While developments in other areas of power electronics may overshadow advances in power-connector design, innovations in this field will become more critical as power systems, especially those for telecom or data centers, are tasked to supply increasingly large loads. To meet this demand, several mechanical and electrical enhancements have been applied to connector design. For example, connectors have been modified to reduce contact resistance and hot-swap arching. Other breakthroughs include the development of industry standards and modular systems.
Meanwhile, expanded functionality complements high current capacity and high reliability in some connector designs. The use of embedded electronics reveals that connectors can do much more than simply complete a circuit.
Extending New Technology
One approach to increasing the current density in connectors is to apply several points of contact with equivalent normal contact forces to evenly distribute the current flow within the connector. In 2005, Tribotek introduced LowR connector technology for round pin connectors. In this technology, a spring-tensioned Kevlar weave creates multiple contact points between the gold-plated conductor within the socket and the inserted pin. The weave applies the same normal force to each point of contact between the pin and the conductor.
Tribotek has also recently implemented this technology in blade connectors, referred to as the BusBlade (Fig. 1), which deliver high current between bus bars. According to Michael Sienkiewicz, vice president of worldwide sales at Tribotek, this connector has a contact resistance of 45 µA and is able to deliver 600 A with only a 30°C rise in temperature within the connector. These connectors are designed to withstand more than 1000 insertion cycles to support equipment replacement, and have an insertion force of 4 lb and an extraction force of 3 lb.
The blade that mates to the BusBlade connector is an industry-standard 1 in. × 0.125 in. In Europe and Asia, the standard blade is the same width, but the thickness is slightly thinner at 3 mm. The target UL rating for the connector is 600 A, and the CSA rating is 425 A.
The resulting reduction in weight and size makes these blade connectors attractive to hybrid-electric vehicle designers. Another manufacturer, DCX, uses the technology for aviation-grade connectors. While this technology has great potential to reduce heat in data centers, there is also the possibility the same LowR weave technology can be applied to data signal connectors to reduce EMI. For more information, see www.tribotek-inc.com.
Another innovative approach explored by Tyco relates both to the shape of the connecting pins and their method of manufacture. While machined contacts are generally restricted to a circular cross section, stamped-and-formed pins can be pressed into a particular shape and include surface features that provide mechanical and electrical improvements for hot-swappable power-supply applications. In Fig. 2, the contact exhibits a leading center blade that acts as a sacrificial electrical contact. When the connector is used to make or break an electrical circuit, the resulting arc is focused on the center blade, which preserves the remaining contact surfaces for long-term reliability.
According to Mike Blanchfield, product manager for Power Interconnect Products, connectors not specifically designed for hot plugging tend to degrade very quickly in hot-plug applications. The electrical arc destroys both the precious metal plating and base metal, and results in significant increases in contact resistance.
Stamp-and-form processing was used to produce lower-cost commercial sub-D connectors from Mil-Spec D-sub connectors. While stamp and form has a higher manufacturing overhead cost than machined-pin connectors, the cost will be offset by volume manufacturing.
Further innovation deals with the shape of the connecting pin's cross section. Studies by Tyco reveal that flat rectangular cross sections have up to 40% more current-carrying capability compared to circular cross sections developed by screw machine processes. This is due to the larger-surface-area-per-unit length in the rectangular shape for a given cross-sectional area. Tyco's Zone-1 (Z1) power connectors use this rectangular pin configuration. The rectangular cross section is produced with stamp-and-form processing.
Another innovation Tyco is pursuing is the development of standards that are rare in this industry. One standard that has been extremely successful is the Multi-Beam XL modular connector system, cooperatively developed with FCI, which makes a similar fully compatible version. According to Blanchfield, this system has become a de facto standard. However, Tyco recently has been awarded a true standard by the telecom industry referred to as MicroTCA; Tyco's Minipak HD connector is based on this standard. Both the Multi-Beam XL and Minipak HD connectors incorporate the sacrifical-contact-tip design to support hot-plug applications. For more information, see www.tycoelectronics.com.
Reliability Is Key
For most connectors, reliability is more important than innovation. However, as connectors support increasing current densities, the most significant innovations in future connector designs may be improvements to connector reliability itself. According to Ken Stead, new product development manager for power at Molex, this will be especially important in telecom applications, which demand increasing power levels without allowing for an increase in space.
In addition to having low contact resistance, a reliable connector also must have a consistent contact resistance over time, temperature and multiple mating cycles. According to Stead, this is a function of contact design and material selection. Molex targets a total variation of less than 10% in the contact resistance of a connector over its operational lifetime.
Board-to-board connections for data center pc boards can be rated as current per inch, which specifically refers to the current-carrying capacity per-unit length along the inserted edge of the card.
By this measure, some Molex customers drive as much as 300 A/in. Molex offers the Power Dock Sr. connector, which is rated for 350 A/in. and has a profile of 25 mm. This series uses a modular approach with a maximum current of 150 A per module.
Apart from sizing these connectors to support the anticipated currents, connector size also can contribute indirectly to thermal management. This is because the profile of a connector can have a significant impact on airflow. To enhance airflow, the Low-Profile Hybrid (LPH) connector from Molex (Fig. 3) is half the height of connectors with the standard 15-mm profile and supports currents from 120 A/in. to 140 A/in. For more information, see www.molex.com.
As shown by these examples, the flexibility of customization combined with the repeatability derived from establishing standards is one approach to enhancing reliability. Another approach adapted by Onanon is both simple and subtle: the concept of incorporating embedded electronics within the connector housing.
Jim Levante of Onanon stated that custom design is key for its Multi-Wise product line. Each of these connectors is equipped with an FR4 board that can house active and passive components. In one application, 3 ICs and 30 discrete devices were incorporated into a single connector. It is also possible to incorporate fiber optics.
Onanon also makes bladed connectors for the auto industry. The blade configuration, pin material and package are carefully designed to be surface mountable and handled by pick-and-place machines, which is keeping with their functioning more as electronic modules than as simple electrical parts. Another area of application is medical equipment. In one project, a 26-pin connector was equipped with a unique resistor that communicated information about the kind of surgery for which the attached cable was designed and the power requirements of the attached accessory. This $1 unit replaced a connector that was $20, highlighting a unique aspect in Onanon's approach to connectors. Rather than focusing on high current-carrying capacity, emphasis is placed on precise current capacity, resulting in lower costs. Another aspect is that connectors can do much more than simply “connect.”
Long-range research efforts by Onanon will continue to explore solutions for automotive applications. In particular, solutions for connecting to ICs mounted directly onto internal combustion engines are being explored. For more information, see www.onanon.com.
Though by no means comprehensive, all of these products and technologies are diverse enough to reflect the continued innovation in the field of power connectors. Perhaps more than any other electrical part, these components epitomize innovation, which is essentially a matter of making the right connections.