Power Considerations in Medical Devices
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Update time : 2023-04-21 16:07:52
The range of power solutions for electronic medical devices are as varied as the applications themselves. Between the power source (e.g., battery, outlet, generator, etc.), the power delivery network (PDN) and the connected circuitry (e.g, sensors, actuators, processors, etc.), it is critical that every component function nominally in the event of a power loss, voltage fluctuations, or potential interference. For a ventilator, this means that an energy storage device such as a battery is required to rapidly switch to backup power in the event that a power loss has occurred. This avoids the catastrophic failure mode of the ventilator shutting down before the longer-term backup power such as a derv generator is engaged.
Medical devices should be able to tolerate a degree of voltage fluctuations around their nominal values. This very same reasoning applies to all critical medical equipment such as blood pressure monitors, incubators, defibrillators, and dialysis machines. On the system-level, redundant backup power and energy storage devices might be employed. However, on the device-level, the power supply and/or AC-DC and DC-DC conversion must ensure both electromagnetic compliance (EMC) as well as overcurrent, overvoltage, overload, short circuit, and over temperature protections in order to minimize unwanted emissions and protect the component and the load from undesired conditions.
The safety of the device for both the operator and the patient is also critical in medical applications. Most safety standards present parameters and testing guidelines in order to ensure this level of safety. However, the quality of the device is dependent on some basic electrical and mechanical specifications.
The default standard for medical devices is the IEC 60601-1 standard that defines the “general requirements for basic safety and essential performance.” For power supplies (i.e., AC-DC and DC-DC converters) within medical equipment, the standard is essential to make certain the medical equipment functions within safety guidelines. These guidelines are defined by the vicinity of the patient to the power supply. The classifications are as follows:
Type B (body): no contact with the patient
Type BF (body floating): physical contact with the patient
Type CF (cardiac floating): physical contact with the heart
Devices without patient contact might include x-rays, MRI scanners, medical lasers, and hospital beds, while devices with limited contact include blood pressure monitors, incubators, and ultrasound equipment. The most stringent CF classification of devices are surgical equipment, dialysis machines, defibrillators, and heart-lung machines. The power supplies themselves do not qualify as medical devices and therefore are not subject to these classifications. However, it is still immensely helpful to the medical equipment designer to understand whether or not the power supply meets the isolation, creepage, insulation, and leakage current requirements for the various categories.
Medical devices should be able to tolerate a degree of voltage fluctuations around their nominal values. This very same reasoning applies to all critical medical equipment such as blood pressure monitors, incubators, defibrillators, and dialysis machines. On the system-level, redundant backup power and energy storage devices might be employed. However, on the device-level, the power supply and/or AC-DC and DC-DC conversion must ensure both electromagnetic compliance (EMC) as well as overcurrent, overvoltage, overload, short circuit, and over temperature protections in order to minimize unwanted emissions and protect the component and the load from undesired conditions.
The safety of the device for both the operator and the patient is also critical in medical applications. Most safety standards present parameters and testing guidelines in order to ensure this level of safety. However, the quality of the device is dependent on some basic electrical and mechanical specifications.
The default standard for medical devices is the IEC 60601-1 standard that defines the “general requirements for basic safety and essential performance.” For power supplies (i.e., AC-DC and DC-DC converters) within medical equipment, the standard is essential to make certain the medical equipment functions within safety guidelines. These guidelines are defined by the vicinity of the patient to the power supply. The classifications are as follows:
Type B (body): no contact with the patient
Type BF (body floating): physical contact with the patient
Type CF (cardiac floating): physical contact with the heart
Devices without patient contact might include x-rays, MRI scanners, medical lasers, and hospital beds, while devices with limited contact include blood pressure monitors, incubators, and ultrasound equipment. The most stringent CF classification of devices are surgical equipment, dialysis machines, defibrillators, and heart-lung machines. The power supplies themselves do not qualify as medical devices and therefore are not subject to these classifications. However, it is still immensely helpful to the medical equipment designer to understand whether or not the power supply meets the isolation, creepage, insulation, and leakage current requirements for the various categories.
