ENGINEERING FEATURE

Medically Qualified Power Solutions for Non-Patient-Contact Applications

The medical market is large, varied and expanding rapidly, because as the population grows and ages it needs more medical care. Few hospitals or healthcare centres can function without electrically powered devices. The market for designers of medical equipment therefore seems unlikely to suffer any slowdown – and power supplies are essential in most of this equipment.

This feature looks at power supplies suitable for some medical applications and products carried by Arrow from four suppliers whose technologies meet the specific demands of this expanding market. These suppliers offer a wide range of device ranges and models and this feature highlights miniature build-in devices from Astrodyne Corporation, high-power products from Emerson Network Power, isolated DC/DC converters from Recom, a new supplier to Arrow, and external supplies from FRIWO.

Power supplies for use in a medical environment must conform to one of two main specifications. Full approval to the EN6061-1 safety standard is the minimum pre-requisite for any product aimed at the medical power supply market; EN6060-2 is the most stringent and used for patient-contact equipment like life support, defibrillator, dialysis and others. EN6060-1 qualification is sufficient for power devices serving less intimately connected systems, such as ward TVs, adjustable beds, patient hoists, blood pressure monitors or laboratory equipment.



In this article, we focus on supplies that conform to the EN6060-1 standard. As in other areas of life, safety, recycling of outdated equipment, reduction of hazardous chemicals or metals and other general concerns influence the choice of equipment for medical applications. All equipment therefore also needs ROHS and WEEE certification.

Flexible, Configurable Power

We look first at the iMP range of devices from Emerson Network Power, a market leader in AC/DC power supplies with an extensive product portfolio. Many of its standard power supplies are available in medically approved versions. The company's low to medium power AC/DC medically approved power supplies, for example, range from 40W to 500W and offer an exceptionally wide variety of configuration options. Most are available with either single or multiple isolated outputs in numerous voltage combinations and several provide auxiliary outputs for powering fans and standby circuits.


Figure 1: Emerson Network Power iMP Series Programmable Supplies

Emerson Network Power's medically approved iMP™ series comprises digitally controlled switchers combining modular design with onboard processing to deliver flexible, intelligent and configurable AC/DC power that can be monitored and controlled via I²C. The series offers power ratings of output modules from 144W to 750W, including single, dual and triple output units. The iMP series offers 25 standard output voltages but by using the I²C interface and the easy to follow GUI, any output voltage from 2VDC to 60VDC can be programmed. Up to 21 fully isolated outputs can be provided in one package.

The iMP series is a development of the hugely successful MP series using the proven modular concept and adding the ability to adjust almost any parameter of the power supply – output voltage, current limit (foldback or constant current), fan speed, inhibit/enable as well as monitoring power supply voltage, current and temperature via an easy to use interface. The user can also save the settings of their power supply requirements using the provided software and send the file to Emerson to have production units configured to their specific settings at the factory before shipping. The iMP delivers higher power density (1500W in 2.5in x 8in x 11in (6.4cm x 20.3cm x 27.9cm) vs 1200W in the MP series) than the still available MP series at a lower price per Watt.

Unlike many other power supplies on the market, the iMP series was designed from the outset for both medical and industrial applications and carries full approval to EN60601-1. Arrow carries stock of all case sizes and output modules in its fully approved, 212,000ft² (19,695m²) facility allowing rapid turn around times for prototype and production quantities.

The iMP series provides designers with flexibility by allowing the configuration of application-optimised AC-DC power solutions that can accommodate new or unforeseen power requirements as they occur. Comprehensive control and monitoring functionality is possible via an I²C bus using the standard PMbus protocol between a host controller and the power supply.

Optimised iMP supplies can be configured using three customisable cases accepting input voltages from 85VAC to 264VAC or 120VDC to 350VDC. Cases can accommodate up to seven individual modules supplying any output voltage from 2VDC to 60VDC. The result is a flexible product range that offers over 200 million different configuration options.

Setting up an iMP series via the PC-based control software is intuitive and straightforward, with the same control screen used for all modules and all operating parameters. In addition to defining a module's output voltage and current, designers can adjust OVP, UVP and OTP limits, change OCP mode and control signals, set DC OK thresholds, program output enable and sequencing and force fan speed over-ride if required.

Miniature and Approved

Founded in 1994, Astrodyne designs and manufactures more than 3,000 cost-effective standard and modified standard products suitable for a broad array of markets and applications. Among its extensive product range are several product series approved for medical power applications. We shall look at three of them here.

The E-Series of miniature medically approved switching power supplies offers output power from 5W to 30W and a high degree of packaging flexibility enabling customers to select the best mechanical and connection fit for their specific applications. All E models accept universal input over the range of 90VAC to 264VAC and provide single, dual and triple output (30W) configurations with voltages from 3.3VDC to 48VDC.


Figure 2: Astrodyne Medical AC/DC Switching Supplies

Just 2.5in x 1.7in x 0.9in (62.6mm x 42.2mm x 23.1mm) in size, with 4kVAC input to output isolation, the E-Series meets EN60601-1-2 immunity and Class B low-leakage specifications for medical/dental instruments and industrial applications. Pin-mount PCB plug-in or screw-terminal chassis mounting is available and either fully encapsulated for durability and environmental protection or as open-frame pin-mount PCB for more environmentally friendly conditions. All operate over an ambient temperature range of 0 to +50ºC without forced air cooling or output power derating. The E-Series is also available with an optional DIN-rail style mounting in the chassis mount style.

