RESOURCES
In December 2024, Monica Cintron, the Marketing Manager at Astrodyne TDI, and Anil Kurugode, a Field Application Engineer for Astrodyne TDI's central region, presented a webinar on the importance of choosing power supplies for medical systems.
Discover their findings and the requirements for power systems in medical applications.
About Astrodyne TDI
Astrodyne TDI has more than 60 years of experience in the power industry. With over one thousand employees in factories in China and Malaysia and our local Hackettstown, New Jersey office, we develop and manufacture power supplies, electromagnetic interference (EMI) filters and isolation transformers.
How the Power Industry Correlates With the Global Health Care Industry
First, Cintron and Kurugode discussed the insights Astrodyne TDI has gained working with health care customers.
The vast majority of modern medical equipment requires stable and reliable power. The global health care industry is massive and rapidly growing, and technology is constantly changing the way medical devices are designed, qualified and used. What was once interference is now a necessity. This includes Wi-Fi, Bluetooth and other forms of connectivity that may arise in the future.
Recognizing that the medical devices industry is constantly evolving and innovating is important. The market is worth more than $518 billion, and the fundamentals never change — even as robotics and artificial intelligence enter the picture. Safety, electromagnetic interference (EMI), emissions and regulatory aspects remain constant.
Requirements of Power Supplies for Medical Applications
According to Kurugode, power systems for medical applications have the following general requirements:
- Functionality: Medical systems must provide proper voltage, proper power and clean noise levels. All subsystems must operate simultaneously without interfering with one another — a principle called electromagnetic compatibility (EMC).
- Regulatory compliance: Meeting safety and environmental sustainability requirements is especially crucial in health care. In particular, Kurugode discusses the Restriction of Hazardous Substances (RoHS) and the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) directives, which were established by the European Union and govern the use of hazardous substances.
- Interface requirements: Interface requirements explain how devices should connect to one another to work safely and effectively. For example, a heart monitor must be connected to a power source in a very specific way, and the connection must be designed carefully.
- Quality, reliability and manufacturability: Designers and system manufacturers must adhere to strict quality standards. International Organization for Standardization (ISO) 13485 is the industry-recognized standard for quality management systems in medical device design and manufacturing.
- Availability and maintainability: The medical industry is a high-investment field, and longevity is fundamental. Professionals expect a high return on investment for in power systems, which means high availability, high uptime and low maintenance.
- Time to market: While the power system industry is extremely competitive and everyone wants to get to market quickly, Kurugode notes that some development procedures cannot be compromised.
- Total cost of ownership: Organizations want to see that their investment in power systems will be worth it over time. The total cost of ownership covers the cost of investment, maintenance and replacement.
The Importance of Reliability and Stability in Powering Medical Systems
Providing stable power begins with input power, which is converted to various voltages — typically direct current (DC) voltages — for all subsystems. An EMI filter filters out high-frequency alternating current (AC) noise while allowing the necessary DC to pass through. Occasionally, a backup battery is involved, too, which needs to blend seamlessly into the system.
While these power concepts are basic, Kurugode says that the medical world adds complexity because of the patient and operator aspect. To provide stable power, power systems for the medical industry must:
- Provide interference- and glitch-free power with clean DC/AC voltages and no harmonics.
- Handle the sequencing of different voltages, as many systems use normal computing techniques with medical-grade embedded computers.
- Provide on/off emergency features that are available to local and remote operators.
- Be able to operate in environments with high ambient temperatures without adding heat to the environment.
- Support normal, subnormal and abnormal conditions due to grid uncertainties, such as lightning, electrostatic discharge (ESD) and EMI.
- Provide a high isolation level between hazardous energy and a vulnerable patient.
This final point involves equipment and power supply classifications. Defining a proper class of equipment is critical. We discuss this in greater depth later.
Power Supply Requirements for Industrial vs. Medical Sectors
The medical world is unique because patients are more vulnerable and unable to respond to hazards — while the risk to body, life and property is always a concern with power systems, the consequences of failure are much higher in the medical field.
