The Problem with Power
By Bob Hult, Bishop & Associates Inc.

The need for speed has been a key mantra since the introduction of electronic computers. Faster means more calculations per second, which equates to more functionality at the system level. Faster processors also typically consume more power and generate more heat. Semiconductor chips are OK with heat up to a point, beyond which reliability begins to drop like a stone.



At the same time, greatly reduced feature dimensions on the wafer have enabled individual chips with more than a billion transistors to switch more quickly, but they concentrate power demand and heat in smaller areas. With such tiny spaces between features, insulating materials allow greater leakage currents, adding to the total power consumption. On the other hand, an advantage is lower manufacturing costs.

Intel ran into this wall about 10 years ago, forcing them to step back and re-evaluate practical methods to increase speed and gate density while reducing power draw. A combination of advanced manufacturing processes, materials, power management software, and the introduction of multi-core processors has been the solution. Chip manufacturers have made remarkable strides in reducing the power consumed per calculation, enabling the continuation of Moore’s Law. Intel recently stated its objective to reduce its mainstream processor chip power consumption, currently in the 35 to 40 watt range, to 15 watts over the next few years. An explosion of new portable electronic devices, ranging from tablet PCs and smartphones to cardiac monitoring equipment, have benefited from the development of chips that enable extended service life operating on battery power. Advanced Micro Devices (AMD) recently announced their new A-Series processors that will greatly extend the battery life of portable devices. The ongoing evolution of the low voltage Intel Atom processor family begun in 2008 and a complete family of low power chips from ARM Holdings PLC has demonstrated the commitment to improving the instructions per watt equation in support of the mobile device market.

The advent of massive data centers and supercomputers that consume electricity comparable to a mid-sized city has provided additional incentive to develop servers that are more energy efficient. Many server farms use more power to cool equipment than what the equipment itself burns.

The Open Compute Project Server was an effort by Facebook to develop a cost- and energy-efficient computing infrastructure using as much off-the-shelf hardware as possible, combined with a no-frills design philosophy. The power supply achieves efficiency of 94.5%. Losses are minimized by replacing 208 VAC with more efficient 277 VAC to the power supply. The thermal design includes larger more efficient cooling fans that rotate more slowly, generating less noise.

More recently, Intel revealed its plan to introduce a new 3D transistor architecture based on 22-nm geometry that will operate at lower voltage with reduced leakage current. Chips using this technology will be available by the end of 2011.

A Silicon Valley start-up, SuVolta Inc, is licensing a new technology that reportedly cuts leakage current by 50%, further reducing power consumption.

One would expect with all of this emphasis on chip power reduction, that energy consumption at the system level would be dropping, and designing power distribution interconnects would be simplified. Not true. Product managers at leading connector manufacturers report demand for power connectors with increased current ratings in smaller envelopes, particularly in board-to board interfaces used in the datacom industry. Although each chip may consume less power than its predecessor, systems often incorporate many more chips to provide greater functionality, upping the total current draw.

Connector suppliers are being pressured to provide higher performance power connectors with greater electrical efficiency. Of particular interest is minimizing voltage drop attributed to the connector. As semiconductor operating voltages continue to drop to less than 1.5 volts, the power distribution loss budget becomes critical. Devices become very sensitive to variations in applied voltage. Designers are looking for power connectors with minimal change in contact resistance and resulting voltage drop over the life of the product. Although few applications anticipate the need to un-mate a connector under load, engineers still want sequenced mating/hot-plugability features in their power distribution connector scheme. Connectors are now often rated in amps per square inch as demand for increased power density grows. These issues are becoming an important connector selection criterion.

While the laws of physics that govern separable interfaces have not changed, suppliers are applying a number of solutions to address the challenge. Recently released connectors feature thicker contact materials using higher conductivity materials, wider beam contacts, and modified geometry to minimize resistance. Efforts to increase contact normal forces must ensure that insertion/withdrawal forces do not become excessive or the integrity of the plating surface is compromised. The layout patterns for power connectors mounted on PCBs are being optimized to minimize construction resistance and thermal buildup.

A study done five years ago indicated that many design engineers took a very conservative approach to specifying power connectors by cutting the suppliers published current rating in half, thus providing a generous safety factor, but adding cost and consuming valuable PCB space. Several product managers now report that they are hearing that some customers use the published power rating as a starting point, and want to know how far they can push the current to even higher levels.

The entire issue of current ratings continues to be a sore point within the industry. The lack of standardized test methods or evaluation boards among suppliers has resulted in widely different ratings among similar connectors. The conditions under which a connector is tested has a huge influence on the results. Factors include wire gauge crimped to a contact, thickness of copper in a PCB, still or moving air, the number of adjacent energized contacts, and ambient temperature. The meaning of end-of-life performance depends on exposure to elevated temperature, vibration, as well as exposure to corrosive salt spray or industrial gasses. Customers are looking for connectors that demonstrate minimal contact resistance change from initial to end-of-life.

The traditional method used to rate a power connector is to apply current to a mated pair of contacts in their housing until the temperature on the contact rises and stabilizes at 30°C above the ambient temperature. A viable method to increase the current rating of a connector is to keep the contact cool. The standard connector housing often acts like a thermal blanket, isolating hot contacts from the ambient environment and allowing heat to build up. Leading connector suppliers traditionally test their power connectors in still air, but are now receiving requests to provide test data with some degree of moving airflow. Molex, for instance, demonstrated significant increases in current carrying capability of a standard interface by increasing airflow at their DesignCon 2011 booth. Designing power connectors that take advantage of cooling airflow has become an important feature in newer power connectors. In some cases, the connector profile has simply been lowered to ensure that the connector does not obstruct the system airflow, while others feature “vented” housings specifically designed to allow air to circulate around the contact.