The ASM Series ultra-miniature, open frame, switching power supplies provide output power between 10W and 15W from universal input from 90VAC to 264VAC. Ten models are available providing single outputs of 3.3VDC to 24VDC. They have corner mounting holes, connector pin-out and mounting size compatible to more costly industry-standard products. The ASM Series features single sided construction for high reliability, an integral power-good LED indicator and an output adjustment potentiometer and operate over an ambient temperature range from 0 to +50°C without forced cooling or output power derating. They contain short-circuit protection and internal input filtering. The dimensions of the 10W model are 2.3in x 2.0in x 0.6in (51.2mm x 45mm x 12.6mm) and all models feature mini Molex style I/O connections.

Thinking Outside the Box

In contrast, FRIWO supplies universal input (100VAC to 240VAC) power adaptors for standalone external use. With products suitable for both stationary and mobile medical equipment, FRIWO is the world's largest manufacturer of high quality plug-in power supplies and battery chargers for medical applications.


Figure 3: FRIWO’s GPP 18 Switch-Mode Plug-In Adaptors with Interchangeable Primary Adaptors

The standard products cover a power range from 8W to 50W with a low leakage current of ≤10μA satisfying the EN 60601-1, Class CF standards for medical technology. The products offer a wide input range in different housing variants: plug-in, desktop and plug-in housing with interchangeable primary adapters. The units have green LED indicators, are continuous short-circuit proof, lightweight and compact with high efficiency and low standby power.

For 8W to 30W, the PP 8 and MPP 5/30 plug-in switch-mode power supplies have interchangeable primary adaptors and suit inhalers, patient monitors and lifts as well as lab equipment and measuring instruments. For the same applications, the DT 12/50 range is in desktop housing and offers 12W to 50W power. GPP 18 is a new range of 18W switch-mode power supplies for blood analysers and similar equipment offering 5V, 3000mA to 24V, 750mA output and 80% efficiency. The PP 8 MPP 15/30 are switch-mode chargers for lead-acid, nickel-cadmium, nickel-metal hydride and lithium-ion batteries in plug-in housings.

These are inexpensive, readily available products suitable for worldwide use and are RoHS and WEEE ready. The devices meet, and sometimes exceed, the strict criteria and standards demanded in medical technology, e.g. for reduced energy consumption at no-load. FRIWO meets the demands of the EU Electrical and Electronic Appliance Act, ElektroG and full medical application class B/BF/CF; products are IEC 60601-1, UL 2601, VDE, CE approved. In addition, FRIWO develops complete customised solutions from design through to a finished product and available in open frame versions.

DC/DC Conversion

Recom is a very recent signing for Arrow adding more than 9,000 different power-related product models - suitable for all markets and applications – to the Arrow power portfolio. To address the medical electronics sector, Recom manufactures a range of DC/DC converters with high isolation voltage rating between input and output that is ideal for medical applications. These devices are part of Recom's Econoline DC/DC converter range. All products offer the option of inbuilt short circuit protection.

Traditional transformer windings cannot satisfy the required creepage and clearance distances required for medical products that require reinforced system of insulation, but Recom has developed a system that uses an unusual two-chamber transformer system to achieve isolation voltage of 5.2kV while satisfying the defined mechanical requirements. Recom is one of only a few manufacturers to have perfected this system.

Each winding is separate in the transformer and the isolation is therefore not wholly reliant on the thickness of the lacquer, as in traditional transformers, but also on the physical separation between the wires. There are two different techniques; separation by means of a separation bridge (see figure 5 left) or the pot system, in which the transformer core and primary windings are entirely encased. One winding is directly around a toroidal kernel placed within a non-conductive, annular plastic pot covered with a lid. The secondary winding is annular around the whole construction (see figure 5 right). This method delivers excellent results in a sub-miniature size.


Figure 4: Separation Bridge (left), Two Chamber System (right), the Arrow Indicates Wires to the Core

Recom's RP series have pot-core transformers and offer 1W, very high isolation of 5.2kVDC per second in a SIP7 case with single or double output.


Figure 5: Recom's RTS-RTD 2W SMD DC/DC Converters

The RxxPxx (1W) / RxxP2xx (2W) series are unregulated converters that use the separation bridge system and offer 5.2kVDC isolation for one minute, also in SIP7 cases. These are commonly used in telecommunication and safety applications.

The RV series are 2W, unregulated converters offering 6kVDC per second in DIP24 cases; these find use in industrial and medical designs.

Summary

The global medical equipment market is likely to continue increasing in size as developments enable new systems and as more geographic markets open up. In turn, the need for safe, medically approved sources of power is also likely to keep increasing. By stocking a wide range of internal and external power conversion technologies from the industry's leading manufacturers, Arrow's aim is to provide designers of medical applications with a comprehensive portfolio of standard and configurable solutions that will allow them to meet the vast majority of requirements in non-patient-contact designs.

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