Bench Talk

(Source: Heng Heng - AI Stock/stock.adobe.com; generated with AI)

Energy is one of the most costly elements of data center operation. With data centers increasing in size and quantity worldwide, finding more efficient ways to deliver power will be essential to reducing costs and environmental impact. In the quest for more efficient data centers, optimizing how power is transmitted will become increasingly important as they grow amid emerging data demands. In this blog, we will examine the power distribution challenges data centers pose and how connector design plays a pivotal role in maximizing power density.

Managing the Heat

Resistance is a feature of every electrical circuit, and it causes some energy to be converted into heat. Many connector manufacturers publish derating charts that present valuable information about how electrical current impacts temperature. These charts show how the current passing through a connector affects the surrounding ambient temperature. 

For example, the derating chart in Figure 1 shows that a current of 10A passing through the contact will increase its temperature by 80°C. If this connector were installed in a comfortable 20°C environment, the temperature of the contact would rise to 100°C, which is high enough to cause injury to unprotected skin. 

Figure 1: This example derating chart shows that a current of 10A passing through the contact will increase its temperature by 80°C. (Source: Author)

We must then compare the effect of this heat on the connector’s published operating temperature, which will be defined by the material from which it is made. A typical operating temperature for an industrial connector is 105°C. If the ambient temperature is high, as we might find inside the server cabinet of a data center, an 80°C temperature rise may risk damage to the connector. 

Getting More from Less

Manufacturers have created several different solutions for the temperature problem. The simplest solution is to provide the connector with larger contacts. Since the electrical resistance of a circuit can be reduced by increasing its mass, a larger contact with more material will have a higher current rating.

Other designs solve the heating issue with a greater pitch. Pitch describes the distance between the centerlines of adjacent terminals within a connector. Increasing it will aid heat dissipation, which should reduce the temperature rise for a given current. 

However, increasing the contact size or pitch will result in a larger connector. At a time when electronic components are becoming smaller, designers do not always have the luxury of using larger connectors.

Therefore, manufacturers are challenged to create connectors that can deliver more power in less space. To illustrate the importance of getting more from less, we need to understand the concept of power density. Connectors are among the largest components on the printed circuit board (PCB). Facing this constraint, designers must pass the highest possible current through every inch of PCB space.

Let's look at two popular connectors to illustrate the importance of power density and how it can be improved. Figure 2 compares an industrial connector, shown in gray, with a larger connector from the Micro-D family, shown as the wireframe outline.

Figure 2: Comparing an industrial connector (gray) to a larger connector from the Micro-D family. (Source: Harwin)

Both connectors feature a similar number of contacts but slightly different performance. The gray connector has 26 contacts, each capable of delivering 2A, for a total capacity of 52A. In contrast, the Micro-D connector has 25 contacts rated at 3A, so the total performance is 75A.

However, the Micro-D connector is more than 60 percent longer than the industrial alternative. Therefore, if we calculate the power density in amps per inch of PCB space, the industrial connector can deliver 11 percent more power per inch than the Micro-D despite having contacts with a lower current rating (70.3A per inch compared with 63.3A for the Micro-D).

Understanding power density is critical to the design of compact power connectors, and the component at the heart of the connector itself—the contact—is key.

The Importance of Contact Design

Conventional electrical contacts are usually a two-part system, with a fixed pin contact that is inserted into a socket. The socket is split or bifurcated to provide constant pressure on the pin to ensure electrical continuity, known as the normal force. The contact area between the terminals’ surfaces can be quite small, so design adjustments must be considered. 

Increasing this area will reduce the electrical resistance and, therefore, improve the current-carrying capability of the contact system. This can be achieved in several ways. Some contact designs replace the conventional bifurcated socket with a basket, or lamella, design. This basket comprises a cylindrical spring that makes 360° contact around the pin, greatly increasing the surface area in contact. However, this is an expensive solution. Alternative designs use stamped-and-formed contact designs that offer multiple points of contact to achieve the same result—more surface area means reduced electrical resistance.

However, these contacts can still be quite large. Using blade-type power terminals (Figure 3) can achieve a similar improvement with a smaller footprint. In place of cylindrical pin terminals, blade terminals allow a large contact area between the two mating halves. The slim design of these terminals allows several such contacts to occupy the same amount of space as a single cylindrical pin. While the current rating of a single-blade terminal may be lower than an equivalent circular pin, the ability to mount many in the same space achieves an improved power density.

Figure 3: PCB connectors using blade contacts allow multiple contacts to be mounted in the same space. (Source: Samtec)

Conclusion

Conventional connector design has often solved the problem of greater power capacity by providing larger contacts. However, designers of the latest data centers and compute modules do not have the luxury of using bulky or cumbersome power connectors. Alternative contact designs deliver superior performance, even if individual current ratings are lower. When creating the power supply for your next application, whether you are designing a data center or a handheld device, remember that power density is often more important than current ratings and that bigger does not necessarily mean better.