Select medical device power supply precautions
In the medical industry, because of the safety of people's lives, all related products will take quality as a priority, so each industry has certain hard indicators for medical power, and the medical industry is no exception. Medical power supply should be able to be used in the medical device power supply, first through the corresponding indicators of medical certification.
1. Requirements for EMC indicators:
The conduction and radiation of medical equipment needs to meet EN55011 with the same limits as EN50552 ITE equipment. Considering that the medical system must meet the requirements of high safety and high isolation, and the transmission and radiation are required to meet the standard requirements, this is a great test for the design of the power supply. The designer must ensure high isolation and EMI in the design. It's actually a very difficult thing to do well, so many medical devices have to compromise, and only require EMI performance to meet the CLASSA level.
2. Safety distance and pressure resistance:
The medical standard is different from the conventional certification. In order to ensure safety and reliability, the safety distance and pressure requirement of the system are clearly defined in the standard. These distance and pressure requirements are differentiated according to the application and the crowd, and are classified according to the protection method. MOPP (Patient Protection Method) and MOOP (Operator Protection Method) are further classified into Class B, Class BF, and Class CF according to the type of equipment. Taking into account the versatility of the module, the power adapter engineer usually meets the most demanding requirements as much as possible during the design process, as follows:
① L, N is isolated from PE 1500VAC, the clearance is 2.5mm, and the creepage distance is 4.0mm.
③ output to PE, 500VDC (floating), clearance of 2.5mm, creepage distance of 4mm.
3, ultra low leakage current requirements:
Low leakage current is the core indicator of the power adapter. The IEC requirements are 264VAC, 50Hz, and leakage current ≤500uA under normal conditions of medical equipment. However, medical equipment is usually far more than one isolated power supply. Some large CTs may even have 5 channels or even Above the power supply. Therefore, for the power supply manufacturer, the leakage current of a power module can preferably be ≤100uA. For the DCDC power supply that is in contact with the human body, because it is in direct contact with the human body, the isolation requirements are more demanding, especially for CF-type equipment that is in contact with the heart. The medical certification clearly requires ≤10uA.
4. Requirements for grounding continuity:
The reason why medical power supply has this requirement is mainly because when the grounding resistance is large, it is easy to cause the ground potential difference of different power supply devices to be large, which may cause harm to seriously ill patients. Therefore, grounding continuity must also be rigorously tested. The IEC requires the resistance of the PE to any accessible metal of the housing to be <0.1Ω.
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