Sometimes the best way of handling specialized power needs is through custom equipment optimized for the situation at hand.
Alex Karapetian, Acopian Technical Co.
Electronic system designers, engineers, program managers and original equipment manufacturers (OEMs) must address numerous challenges in the selection or development of an appropriate power supply for their systems.
In some cases, the best approach is to adapt an existing power supply from a different application. In other cases, it may be necessary to develop a new or custom power supply.
To understand how a custom approach to power sources can be helpful, it is useful to examine five major challenges faced in the design of power supplies.
Older systems that have not been updated for several years tend to use older-generation power supply technology with larger form factors. Depending upon the physical requirements of an application, power supply designers have had to become increasingly creative to adapt to changing space demands. We have reached a point where “off-the-shelf” supplies may be inadequate.
For example, in one case a leading auto manufacturer needed a linearly regulated rack-mounting power system for a high-speed test data acquisition console. The system had to be custom-designed to fit in the 3U space that was available while operating at no more than 55°C. Customization included chassis slides modified to fit a special cabinet, and top and bottom covers.
Non-Standard ac and dc Inputs — Today’s world is increasingly run by microprocessors that are sensitive to even small voltage fluctuations. Many power problems originate in the commercial power grid, which, with its thousands of miles of transmission lines, is subject to numerous power disturbances related to weather conditions, equipment failure, traffic accidents, and switching problems. Some of these problems include transients, interruptions, voltage fluctuations and frequency variations.
A robust power supply must reliably operate through input power disturbances to ensure the reliable operation of the systems it supports. While most applications still use 115 or 230-V inputs, new applications may call for special ac and dc input voltages, and power supply companies are adapting to meet these changing requirements.
For example, in one case an industrial firm needed a redundant power supply system that accepted inputs from two separate power sources, one a battery backup. The use of the redundant inputs would ensure uninterrupted production on an automated assembly line. The solution came in the form of custom redundant supplies built with both 24-Vdc and 125-Vdc inputs and included dual voltmeters and ammeters.
Non-standard output voltages — Electronic components and systems that operate at “standard” or “generic” voltages (e.g., 5, 12, 24, and 48 V) may be inefficient because the power that is not used produces extra heat in the system, which must be dissipated to keep the supply within its operating temperature range. Modern electronic components may need to operate at non-standard voltages to maintain high system efficiency while taking up a small amount of space. This requirement poses problems when off-the shelf power supplies aren’t feasible.
For example, a company specializing in optoacoustic imaging needed a custom-designed rack-mount power system with many specific physical attributes. It had to have dc outputs providing 0.5 A at 5 V, 10 A at 6 V, and 25 A at 6 V. The supply also needed a 230-Vac IEC output to power a second rack-mounted power supply. Additionally, all inputs, outputs, and controls had to reside discreetly on the rear panel, leaving the front panel completely blank. The supply needed provisions for airflow to cool both the custom supply and the second rack-mounting supply. But because of the existing setup, the cooling fan had to pull air in from the bottom of the unit.
Ruggedization — Systems exposed to extreme temperature environments or high vibration often require environmental qualification in various, and often harsh, environments. Power supplies for the armed services must be built to specific standards. Many older systems don’t use components qualified for such environments.
For example, in one case a major university research lab needed a redundant power source designed to handle extremes in temperature, elevation, and vibration. The application called for a custom power source that included features such as four sets of individually fused 48-V, 2.5-A dc outputs each with an output-fail LED, cascaded alarm contacts with audible alarms for each output, an alarm disable/timer switch, and a switchable 115/230 Vac input.
Component obsolescence — Short consumer product life cycles make components become obsolete quickly. For markets with long life cycles, component obsolescence becomes a critical issue, especially when OEMs are required to maintain hardware in the field. Many older electronic systems may have power supplies that are obsolete or whose manufacturer is no longer in business. When these systems fail, users must find alternative power supplies that meet the form, fit and function of the older system. If such supplies aren’t readily available, it may be necessary to redesign and recertify a new power supply.
In one case, the original manufacturer of a power system at an industrial firm had ceased operation. The dc-dc power supplies powered alarm systems at multiple facilities. To duplicate these supplies, engineers had to get photos of the existing supplies and copies of the literature that originally accompanied them. This approach enabled engineers to refine specifications prior to designing replacements. Features of these supplies included a 125-V dc input, outputs at 5.6-V and 4 A, 12 V and 15 A, and 125 V at 500 mA, provided through six sets of output terminals.
Customization — Specialized needs have made manufacturers more aware of power supply customization. An example is that of a leading manufacturer in the medical device field. It needed a special rack-mount power system that would sit in a dark room used for developing X-ray images. The equipment that generated and managed X-Ray data required reliable, consistent and clean power. This meant that in addition to standard power system requirements like multiple outputs and failure alarms, all LED indicators and digital meter lighting had to be capable of being switched off while the power system was still in use. And the power supplies had to provide consistently clean and reliable power within a tight tolerance of output current. The resulting custom design employed linear power supply modules and toggle switches on the front panel for individual control of LED indicators and digital meter backlighting.