Putting designs on power supplies

  • 30-Apr-2009 11:55 EDT
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Working closely with its component suppliers, Orchid developed this power supply that offers a proven 150,000-h meantime between failure. Brown-out detection, over- and under-voltage protection, and thermal protection are performed with an onboard power supply microcontroller.

Power supply design for avionics and ground-vehicle electronics has become an area of increased activity over the past few years. Today’s designers voice common concerns about power supplies, including the need to reduce weight, improve both efficiency and reliability, and hot-swap and load-sharing features.

New to the market are high-current, lithium-based battery systems. Available from a wide variety of vendors, these industrial-quality batteries are characterized by their low weight and high energy availability. In both avionics and ground-vehicle applications, every pound saved counts.

Typical older equipment provided portable power with heavy lead-acid battery systems. Redesign of these older lead-acid systems can result in a 50% or more weight reduction without sacrificing stored energy performance. Couple low-mass lithium batteries with reduced-weight electronics design and a modern battery power supply can vastly improve the available energy-to-weight ratio of the entire power system.

Efficiency improvements in power supplies can be achieved through careful selection of the power supply topology for the required application. Core efficiencies of 90% can be achieved; core efficiency refers to the actual switcher design efficiency prior to application of additional features.

Supervisory features such as over- and under-voltage lockout, current fold-back, over-voltage detection, redundant controls, and power factor correction can rapidly eat away at a power supply’s core efficiency number. Working closely with mechanical designers, a power supply can be crafted that is small in size, efficient, and easy to cool.

Power supply reliability and proven meantime between failures—in short, design quality—is of paramount importance in avionics. Power supply reliability can be greatly increased through conservative design techniques, referred to by Orchid Technolgies Engineering and Consulting as “design discipline.” Orchid designs custom electronics for the telecommunications, cable TV, military, and avionics industries.

A high-reliability, thus high-quality, power supply design is one in which every component part has been analyzed. A component’s normal operating range, de-rating curves, altitude effects, and known useful life characteristics must be considered by the conservative designer. Experience counts when making component selection. Often a thankless task, part selection is easily 75% of the challenge in high-reliability design.

Balancing circuit board physical area constraints, de-rating requirements, and component cost is a delicate art. The best designs are achieved when component selection is not rushed.

Power supply hot-swap and load-sharing features have become extremely popular. The ability to swap one power module for another results in greatly reduced overall system meantime to repair (MTTR). When aircraft or ground-vehicle service must be performed quickly, low MTTR power supply subassembly designs really help. Use of low-cost edge finger contacts, modular subsystem design, and the ability for subsystems to load-share makes hot swap possible. Ideal diode field-effect transistor output stages can perform load sharing with great efficiency, low cost, low weight, and low heat.

Microcontroller supervision can add a layer of system-level monitoring of power supply health. IPMI (Intelligent Platform Management Interface)-based power systems provide an industry-standard method of performing power management. Alternately, custom communications can be implemented to supervise power management.

Paul Nickelsberg, President and Senior Engineer, Orchid Technologies Engineering and Consulting, wrote this article for SAE Magazines.

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