What are the special requirements for medical device power?

Issue Time:2019-07-10
Medical power has special considerations for safety and has its particularity. The following is a description of leakage current and protection level.

Whether leakage current
The isolated power module acts as the primary isolation component of the entire medical system and also greatly affects the leakage current of the entire system. Therefore, for the leakage current required by medical equipment, the power module must be as satisfactory as possible, and the system-to-ground design must be considered. The leakage current is the best.

(1) Different medical equipment have different requirements for leakage current and protection level
At present, the latest third edition of the medical certification IEC60601-1-3rd, according to the application part, the medical equipment is divided into three categories: B, BF and CF, as follows:

Class B: The lowest patient protection rating of all application types, devices that may not be in contact with the patient's body, such as laser therapy devices.

Class BF: A higher degree of patient protection than the Type B application, equipment that is in contact with the patient's body, such as ultrasound, various monitors (including EGC equipment), and operating tables.

CF: The highest level of patient protection, suitable for direct heart applications, such as cardiac puncture monitors.

(2) Leakage current classification and requirements
For medical devices, the leakage current can be divided into patient leakage current, patient auxiliary leakage current, contactable leakage current, and ground leakage current according to the application of the device.

The patient leakage current refers to the current flowing into the ground through the patient and the F-type application when the external voltage is applied. In the actual test, an MD module is connected in series in the loop to simulate the impedance of the human body.

The patient's auxiliary leakage current refers to the current flowing through the B patient through the A patient through the device, and the requirement is that the physiological response of the human body cannot be brought about.

Contactable leakage current refers to the leakage current between the human body and the point where it can be contacted. Usually, the requirement is 100uA under normal conditions and 500uA under single fault condition. Leakage current between the MD module and ground, as well as the enclosure not protected by grounding, etc., is typically measured during testing.

The earth leakage current refers to the current of the device to the ground, the requirement is 5 mA, and the single fault state is 10 mA.

The above leakage current test is more than 110% of the rated network voltage in the medical certification requirements, which is not the definition of leakage current that we generally understand. Generally, the medical equipment has a network voltage range of 100-250 VAC. According to the worst conditions, the test should be 265 VAC, 60 Hz. Therefore, it is necessary to pay attention to the customer's test conditions when the power adapter demand is raised.

Protection level
The degree of protection refers to the specification of the protective strength of different medical devices. The medical device operator is the doctor and the target is the patient. In the third edition of IEC60601-1, the degree of protection is divided into MOOP (Means of Operator Protection) and MOPP (Means of Patient Protection). Different levels of protection correspond to different withstand voltage test requirements, usually 1*MOOP, 2*MOOP, 1*MOPP, 2*MOPP. The pressure resistance requirement of MOPP protection is higher than that of MOOP. Usually the working voltage of medical equipment is 250VAC. To meet the protection requirements of 2 MOPP, the pressure resistance 4000VAC is the basic requirement.

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