Table Of Contents
DC-DC converters have many applications, from aerospace and military to commercial and industrial. Regardless of the circuit architecture of the DC-DC converter used, designers must meet minimum specifications, certifications, and some level of ruggedization requirements. A power supply or converter is often determined by its isolation and leakage current during certification and testing for medical applications. Both of these characteristics relate to the level of protection a patient will experience when making electrical contact with the power supply. However, there are many other factors that need to be considered when selecting a DC-DC converter to ensure optimal performance over the life of the device.
We will look at the certifications for medical-grade DC-DC converters and the basic factors to consider when selecting these devices. Power Supply Considerations in Medical Devices
Power solutions for electronic medical devices are as diverse as their uses. It is critical that every component in the power source (e.g., battery, socket, generator, etc.), power delivery network (PDN), and associated electronics (e.g., sensors, actuators, processors, etc.) function properly in the event of a power outage, voltage fluctuation, or potential disturbance. This means that in the case of a ventilator, an energy storage device, such as a battery, is needed to quickly switch to a backup power source in the event of a power outage. This prevents the ventilator from suddenly shutting down before a long-term backup power source, such as a diesel generator, kicks in.
Basic Parameters of DC-DC Converters
DC-DC converters are found in almost all electronic medical devices to receive an input DC signal and provide a tightly regulated output DC signal. Regardless of the DC-DC converter topology, there are specific electrical, thermal, and mechanical variables that are critical to optimizing for a particular end application. The most basic parameters are the input and output voltages and output current/power required for the use case, which are easily defined as system requirements. DC-DC converters are beginning to differentiate themselves through factors such as efficiency, power density, reliability, and certification/standards compliance. High power density will allow designers to save space by fitting a DC-DC converter with a greater power rating into a smaller form factor. For medical applications, medical certification is the primary qualification factor. Beyond this, reliability is also key, so circuit protection is needed to buffer components from unpredictable voltage fluctuations and surge events.
Depending on the environment in which the DC-DC converter is deployed, additional component ruggedization may be critical. In outdoor environments, it is necessary to ensure that the converter will not experience any failure modes due to cycling between high and low temperatures or in high humidity environments. The MIL-STD-810 specification is the most common standard used in electronic component datasheets for environmental engineering considerations. This is due to the exhaustive guidelines and test conditions listed in the standard for potential environmental stressors, ranging from high and low temperature conditions to fungus, explosive environments, and ballistic shock. While most medical components may not be subject to mechanical strains from gunshots, thermal shock, relative humidity, vibration, and even altitude can be tested to represent the mechanical robustness of the device. This accounts for the thermal stability of the DC-DC converter and its ability to operate in shock and vibration environments (e.g., mobile emergency/first aid equipment) and high altitude environments (e.g., mountains, airplanes, etc.).
While many of these parameters ensure that the device does not fail prematurely due to adverse electrical, mechanical, and environmental conditions, the mean time between failures (MTBF) is a critical parameter that represents the long-term wear and tear of the device under steady-state conditions.
Power Supply Requirements for Medical Applications
The default standard for medical devices is the IEC 60601-1 standard that defines “General requirements for basic safety and essential performance.” For power supplies in medical devices (i.e., AC-DC and DC-DC converters), this standard is critical to ensure that medical devices function within safety guidelines. These guidelines are defined based on the proximity 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 that do not come into contact with the patient may 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 device classifications are surgical equipment, dialysis machines, defibrillators, and heart-lung machines. Surgical equipment, dialysis machines, defibrillators, and heart-lung machines are the devices with the most stringent CF classifications. However, it is still very helpful for medical device designers to understand whether the power supply meets the isolation, creepage, insulation, and leakage current requirements for the various categories (Table 1).
| Classification of power requirements for medical applications |
2nd Edition Requirements by Classification
| Classification | Creepage /Clearance | Insulation | I/ O Isolation |
| Type B | 2.5 mm | Basic | 1500 Vac |
| Type BF | 5mm | Double | 3000 Vac |
| Type CF | 8 mm | Double | 4000 Vac |
Today’s content is written here, please read more related content, thank you
