Power supply cooling is more important than ever

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It's an old engineering story, sometimes told in jest, but usually not: The power supply is a specific last-minute item. The idea is "once we know our power requirements, we have to find a suitable power supply." With increasing demands for greater energy efficiency, higher reliability, and faster design cycles, as well as increasing regulation, this approach is unacceptable.

An effective engineering team will consider all aspects of power requirements, including thermals and packaging, early in the project. Considering the power system early in the project is critical if you are to avoid the unpleasant surprise of needing a larger power supply, or a new cooling strategy. No one wants to hear, “Don’t forget, I thought we might add a fan here,” as the project nears completion.

Vicor's Power Component Design Methodology is a power system design approach that helps engineers build power chains while maintaining flexibility. If requirements change, it can simply replace the selected power components with devices that will meet the new specifications. This is easier than using a large centralized power supply, whose entire power system may have to change to meet the revised specifications.

Now with various tools that simulate and connect electrical and thermal performance, such as PowerBench Whiteboard, it is easier to create optimized thermal designs. Sometimes it is even possible to squeeze more performance out of the system's available power, reduce the need for "just in case" tolerance buffers, or increase reliability due to cooler operation.

Selecting the right power components is key. Open frame power supplies have been used in the past because of convenience, but they present some challenges. Due to their irregular "contour" lines, airflow can be uneven and can be blocked ("shadowed") by adjacent components. Heat sinks can solve this problem, but require the use of an interposed elastomeric gasket between the converter and heat sink, or a dedicated pre-heat sink.

At the same time, the available heat conduction range through the converter pins to the system PC board copper is modest to negligible at best. The result is poor cooling and the appearance of local hot spots where individual components may experience thermal stress, especially in “corner conditions,” even if the overall average temperature is within the allowable range.

Recent molded (encapsulated) converter packages, such as the Vicor ChiP platform, overcome these limitations. The smooth, flat top surface means heat sinks are easy to attach and use effectively.

Likewise, the latest designs and increased lead counts provide a simple, efficient, low-impedance thermal path to the case or cold plate. So it’s a win-win for both convection and conduction, see Figure 1. (With dual-convection convection, there’s even a few percent extra cooling, which is an added bonus.)

Figure 1 : Modeling and analysis of the molded package shows that it provides multiple effective thermal paths.

ChiP packaging provides double-sided cooling, which doubles the ability to remove package heat but increases the complexity of heat sink design. Optimizing thermal design presents the greatest challenge to the front end of the power chain, where power levels are often the highest.

The new Vicor Integrated Adapter (VIA) packaging technology greatly simplifies the design of the front end of the power chain, especially the thermal design. By providing new levels of power density, efficiency and thermal performance in an easy-to-use package while integrating some peripheral circuits such as filtering, the VIA package helps engineers more easily develop efficient and thermally efficient power chains.

Figure 2 : Vicor Integrated Adapter ( VIA ) packaging technology

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