Although power connectors have been a staple interface for many years, many product managers report customers are now looking for more application-specific performance data, and general “hand holding” as they try to squeeze the most performance possible from the connector while minimizing costs. Engineers have asked their power connector suppliers for current/thermal modeling, as well as estimated current ratings given a specific airflow rate. The introduction of IPC-2152, a standard that addresses current carrying capacity of traces in a PCB, has minimized at least some of the confusion related to power circuit design.

Another trend that is impacting the industry is the movement toward higher voltages in the distribution system. Ohms Law indicates that higher operating voltages suffer less loss in a distribution system. Designers are now looking at more than 48 VCD in order to increase efficiency. Going above 48 volts presents a potential shock hazard. Several connector suppliers indicated increased interest in connectors that are designed to handle higher voltages and are “touch safe.”

Traditional applications for power connectors have been focused in the telecom and computing equipment markets, but suppliers are seeing rapid growth in emerging alternative power generation, and transportation. Wind and solar power generators, as well as associated storage and system management equipment, must withstand harsh environments that may include exposure to dust, salt spray, and rain in temperatures that may reach 105°C. Several connector suppliers have developed extensive power product lines that support the unique requirements of these industries.



Other connectors are designed for the burgeoning electric automotive market, and must be rugged enough to operate in challenging under-the-hood environments, as well as consumer battery charging stations. Power connectors designed to meet IP-68 can survive these dusty and wet locations for many years.

In response to these needs, connector suppliers have been busy expanding their product offerings.



Anderson Power focuses exclusively on power connectors using large spring-loaded contacts in a wide variety of configurations. The SPEC Pak™ series is a rugged waterproof connector family that is rated to IP-68 with touch-safe housings and contacts rated to 45 amps.

The modular housings simplify custom configurations and feature integrated latches.







The Saf-D-Grid® receptacle and plug are rated to 600 VDC, and feature first mate, last break ground contacts.

All contacts are recessed into the housing to pass UL and IEC finger probe tests.



 

FCI offers an extensive array of power connectors serving many industries.

The High Power Card Edge (HPCE™) connector family offers a low-profile, low-cost power interface with contacts rated to 9 amps in still air. The low profile of less than 7.5mm facilitates the movement of cooling air. Hybrid housing with both signal and power are available.

The HCI® connector system was designed specifically to address the needs of the power supply industry. Press-fit connectors are vented to maximize the current rating. Housings contain touch-proof power and signal contacts that offer sequential mating for hot plugging applications.

Contacts are rated to 52 amps in a loaded housing in still air.


 

Molex has consolidated many of their high current product lines under the EXTreme Power™ banner. These products offer increased current density and design flexibility.

Their EXtreme Power ten60™ family features up to 60 amps per blade and current density of 278 amps per square inch. Low profile housings facilitate airflow. Modular construction allows customers to create unique combinations of signal and power circuits.





The Molex Mini-Fit Sr.™ .is a higher current evolution of the popular standard Mini-Fit wire-to-board and wire-to-wire interconnect family. Connectors are available in 2-14 positions with a power rating of up to 50 amps in a two-circuit configuration.





Positronic Industries specializes in the manufacture of power connectors. The newest addition to their Dragonfly Series is a three-position AC/DC power input connector.

Screw machined contacts are rated to 20 amps each.
 

The Wondersun Power Connector is an example of an interface applicable to a wide range of applications in UPS, telecom, datacom, server power distribution transportation, and process controls.

The contacts are rated to 60 amps each and use their Large Surface Area technology to minimize contact resistance.

 



TE Connectivity offers a full range of connectors, including those designed for power. The MINI-PAK HDL series is an example of a low profile, vented hybrid connector designed for 1U server applications. Housings feature a generous +/- 2mm pre-alignment for reliable blind mating, and stand only 8mm above the surface of the PCB. Power contacts are rated to 16 amps each with mating forces of less than 0.3 pounds per contact.


The Dual Crown Clip™ contact is designed to mate directly to a solid or laminated bus bar in high current applications to 350 amps. It is designed for hot mating, and features a unique feed through design allowing multiple power supplies or loads to access a common bus bar. 

Bishop & Associates Comments:

1. In spite of advances in semiconductors that consume less power per instruction, power demand at the system level continues to rise. Applications that range from mobile devices to data center installations are demanding greater connector efficiency.

2. The physical envelope of systems is shrinking, which mandates that power connectors offer greater current density per square inch.

3. Power connector profiles are being reduced not only to prevent obstruction of system cooling airflow, but also to allow more air to circulate around the power contacts, resulting in higher current ratings.

4. Vented housings with airflow have been used to raise the current rating beyond the published rating.

5. Power connector manufacturers are being asked for increased technical support by their customers when specifying power connectors.

6. Recent emphasis on power connector development has resulted in many new interfaces that offer increased power density, design flexibility, and consume less space.

7. There will always be a need for custom power connectors in highly specialized applications, but the majority of commercial applications can now be satisfied with off-the-shelf or customer-specified modular interfaces.

Bishop & Associates, Inc. © 2011