Originally Published MEM Fall 2001
POWER SUPPLIES
Modular Power Supplies: Meeting the Requirements of Medical Electronics
Modular power supplies offer a flexible solution to power output needs.
Terry Hill
 |
|
Figure
1. Different dc output modules can be plugged into an ac power platform
to meet a variety of power requirements.
|
The electronics industry is changing rapidly, and product life cycles continue to get shorter. In addition, medical electronics manufacturers are faced with relatively small production volumes within each model range of their equipment. The result is a substantial amount of added pressure on engineers who are required to move product concepts from design into product shipments in the shortest possible time.
The power supply is one of the last devices to be finalized in many systems integrated after the broad product design is near completion. Late-stage integration adds an enormous amount of time pressure on the selection and sourcing of a power supply that meets the requirements of the system being designed.
Furthermore, in line with the shorter product life cycles, a revision, upgrade, or modification to the system will likely be required shortly after a product reaches the market. Such marketing and production requirements mean that allowing 6–8 weeks to obtain a prototype power supply followed by 12 weeks for delivery of production quantities is simply not feasible.
Modular Solutions
Modular switching power supplies promise to do for the electronics industry what plug-and-play accessories did for the Windows PC market. Built from stock modules, a modular power supply can be configured to meet system specifications. For example, a manufacturer can configure a custom power supply from more than 250,000 options by selecting stock modules using a Web-based utility, submit the order electronically, and receive the power supply in a few days. After reviewing the power supply, a batch of prototype units can be ordered and delivered by the following week, with volume shipments following as the manufacturer's device goes into production in just a matter of months.
Modular power supplies are based on two major components that make all of this possible (see Figure 1). The first is a power platform that takes in ac power and converts it into power factor–corrected dc power. This dc power is supplied to the output modules, which are designed to provide regulated dc power at specified voltages. In most cases, a selection of different modules can be installed into the power platform to provide the entire range of output voltages to meet system load demands.
Not only does this make economic sense by providing exactly the right power source in a very short time for the prototype stage, it also makes very good economic sense for production quantities. Manufacturers who use modular power supplies no longer need to stock a large inventory of power supplies that could become obsolete before they can be used. In addition, device manufacturers get the benefits of cost-effective, high-volume manufacturing, even on small quantities. Power platforms and output modules used in modular power supplies are manufactured in large quantities, very often in cost-effective manufacturing centers in the Far East. They are then stocked, assembled, and tested in efficient plants close to the market, ready for delivery to domestic users as required.
Modular power supplies are increasingly attractive to both small- and large-volume manufacturers because they eliminate costs associated with safety-agency approval. Because power platforms and output modules carry recognized global agency approval, regardless of the particular configuration chosen, power supplies arrive preapproved. Such power supplies have demonstrated mean-time-between-failure numbers because the component power platforms and output modules have been field tested in many applications, including medical electronics.
The process of configuring a different power supply for a new variant to the current system is made simpler by the use of modular power supplies. A power supply built on an architecture with which the manufacturer is already familiar and has worked with before can speed the time to market.
The new generation of modular power supplies are rated at 150–2000 W, with outputs in all the common voltages, from 1.8 to 48 V, at currents as high as 100 A. Some are packaged into open-frame designs as small as 1.5 x 5 x 7 in. that fit into a 1U rack space. Most are available with built-in cooling fans and covers to maximize cooling and minimize electromagnetic interference, respectively. Many are approved for operation in medical environments. Modular switching power supplies offer manufacturers the ability to integrate the required power source quickly without building their own power supply.
Terry Hill is a program manager at Switching Systems International (Anaheim, CA), where he manages product development and marketing of the company's power supplies. He can be reached at thill@ssi4power.com.
Copyright © 2001 Medical Electronics Manufacturing
