Single-Output "Brick" DC-DC Converter Modules

Currently, distributed power techniques, called distributed power architecture (DPA), are used for systems that dissipate hundreds of watts. The DPA approach converts the incoming ac power line to a dc bus voltage, usually called a front-end supply. This dc bus voltage is usually 24V or 48V and less than 60V. Single-output "brick" supplies accept a 24V or 48V bus input and furnish a single output voltage from15V to 1.0V.

Modular "brick" dc-dc converters supplied by the front-end supply provide electrical isolation, increased load transient performance and a modular upgrade path. Their lower output voltage draws a larger current (for a given power level) and has less tolerance for deviations in its voltage caused by voltage drops on the lines between the converter output and its load.

An advantage of the DPA approach with multiple dc-dc converter "brick" modules is that the heat produced by each of the modules is spread throughout a system. In contrast, most of the heat associated with a centralized power system is in the single power supply.

Use of a dc bus voltage, typically 48V, also means cables with lower current are bussed throughout the system. Higher current requirements are handled by the dc-dc converter modules that are located close to their loads, which minimizes distribution losses and enables smaller, less expensive conductors to be used for the cables that bus the intermediate voltage.

From a reliability standpoint, each element in a DPA has its own power supply, so failure of a single dc-dc converter module will only affect a single function or p. c. board, which aids the design of fault-tolerant systems.

DC-DC converter "brick" modules are a key ingredient in distributed processing architecture systems. The performance of these converters is directly related to the IC operating voltage requirements that are dropping from the historic standard of 5V to 1.5V, with projections of less than 1V over the next decade. Besides the 5V and 3.3V outputs, some converters now provide 2.5V, 1.8V, 1.2V and some can supply 0.8V.

"Off-the-shelf" standard "brick" converters can lower system development costs and also shorten design cycles because of they have already been tested and are available from multiple sources. If the system's powering requirements change, it is relatively simple to replace one converter module with another, that is, no major redesign is usually required.

The majority of packaged dc-dc converter "brick" modules are mounted on p.c. boards holding associated digital circuits. Therefore, the converter module's size impacts a board's circuit density. This includes the converter's footprint area that determines how much circuitry can be placed on the board. Converter module height is also important because it affects spacing between boards within the system. Eliminating the need for a heat sink also allows tighter board-to-board spacing.

To operate without a heat sink and provide more power output, the "brick" dc-dc converter must be efficient, particularly at the new lower semiconductor operating voltages. Therefore, the converter must minimize its internal power loss and the operating temperature of its components. Achieving higher efficiency also reduces the system's input power and cooling requirements. Plus, it influences system manufacturing and operating costs.

Minimizing internal power loss lowers the converter's case temperature, which may eliminate the need to employ forced-air cooling. Most converters have maximum case temperature ratings less than 100° C.

One approach to reducing internal power loss and improving converter efficiency is to employ synchronous rectifiers that use MOSFET transistors. This higher efficiency obtained by synchronous rectifiers means the converter dissipates less heat and may no longer require a heat sink.

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