Additionally, in an industrial sector, trained personnel operate equipment and can handle any faults that arise. However, medical industry operators do not typically have the same technical background or technical expertise as engineers. So, equipment designed for medical use must consider these differences in experience to keep operators safe and avoid accidental contact.
Classification Standards for Powering Medical Devices
Classification standards are essential for safety when dealing with medical devices.
IEC 60601-1
The International Electrotechnical Commission (IEC) defines standards specific to the medical field. IEC 60601-1 governs safety and performance requirements for medical electrical equipment. This standard eliminates much of the worry about definitions, classes of equipment and control standards.
IEC 60601-1 is the general standard for medical electrical equipment, such as X-rays, ultrasound machines, dialysis machines, ventilators and blood pressure monitors. It is further divided into several parts, including:
- IEC 60601-1-11: This standard applies to medical electrical equipment for use in the home health care environment. Examples include portable blood pressure monitors and electric wheelchairs.
- IEC 60601-1-12: Equipment intended for use in the emergency medical services environment, such as defibrillators and ventilators, are covered under IEC 60601-1-12.
Safety standards differ in the industrial world. In the medical field, the IEC 60601-1 standard clearly specifies acceptable levels of performance for various equipment classes.
Type B, BF and CF Applied Parts
IEC 60601-1 classifies applied parts — equipment that comes in contact with a patient — further into body (B), body floating (BF) and cardiac floating (CF) categories. The most benign operation mode (B) occurs when a patient is monitored without electrical contact. BF devices have physical connections to the patient. CF devices have direct contact with the heart or bloodstream. Here are a few examples:
- B applied parts: Magnetic resonance imaging (MRI) scanners, hospital beds and phototherapy equipment.
- BF applied parts: Ultrasound equipment, incubators and blood pressure cuffs.
- CF applied parts: Dialysis and surgical equipment.
Because these applied parts come into contact with the heart or bloodstream, cardiac floating requirements are the strictest and the least allowed leakage.
Class I vs. Class II Equipment
Next, Kurugode discusses selecting the proper equipment class in greater depth. Equipment is categorized according to the method of protection against electric shock:
- Class I equipment: This equipment has a protective earth connection to avoid electric shock. It poses the least risk and is required for some hospital equipment. Class I equipment is recognized by its three-pin plug and is typically classified as Type B or BF.
- Class II equipment: This equipment is double-insulated and does not rely on the earth connection. Design procedures are extremely rigorous to ensure safety. According to IEC 60601-1-11, Class II equipment is required for home use and can be classified as Type B, BF or CF.
Fundamentals of Insulation and Isolation
Next, Kurugode covers insulation and isolation, reinforcing that the most critical parameter for safety is the risk of electric shock. The person at the receiving end should never receive a shock, and this is accomplished with an insulation system.
Kurogode gives the example that if the primary live circuit (wall power) is 120 or 230 volts, the insulation system must be able to withstand about 20 times that voltage. Here's some more information from the presentation.
Operational Insulation: Live Circuit From Primary to Primary
Operational insulation, or functional insulation, is not designed to protect users from shocks but helps prevent short circuits between components within a device.
Basic Insulation: Primary Circuit Connected to Earth Circuit
The equipment connected to the earth circuit requires one level of basic insulation, or one Means of Protection (MOP).
Double or Reinforced Insulation: Primary Circuit to Safety Extra Low Voltage (SELV)
SELV circuits must be separated from hazardous voltages by two levels of protection (two MOPs). These circuits are designed to be safe even if touched.
The two levels of insulation may be double insulation, which involves basic and supplemental insulation, or reinforced insulation, which is a single layer that provides the same level of protection as double insulation. If one layer fails, the other should remain intact to ensure safety.
If you have SELV circuits and the outlets are completely uncommitted, meaning the return is not earthed, you can feel free to earth it. However, the system designer must ensure that this connection is functional and safe.
Another Component of Electric Shock Safety: Creepage and Clearance
Clearance and creepage are essential for separating hazardous and safe circuits. These parameters are nonnegotiable for certain classes of equipment. They describe the shortest distance between two conductive parts, measured along the surface of an insulator (creepage) or through the air (clearance).
