Standard Measures to Keep in Check While Selecting Best Medical Power Supply Units

The term medical grade is applied to medical power supply units in a variety of package styles. These power supplies at a glance may look no different than their commercial grade counterparts. However, medical power supply units have been specially designed to meet and approved to the medical equipment safety standard which influences the internal power supply design.

However, safety is not the only factor that distinguishes medical grade power supplies from commercial models. Medical equipment typically requires longer design cycles than other types of equipment and medical equipment designers often require more design support from the power supply vendor. Additionally, medical equipment usually has greater life expectancy than other equipment. Therefore, medical power supply units are designated as medical grade generally need to be supported by the power supply vendor for many years.

Criteria to Follow for Selecting Best Grade Medical Power Supply Units

• Output Voltage & Current: Application requirements for supply voltage vary widely. To accommodate these needs, medical power supply units offer either single or multiple output voltages, typically in a varying range of 3 to 48Vdc. When determining the supply voltage levels required in an application, note the current levels that will be required at each voltage.

• Power Rating: If only a single supply voltage is needed, the power rating required of the supply will simply be the supply voltage times the maximum current required in the application. If multiple outputs are needed, add up the voltage-times-current products for all of the supply voltages to determine the power rating. Good engineering practice dictates that you select a power supply model with a rating that provides some design margin.

• Form Factor and Mounting: Medical power supply units are offered in a variety of package styles including open-frame, enclosed, encapsulated, and external adapter with a range of mounting options such as PCB mount and chassis mount. The selection of a particular package style depends on a number of application considerations. The advantage of the various package types are described in the other sections of this source book.
• Electrical Connection: The options for medical power supply input and output connections are related to the choice of mounting options. With PC-board mount packaging, I/O pins on the bottom of the supply insert into plated-through holes or sockets on an application pc board. With chassis mount packaging, the medical power supply units may include Molex headers or screw terminals that enable interconnects to be made using wire harness assemblies.

• Thermal Management: The ambient temperature range expected in the application together with medical power supply thermal specifications will determine whether convection cooling is sufficient or if forced air cooling may be required. Note that the packaging style will affect thermal performance and cooling requirements as outlined in the other sections of this source book.

• Environmental Factors: For applications where the medical power supply may be exposed to vibration or contaminants, the reliability of these medical power supply units can be further enhanced by the selection of an encapsulated power supply.

• Safety Standards: Medical power supply units must meet the safety standard for medical electrical equipment as implemented in regional versions. These standards impose additional safety requirements relating to creepage and clearance spacing, isolation voltage and leakage current beyond the requirements of the general safety standards. Medical power supply units also must meet these general standards. With regard to leakage, the regulatory specifies limit of 0.3mA of leakage current from input to output for class-1 equipment. Within a power supply, most of the leakage is caused by the EMC filter on the input. However, equipment designers should be aware that other components in the system can contribute additional leakage.

• Patient Connect vs. Patient Vicinity: According to safety standards, electrical equipment is classified as patient vicinity if it is intended to be located within 6-feet of a patient. If electrical equipment is intended to come into direct contact with a patient, it is classified as patient connects and requires an additional level of isolation. Medical power supply units are typically certified under the patient vicinity requirements since they do not come into direct contact with patients.

Checking these factors can help you select the best grade medical power supply units for your healthcare division. Don’t neglect these points or else you may face difficulties.