10 Important Criteria for Medical-Grade Power Supplies
Although medical power supplies may appear similar to commercial-grade power supplies in terms of packaging, they are specifically designed to meet the IEC60601-1 medical equipment safety standard. This standard influences the internal power supply design and ensures that medical equipment is safe.
While meeting the IEC60601-1 safety standard is a crucial aspect of medical power supply design, it is not the only factor that sets them apart from their commercial counterparts. Medical equipment demands longer design cycles and necessitates more support from power supply vendors due to its extended lifespan. Therefore, medical-grade power supplies require long-term vendor support to ensure their reliability for years.
To ensure the right fit for your medical equipment, take into account these criteria when selecting a medical-grade power supply that aligns with your application requirements:
Output Voltage (V) and Current (A):
Medical power supplies are designed to meet different applications' varying supply voltage needs by offering single or multiple output voltages, typically ranging from 3.3 to 48 Vdc. It's important to note that when determining the appropriate supply voltage levels for your application, it's not the current levels needed for each voltage that should be considered.
Power Rating (W):
When determining the required power rating for a medical power supply, it's essential to consider the maximum current needed for the application and to select a model with a rating that provides some design margin. If multiple output voltages are required, add the voltage-times-current products for all supply voltages to calculate the power rating. This is a good engineering practice that ensures the reliability and safety of the medical equipment.
Form Factor and Mounting:
Medical grade supplies are offered in various package styles, including open-frame, enclosed, encapsulated, and external adapters with different mounting options, such as PCB and chassis mounts. The selection of a particular package style depends on several application considerations.
The options for power supply input and output connections (I/Os) are related to the mounting options. With pc-board mount packaging, I/O pins on the bottom of the supplied insert into plated-through holes or sockets on an application pc board. With chassis-mount packaging, the supply may include Molex headers or screw terminals that enable interconnects using wire harness assemblies.
Thermal Management:To ensure that your medical power supply stays cool, it's essential to consider the ambient temperature range of your application and power supply thermal specifications. This will determine if convection cooling will suffice or if forced-air cooling is needed. Remember that the type of packaging you choose will also impact thermal performance and cooling requirements.
Environmental Factors:Choosing an encapsulated power supply can improve reliability if your medical equipment is likely exposed to vibrations or contaminants.
Safety Standards:Meeting the IEC60601-1 safety standard is just the beginning for medical-grade power supplies. They must also comply with regional versions such as UL60601-1 and EN60601-1, which impose additional safety requirements beyond general safety standards such as UL/EN60950-1. Leakage is also a concern, with UL60601-1 limiting it to 0.3 mA from input to output for Class I equipment. While the EMC filter on the input is the primary cause of leakage, other components in the system can contribute, and designers should be aware of this.
Patient Connect vs. Patient Vicinity:
Regarding medical-grade power supplies, it's important to distinguish between "patient connect" and "patient vicinity" equipment. The former is designed to come into direct contact with patients and requires additional isolation, while the latter is intended to be located within 6 feet of a patient. Medical power supplies are typically certified under the patient vicinity requirements, as they do not come into direct contact with patients. This is by the UL60601-1 safety standard.
Additional Horizontal Standards:
Aside from the IEC60601-1 standard, other collateral medical equipment standards must be considered, such as IEC60601-1-2, which outlines the requirements for electromagnetic compatibility. There are a plethora of different collateral standards that relate to specific medical applications and hazards. It is crucial to identify which standards apply to your application and how they impact your power supply selection.
Dual Line Fusing:
To ensure compliance with UL/EN60601-1 safety standards, equipment with a protective earth ground requires fusing on the line and neutral wires. This can be achieved through the power supply or externally within the system.
Selecting the appropriate medical power supply is crucial to ensure the safety and reliability of medical equipment. Meeting the IEC60601-1 safety standard is just the first step, as multiple factors such as output voltage, power rating, form factor, electrical connection, thermal management, environmental factors, safety standards, patient connect vs. patient vicinity, and additional horizontal standards must be carefully considered. By considering these criteria, medical equipment designers can choose the right power supply for their application and establish a long-term partnership with their power supply vendor. For more information on selecting the correct medical power supply, check out our blog post, 'Choosing Medical Power Supplies'.
Learn how to select a power supply for medical applications on our blog post 'Choosing Medical Power Supplies'.