Summary of EMC and Safety Requirements for Medical Systems
Kurugode next summarized these general safety requirements:
- Selecting equipment class: Once you define the class of equipment (Class I or II), certain features fall into place automatically.
- Open vs. enclosed systems: Open and enclosed systems significantly differ in safety, particularly concerning accidental contact with hazardous circuits.
- B, BF and CF applied parts: The level of electric shock protection depends on the applied part classification according to IEC 60601-1. Because CF applied parts are used directly in the heart or bloodstream, there are some special requirements.
- Insulation and isolation: The level of insulation and isolation protects operators and patients.
- Clearance and creepage: The distance between circuits should be lower due to the potential for patient and operator contact.
- Fusing: Fusing involves using two fuses in a single circuit — one on the live (line) wire and one on the neutral wire.
- Humidity and pollution: Insulation damage can occur from long-term exposure to humidity and pollution, such as if the device is stored in a closet. Special techniques can deal with these possibilities.
- Implantable devices: These life-sustaining devices require high rigor in design and manufacturing.
Safety considerations are well-defined and nonnegotiable. Electromagnetic compatibility considerations are also critical to ensure devices are not affected by EMI.
EMC includes both emissions and immunity — the electromagnetic energy released by a device and the device's ability to withstand interference from external electromagnetic sources. The primary standard for EMC is IEC 60601-1-2. Meeting this standard is crucial to:
- Ensure medical systems do not interfere with one another, as this could lead to regulatory noncompliance.
- Keep patients safe by ensuring medical devices do not emit EMI that interferes with life-supporting devices.
- Ensure devices continue functioning reliably.
- Reduce a manufacturer's risk of legal liability.
Regulatory Compliance in the United States
The Food and Drug Administration (FDA) governs products in the United States. There are three medical device classifications according to the FDA:
- Class I devices: These devices are subject to the least regulatory control and are not intended to help support or sustain life. Examples include examination gloves and hand-held nonpower surgical instruments.
- Class II devices: Examples include powered wheelchairs, infusion pumps, ventilators and surgical drapes. With these devices, general controls alone cannot assure safety and effectiveness.
- Class III devices: Class III devices support or sustain human life, such as implantable pacemakers, pulse generators and automated external defibrillators.
Voltage and structural requirements differ in Europe. However, both regions prioritize safety and efficacy.
Purchasing Certified Products
Medical-grade products clearly state their certifications on their labels. For example, labels will reveal:
- Critical ratings.
- Installation class.
- Leakage.
- Insulation and isolation.
- EMC standard compliance.
- Certifying agency.
Purchasing certified products reduces the burden on the purchaser, as the manufacturer has already ensured safety. However, insulation systems can sometimes break down due to factors like aging, humidity, pollution and lightning, so remaining vigilant about potential breakdowns is vital. Double or reinforced insulation is extremely beneficial should the system fault.
Astrodyne TDI's Isolation Transformers and EMI Filters
Isolation transformers help manage the leakage current in complex systems. They connect to mains power and provide safe, isolated output, reducing the leakage current downstream. They are compact, efficient and available in various ratings, making them suitable for diverse applications.
At Astrodyne TDI, our isolation transformers offer the following features:
- 90%-98% efficiency
- Built-in thermal protection
- Double-reinforced insulation
- Low magnetic stray field
- Low mechanical noise
- High efficiency
- Cool operating temperature
- Full medical certifications
EMI filters also help ensure compliance and minimize interference in medical devices. Astrodyne TDI's complete line of off-the-shelf filters is available in medical-grade versions. Applications for these devices include:
- Surgical beds.
- Patient medical devices.
- Diagnostic equipment.
- MRI and X-ray machines.
All filters are approved to meet the leakage current requirements of diverse environments.
Purchase Isolation Transformers and EMI Filters From Astrodyne TDI
We offer a range of products tailored for various medical applications. Our systems are designed with safety and compliance in mind and meet rigorous health care industry standards.
If you have any questions about our products or need assistance, reach out through our website today. You can also find a rep or shop power supplies online.
