【Medical Power Supply】Understand the medical power supply leakage current

With the popularity of home medical equipment (HME), more and more people are exposed to medical power supplies. However, a medical power supply and a consumer electronic power supply are two very different products. The medical power supply must comply with IEC60601 standard whereas the consumer electronic power supply needs to comply with IEC60950/60065 (will be replaced by IEC62368 later on) standards. Designs derived from these two different standard requirements have significant differences, such as safety isolation, leakage current level, radiation and anti-interference ability, reliability, requirements of usage life, etc.

When selecting a medical power supply product, it is often seen that the power supply manufacturer marks the leakage current to be in compliance with Type B, Type BF, and Type CF classifications. However, what are these classifications and requirements? Here, an overview is provided. Before introducing the “leakage current level”, the concept of “applied parts” needs to be explained.

 

“Applied parts” are “parts of medical equipment that, in normal use, necessarily come into physical contact with the patient” such as probes, electrocardiograms, blood pressure sticks, operating tables. In general, applied parts are embedded in medical electrical equipment that has direct contact with patients.

According to the regulations of protection against electric shock, applied parts can be classified into three types:

• Type CF：Type CF is the most stringent classification, required for those applications where the applied part is in direct conductive contact with the heart or other applications as considered necessary.
• Type BF ：Type BF is less stringent than Type CF and is generally for devices that have conductive contact with the patient, and are allowed to be connected with other applied parts that have conductive contact with the patient.
• Type B ：Type B is the least stringent classification and is used for applied parts that are generally not conductive and can be immediately released from the patient.

According to the regulations, there are three types of system leakage current requirements as follows:

NC=Normal Conditions / SFC=Single Fault Conditions

The above definitions are for the medical system equipment. In the actual utilization, the medical power supply is usually not in direct conductive contact with the patient. Therefore, the medical power supply product itself does not need to comply with the regulations of applied parts. However, as the end product is powered by power supply still needs to be verified based on the part classifications (Types B/BF/CF).

The medical power supply is inherently with leakage current which is mainly caused by parasitic capacitance across the transformer and the Y capacitance for EMC requirements. For the medical electrical system to meet system leakage current requirement base on its “applied parts” classification, the power supply must also comply with the leakage current regulations. With many years of experience in medical power supply design, Asian Power Devices (APD) can provide you with a medical power solution with cost-effectiveness, reliable quality, and in compliance with system leakage current requirements.