supplies give the Patton system two important advantages:

First, rather than sending all operationg power through one substantially stressed circuit, the Patton system divides a comparable amount of power between sixteen power supplies (ie. each power supply handles 1/16 as much power). With mulitplied PC board space and lower current handling requirement, each power supply circuit can be comparatively over-engineered and more conservatively rated. This translates into less failures per power supply circuit than in the typical redundant power supply.

Second , if one power supply circuit does fail (which is less likely), Patton's distributed system ensures that only one connection will go down -- the other fifteen cards will remain in operation! If two power supply circuits fail (also less likely), only two connections will have failed, and 14 will remain in operation. Contrast this to the typical redundant power supply set-up: If the primary power supply fails (more likely because of a higher stress on the components), and the secondary supply takes over successfully, all cards will remain in operation. But if the secondary supply fails (same high component stress level), all 16 cards will go down. That is a catastrophic failure -- one that Patton's distributed power supply system can prevent.

An additional advantage of Patton's distributed power supply system is that, in the event that a power supply circuit fails, the fialed card can be replaced without taking the whole rack down. That is Patton's hot-swappable advantage!

Conclusion
While Patton's hot-swappable rack chassis gains high marks for flexibility and convenience, its most important benefit may be reliability: less likelihood of power supply circuit failure, less harm to the system should failure occur, and less overall down time for repair. When the time comes to specify or purchase a rack system, choose the Patton rack chassis -- the dependable rack with the distributed power system.