Challenges of power supply design for harsh environments
Compact DC-DC converters have made their way into millions of electronic products and systems. The majority of these depend upon an AC front-end power supply box to convert the AC power source into a DC voltage from which the converters operate.
Regulations have required that these front-end boxes include Power Factor & Harmonic Correction (PFHC). Add to this the need to achieve compact size and often operate with severe ambient temperature extremes and the designer is faced with a problem that is not easily solved.
Traditional designs that employ distributed power architecture place non-isolated DC-DC converters on PC boards very close to the point-of-load (POL) to maximise system speeds and efficiencies. These are fed from a high power isolated DC-DC that is also PCB mounted.
These isolated converters will be typically supplied with 48V or 24V from a fan cooled AC-DC power supply with PFHC mounted somewhere in the system’s enclosure, external to the main PC board.
This technique is quite practical for most applications. However, when it comes to equipment that must be situated in an outdoor enclosure and occupy the smallest possible volume a complete brick-based solution is the most common method used.
Manufacturers of DC-DC converters have been providing AC input PFHC front-end modules with high voltage (typically 360V) DC output that are PCB mountable. These modules supply typical high power (400-700W) DC-DC converters packaged in half and full “brick” sizes that can accept high voltage input (between 200V and 400V). This has the advantage of placing all the power components on the same PC-board thus reducing the end product’s size and eliminating the power interconnect wires.
These AC-DC w/PFHC front-end modules require some external passive components, such as storage and filter capacitors, but the space required for these items is small in comparison to the elimination of the external metal cased AC-DC power supply and these external components can be inserted automatically during the production of the PC-board.
An added advantage of using modules is that they are base-plate cooled and, therefore, fans can be eliminated with cooling effected by means of heat sinks or conduction through the system’s metal enclosure.
Recent advances in components and power design technologies have made it possible to shrink the two brick design into smaller “2-in-1” PCB-mount power bricks. To increase power densities, special permalloy cores have been developed and employed in the inductors.
New substrates and innovative transformer winding techniques have facilitated component height compressions and improved thermal management. And, of course, advances in integrated and hybrid circuits have contributed greatly to this next generation of power products. For example, the PFE series of integrated 2-in-1 AC-DC power bricks are suitable for both indoor and outdoor applications.
The regulated models are available in 12, 28 and 48V nominal outputs and can be adjusted over a +/-20% range. These PCB-mounted power bricks are suitable for distributed power architectures because they can drive POL converters directly, with no intermediate bus voltage needed.
David Buck is market development manager for Lambda Europe